# This is how we compile
#
TCCX = $(TCC) $(OPTS) $(THREADSAFE) $(USLEEP) -I. -I$(TOP)/src

# Object files for the SQLite library.
#



LIBOBJ = attach.o auth.o btree.o btree_rb.o build.o copy.o date.o delete.o \
         expr.o func.o hash.o insert.o \
         main.o opcodes.o os.o pager.o parse.o pragma.o printf.o random.o \
         select.o table.o tokenize.o trigger.o update.o util.o \
         vacuum.o vdbe.o vdbeaux.o where.o tclsqlite.o

# All of the source code files.
#
SRC = \









  $(TOP)/src/attach.c \
  $(TOP)/src/auth.c \
  $(TOP)/src/btree.c \
  $(TOP)/src/btree.h \
  $(TOP)/src/btree_rb.c \
  $(TOP)/src/build.c \
  $(TOP)/src/copy.c \
................................................................................
  $(TOP)/src/vdbeaux.c \
  $(TOP)/src/vdbeInt.h \
  $(TOP)/src/where.c

# Source code to the test files.
#
TESTSRC = \






  $(TOP)/src/btree.c \
  $(TOP)/src/func.c \
  $(TOP)/src/os.c \
  $(TOP)/src/pager.c \
  $(TOP)/src/test1.c \
  $(TOP)/src/test2.c \
  $(TOP)/src/test3.c \

# This is how we compile
#
TCCX = $(TCC) $(OPTS) $(THREADSAFE) $(USLEEP) -I. -I$(TOP)/src

# Object files for the SQLite library.
#
LIBOBJ = hash.o os.o pager.o random.o \
         util.o tclsqlite.o

LIBOBJ_ORIG = attach.o auth.o btree.o btree_rb.o build.o copy.o date.o delete.o \
         expr.o func.o hash.o insert.o \
         main.o opcodes.o os.o pager.o parse.o pragma.o printf.o random.o \
         select.o table.o tokenize.o trigger.o update.o util.o \
         vacuum.o vdbe.o vdbeaux.o where.o tclsqlite.o

# All of the source code files.
#
SRC = \
  $(TOP)/src/hash.c \
  $(TOP)/src/hash.h \
  $(TOP)/src/os.c \
  $(TOP)/src/pager.c \
  $(TOP)/src/pager.h \
  $(TOP)/src/random.c \
  $(TOP)/src/util.c 

SRC_ORIG = \
  $(TOP)/src/attach.c \
  $(TOP)/src/auth.c \
  $(TOP)/src/btree.c \
  $(TOP)/src/btree.h \
  $(TOP)/src/btree_rb.c \
  $(TOP)/src/build.c \
  $(TOP)/src/copy.c \
................................................................................
  $(TOP)/src/vdbeaux.c \
  $(TOP)/src/vdbeInt.h \
  $(TOP)/src/where.c

# Source code to the test files.
#
TESTSRC = \
  $(TOP)/src/os.c \
  $(TOP)/src/pager.c \
  $(TOP)/src/test2.c \
  $(TOP)/src/md5.c

TESTSRC_ORIG = \
  $(TOP)/src/btree.c \
  $(TOP)/src/func.c \
  $(TOP)/src/os.c \
  $(TOP)/src/pager.c \
  $(TOP)/src/test1.c \
  $(TOP)/src/test2.c \
  $(TOP)/src/test3.c \

** a legal notice, here is a blessing:
**
**    May you do good and not evil.
**    May you find forgiveness for yourself and forgive others.
**    May you share freely, never taking more than you give.
**
*************************************************************************
** $Id: btree.c,v 1.104 2004/04/23 23:43:10 drh Exp $
**
** This file implements a external (disk-based) database using BTrees.
** For a detailed discussion of BTrees, refer to
**
**     Donald E. Knuth, THE ART OF COMPUTER PROGRAMMING, Volume 3:
**     "Sorting And Searching", pages 473-480. Addison-Wesley
**     Publishing Company, Reading, Massachusetts.
................................................................................
**
** Cells are of variable length.  The first cell begins on the byte defined
** in the page header.  Cells do not necessarily occur in order - they can
** skip around on the page.
**
**    SIZE    DESCRIPTION
**      2     Byte offset of the next cell.  0 if this is the last cell
**      4     Page number of the left child.  Omitted if leaf flag is set.
**     var    Number of bytes of data.  Omitted if the zerodata flag is set.
**     var    Number of bytes of key.  Omitted if the intkey flag is set.
**      *     Payload
**      4     First page of the overflow chain.  Omitted if no overflow
**
** Overflow pages form a linked list.  Each page except the last is completely
** filled with data (pagesize - 4 bytes).  The last page can have as little
** as 1 byte of data.
**
................................................................................
*/
#include "sqliteInt.h"
#include "pager.h"
#include "btree.h"
#include <assert.h>

/* Forward declarations */
static BtOps sqliteBtreeOps;
static BtCursorOps sqliteBtreeCursorOps;

/*
** This is a magic string that appears at the beginning of every
** SQLite database in order to identify the file as a real database.
**                                  0123456789 123456 */
static const char zMagicHeader[] = "SQLite version 3";

................................................................................
**
** The pParent field points back to the parent page.  This allows us to
** walk up the BTree from any leaf to the root.  Care must be taken to
** unref() the parent page pointer when this page is no longer referenced.
** The pageDestructor() routine handles that chore.
*/
struct MemPage {
  struct BTree *pBt;             /* Pointer back to BTree structure */
  unsigned char *aData;          /* Pointer back to the start of the page */

  u8 idxShift;                   /* True if Cell indices have changed */
  u8 isOverfull;                 /* Some aCell[] points outside u.aDisk[] */
  u8 intKey;                     /* True if intkey flag is set */
  u8 leaf;                       /* True if leaf flag is set */
  u8 zeroData;                   /* True if zero data flag is set */
  u8 hdrOffset;                  /* 100 for page 1.  0 otherwise */
  Pgno pgno;                     /* Page number for this page */
  MemPage *pParent;              /* The parent of this page.  NULL for root */
  int idxParent;                 /* Index in pParent->apCell[] of this node */
  int nFree;                     /* Number of free bytes on the page */
  int nCell;                     /* Number of entries on this page */
  unsigned char **aCell;         /* Pointer to start of each cell */
};

/*
** The in-memory image of a disk page has the auxiliary information appended
** to the end.  EXTRA_SIZE is the number of bytes of space needed to hold
** that extra information.
*/
#define EXTRA_SIZE sizeof(Mempage)

/*
** Everything we need to know about an open database
*/
struct Btree {
  BtOps *pOps;          /* Function table */
  Pager *pPager;        /* The page cache */
  BtCursor *pCursor;    /* A list of all open cursors */
  MemPage *page1;       /* First page of the database */
  u8 inTrans;           /* True if a transaction is in progress */
  u8 inCkpt;            /* True if there is a checkpoint on the transaction */
  u8 readOnly;          /* True if the underlying file is readonly */
  int pageSize;         /* Number of usable bytes on each page */
  int maxLocal;         /* Maximum local payload */
};
typedef Btree Bt;

/*
** A cursor is a pointer to a particular entry in the BTree.
** The entry is identified by its MemPage and the index in
** MemPage.apCell[] of the entry.
*/
struct BtCursor {
  BtCursorOps *pOps;        /* Function table */
  Btree *pBt;               /* The Btree to which this cursor belongs */
  BtCursor *pNext, *pPrev;  /* Forms a linked list of all cursors */
  BtCursor *pShared;        /* Loop of cursors with the same root page */


  Pgno pgnoRoot;            /* The root page of this tree */
  MemPage *pPage;           /* Page that contains the entry */
  int idx;                  /* Index of the entry in pPage->apCell[] */
  u8 wrFlag;                /* True if writable */
  u8 eSkip;                 /* Determines if next step operation is a no-op */
  u8 iMatch;                /* compare result from last sqliteBtreeMoveto() */
};

/*
** Legal values for BtCursor.eSkip.
*/
#define SKIP_NONE     0   /* Always step the cursor */
#define SKIP_NEXT     1   /* The next sqliteBtreeNext() is a no-op */
#define SKIP_PREV     2   /* The next sqliteBtreePrevious() is a no-op */
#define SKIP_INVALID  3   /* Calls to Next() and Previous() are invalid */

/* Forward declarations */
static int fileBtreeCloseCursor(BtCursor *pCur);

/*
** Read or write a two-, four-, and eight-byte integer values
*/
static u32 get2byte(unsigned char *p){
  return (p[0]<<8) | p[1];
}
static u32 get4byte(unsigned char *p){
  return (p[0]<<24) | (p[1]<<16) | (p[2]<<8) | p[3];
}
static u64 get4byte(unsigned char *p){
  u64 v = get4byte(p);
  return (v<<32) | get4byte(&p[4]);
}
static void put2byte(unsigned char *p, u32 v){
  p[0] = v>>8;
  p[1] = v;
}
................................................................................
  do{
    p[i++] = v & 0x7f;
    v >>= 7;
  }while( v!=0 );
  p[i-1] |= 0x80;
  return i;
}


























/*
** Compute the total number of bytes that a Cell needs on the main
** database page.  The number returned includes the Cell header,
** local payload storage, and the pointer to overflow pages (if
** applicable).  Additional space allocated on overflow pages
** is NOT included in the value returned from this routine.
*/
static int cellSize(MemPage *pPage, unsigned char *pCell){

  int n, nPayload;
  u64 nData, nKey;
  int maxPayload;
  if( pPage->leaf ){
    n = 2;
  }else{
    n = 6;
  }
  if( pPage->zeroData ){
    nData = 0;
  }else{
    n += getVarint(&pCell[n], &nData);
  }


  if( pPage->intKey ){
    u64 dummy;
    nKey = getVarint(&pCell[n], &dummy);
  }else{
    n += getVarint(pCell, &nKey);

  }
  nPayload = nKey + nData;
  maxPayload = pPage->pBt->maxPayload;
  if( nPayload>maxPayload ){
    nPayload = maxPayload + 4;
  }
  return n + nPayload;
}

/*
** Defragment the page given.  All Cells are moved to the
** beginning of the page and all free space is collected 
** into one big FreeBlk at the end of the page.
*/
static void defragmentPage(MemPage *pPage){
  int pc, i, n;
  int start, hdr;
  int leftover;
  unsigned char *oldPage;
  unsigned char newPage[SQLITE_PAGE_SIZE];

  assert( sqlitepager_iswriteable(pPage->aData) );
  assert( pPage->pBt!=0 );
  assert( pPage->pageSize <= SQLITE_PAGE_SIZE );
  oldPage = pPage->aData;
  hdr = pPage->hdrOffset;
  ptr = 3+hdr;
  n = 6+hdr;
  if( !pPage->leaf ){
    n += 4;
  }
  start = n;
  pc = get2byte(&oldPage[ptr]);
  i = 0;
  while( pc>0 ){
    assert( n<pPage->pageSize );
    size = cellSize(pPage, &oldPage[pc]);
    memcpy(&newPage[n], &oldPage[pc], size);
    put2byte(&newPage[ptr],n);
    pPage->aCell[i] = &oldPage[n];
    n += size;
    ptr = pc;
    pc = get2byte(&oldPage[pc]);
  }
  leftover = pPage->pageSize - n;
  assert( leftover>=0 );
  assert( pPage->nFree==leftover );
  if( leftover<4 ){
    oldPage[hdr+5] = leftover;
    leftover = 0;
    n = pPage->pageSize;
  }
  memcpy(&oldPage[start], &newPage[start], n-start);
  if( leftover==0 ){
    put2byte(&oldPage[hdr+3], 0);
  }else if( leftover>=4 ){
    put2byte(&oldPage[hdr+3], n);
    put2byte(&oldPage[n], 0);
................................................................................
** calls defragementPage() to consolidate all free space before 
** allocating the new chunk.
**
** Algorithm:  Carve a piece off of the first freeblock that is
** nByte in size or that larger.
*/
static int allocateSpace(MemPage *pPage, int nByte){
  int ptr, pc, hdr;
  int size;
  unsigned char *data;
#ifndef NDEBUG
  int cnt = 0;
#endif

  data = pPage->aData;
................................................................................
  assert( pPage->pBt );
  if( nByte<4 ) nByte = 4;
  if( pPage->nFree<nByte || pPage->isOverfull ) return 0;
  hdr = pPage->hdrOffset;
  if( data[hdr+5]>=252 ){
    defragmentPage(pPage);
  }
  ptr = hdr+1;
  pc = get2byte(&data[ptr]);
  assert( ptr<pc );
  assert( pc<=pPage->pageSize-4 );
  while( (size = get2byte(&data[pc+2])<nByte ){
    ptr = pc;
    pc = get2byte(&data[ptr]);
    assert( pc<=pPage->pageSize-4 );
    assert( pc>=ptr+size+4 || pc==0 );
    if( pc==0 ){
      assert( (cnt++)==0 );
      defragmentPage(pPage);
      assert( data[hdr+5]==0 );
      ptr = pPage->hdrOffset+1;
      pc = get2byte(&data[ptr]);
    }
  }
  assert( pc>0 && size>=nByte );
  assert( pc+size<=pPage->pageSize );
  if( size>nByte+4 ){
    put2byte(&data[ptr], pc+nByte);
    put2byte(&data[pc+size], get2byte(&data[pc]));
    put2byte(&data[pc+size+2], size-nByte);
  }else{
    put2byte(&data[ptr], get2byte(&data[pc]));
    data[hdr+5] += size-nByte;
  }
  pPage->nFree -= nByte;
  assert( pPage->nFree>=0 );
  return pc;
}

................................................................................
** and the size of the block is "size" bytes.
**
** Most of the effort here is involved in coalesing adjacent
** free blocks into a single big free block.
*/
static void freeSpace(MemPage *pPage, int start, int size){
  int end = start + size;  /* End of the segment being freed */
  int ptr, pbegin, pend;
#ifndef NDEBUG
  int tsize = 0;          /* Total size of all freeblocks */
#endif
  unsigned char *data = pPage->aData;

  assert( pPage->pBt!=0 );
  assert( sqlitepager_iswriteable(data) );
  assert( start>=pPage->hdrOffset+6+(pPage->leaf?0:4) );
  assert( end<=pPage->pBt->pageSize );
  if( size<4 ) size = 4;

  /* Add the space back into the linked list of freeblocks */
  ptr = pPage->hdrOffset + 1;
  while( (pbegin = get2byte(&data[ptr]))<start && pbegin>0 ){
    assert( pbegin<=pPage->pBt->pageSize-4 );
    assert( pbegin>ptr );
    ptr = pbegin;
  }
  assert( pbegin<=pPage->pBt->pageSize-4 );
  assert( pbegin>ptr || pbegin==0 );
  put2bytes(&data[ptr], start);
  put2bytes(&data[start], pbegin);
  put2bytes(&data[start+2], size);
  pPage->nFree += size;

  /* Coalesce adjacent free blocks */
  ptr = pPage->hdrOffset + 1;
  while( (pbegin = get2byte(&data[ptr]))>0 ){
    int pnext, psize;
    assert( pbegin>ptr );
    assert( pbegin<pPage->pBt->pageSize-4 );
    pnext = get2byte(&data[pbegin]);
    psize = get2byte(&data[pbegin+2]);
    if( pbegin + psize + 3 >= pnext && pnext>0 ){
      int frag = pnext - (pbegin+psize);
      assert( frag<=data[pPage->hdrOffset+5] );
      data[pPage->hdrOffset+5] -= frag;
      put2byte(&data[pbegin], get2byte(&data[pnext]));
      put2byte(&data[pbegin+2], pnext+get2byte(&data[pnext+2])-pbegin);
    }else{
      assert( (tsize += psize)>0 );
      ptr = pbegin;
    }
  }
  assert( tsize+data[pPage->hdrOffset+5]==pPage->nFree );
}


/*
** The following is the default comparison function for (non-integer)
** keys in the btrees.  This function returns negative, zero, or
** positive if the first key is less than, equal to, or greater than
** the second.
**
*/
................................................................................
    } 
  }
  return 0;

bad_key:
  return 1;
}
  

/*
** Initialize the auxiliary information for a disk block.
**
** The pParent parameter must be a pointer to the MemPage which
** is the parent of the page being initialized.  The root of a
** BTree has no parent and so for that page, pParent==NULL.
................................................................................
** Return SQLITE_OK on success.  If we see that the page does
** not contain a well-formed database page, then return 
** SQLITE_CORRUPT.  Note that a return of SQLITE_OK does not
** guarantee that the page is well-formed.  It only shows that
** we failed to detect any corruption.
*/
static int initPage(
  Bt *pBt,               /* The Btree */
  unsigned char *data,   /* Start of the data for the page */
  Pgno pgnoThis,         /* The page number */
  MemPage *pParent       /* The parent.  Might be NULL */
){
  MemPage *pPage;
  int c, pc, i;
  int sumCell = 0;       /* Total size of all cells */
  unsigned char *data;

  pPage = (MemPage*)&aData[pBt->pageSize];


  if( pPage->pParent ){
    assert( pPage->pParent==pParent );
    return SQLITE_OK;
  }
  if( pParent ){
    pPage->pParent = pParent;
    sqlitepager_ref(pParent->aData);
  }
  if( pPage->pBt!=0 ) return SQLITE_OK;
  pPage->pBt = pBt;
  pPage->nCell = 0;
  pPage->pgno = pgnoThis;

  pPage->hdrOffset = hdr = pgnoThis==1 ? 100 : 0;
  c = data[pPage->hdrOffset];
  pPage->intKey = (c & PTF_INTKEY)!=0;
  pPage->zeroData = (c & PTF_ZERODATA)!=0;
  pPage->leaf = (c & PTF_INTKEY)!=0;

  /* Initialize the cell count and cell pointers */
  pc = get2byte(&data[hdr+3]);
  while( pc>0 ){
................................................................................
  pPage->nFree = data[hdr+5];
  pc = get2byte(&data[hdr+1]);
  while( pc>0 ){
    int next, size;
    if( pc>=pBt->pageSize ) return SQLITE_CORRUPT;
    next = get2byte(&data[pc]);
    size = get2byte(&data[pc+2]);
    if( next>0 && next<=pc+size+3 ) return SQLITE_CURRUPT;
    pPage->nFree += size;
    pc = next;
  }
  if( pPage->nFree>=pBt->pageSize ) return SQLITE_CORRUPT;

  /* Sanity check:  Cells and freespace and header must sum to the size
  ** a page. */
................................................................................
/*
** Set up a raw page so that it looks like a database page holding
** no entries.
*/
static void zeroPage(MemPage *pPage, int flags){
  unsigned char *data = pPage->aData;
  Btree *pBt = pPage->pBt;
  int hdr = pPage->pgno==1 ? 100 : 0;
  int first;

  assert( sqlitepager_iswriteable(data) );
  memset(&data[hdr], 0, pBt->pageSize - hdr);
  data[hdr] = flags;
  first = hdr + 6 + 4*((flags&0x01)!=0);
  put2byte(&data[hdr+1], first);
................................................................................
  pPage->nCell = 0;
  pPage->nFree = pBt->pageSize - first;
  pPage->intKey = (flags & PTF_INTKEY)!=0;
  pPage->leaf = (flags & PTF_LEAF)!=0;
  pPage->zeroData = (flags & PTF_ZERODATA)!=0;
  pPage->hdrOffset = hdr;
}
































/*
** This routine is called when the reference count for a page
** reaches zero.  We need to unref the pParent pointer when that
** happens.
*/
static void pageDestructor(void *pData){
  MemPage *pPage = (MemPage*)&((char*)pData)[SQLITE_PAGE_SIZE];
  if( pPage->pParent ){
    MemPage *pParent = pPage->pParent;
    pPage->pParent = 0;
    sqlitepager_unref(pParent->aData);
  }
  sqliteFree(pPage->aCell);
  pPage->aCell = 0;

}

/*
** Open a new database.
**
** Actually, this routine just sets up the internal data structures
** for accessing the database.  We do not open the database file 
................................................................................
** until the first page is loaded.
**
** zFilename is the name of the database file.  If zFilename is NULL
** a new database with a random name is created.  This randomly named
** database file will be deleted when sqliteBtreeClose() is called.
*/
int sqliteBtreeOpen(
  const char *zFilename,    /* Name of the file containing the BTree database */
  int omitJournal,          /* if TRUE then do not journal this file */
  int nCache,               /* How many pages in the page cache */
  Btree **ppBtree           /* Pointer to new Btree object written here */


){
  Btree *pBt;
  int rc;



  /*
  ** The following asserts make sure that structures used by the btree are
  ** the right size.  This is to guard against size changes that result
  ** when compiling on a different architecture.
  */
  assert( sizeof(u64)==8 );
................................................................................
  pBt = sqliteMalloc( sizeof(*pBt) );
  if( pBt==0 ){
    *ppBtree = 0;
    return SQLITE_NOMEM;
  }
  if( nCache<10 ) nCache = 10;
  rc = sqlitepager_open(&pBt->pPager, zFilename, nCache, EXTRA_SIZE,
                        !omitJournal);
  if( rc!=SQLITE_OK ){
    if( pBt->pPager ) sqlitepager_close(pBt->pPager);
    sqliteFree(pBt);
    *ppBtree = 0;
    return rc;
  }
  sqlitepager_set_destructor(pBt->pPager, pageDestructor);
  pBt->pCursor = 0;
  pBt->page1 = 0;
  pBt->readOnly = sqlitepager_isreadonly(pBt->pPager);
  pBt->pOps = &sqliteBtreeOps;
  pBt->pageSize = SQLITE_PAGE_SIZE;
  pBt->maxLocal = (SQLITE_PAGE_SIZE-10)/4-12;
  *ppBtree = pBt;
  return SQLITE_OK;
}

/*
** Close an open database and invalidate all cursors.
*/
static int fileBtreeClose(Btree *pBt){
  while( pBt->pCursor ){
    fileBtreeCloseCursor(pBt->pCursor);
  }
  sqlitepager_close(pBt->pPager);
  sqliteFree(pBt);
  return SQLITE_OK;
}

/*
................................................................................
** and the database cannot be corrupted if this program
** crashes.  But if the operating system crashes or there is
** an abrupt power failure when synchronous is off, the database
** could be left in an inconsistent and unrecoverable state.
** Synchronous is on by default so database corruption is not
** normally a worry.
*/
static int fileBtreeSetCacheSize(Btree *pBt, int mxPage){
  sqlitepager_set_cachesize(pBt->pPager, mxPage);
  return SQLITE_OK;
}

/*
** Change the way data is synced to disk in order to increase or decrease
** how well the database resists damage due to OS crashes and power
** failures.  Level 1 is the same as asynchronous (no syncs() occur and
** there is a high probability of damage)  Level 2 is the default.  There
** is a very low but non-zero probability of damage.  Level 3 reduces the
** probability of damage to near zero but with a write performance reduction.
*/
static int fileBtreeSetSafetyLevel(Btree *pBt, int level){
  sqlitepager_set_safety_level(pBt->pPager, level);
  return SQLITE_OK;
}

/*
** Get a reference to page1 of the database file.  This will
** also acquire a readlock on that file.
................................................................................
** well-formed database file, then SQLITE_CORRUPT is returned.
** SQLITE_BUSY is returned if the database is locked.  SQLITE_NOMEM
** is returned if we run out of memory.  SQLITE_PROTOCOL is returned
** if there is a locking protocol violation.
*/
static int lockBtree(Btree *pBt){
  int rc;
  unsigned char *data;
  if( pBt->page1 ) return SQLITE_OK;
  rc = sqlitepager_get(pBt->pPager, 1, (void**)&data);
  if( rc!=SQLITE_OK ) return rc;


  /* Do some checking to help insure the file we opened really is
  ** a valid database file. 
  */
  if( sqlitepager_pagecount(pBt->pPager)>0 ){
    if( memcmp(data, zMagicHeader, 16)!=0 ){
      rc = SQLITE_NOTADB;
      goto page1_init_failed;
    }
    /*** TBD:  Other header checks such as page size ****/
  }
  pBt->page1 = (MemPage*)&data[SQLITE_PAGE_SIZE];
  return rc;

page1_init_failed:
  sqlitepager_unref(pBt->data);
  pBt->page1 = 0;
  return rc;
}

/*
** If there are no outstanding cursors and we are not in the middle
** of a transaction but there is a read lock on the database, then
** this routine unrefs the first page of the database file which 
................................................................................
** has the effect of releasing the read lock.
**
** If there are any outstanding cursors, this routine is a no-op.
**
** If there is a transaction in progress, this routine is a no-op.
*/
static void unlockBtreeIfUnused(Btree *pBt){
  if( pBt->inTrans==0 && pBt->pCursor==0 && pBt->page1!=0 ){
    sqlitepager_unref(pBt->page1->aData);
    pBt->page1 = 0;
    pBt->inTrans = 0;
    pBt->inCkpt = 0;
  }
}

/*
** Create a new database by initializing the first page of the
** file.
*/
static int newDatabase(Btree *pBt){
  MemPage *pP1;
  unsigned char *data;
  int rc;
  if( sqlitepager_pagecount(pBt->pPager)>1 ) return SQLITE_OK;
  pP1 = pBt->page1;
  assert( pP1!=0 );
  data = pP1->aData;
  rc = sqlitepager_write(data);
  if( rc ) return rc;
  memcpy(data, zMagicHeader, sizeof(zMagicHeader));
  assert( sizeof(zMagicHeader)==16 );
  put2byte(&data[16], SQLITE_PAGE_SIZE);
................................................................................
**      sqliteBtreeCreateIndex()
**      sqliteBtreeClearTable()
**      sqliteBtreeDropTable()
**      sqliteBtreeInsert()
**      sqliteBtreeDelete()
**      sqliteBtreeUpdateMeta()
*/
static int fileBtreeBeginTrans(Btree *pBt){
  int rc;
  if( pBt->inTrans ) return SQLITE_ERROR;
  if( pBt->readOnly ) return SQLITE_READONLY;
  if( pBt->page1==0 ){
    rc = lockBtree(pBt);
    if( rc!=SQLITE_OK ){
      return rc;
    }
  }
  rc = sqlitepager_begin(pBt->page1);
  if( rc==SQLITE_OK ){
    rc = newDatabase(pBt);
  }
  if( rc==SQLITE_OK ){
    pBt->inTrans = 1;
    pBt->inCkpt = 0;
  }else{
    unlockBtreeIfUnused(pBt);
  }
  return rc;
}

/*
** Commit the transaction currently in progress.
**
** This will release the write lock on the database file.  If there
** are no active cursors, it also releases the read lock.
*/
static int fileBtreeCommit(Btree *pBt){
  int rc;
  rc = pBt->readOnly ? SQLITE_OK : sqlitepager_commit(pBt->pPager);
  pBt->inTrans = 0;
  pBt->inCkpt = 0;
  unlockBtreeIfUnused(pBt);
  return rc;
}

/*
** Rollback the transaction in progress.  All cursors will be
** invalided by this operation.  Any attempt to use a cursor
** that was open at the beginning of this operation will result
** in an error.
**
** This will release the write lock on the database file.  If there
** are no active cursors, it also releases the read lock.
*/
static int fileBtreeRollback(Btree *pBt){
  int rc;
  BtCursor *pCur;
  if( pBt->inTrans==0 ) return SQLITE_OK;
  pBt->inTrans = 0;
  pBt->inCkpt = 0;
  rc = pBt->readOnly ? SQLITE_OK : sqlitepager_rollback(pBt->pPager);
  for(pCur=pBt->pCursor; pCur; pCur=pCur->pNext){
    if( pCur->pPage && pCur->pPage->pBt==0 ){
      sqlitepager_unref(pCur->pPage);

      pCur->pPage = 0;
    }
  }
  unlockBtreeIfUnused(pBt);
  return rc;
}

................................................................................
** main transaction.  You must start a transaction before starting a
** checkpoint.  The checkpoint is ended automatically if the transaction
** commits or rolls back.
**
** Only one checkpoint may be active at a time.  It is an error to try
** to start a new checkpoint if another checkpoint is already active.
*/
static int fileBtreeBeginCkpt(Btree *pBt){
  int rc;
  if( !pBt->inTrans || pBt->inCkpt ){
    return pBt->readOnly ? SQLITE_READONLY : SQLITE_ERROR;
  }
  rc = pBt->readOnly ? SQLITE_OK : sqlitepager_ckpt_begin(pBt->pPager);
  pBt->inCkpt = 1;
  return rc;
}


/*
** Commit a checkpoint to transaction currently in progress.  If no
** checkpoint is active, this is a no-op.
*/
static int fileBtreeCommitCkpt(Btree *pBt){
  int rc;
  if( pBt->inCkpt && !pBt->readOnly ){
    rc = sqlitepager_ckpt_commit(pBt->pPager);
  }else{
    rc = SQLITE_OK;
  }
  pBt->inCkpt = 0;
  return rc;
}

/*
** Rollback the checkpoint to the current transaction.  If there
** is no active checkpoint or transaction, this routine is a no-op.
**
** All cursors will be invalided by this operation.  Any attempt
** to use a cursor that was open at the beginning of this operation
** will result in an error.
*/
static int fileBtreeRollbackCkpt(Btree *pBt){
  int rc;
  BtCursor *pCur;
  if( pBt->inCkpt==0 || pBt->readOnly ) return SQLITE_OK;
  rc = sqlitepager_ckpt_rollback(pBt->pPager);
  for(pCur=pBt->pCursor; pCur; pCur=pCur->pNext){
    if( pCur->pPage && pCur->pPage->isInit==0 ){
      sqlitepager_unref(pCur->pPage);

      pCur->pPage = 0;
    }
  }
  pBt->inCkpt = 0;
  return rc;
}


















/*
** Create a new cursor for the BTree whose root is on the page
** iTable.  The act of acquiring a cursor gets a read lock on 
** the database file.
**
** If wrFlag==0, then the cursor can only be used for reading.
................................................................................
** intend to use the sqliteBtreeNext() system call.  All other cursors
** should be opened with wrFlag==1 even if they never really intend
** to write.
** 
** No checking is done to make sure that page iTable really is the
** root page of a b-tree.  If it is not, then the cursor acquired
** will not work correctly.






*/
static 
int fileBtreeCursor(Btree *pBt, int iTable, int wrFlag, BtCursor **ppCur){








  int rc;
  BtCursor *pCur, *pRing;

  if( pBt->readOnly && wrFlag ){
    *ppCur = 0;
    return SQLITE_READONLY;
  }
................................................................................
  }
  pCur = sqliteMalloc( sizeof(*pCur) );
  if( pCur==0 ){
    rc = SQLITE_NOMEM;
    goto create_cursor_exception;
  }
  pCur->pgnoRoot = (Pgno)iTable;
  rc = sqlitepager_get(pBt->pPager, pCur->pgnoRoot, (void**)&pCur->pPage);
  if( rc!=SQLITE_OK ){
    goto create_cursor_exception;
  }
  rc = initPage(pBt, pCur->pPage, pCur->pgnoRoot, 0);
  if( rc!=SQLITE_OK ){
    goto create_cursor_exception;
  }
  pCur->pOps = &sqliteBtreeCursorOps;

  pCur->pBt = pBt;
  pCur->wrFlag = wrFlag;
  pCur->idx = 0;
  pCur->eSkip = SKIP_INVALID;
  pCur->pNext = pBt->pCursor;
  if( pCur->pNext ){
    pCur->pNext->pPrev = pCur;
................................................................................
  pBt->pCursor = pCur;
  *ppCur = pCur;
  return SQLITE_OK;

create_cursor_exception:
  *ppCur = 0;
  if( pCur ){
    if( pCur->pPage ) sqlitepager_unref(pCur->pPage);
    sqliteFree(pCur);
  }
  unlockBtreeIfUnused(pBt);
  return rc;
}

/*
** Close a cursor.  The read lock on the database file is released
** when the last cursor is closed.
*/
static int fileBtreeCloseCursor(BtCursor *pCur){
  Btree *pBt = pCur->pBt;
  if( pCur->pPrev ){
    pCur->pPrev->pNext = pCur->pNext;
  }else{
    pBt->pCursor = pCur->pNext;
  }
  if( pCur->pNext ){
    pCur->pNext->pPrev = pCur->pPrev;
  }
  if( pCur->pPage ){
    sqlitepager_unref(pCur->pPage);
  }
  if( pCur->pShared!=pCur ){
    BtCursor *pRing = pCur->pShared;
    while( pRing->pShared!=pCur ){ pRing = pRing->pShared; }
    pRing->pShared = pCur->pShared;
  }
  unlockBtreeIfUnused(pBt);
  sqliteFree(pCur);
................................................................................
** The temporary cursor is not on the cursor list for the Btree.
*/
static void getTempCursor(BtCursor *pCur, BtCursor *pTempCur){
  memcpy(pTempCur, pCur, sizeof(*pCur));
  pTempCur->pNext = 0;
  pTempCur->pPrev = 0;
  if( pTempCur->pPage ){
    sqlitepager_ref(pTempCur->pPage);
  }
}

/*
** Delete a temporary cursor such as was made by the CreateTemporaryCursor()
** function above.
*/
static void releaseTempCursor(BtCursor *pCur){
  if( pCur->pPage ){
    sqlitepager_unref(pCur->pPage);
  }
}

/*
** Set *pSize to the number of bytes of key in the entry the
** cursor currently points to.  Always return SQLITE_OK.
** Failure is not possible.  If the cursor is not currently
** pointing to an entry (which can happen, for example, if
** the database is empty) then *pSize is set to 0.
*/
static int fileBtreeKeySize(BtCursor *pCur, int *pSize){
  Cell *pCell;
  MemPage *pPage;

  pPage = pCur->pPage;
  assert( pPage!=0 );
  if( pCur->idx >= pPage->nCell ){
    *pSize = 0;
  }else{
    pCell = pPage->apCell[pCur->idx];
    *pSize = NKEY(pCur->pBt, pCell->h);







  }
  return SQLITE_OK;
}

/*
** Read payload information from the entry that the pCur cursor is
** pointing to.  Begin reading the payload at "offset" and read
** a total of "amt" bytes.  Put the result in zBuf.
**
** This routine does not make a distinction between key and data.
** It just reads bytes from the payload area.
*/
static int getPayload(BtCursor *pCur, int offset, int amt, char *zBuf){






  char *aPayload;
  Pgno nextPage;
  int rc;

  Btree *pBt = pCur->pBt;



  assert( pCur!=0 && pCur->pPage!=0 );


  assert( pCur->idx>=0 && pCur->idx<pCur->pPage->nCell );
  aPayload = pCur->pPage->apCell[pCur->idx]->aPayload;






















  if( offset<MX_LOCAL_PAYLOAD ){
    int a = amt;
    if( a+offset>MX_LOCAL_PAYLOAD ){
      a = MX_LOCAL_PAYLOAD - offset;

    }
    memcpy(zBuf, &aPayload[offset], a);
    if( a==amt ){
      return SQLITE_OK;
    }
    offset = 0;
    zBuf += a;
    amt -= a;
  }else{
    offset -= MX_LOCAL_PAYLOAD;
  }
  if( amt>0 ){
    nextPage = SWAB32(pBt, pCur->pPage->apCell[pCur->idx]->ovfl);
  }

  while( amt>0 && nextPage ){
    OverflowPage *pOvfl;
    rc = sqlitepager_get(pBt->pPager, nextPage, (void**)&pOvfl);
    if( rc!=0 ){
      return rc;
    }
    nextPage = SWAB32(pBt, pOvfl->iNext);
    if( offset<OVERFLOW_SIZE ){
      int a = amt;
      if( a + offset > OVERFLOW_SIZE ){
        a = OVERFLOW_SIZE - offset;
      }
      memcpy(zBuf, &pOvfl->aPayload[offset], a);
      offset = 0;
      amt -= a;
      zBuf += a;
    }else{
      offset -= OVERFLOW_SIZE;
    }
    sqlitepager_unref(pOvfl);
  }
  if( amt>0 ){
    return SQLITE_CORRUPT;
  }
  return SQLITE_OK;
}

/*
** Read part of the key associated with cursor pCur.  A maximum
** of "amt" bytes will be transfered into zBuf[].  The transfer
** begins at "offset".  The number of bytes actually read is
** returned. 
**

** Change:  It used to be that the amount returned will be smaller
** than the amount requested if there are not enough bytes in the key
** to satisfy the request.  But now, it must be the case that there
** is enough data available to satisfy the request.  If not, an exception
** is raised.  The change was made in an effort to boost performance
** by eliminating unneeded tests.
*/
static int fileBtreeKey(BtCursor *pCur, int offset, int amt, char *zBuf){
  MemPage *pPage;

  assert( amt>=0 );
  assert( offset>=0 );
  assert( pCur->pPage!=0 );
  pPage = pCur->pPage;
  if( pCur->idx >= pPage->nCell ){

    return 0;
  }
  assert( amt+offset <= NKEY(pCur->pBt, pPage->apCell[pCur->idx]->h) );
  getPayload(pCur, offset, amt, zBuf);



































  return amt;
}




/*
** Set *pSize to the number of bytes of data in the entry the
** cursor currently points to.  Always return SQLITE_OK.
** Failure is not possible.  If the cursor is not currently
** pointing to an entry (which can happen, for example, if
** the database is empty) then *pSize is set to 0.
*/
static int fileBtreeDataSize(BtCursor *pCur, int *pSize){
  Cell *pCell;
  MemPage *pPage;

  pPage = pCur->pPage;
  assert( pPage!=0 );
  if( pCur->idx >= pPage->nCell ){
    *pSize = 0;
  }else{


    pCell = pPage->apCell[pCur->idx];
    *pSize = NDATA(pCur->pBt, pCell->h);







  }
  return SQLITE_OK;
}

/*
** Read part of the data associated with cursor pCur.  A maximum
** of "amt" bytes will be transfered into zBuf[].  The transfer
** begins at "offset".  The number of bytes actually read is
** returned.  The amount returned will be smaller than the
** amount requested if there are not enough bytes in the data
** to satisfy the request.

*/
static int fileBtreeData(BtCursor *pCur, int offset, int amt, char *zBuf){
  Cell *pCell;
  MemPage *pPage;

  assert( amt>=0 );
  assert( offset>=0 );
  assert( pCur->pPage!=0 );
  pPage = pCur->pPage;
  if( pCur->idx >= pPage->nCell ){
    return 0;
  }
  pCell = pPage->apCell[pCur->idx];
  assert( amt+offset <= NDATA(pCur->pBt, pCell->h) );
  getPayload(pCur, offset + NKEY(pCur->pBt, pCell->h), amt, zBuf);
  return amt;
}

/*
** Compare an external key against the key on the entry that pCur points to.
**
** The external key is pKey and is nKey bytes long.  The last nIgnore bytes
** of the key associated with pCur are ignored, as if they do not exist.
** (The normal case is for nIgnore to be zero in which case the entire
** internal key is used in the comparison.)
**
** The comparison result is written to *pRes as follows:
**
**    *pRes<0    This means pCur<pKey
**
**    *pRes==0   This means pCur==pKey for all nKey bytes
**
**    *pRes>0    This means pCur>pKey
**
** When one key is an exact prefix of the other, the shorter key is
** considered less than the longer one.  In order to be equal the
** keys must be exactly the same length. (The length of the pCur key
** is the actual key length minus nIgnore bytes.)
*/
static int fileBtreeKeyCompare(
  BtCursor *pCur,       /* Pointer to entry to compare against */
  const void *pKey,     /* Key to compare against entry that pCur points to */
  int nKey,             /* Number of bytes in pKey */
  int nIgnore,          /* Ignore this many bytes at the end of pCur */
  int *pResult          /* Write the result here */
){
  Pgno nextPage;
  int n, c, rc, nLocal;
  Cell *pCell;
  Btree *pBt = pCur->pBt;
  const char *zKey  = (const char*)pKey;

  assert( pCur->pPage );
  assert( pCur->idx>=0 && pCur->idx<pCur->pPage->nCell );
  pCell = pCur->pPage->apCell[pCur->idx];
  nLocal = NKEY(pBt, pCell->h) - nIgnore;
  if( nLocal<0 ) nLocal = 0;
  n = nKey<nLocal ? nKey : nLocal;
  if( n>MX_LOCAL_PAYLOAD ){
    n = MX_LOCAL_PAYLOAD;
  }
  c = memcmp(pCell->aPayload, zKey, n);
  if( c!=0 ){
    *pResult = c;
    return SQLITE_OK;
  }
  zKey += n;
  nKey -= n;
  nLocal -= n;
  nextPage = SWAB32(pBt, pCell->ovfl);
  while( nKey>0 && nLocal>0 ){
    OverflowPage *pOvfl;
    if( nextPage==0 ){
      return SQLITE_CORRUPT;
    }
    rc = sqlitepager_get(pBt->pPager, nextPage, (void**)&pOvfl);
    if( rc ){
      return rc;
    }
    nextPage = SWAB32(pBt, pOvfl->iNext);
    n = nKey<nLocal ? nKey : nLocal;
    if( n>OVERFLOW_SIZE ){
      n = OVERFLOW_SIZE;
    }
    c = memcmp(pOvfl->aPayload, zKey, n);
    sqlitepager_unref(pOvfl);
    if( c!=0 ){
      *pResult = c;
      return SQLITE_OK;
    }
    nKey -= n;
    nLocal -= n;
    zKey += n;
  }
  if( c==0 ){
    c = nLocal - nKey;
  }
  *pResult = c;
  return SQLITE_OK;
}

/*
** Move the cursor down to a new child page.  The newPgno argument is the
** page number of the child page in the byte order of the disk image.
*/
static int moveToChild(BtCursor *pCur, int newPgno){
  int rc;
  MemPage *pNewPage;


  Btree *pBt = pCur->pBt;

  newPgno = SWAB32(pBt, newPgno);
  rc = sqlitepager_get(pBt->pPager, newPgno, (void**)&pNewPage);
  if( rc ) return rc;
  rc = initPage(pBt, pNewPage, newPgno, pCur->pPage);

  if( rc ) return rc;
  assert( pCur->idx>=pCur->pPage->nCell
          || pCur->pPage->apCell[pCur->idx]->h.leftChild==SWAB32(pBt,newPgno) );
  assert( pCur->idx<pCur->pPage->nCell
          || pCur->pPage->u.hdr.rightChild==SWAB32(pBt,newPgno) );
  pNewPage->idxParent = pCur->idx;

  pCur->pPage->idxShift = 0;
  sqlitepager_unref(pCur->pPage);

  pCur->pPage = pNewPage;
  pCur->idx = 0;
  if( pNewPage->nCell<1 ){
    return SQLITE_CORRUPT;
  }
  return SQLITE_OK;
}
................................................................................
** the largest cell index.
*/
static void moveToParent(BtCursor *pCur){
  Pgno oldPgno;
  MemPage *pParent;
  MemPage *pPage;
  int idxParent;

  pPage = pCur->pPage;
  assert( pPage!=0 );
  pParent = pPage->pParent;
  assert( pParent!=0 );
  idxParent = pPage->idxParent;
  sqlitepager_ref(pParent);

  sqlitepager_unref(pPage);
  pCur->pPage = pParent;
  assert( pParent->idxShift==0 );
  if( pParent->idxShift==0 ){
    pCur->idx = idxParent;
#ifndef NDEBUG  
    /* Verify that pCur->idx is the correct index to point back to the child
    ** page we just came from 
    */
    oldPgno = SWAB32(pCur->pBt, sqlitepager_pagenumber(pPage));
    if( pCur->idx<pParent->nCell ){
      assert( pParent->apCell[idxParent]->h.leftChild==oldPgno );

    }else{
      assert( pParent->u.hdr.rightChild==oldPgno );

    }
#endif
  }else{
    /* The MemPage.idxShift flag indicates that cell indices might have 
    ** changed since idxParent was set and hence idxParent might be out
    ** of date.  So recompute the parent cell index by scanning all cells
    ** and locating the one that points to the child we just came from.
    */
    int i;
    pCur->idx = pParent->nCell;
    oldPgno = SWAB32(pCur->pBt, sqlitepager_pagenumber(pPage));
    for(i=0; i<pParent->nCell; i++){
      if( pParent->apCell[i]->h.leftChild==oldPgno ){

        pCur->idx = i;
        break;
      }
    }
  }
}

/*
** Move the cursor to the root page
*/
static int moveToRoot(BtCursor *pCur){
  MemPage *pNew;
  int rc;
  Btree *pBt = pCur->pBt;

  rc = sqlitepager_get(pBt->pPager, pCur->pgnoRoot, (void**)&pNew);
  if( rc ) return rc;
  rc = initPage(pBt, pNew, pCur->pgnoRoot, 0);
  if( rc ) return rc;
  sqlitepager_unref(pCur->pPage);
  pCur->pPage = pNew;
  pCur->idx = 0;
  return SQLITE_OK;
}

/*
** Move the cursor down to the left-most leaf entry beneath the
** entry to which it is currently pointing.
*/
static int moveToLeftmost(BtCursor *pCur){
  Pgno pgno;
  int rc;


  while( (pgno = pCur->pPage->apCell[pCur->idx]->h.leftChild)!=0 ){



    rc = moveToChild(pCur, pgno);
    if( rc ) return rc;
  }
  return SQLITE_OK;
}

/*
................................................................................
** between moveToLeftmost() and moveToRightmost().  moveToLeftmost()
** finds the left-most entry beneath the *entry* whereas moveToRightmost()
** finds the right-most entry beneath the *page*.
*/
static int moveToRightmost(BtCursor *pCur){
  Pgno pgno;
  int rc;


  while( (pgno = pCur->pPage->u.hdr.rightChild)!=0 ){


    pCur->idx = pCur->pPage->nCell;
    rc = moveToChild(pCur, pgno);
    if( rc ) return rc;
  }
  pCur->idx = pCur->pPage->nCell - 1;
  return SQLITE_OK;
}

/* Move the cursor to the first entry in the table.  Return SQLITE_OK
** on success.  Set *pRes to 0 if the cursor actually points to something
** or set *pRes to 1 if the table is empty.
*/
static int fileBtreeFirst(BtCursor *pCur, int *pRes){
  int rc;
  if( pCur->pPage==0 ) return SQLITE_ABORT;
  rc = moveToRoot(pCur);
  if( rc ) return rc;
  if( pCur->pPage->nCell==0 ){
    *pRes = 1;
    return SQLITE_OK;
................................................................................
  return rc;
}

/* Move the cursor to the last entry in the table.  Return SQLITE_OK
** on success.  Set *pRes to 0 if the cursor actually points to something
** or set *pRes to 1 if the table is empty.
*/
static int fileBtreeLast(BtCursor *pCur, int *pRes){
  int rc;
  if( pCur->pPage==0 ) return SQLITE_ABORT;
  rc = moveToRoot(pCur);
  if( rc ) return rc;
  assert( pCur->pPage->isInit );
  if( pCur->pPage->nCell==0 ){
    *pRes = 1;
................................................................................
  }
  *pRes = 0;
  rc = moveToRightmost(pCur);
  pCur->eSkip = SKIP_NONE;
  return rc;
}

/* Move the cursor so that it points to an entry near pKey.
** Return a success code.





**
** If an exact match is not found, then the cursor is always
** left pointing at a leaf page which would hold the entry if it
** were present.  The cursor might point to an entry that comes
** before or after the key.
**
** The result of comparing the key with the entry to which the
................................................................................
**
**     *pRes==0     The cursor is left pointing at an entry that
**                  exactly matches pKey.
**
**     *pRes>0      The cursor is left pointing at an entry that
**                  is larger than pKey.
*/
static
int fileBtreeMoveto(BtCursor *pCur, const void *pKey, int nKey, int *pRes){
  int rc;
  if( pCur->pPage==0 ) return SQLITE_ABORT;
  pCur->eSkip = SKIP_NONE;
  rc = moveToRoot(pCur);
  if( rc ) return rc;
  for(;;){
    int lwr, upr;
    Pgno chldPg;
    MemPage *pPage = pCur->pPage;
    int c = -1;  /* pRes return if table is empty must be -1 */
    lwr = 0;
    upr = pPage->nCell-1;
    while( lwr<=upr ){


      pCur->idx = (lwr+upr)/2;
      rc = fileBtreeKeyCompare(pCur, pKey, nKey, 0, &c);

















      if( rc ) return rc;

      if( c==0 ){
        pCur->iMatch = c;
        if( pRes ) *pRes = 0;
        return SQLITE_OK;
      }
      if( c<0 ){
        lwr = pCur->idx+1;
      }else{
        upr = pCur->idx-1;
      }
    }
    assert( lwr==upr+1 );
    assert( pPage->isInit );


    if( lwr>=pPage->nCell ){
      chldPg = pPage->u.hdr.rightChild;

    }else{
      chldPg = pPage->apCell[lwr]->h.leftChild;

    }
    if( chldPg==0 ){
      pCur->iMatch = c;
      if( pRes ) *pRes = c;
      return SQLITE_OK;
    }
    pCur->idx = lwr;
................................................................................

/*
** Advance the cursor to the next entry in the database.  If
** successful then set *pRes=0.  If the cursor
** was already pointing to the last entry in the database before
** this routine was called, then set *pRes=1.
*/
static int fileBtreeNext(BtCursor *pCur, int *pRes){
  int rc;
  MemPage *pPage = pCur->pPage;
  assert( pRes!=0 );
  if( pPage==0 ){
    *pRes = 1;
    return SQLITE_ABORT;
  }
................................................................................
    pCur->eSkip = SKIP_NONE;
    *pRes = 0;
    return SQLITE_OK;
  }
  pCur->eSkip = SKIP_NONE;
  pCur->idx++;
  if( pCur->idx>=pPage->nCell ){
    if( pPage->u.hdr.rightChild ){
      rc = moveToChild(pCur, pPage->u.hdr.rightChild);
      if( rc ) return rc;
      rc = moveToLeftmost(pCur);
      *pRes = 0;
      return rc;
    }
    do{
      if( pPage->pParent==0 ){
................................................................................
      moveToParent(pCur);
      pPage = pCur->pPage;
    }while( pCur->idx>=pPage->nCell );
    *pRes = 0;
    return SQLITE_OK;
  }
  *pRes = 0;
  if( pPage->u.hdr.rightChild==0 ){
    return SQLITE_OK;
  }
  rc = moveToLeftmost(pCur);
  return rc;
}

/*
** Step the cursor to the back to the previous entry in the database.  If
** successful then set *pRes=0.  If the cursor
** was already pointing to the first entry in the database before
** this routine was called, then set *pRes=1.
*/
static int fileBtreePrevious(BtCursor *pCur, int *pRes){
  int rc;
  Pgno pgno;
  MemPage *pPage;
  pPage = pCur->pPage;
  if( pPage==0 ){
    *pRes = 1;
    return SQLITE_ABORT;
................................................................................
  if( pCur->eSkip==SKIP_PREV ){
    pCur->eSkip = SKIP_NONE;
    *pRes = 0;
    return SQLITE_OK;
  }
  pCur->eSkip = SKIP_NONE;
  assert( pCur->idx>=0 );
  if( (pgno = pPage->apCell[pCur->idx]->h.leftChild)!=0 ){

    rc = moveToChild(pCur, pgno);
    if( rc ) return rc;
    rc = moveToRightmost(pCur);
  }else{
    while( pCur->idx==0 ){
      if( pPage->pParent==0 ){
        if( pRes ) *pRes = 1;
................................................................................
**
** If the "nearby" parameter is not 0, then a (feeble) effort is made to 
** locate a page close to the page number "nearby".  This can be used in an
** attempt to keep related pages close to each other in the database file,
** which in turn can make database access faster.
*/
static int allocatePage(Btree *pBt, MemPage **ppPage, Pgno *pPgno, Pgno nearby){

  PageOne *pPage1 = pBt->page1;

  int rc;
  if( pPage1->freeList ){
    OverflowPage *pOvfl;
    FreelistInfo *pInfo;







    rc = sqlitepager_write(pPage1);
    if( rc ) return rc;
    SWAB_ADD(pBt, pPage1->nFree, -1);
    rc = sqlitepager_get(pBt->pPager, SWAB32(pBt, pPage1->freeList),
                        (void**)&pOvfl);


    if( rc ) return rc;
    rc = sqlitepager_write(pOvfl);
    if( rc ){
      sqlitepager_unref(pOvfl);

      return rc;
    }
    pInfo = (FreelistInfo*)pOvfl->aPayload;

    if( pInfo->nFree==0 ){
      *pPgno = SWAB32(pBt, pPage1->freeList);
      pPage1->freeList = pOvfl->iNext;




      *ppPage = (MemPage*)pOvfl;
    }else{

      int closest, n;
      n = SWAB32(pBt, pInfo->nFree);

      if( n>1 && nearby>0 ){
        int i, dist;
        closest = 0;
        dist = SWAB32(pBt, pInfo->aFree[0]) - nearby;

        if( dist<0 ) dist = -dist;
        for(i=1; i<n; i++){
          int d2 = SWAB32(pBt, pInfo->aFree[i]) - nearby;

          if( d2<0 ) d2 = -d2;
          if( d2<dist ) closest = i;
        }
      }else{
        closest = 0;
      }
      SWAB_ADD(pBt, pInfo->nFree, -1);
      *pPgno = SWAB32(pBt, pInfo->aFree[closest]);
      pInfo->aFree[closest] = pInfo->aFree[n-1];
      rc = sqlitepager_get(pBt->pPager, *pPgno, (void**)ppPage);
      sqlitepager_unref(pOvfl);
      if( rc==SQLITE_OK ){
        sqlitepager_dont_rollback(*ppPage);
        rc = sqlitepager_write(*ppPage);
      }
    }
  }else{
    *pPgno = sqlitepager_pagecount(pBt->pPager) + 1;
    rc = sqlitepager_get(pBt->pPager, *pPgno, (void**)ppPage);
    if( rc ) return rc;
    rc = sqlitepager_write(*ppPage);
  }
  return rc;
}

/*
** Add a page of the database file to the freelist.  Either pgno or
** pPage but not both may be 0. 
**
** sqlitepager_unref() is NOT called for pPage.
*/
static int freePage(Btree *pBt, void *pPage, Pgno pgno){
  PageOne *pPage1 = pBt->page1;
  OverflowPage *pOvfl = (OverflowPage*)pPage;
  int rc;
  int needUnref = 0;
  MemPage *pMemPage;

  if( pgno==0 ){
    assert( pOvfl!=0 );
    pgno = sqlitepager_pagenumber(pOvfl);
  }
  assert( pgno>2 );
  assert( sqlitepager_pagenumber(pOvfl)==pgno );
  pMemPage = (MemPage*)pPage;
  pMemPage->isInit = 0;
  if( pMemPage->pParent ){
    sqlitepager_unref(pMemPage->pParent);
    pMemPage->pParent = 0;
  }
  rc = sqlitepager_write(pPage1);
  if( rc ){
    return rc;
  }
  SWAB_ADD(pBt, pPage1->nFree, 1);
  if( pPage1->nFree!=0 && pPage1->freeList!=0 ){
    OverflowPage *pFreeIdx;
    rc = sqlitepager_get(pBt->pPager, SWAB32(pBt, pPage1->freeList),
                        (void**)&pFreeIdx);
    if( rc==SQLITE_OK ){
      FreelistInfo *pInfo = (FreelistInfo*)pFreeIdx->aPayload;
      int n = SWAB32(pBt, pInfo->nFree);
      if( n<(sizeof(pInfo->aFree)/sizeof(pInfo->aFree[0])) ){
        rc = sqlitepager_write(pFreeIdx);
        if( rc==SQLITE_OK ){
          pInfo->aFree[n] = SWAB32(pBt, pgno);
          SWAB_ADD(pBt, pInfo->nFree, 1);
          sqlitepager_unref(pFreeIdx);
          sqlitepager_dont_write(pBt->pPager, pgno);
          return rc;
        }
      }
      sqlitepager_unref(pFreeIdx);
    }
  }
  if( pOvfl==0 ){
    assert( pgno>0 );
    rc = sqlitepager_get(pBt->pPager, pgno, (void**)&pOvfl);
    if( rc ) return rc;
    needUnref = 1;
  }
  rc = sqlitepager_write(pOvfl);
  if( rc ){
    if( needUnref ) sqlitepager_unref(pOvfl);
    return rc;
  }
  pOvfl->iNext = pPage1->freeList;
  pPage1->freeList = SWAB32(pBt, pgno);
  memset(pOvfl->aPayload, 0, OVERFLOW_SIZE);
  if( needUnref ) rc = sqlitepager_unref(pOvfl);
  return rc;
}

/*
** Erase all the data out of a cell.  This involves returning overflow
** pages back the freelist.
*/
static int clearCell(Btree *pBt, Cell *pCell){
  Pager *pPager = pBt->pPager;
  OverflowPage *pOvfl;
  Pgno ovfl, nextOvfl;
  int rc;

  if( NKEY(pBt, pCell->h) + NDATA(pBt, pCell->h) <= MX_LOCAL_PAYLOAD ){
    return SQLITE_OK;
  }
  ovfl = SWAB32(pBt, pCell->ovfl);
  pCell->ovfl = 0;
  while( ovfl ){
    rc = sqlitepager_get(pPager, ovfl, (void**)&pOvfl);
    if( rc ) return rc;
    nextOvfl = SWAB32(pBt, pOvfl->iNext);
    rc = freePage(pBt, pOvfl, ovfl);
    if( rc ) return rc;
    sqlitepager_unref(pOvfl);
    ovfl = nextOvfl;
  }
  return SQLITE_OK;
}

/*
** Create a new cell from key and data.  Overflow pages are allocated as
** necessary and linked to this cell.  
*/
static int fillInCell(
  Btree *pBt,              /* The whole Btree.  Needed to allocate pages */
  Cell *pCell,             /* Populate this Cell structure */
  const void *pKey, int nKey,    /* The key */
  const void *pData,int nData    /* The data */
){
  OverflowPage *pOvfl, *pPrior;
  Pgno *pNext;
  int spaceLeft;
  int n, rc;
  int nPayload;
  const char *pPayload;
  char *pSpace;
  Pgno nearby = 0;

  pCell->h.leftChild = 0;
  pCell->h.nKey = SWAB16(pBt, nKey & 0xffff);
  pCell->h.nKeyHi = nKey >> 16;
  pCell->h.nData = SWAB16(pBt, nData & 0xffff);
  pCell->h.nDataHi = nData >> 16;
  pCell->h.iNext = 0;

  pNext = &pCell->ovfl;
  pSpace = pCell->aPayload;
  spaceLeft = MX_LOCAL_PAYLOAD;
  pPayload = pKey;
  pKey = 0;
  nPayload = nKey;
  pPrior = 0;
  while( nPayload>0 ){
    if( spaceLeft==0 ){
      rc = allocatePage(pBt, (MemPage**)&pOvfl, pNext, nearby);
      if( rc ){
        *pNext = 0;
      }else{
        nearby = *pNext;
      }
      if( pPrior ) sqlitepager_unref(pPrior);
      if( rc ){
        clearCell(pBt, pCell);
        return rc;
      }
      if( pBt->needSwab ) *pNext = swab32(*pNext);
      pPrior = pOvfl;
      spaceLeft = OVERFLOW_SIZE;
      pSpace = pOvfl->aPayload;
      pNext = &pOvfl->iNext;
















    }
    n = nPayload;
    if( n>spaceLeft ) n = spaceLeft;
    memcpy(pSpace, pPayload, n);

    nPayload -= n;
    if( nPayload==0 && pData ){
      pPayload = pData;


      nPayload = nData;
      pData = 0;
    }else{
      pPayload += n;
    }
    spaceLeft -= n;
    pSpace += n;
  }
  *pNext = 0;
  if( pPrior ){
    sqlitepager_unref(pPrior);
  }
  return SQLITE_OK;
}

/*
** Change the MemPage.pParent pointer on the page whose number is
** given in the second argument so that MemPage.pParent holds the
................................................................................

/*
** Insert a new record into the BTree.  The key is given by (pKey,nKey)
** and the data is given by (pData,nData).  The cursor is used only to
** define what database the record should be inserted into.  The cursor
** is left pointing at the new record.
*/
static int fileBtreeInsert(
  BtCursor *pCur,                /* Insert data into the table of this cursor */
  const void *pKey, int nKey,    /* The key of the new record */
  const void *pData, int nData   /* The data of the new record */
){
  Cell newCell;
  int rc;
  int loc;
................................................................................
  assert( !pBt->readOnly );
  if( !pCur->wrFlag ){
    return SQLITE_PERM;   /* Cursor not open for writing */
  }
  if( checkReadLocks(pCur) ){
    return SQLITE_LOCKED; /* The table pCur points to has a read lock */
  }
  rc = fileBtreeMoveto(pCur, pKey, nKey, &loc);
  if( rc ) return rc;
  pPage = pCur->pPage;
  assert( pPage->isInit );
  rc = sqlitepager_write(pPage);
  if( rc ) return rc;
  rc = fillInCell(pBt, &newCell, pKey, nKey, pData, nData);
  if( rc ) return rc;
................................................................................
** sqliteBtreeNext() after a delete and the cursor will be left
** pointing to the first entry after the deleted entry.  Similarly,
** pCur->eSkip is set to SKIP_PREV is the cursor is left pointing to
** the entry prior to the deleted entry so that a subsequent call to
** sqliteBtreePrevious() will always leave the cursor pointing at the
** entry immediately before the one that was deleted.
*/
static int fileBtreeDelete(BtCursor *pCur){
  MemPage *pPage = pCur->pPage;
  Cell *pCell;
  int rc;
  Pgno pgnoChild;
  Btree *pBt = pCur->pBt;

  assert( pPage->isInit );
................................................................................
    ** to be a leaf so we can use it.
    */
    BtCursor leafCur;
    Cell *pNext;
    int szNext;
    int notUsed;
    getTempCursor(pCur, &leafCur);
    rc = fileBtreeNext(&leafCur, &notUsed);
    if( rc!=SQLITE_OK ){
      if( rc!=SQLITE_NOMEM ) rc = SQLITE_CORRUPT;
      return rc;
    }
    rc = sqlitepager_write(leafCur.pPage);
    if( rc ) return rc;
    dropCell(pBt, pPage, pCur->idx, cellSize(pBt, pCell));
................................................................................
**
** In the current implementation, BTree tables and BTree indices are the 
** the same.  In the future, we may change this so that BTree tables
** are restricted to having a 4-byte integer key and arbitrary data and
** BTree indices are restricted to having an arbitrary key and no data.
** But for now, this routine also serves to create indices.
*/
static int fileBtreeCreateTable(Btree *pBt, int *piTable){
  MemPage *pRoot;
  Pgno pgnoRoot;
  int rc;
  if( !pBt->inTrans ){
    /* Must start a transaction first */
    return pBt->readOnly ? SQLITE_READONLY : SQLITE_ERROR;
  }
................................................................................
  sqlitepager_unref(pPage);
  return rc;
}

/*
** Delete all information from a single table in the database.
*/
static int fileBtreeClearTable(Btree *pBt, int iTable){
  int rc;
  BtCursor *pCur;
  if( !pBt->inTrans ){
    return pBt->readOnly ? SQLITE_READONLY : SQLITE_ERROR;
  }
  for(pCur=pBt->pCursor; pCur; pCur=pCur->pNext){
    if( pCur->pgnoRoot==(Pgno)iTable ){
      if( pCur->wrFlag==0 ) return SQLITE_LOCKED;
      moveToRoot(pCur);
    }
  }
  rc = clearDatabasePage(pBt, (Pgno)iTable, 0);
  if( rc ){
    fileBtreeRollback(pBt);
  }
  return rc;
}

/*
** Erase all information in a table and add the root of the table to
** the freelist.  Except, the root of the principle table (the one on
** page 2) is never added to the freelist.
*/
static int fileBtreeDropTable(Btree *pBt, int iTable){
  int rc;
  MemPage *pPage;
  BtCursor *pCur;
  if( !pBt->inTrans ){
    return pBt->readOnly ? SQLITE_READONLY : SQLITE_ERROR;
  }
  for(pCur=pBt->pCursor; pCur; pCur=pCur->pNext){
    if( pCur->pgnoRoot==(Pgno)iTable ){
      return SQLITE_LOCKED;  /* Cannot drop a table that has a cursor */
    }
  }
  rc = sqlitepager_get(pBt->pPager, (Pgno)iTable, (void**)&pPage);
  if( rc ) return rc;
  rc = fileBtreeClearTable(pBt, iTable);
  if( rc ) return rc;
  if( iTable>2 ){
    rc = freePage(pBt, pPage, iTable);
  }else{
    zeroPage(pBt, pPage);
  }
  sqlitepager_unref(pPage);
................................................................................
  return rc;
}
#endif

/*
** Read the meta-information out of a database file.
*/
static int fileBtreeGetMeta(Btree *pBt, int *aMeta){
  PageOne *pP1;
  int rc;
  int i;

  rc = sqlitepager_get(pBt->pPager, 1, (void**)&pP1);
  if( rc ) return rc;
  aMeta[0] = SWAB32(pBt, pP1->nFree);
  for(i=0; i<sizeof(pP1->aMeta)/sizeof(pP1->aMeta[0]); i++){
................................................................................
  sqlitepager_unref(pP1);
  return SQLITE_OK;
}

/*
** Write meta-information back into the database.
*/
static int fileBtreeUpdateMeta(Btree *pBt, int *aMeta){
  PageOne *pP1;
  int rc, i;
  if( !pBt->inTrans ){
    return pBt->readOnly ? SQLITE_READONLY : SQLITE_ERROR;
  }
  pP1 = pBt->page1;
  rc = sqlitepager_write(pP1);
................................................................................
}
#endif

/*
** Return the pager associated with a BTree.  This routine is used for
** testing and debugging only.
*/
static Pager *fileBtreePager(Btree *pBt){
  return pBt->pPager;
}

/*
** This structure is passed around through all the sanity checking routines
** in order to keep track of some global state information.
*/
................................................................................
** a table.  nRoot is the number of entries in aRoot.
**
** If everything checks out, this routine returns NULL.  If something is
** amiss, an error message is written into memory obtained from malloc()
** and a pointer to that error message is returned.  The calling function
** is responsible for freeing the error message when it is done.
*/
char *fileBtreeIntegrityCheck(Btree *pBt, int *aRoot, int nRoot){
  int i;
  int nRef;
  IntegrityCk sCheck;

  nRef = *sqlitepager_stats(pBt->pPager);
  if( lockBtree(pBt)!=SQLITE_OK ){
    return sqliteStrDup("Unable to acquire a read lock on the database");
................................................................................
  sqliteFree(sCheck.anRef);
  return sCheck.zErrMsg;
}

/*
** Return the full pathname of the underlying database file.
*/
static const char *fileBtreeGetFilename(Btree *pBt){
  assert( pBt->pPager!=0 );
  return sqlitepager_filename(pBt->pPager);
}

/*
** Copy the complete content of pBtFrom into pBtTo.  A transaction
** must be active for both files.
**
** The size of file pBtFrom may be reduced by this operation.
** If anything goes wrong, the transaction on pBtFrom is rolled back.
*/
static int fileBtreeCopyFile(Btree *pBtTo, Btree *pBtFrom){
  int rc = SQLITE_OK;
  Pgno i, nPage, nToPage;

  if( !pBtTo->inTrans || !pBtFrom->inTrans ) return SQLITE_ERROR;
  if( pBtTo->needSwab!=pBtFrom->needSwab ) return SQLITE_ERROR;
  if( pBtTo->pCursor ) return SQLITE_BUSY;
  memcpy(pBtTo->page1, pBtFrom->page1, SQLITE_USABLE_SIZE);
................................................................................
    sqlitepager_unref(pPage);
    sqlitepager_dont_write(pBtTo->pPager, i);
  }
  if( !rc && nPage<nToPage ){
    rc = sqlitepager_truncate(pBtTo->pPager, nPage);
  }
  if( rc ){
    fileBtreeRollback(pBtTo);
  }
  return rc;  
}

/*
** The following tables contain pointers to all of the interface
** routines for this implementation of the B*Tree backend.  To
** substitute a different implemention of the backend, one has merely
** to provide pointers to alternative functions in similar tables.
*/
static BtOps sqliteBtreeOps = {
    fileBtreeClose,
    fileBtreeSetCacheSize,
    fileBtreeSetSafetyLevel,
    fileBtreeBeginTrans,
    fileBtreeCommit,
    fileBtreeRollback,
    fileBtreeBeginCkpt,
    fileBtreeCommitCkpt,
    fileBtreeRollbackCkpt,
    fileBtreeCreateTable,
    fileBtreeCreateTable,  /* Really sqliteBtreeCreateIndex() */
    fileBtreeDropTable,
    fileBtreeClearTable,
    fileBtreeCursor,
    fileBtreeGetMeta,
    fileBtreeUpdateMeta,
    fileBtreeIntegrityCheck,
    fileBtreeGetFilename,
    fileBtreeCopyFile,
    fileBtreePager,
#ifdef SQLITE_TEST
    fileBtreePageDump,
#endif
};
static BtCursorOps sqliteBtreeCursorOps = {
    fileBtreeMoveto,
    fileBtreeDelete,
    fileBtreeInsert,
    fileBtreeFirst,
    fileBtreeLast,
    fileBtreeNext,
    fileBtreePrevious,
    fileBtreeKeySize,
    fileBtreeKey,
    fileBtreeKeyCompare,
    fileBtreeDataSize,
    fileBtreeData,
    fileBtreeCloseCursor,
#ifdef SQLITE_TEST
    fileBtreeCursorDump,
#endif
};

** a legal notice, here is a blessing:
**
**    May you do good and not evil.
**    May you find forgiveness for yourself and forgive others.
**    May you share freely, never taking more than you give.
**
*************************************************************************
** $Id: btree.c,v 1.105 2004/04/26 14:10:21 drh Exp $
**
** This file implements a external (disk-based) database using BTrees.
** For a detailed discussion of BTrees, refer to
**
**     Donald E. Knuth, THE ART OF COMPUTER PROGRAMMING, Volume 3:
**     "Sorting And Searching", pages 473-480. Addison-Wesley
**     Publishing Company, Reading, Massachusetts.
................................................................................
**
** Cells are of variable length.  The first cell begins on the byte defined
** in the page header.  Cells do not necessarily occur in order - they can
** skip around on the page.
**
**    SIZE    DESCRIPTION
**      2     Byte offset of the next cell.  0 if this is the last cell
**      4     Page number of the left child. Omitted if leaf flag is set.
**     var    Number of bytes of data. Omitted if the zerodata flag is set.
**     var    Number of bytes of key. Or the key itself if intkey flag is set.
**      *     Payload
**      4     First page of the overflow chain.  Omitted if no overflow
**
** Overflow pages form a linked list.  Each page except the last is completely
** filled with data (pagesize - 4 bytes).  The last page can have as little
** as 1 byte of data.
**
................................................................................
*/
#include "sqliteInt.h"
#include "pager.h"
#include "btree.h"
#include <assert.h>

/* Forward declarations */
typedef struct MemPage MemPage;


/*
** This is a magic string that appears at the beginning of every
** SQLite database in order to identify the file as a real database.
**                                  0123456789 123456 */
static const char zMagicHeader[] = "SQLite version 3";

................................................................................
**
** The pParent field points back to the parent page.  This allows us to
** walk up the BTree from any leaf to the root.  Care must be taken to
** unref() the parent page pointer when this page is no longer referenced.
** The pageDestructor() routine handles that chore.
*/
struct MemPage {
  struct Btree *pBt;             /* Pointer back to BTree structure */
  unsigned char *aData;          /* Pointer back to the start of the page */
  u8 isInit;                     /* True if previously initialized */
  u8 idxShift;                   /* True if Cell indices have changed */
  u8 isOverfull;                 /* Some aCell[] do not fit on page */
  u8 intKey;                     /* True if intkey flag is set */
  u8 leaf;                       /* True if leaf flag is set */
  u8 zeroData;                   /* True if zero data flag is set */
  u8 hdrOffset;                  /* 100 for page 1.  0 otherwise */
  Pgno pgno;                     /* Page number for this page */
  MemPage *pParent;              /* The parent of this page.  NULL for root */
  int idxParent;                 /* Index in pParent->aCell[] of this node */
  int nFree;                     /* Number of free bytes on the page */
  int nCell;                     /* Number of entries on this page */
  unsigned char **aCell;         /* Pointer to start of each cell */
};

/*
** The in-memory image of a disk page has the auxiliary information appended
** to the end.  EXTRA_SIZE is the number of bytes of space needed to hold
** that extra information.
*/
#define EXTRA_SIZE sizeof(MemPage)

/*
** Everything we need to know about an open database
*/
struct Btree {

  Pager *pPager;        /* The page cache */
  BtCursor *pCursor;    /* A list of all open cursors */
  MemPage *pPage1;      /* First page of the database */
  u8 inTrans;           /* True if a transaction is in progress */
  u8 inStmt;            /* True if there is a checkpoint on the transaction */
  u8 readOnly;          /* True if the underlying file is readonly */
  int pageSize;         /* Number of usable bytes on each page */
  int maxLocal;         /* Maximum local payload */
};
typedef Btree Bt;

/*
** A cursor is a pointer to a particular entry in the BTree.
** The entry is identified by its MemPage and the index in
** MemPage.apCell[] of the entry.
*/
struct BtCursor {

  Btree *pBt;               /* The Btree to which this cursor belongs */
  BtCursor *pNext, *pPrev;  /* Forms a linked list of all cursors */
  BtCursor *pShared;        /* Loop of cursors with the same root page */
  int (*xCompare)(void*,int,const void*,int,const void*); /* Key comp func */
  void *pArg;               /* First arg to xCompare() */
  Pgno pgnoRoot;            /* The root page of this tree */
  MemPage *pPage;           /* Page that contains the entry */
  int idx;                  /* Index of the entry in pPage->aCell[] */
  u8 wrFlag;                /* True if writable */
  u8 eSkip;                 /* Determines if next step operation is a no-op */
  u8 iMatch;                /* compare result from last sqliteBtreeMoveto() */
};

/*
** Legal values for BtCursor.eSkip.
*/
#define SKIP_NONE     0   /* Always step the cursor */
#define SKIP_NEXT     1   /* The next sqliteBtreeNext() is a no-op */
#define SKIP_PREV     2   /* The next sqliteBtreePrevious() is a no-op */
#define SKIP_INVALID  3   /* Calls to Next() and Previous() are invalid */




/*
** Read or write a two-, four-, and eight-byte big-endian integer values.
*/
static u32 get2byte(unsigned char *p){
  return (p[0]<<8) | p[1];
}
static u32 get4byte(unsigned char *p){
  return (p[0]<<24) | (p[1]<<16) | (p[2]<<8) | p[3];
}
static u64 get8byte(unsigned char *p){
  u64 v = get4byte(p);
  return (v<<32) | get4byte(&p[4]);
}
static void put2byte(unsigned char *p, u32 v){
  p[0] = v>>8;
  p[1] = v;
}
................................................................................
  do{
    p[i++] = v & 0x7f;
    v >>= 7;
  }while( v!=0 );
  p[i-1] |= 0x80;
  return i;
}

/*
** Parse a cell header and fill in the CellInfo structure.
*/
static void parseCellHeader(
  MemPage *pPage,         /* Page containing the cell */
  unsigned char *pCell,   /* The cell */
  u64 *pnData,            /* Number of bytes of data in payload */
  u64 *pnKey,             /* Number of bytes of key, or key value for intKey */
  int *pnHeader           /* Size of header in bytes.  Offset to payload */
){
  int n;
  if( pPage->leaf ){
    n = 2;
  }else{
    n = 6;
  }
  if( pPage->zeroData ){
    *pnData = 0;
  }else{
    n += getVarint(&pCell[n], pnData);
  }
  n += getVarint(pCell, pnKey);
  *pnHeader = n;
}

/*
** Compute the total number of bytes that a Cell needs on the main
** database page.  The number returned includes the Cell header,
** local payload storage, and the pointer to overflow pages (if
** applicable).  Additional space allocated on overflow pages
** is NOT included in the value returned from this routine.
*/
static int cellSize(MemPage *pPage, unsigned char *pCell){
  CellInfo info;
  int n;
  u64 nData, nKey;
  int nPayload, maxPayload;










  parseCellHeader(pPage, pCell, &nData, &nKey, &n);
  nPayload = (int)nData;
  if( !pPage->intKey ){




    nPayload += (int)nKey;
  }

  maxPayload = pPage->pBt->maxLocal;
  if( nPayload>maxPayload ){
    nPayload = maxPayload + 4;
  }
  return n + nPayload;
}

/*
** Defragment the page given.  All Cells are moved to the
** beginning of the page and all free space is collected 
** into one big FreeBlk at the end of the page.
*/
static void defragmentPage(MemPage *pPage){
  int pc, i, n, addr;
  int start, hdr, size;
  int leftover;
  unsigned char *oldPage;
  unsigned char newPage[SQLITE_PAGE_SIZE];

  assert( sqlitepager_iswriteable(pPage->aData) );
  assert( pPage->pBt!=0 );
  assert( pPage->pageSize <= SQLITE_PAGE_SIZE );
  oldPage = pPage->aData;
  hdr = pPage->hdrOffset;
  addr = 3+hdr;
  n = 6+hdr;
  if( !pPage->leaf ){
    n += 4;
  }
  start = n;
  pc = get2byte(&oldPage[addr]);
  i = 0;
  while( pc>0 ){
    assert( n<pPage->pBt->pageSize );
    size = cellSize(pPage, &oldPage[pc]);
    memcpy(&newPage[n], &oldPage[pc], size);
    put2byte(&newPage[addr],n);
    pPage->aCell[i] = &oldPage[n];
    n += size;
    addr = pc;
    pc = get2byte(&oldPage[pc]);
  }
  leftover = pPage->pBt->pageSize - n;
  assert( leftover>=0 );
  assert( pPage->nFree==leftover );
  if( leftover<4 ){
    oldPage[hdr+5] = leftover;
    leftover = 0;
    n = pPage->pBt->pageSize;
  }
  memcpy(&oldPage[start], &newPage[start], n-start);
  if( leftover==0 ){
    put2byte(&oldPage[hdr+3], 0);
  }else if( leftover>=4 ){
    put2byte(&oldPage[hdr+3], n);
    put2byte(&oldPage[n], 0);
................................................................................
** calls defragementPage() to consolidate all free space before 
** allocating the new chunk.
**
** Algorithm:  Carve a piece off of the first freeblock that is
** nByte in size or that larger.
*/
static int allocateSpace(MemPage *pPage, int nByte){
  int addr, pc, hdr;
  int size;
  unsigned char *data;
#ifndef NDEBUG
  int cnt = 0;
#endif

  data = pPage->aData;
................................................................................
  assert( pPage->pBt );
  if( nByte<4 ) nByte = 4;
  if( pPage->nFree<nByte || pPage->isOverfull ) return 0;
  hdr = pPage->hdrOffset;
  if( data[hdr+5]>=252 ){
    defragmentPage(pPage);
  }
  addr = hdr+1;
  pc = get2byte(&data[addr]);
  assert( addr<pc );
  assert( pc<=pPage->pageSize-4 );
  while( (size = get2byte(&data[pc+2]))<nByte ){
    addr = pc;
    pc = get2byte(&data[addr]);
    assert( pc<=pPage->pageSize-4 );
    assert( pc>=addr+size+4 || pc==0 );
    if( pc==0 ){
      assert( (cnt++)==0 );
      defragmentPage(pPage);
      assert( data[hdr+5]==0 );
      addr = pPage->hdrOffset+1;
      pc = get2byte(&data[addr]);
    }
  }
  assert( pc>0 && size>=nByte );
  assert( pc+size<=pPage->pageSize );
  if( size>nByte+4 ){
    put2byte(&data[addr], pc+nByte);
    put2byte(&data[pc+size], get2byte(&data[pc]));
    put2byte(&data[pc+size+2], size-nByte);
  }else{
    put2byte(&data[addr], get2byte(&data[pc]));
    data[hdr+5] += size-nByte;
  }
  pPage->nFree -= nByte;
  assert( pPage->nFree>=0 );
  return pc;
}

................................................................................
** and the size of the block is "size" bytes.
**
** Most of the effort here is involved in coalesing adjacent
** free blocks into a single big free block.
*/
static void freeSpace(MemPage *pPage, int start, int size){
  int end = start + size;  /* End of the segment being freed */
  int addr, pbegin, pend;
#ifndef NDEBUG
  int tsize = 0;          /* Total size of all freeblocks */
#endif
  unsigned char *data = pPage->aData;

  assert( pPage->pBt!=0 );
  assert( sqlitepager_iswriteable(data) );
  assert( start>=pPage->hdrOffset+6+(pPage->leaf?0:4) );
  assert( end<=pPage->pBt->pageSize );
  if( size<4 ) size = 4;

  /* Add the space back into the linked list of freeblocks */
  addr = pPage->hdrOffset + 1;
  while( (pbegin = get2byte(&data[addr]))<start && pbegin>0 ){
    assert( pbegin<=pPage->pBt->pageSize-4 );
    assert( pbegin>addr );
    addr = pbegin;
  }
  assert( pbegin<=pPage->pBt->pageSize-4 );
  assert( pbegin>addr || pbegin==0 );
  put2bytes(&data[addr], start);
  put2bytes(&data[start], pbegin);
  put2bytes(&data[start+2], size);
  pPage->nFree += size;

  /* Coalesce adjacent free blocks */
  addr = pPage->hdrOffset + 1;
  while( (pbegin = get2byte(&data[addr]))>0 ){
    int pnext, psize;
    assert( pbegin>addr );
    assert( pbegin<pPage->pBt->pageSize-4 );
    pnext = get2byte(&data[pbegin]);
    psize = get2byte(&data[pbegin+2]);
    if( pbegin + psize + 3 >= pnext && pnext>0 ){
      int frag = pnext - (pbegin+psize);
      assert( frag<=data[pPage->hdrOffset+5] );
      data[pPage->hdrOffset+5] -= frag;
      put2byte(&data[pbegin], get2byte(&data[pnext]));
      put2byte(&data[pbegin+2], pnext+get2byte(&data[pnext+2])-pbegin);
    }else{
      assert( (tsize += psize)>0 );
      addr = pbegin;
    }
  }
  assert( tsize+data[pPage->hdrOffset+5]==pPage->nFree );
}

#if 0
/*
** The following is the default comparison function for (non-integer)
** keys in the btrees.  This function returns negative, zero, or
** positive if the first key is less than, equal to, or greater than
** the second.
**
*/
................................................................................
    } 
  }
  return 0;

bad_key:
  return 1;
}
#endif

/*
** Initialize the auxiliary information for a disk block.
**
** The pParent parameter must be a pointer to the MemPage which
** is the parent of the page being initialized.  The root of a
** BTree has no parent and so for that page, pParent==NULL.
................................................................................
** Return SQLITE_OK on success.  If we see that the page does
** not contain a well-formed database page, then return 
** SQLITE_CORRUPT.  Note that a return of SQLITE_OK does not
** guarantee that the page is well-formed.  It only shows that
** we failed to detect any corruption.
*/
static int initPage(
  MemPage *pPage,        /* The page to be initialized */


  MemPage *pParent       /* The parent.  Might be NULL */
){

  int c, pc, i, hdr;
  int sumCell = 0;       /* Total size of all cells */



  assert( pPage->pBt!=0 );
  assert( pPage->aData == &((unsigned char*)pPage)[pPage->pBt->pageSize] );
  if( pPage->pParent ){
    assert( pPage->pParent==pParent );
    return SQLITE_OK;
  }
  if( pParent ){
    pPage->pParent = pParent;
    sqlitepager_ref(pParent->aData);
  }
  if( pPage->isInit ) return SQLITE_OK;

  pPage->nCell = 0;

  assert( sqlitepager_pagenumber(pPage->aData)==pPage->pgno );
  pPage->hdrOffset = hdr = pgnoThis==1 ? 100 : 0;
  c = pPage->aData[pPage->hdrOffset];
  pPage->intKey = (c & PTF_INTKEY)!=0;
  pPage->zeroData = (c & PTF_ZERODATA)!=0;
  pPage->leaf = (c & PTF_INTKEY)!=0;

  /* Initialize the cell count and cell pointers */
  pc = get2byte(&data[hdr+3]);
  while( pc>0 ){
................................................................................
  pPage->nFree = data[hdr+5];
  pc = get2byte(&data[hdr+1]);
  while( pc>0 ){
    int next, size;
    if( pc>=pBt->pageSize ) return SQLITE_CORRUPT;
    next = get2byte(&data[pc]);
    size = get2byte(&data[pc+2]);
    if( next>0 && next<=pc+size+3 ) return SQLITE_CORRUPT;
    pPage->nFree += size;
    pc = next;
  }
  if( pPage->nFree>=pBt->pageSize ) return SQLITE_CORRUPT;

  /* Sanity check:  Cells and freespace and header must sum to the size
  ** a page. */
................................................................................
/*
** Set up a raw page so that it looks like a database page holding
** no entries.
*/
static void zeroPage(MemPage *pPage, int flags){
  unsigned char *data = pPage->aData;
  Btree *pBt = pPage->pBt;
  int hdr = pPage->hdrOffset;
  int first;

  assert( sqlitepager_iswriteable(data) );
  memset(&data[hdr], 0, pBt->pageSize - hdr);
  data[hdr] = flags;
  first = hdr + 6 + 4*((flags&0x01)!=0);
  put2byte(&data[hdr+1], first);
................................................................................
  pPage->nCell = 0;
  pPage->nFree = pBt->pageSize - first;
  pPage->intKey = (flags & PTF_INTKEY)!=0;
  pPage->leaf = (flags & PTF_LEAF)!=0;
  pPage->zeroData = (flags & PTF_ZERODATA)!=0;
  pPage->hdrOffset = hdr;
}

/*
** Get a page from the pager.  Initialize the MemPage.pBt and
** MemPage.aData elements if needed.
*/
static int getPage(Btree *pBt, Pgno pgno, MemPage **ppPage){
  int rc;
  unsigned char *aData;
  MemPage *pPage;
  rc = sqlitepager_get(pBt->pPager, pgno, &aData);
  if( rc ) return rc;
  pPage = (MemPage*)aData[pBt->pageSize];
  pPage->aData = aData;
  pPage->pBt = pBt;
  pPage->pgno = pgno;
  *ppPage = pPage;
  return SQLITE_OK;
}

/*
** Release a MemPage.  This should be called once for each prior
** call to getPage.
*/
static int releasePage(MemPage *pPage){
  if( pPage ){
    assert( pPage->aData );
    assert( pPage->pBt );
    assert( &pPage->aData[pPage->pBt->pageSize]==(unsigned char*)pPage );
    sqlitepager_unref(pPage->aData);
  }
}

/*
** This routine is called when the reference count for a page
** reaches zero.  We need to unref the pParent pointer when that
** happens.
*/
static void pageDestructor(void *pData){
  MemPage *pPage = (MemPage*)&((char*)pData)[SQLITE_PAGE_SIZE];
  if( pPage->pParent ){
    MemPage *pParent = pPage->pParent;
    pPage->pParent = 0;
    releasepage(pParent);
  }
  sqliteFree(pPage->aCell);
  pPage->aCell = 0;
  pPage->isInit = 0;
}

/*
** Open a new database.
**
** Actually, this routine just sets up the internal data structures
** for accessing the database.  We do not open the database file 
................................................................................
** until the first page is loaded.
**
** zFilename is the name of the database file.  If zFilename is NULL
** a new database with a random name is created.  This randomly named
** database file will be deleted when sqliteBtreeClose() is called.
*/
int sqliteBtreeOpen(
  const char *zFilename,  /* Name of the file containing the BTree database */


  Btree **ppBtree,        /* Pointer to new Btree object written here */
  int nCache,             /* Number of cache pages */
  int flags               /* Options */
){
  Btree *pBt;
  int rc, i;
  int nCache = 2000;
  int omitJournal = 0;

  /*
  ** The following asserts make sure that structures used by the btree are
  ** the right size.  This is to guard against size changes that result
  ** when compiling on a different architecture.
  */
  assert( sizeof(u64)==8 );
................................................................................
  pBt = sqliteMalloc( sizeof(*pBt) );
  if( pBt==0 ){
    *ppBtree = 0;
    return SQLITE_NOMEM;
  }
  if( nCache<10 ) nCache = 10;
  rc = sqlitepager_open(&pBt->pPager, zFilename, nCache, EXTRA_SIZE,
                        (flags & BTREE_OMIT_JOURNAL)==0);
  if( rc!=SQLITE_OK ){
    if( pBt->pPager ) sqlitepager_close(pBt->pPager);
    sqliteFree(pBt);
    *ppBtree = 0;
    return rc;
  }
  sqlitepager_set_destructor(pBt->pPager, pageDestructor);
  pBt->pCursor = 0;
  pBt->page1 = 0;
  pBt->readOnly = sqlitepager_isreadonly(pBt->pPager);

  pBt->pageSize = SQLITE_PAGE_SIZE;
  pBt->maxLocal = (SQLITE_PAGE_SIZE-10)/4-12;
  *ppBtree = pBt;
  return SQLITE_OK;
}

/*
** Close an open database and invalidate all cursors.
*/
int sqlite3BtreeClose(Btree *pBt){
  while( pBt->pCursor ){
    sqlite3BtreeCloseCursor(pBt->pCursor);
  }
  sqlitepager_close(pBt->pPager);
  sqliteFree(pBt);
  return SQLITE_OK;
}

/*
................................................................................
** and the database cannot be corrupted if this program
** crashes.  But if the operating system crashes or there is
** an abrupt power failure when synchronous is off, the database
** could be left in an inconsistent and unrecoverable state.
** Synchronous is on by default so database corruption is not
** normally a worry.
*/
int sqilte3BtreeSetCacheSize(Btree *pBt, int mxPage){
  sqlitepager_set_cachesize(pBt->pPager, mxPage);
  return SQLITE_OK;
}

/*
** Change the way data is synced to disk in order to increase or decrease
** how well the database resists damage due to OS crashes and power
** failures.  Level 1 is the same as asynchronous (no syncs() occur and
** there is a high probability of damage)  Level 2 is the default.  There
** is a very low but non-zero probability of damage.  Level 3 reduces the
** probability of damage to near zero but with a write performance reduction.
*/
int sqlite3BtreeSetSafetyLevel(Btree *pBt, int level){
  sqlitepager_set_safety_level(pBt->pPager, level);
  return SQLITE_OK;
}

/*
** Get a reference to page1 of the database file.  This will
** also acquire a readlock on that file.
................................................................................
** well-formed database file, then SQLITE_CORRUPT is returned.
** SQLITE_BUSY is returned if the database is locked.  SQLITE_NOMEM
** is returned if we run out of memory.  SQLITE_PROTOCOL is returned
** if there is a locking protocol violation.
*/
static int lockBtree(Btree *pBt){
  int rc;
  MemPage *pPage1;
  if( pBt->page1 ) return SQLITE_OK;
  rc = getPage(pBt, 1, &pPage1);
  if( rc!=SQLITE_OK ) return rc;
  

  /* Do some checking to help insure the file we opened really is
  ** a valid database file. 
  */
  if( sqlitepager_pagecount(pBt->pPager)>0 ){
    if( memcmp(pPage1->aData, zMagicHeader, 16)!=0 ){
      rc = SQLITE_NOTADB;
      goto page1_init_failed;
    }
    /*** TBD:  Other header checks such as page size ****/
  }
  pBt->pPage1 = pPage1;
  return rc;

page1_init_failed:
  releasePage(pPage1);
  pBt->pPage1 = 0;
  return rc;
}

/*
** If there are no outstanding cursors and we are not in the middle
** of a transaction but there is a read lock on the database, then
** this routine unrefs the first page of the database file which 
................................................................................
** has the effect of releasing the read lock.
**
** If there are any outstanding cursors, this routine is a no-op.
**
** If there is a transaction in progress, this routine is a no-op.
*/
static void unlockBtreeIfUnused(Btree *pBt){
  if( pBt->inTrans==0 && pBt->pCursor==0 && pBt->pPage1!=0 ){
    releasePage(pBt->pPage1);
    pBt->pPage1 = 0;
    pBt->inTrans = 0;
    pBt->inStmt = 0;
  }
}

/*
** Create a new database by initializing the first page of the
** file.
*/
static int newDatabase(Btree *pBt){
  MemPage *pP1;
  unsigned char *data;
  int rc;
  if( sqlitepager_pagecount(pBt->pPager)>1 ) return SQLITE_OK;
  pP1 = pBt->pPage1;
  assert( pP1!=0 );
  data = pP1->aData;
  rc = sqlitepager_write(data);
  if( rc ) return rc;
  memcpy(data, zMagicHeader, sizeof(zMagicHeader));
  assert( sizeof(zMagicHeader)==16 );
  put2byte(&data[16], SQLITE_PAGE_SIZE);
................................................................................
**      sqliteBtreeCreateIndex()
**      sqliteBtreeClearTable()
**      sqliteBtreeDropTable()
**      sqliteBtreeInsert()
**      sqliteBtreeDelete()
**      sqliteBtreeUpdateMeta()
*/
int sqlite3BtreeBeginTrans(Btree *pBt){
  int rc;
  if( pBt->inTrans ) return SQLITE_ERROR;
  if( pBt->readOnly ) return SQLITE_READONLY;
  if( pBt->pPage1==0 ){
    rc = lockBtree(pBt);
    if( rc!=SQLITE_OK ){
      return rc;
    }
  }
  rc = sqlitepager_begin(pBt->pPage1->aData);
  if( rc==SQLITE_OK ){
    rc = newDatabase(pBt);
  }
  if( rc==SQLITE_OK ){
    pBt->inTrans = 1;
    pBt->inStmt = 0;
  }else{
    unlockBtreeIfUnused(pBt);
  }
  return rc;
}

/*
** Commit the transaction currently in progress.
**
** This will release the write lock on the database file.  If there
** are no active cursors, it also releases the read lock.
*/
int sqlite3BtreeCommit(Btree *pBt){
  int rc;
  rc = pBt->readOnly ? SQLITE_OK : sqlitepager_commit(pBt->pPager);
  pBt->inTrans = 0;
  pBt->inStmt = 0;
  unlockBtreeIfUnused(pBt);
  return rc;
}

/*
** Rollback the transaction in progress.  All cursors will be
** invalided by this operation.  Any attempt to use a cursor
** that was open at the beginning of this operation will result
** in an error.
**
** This will release the write lock on the database file.  If there
** are no active cursors, it also releases the read lock.
*/
int sqlite3BtreeRollback(Btree *pBt){
  int rc;
  BtCursor *pCur;
  if( pBt->inTrans==0 ) return SQLITE_OK;
  pBt->inTrans = 0;
  pBt->inStmt = 0;
  rc = pBt->readOnly ? SQLITE_OK : sqlitepager_rollback(pBt->pPager);
  for(pCur=pBt->pCursor; pCur; pCur=pCur->pNext){
    MemPage *pPage = pCur->pPage;
    if( pPage && !pPage->isInit ){
      releasePage(pPage);
      pCur->pPage = 0;
    }
  }
  unlockBtreeIfUnused(pBt);
  return rc;
}

................................................................................
** main transaction.  You must start a transaction before starting a
** checkpoint.  The checkpoint is ended automatically if the transaction
** commits or rolls back.
**
** Only one checkpoint may be active at a time.  It is an error to try
** to start a new checkpoint if another checkpoint is already active.
*/
int sqlite3BtreeBeginStmt(Btree *pBt){
  int rc;
  if( !pBt->inTrans || pBt->inStmt ){
    return pBt->readOnly ? SQLITE_READONLY : SQLITE_ERROR;
  }
  rc = pBt->readOnly ? SQLITE_OK : sqlitepager_ckpt_begin(pBt->pPager);
  pBt->inStmt = 1;
  return rc;
}


/*
** Commit a checkpoint to transaction currently in progress.  If no
** checkpoint is active, this is a no-op.
*/
int sqlite3BtreeCommitStmt(Btree *pBt){
  int rc;
  if( pBt->inStmt && !pBt->readOnly ){
    rc = sqlitepager_ckpt_commit(pBt->pPager);
  }else{
    rc = SQLITE_OK;
  }
  pBt->inStmt = 0;
  return rc;
}

/*
** Rollback the checkpoint to the current transaction.  If there
** is no active checkpoint or transaction, this routine is a no-op.
**
** All cursors will be invalided by this operation.  Any attempt
** to use a cursor that was open at the beginning of this operation
** will result in an error.
*/
int sqlite3BtreeRollbackStmt(Btree *pBt){
  int rc;
  BtCursor *pCur;
  if( pBt->inStmt==0 || pBt->readOnly ) return SQLITE_OK;
  rc = sqlitepager_ckpt_rollback(pBt->pPager);
  for(pCur=pBt->pCursor; pCur; pCur=pCur->pNext){
    MemPage *pPage = pCur->pPage;
    if( pPage && !pPage->isInit ){
      releasePage(pPage);
      pCur->pPage = 0;
    }
  }
  pBt->inStmt = 0;
  return rc;
}

/*
** Default key comparison function to be used if no comparison function
** is specified on the sqlite3BtreeCursor() call.
*/
static int dfltCompare(
  void *NotUsed,             /* User data is not used */
  int n1, const void *p1,    /* First key to compare */
  int n2, const void *p2     /* Second key to compare */
){
  int c;
  c = memcmp(p1, p2, n1<n2 ? n1 : n2);
  if( c==0 ){
    c = n1 - n2;
  }
  return c;
}

/*
** Create a new cursor for the BTree whose root is on the page
** iTable.  The act of acquiring a cursor gets a read lock on 
** the database file.
**
** If wrFlag==0, then the cursor can only be used for reading.
................................................................................
** intend to use the sqliteBtreeNext() system call.  All other cursors
** should be opened with wrFlag==1 even if they never really intend
** to write.
** 
** No checking is done to make sure that page iTable really is the
** root page of a b-tree.  If it is not, then the cursor acquired
** will not work correctly.
**
** The comparison function must be logically the same for every cursor
** on a particular table.  Changing the comparison function will result
** in incorrect operations.  If the comparison function is NULL, a
** default comparison function is used.  The comparison function is
** always ignored for INTKEY tables.
*/


int sqlite3BtreeCursor(
  Btree *pBt,                                 /* The btree */
  int iTable,                                 /* Root page of table to open */
  int wrFlag,                                 /* 1 to write. 0 read-only */
  int (*xCmp)(void*,int,const void*,int,const void*), /* Key Comparison func */
  void *pArg,                                 /* First arg to xCompare() */
  BtCursor **ppCur                            /* Write new cursor here */
){
  int rc;
  BtCursor *pCur, *pRing;

  if( pBt->readOnly && wrFlag ){
    *ppCur = 0;
    return SQLITE_READONLY;
  }
................................................................................
  }
  pCur = sqliteMalloc( sizeof(*pCur) );
  if( pCur==0 ){
    rc = SQLITE_NOMEM;
    goto create_cursor_exception;
  }
  pCur->pgnoRoot = (Pgno)iTable;
  rc = getPage(pBt, pCur->pgnoRoot, (void**)&pCur->pPage);
  if( rc!=SQLITE_OK ){
    goto create_cursor_exception;
  }
  rc = initPage(pCur->pPage, 0);
  if( rc!=SQLITE_OK ){
    goto create_cursor_exception;
  }
  pCur->xCompare = xCmp ? xCmp : dfltCompare;
  pCur->pArg = pArg;
  pCur->pBt = pBt;
  pCur->wrFlag = wrFlag;
  pCur->idx = 0;
  pCur->eSkip = SKIP_INVALID;
  pCur->pNext = pBt->pCursor;
  if( pCur->pNext ){
    pCur->pNext->pPrev = pCur;
................................................................................
  pBt->pCursor = pCur;
  *ppCur = pCur;
  return SQLITE_OK;

create_cursor_exception:
  *ppCur = 0;
  if( pCur ){
    releasePage(pCur->pPage);
    sqliteFree(pCur);
  }
  unlockBtreeIfUnused(pBt);
  return rc;
}

/*
** Close a cursor.  The read lock on the database file is released
** when the last cursor is closed.
*/
int sqlite3BtreeCloseCursor(BtCursor *pCur){
  Btree *pBt = pCur->pBt;
  if( pCur->pPrev ){
    pCur->pPrev->pNext = pCur->pNext;
  }else{
    pBt->pCursor = pCur->pNext;
  }
  if( pCur->pNext ){
    pCur->pNext->pPrev = pCur->pPrev;
  }
  releasePage(pCur->pPage);


  if( pCur->pShared!=pCur ){
    BtCursor *pRing = pCur->pShared;
    while( pRing->pShared!=pCur ){ pRing = pRing->pShared; }
    pRing->pShared = pCur->pShared;
  }
  unlockBtreeIfUnused(pBt);
  sqliteFree(pCur);
................................................................................
** The temporary cursor is not on the cursor list for the Btree.
*/
static void getTempCursor(BtCursor *pCur, BtCursor *pTempCur){
  memcpy(pTempCur, pCur, sizeof(*pCur));
  pTempCur->pNext = 0;
  pTempCur->pPrev = 0;
  if( pTempCur->pPage ){
    sqlitepager_ref(pTempCur->pPage->aData);
  }
}

/*
** Delete a temporary cursor such as was made by the CreateTemporaryCursor()
** function above.
*/
static void releaseTempCursor(BtCursor *pCur){
  if( pCur->pPage ){
    sqlitepager_unref(pCur->pPage->aData);
  }
}

/*
** Set *pSize to the size of the buffer needed to hold the value of
** the key for the current entry.  If the cursor is not pointing
** to a valid entry, *pSize is set to 0. 
**
** For a table with the intKey flag set, this routine returns the key
** itself, not the number of bytes in the key.
*/
int sqlite3BtreeKeySize(BtCursor *pCur, u64 *pSize){
  MemPage *pPage;

  pPage = pCur->pPage;
  assert( pPage!=0 );
  if( pCur->idx >= pPage->nCell ){
    *pSize = 0;
  }else{
    unsigned char *cell = pPage->aCell[pCur->idx];
    cell += 2;   /* Skip the offset to the next cell */
    if( pPage->leaf ){
      cell += 4;  /* Skip the child pointer */
    }
    if( !pPage->zeroData ){
      while( (0x80&*(data++))!=0 ){}  /* Skip the data size number */
    }
    getVarint(data, pSize);
  }
  return SQLITE_OK;
}

/*
** Read payload information from the entry that the pCur cursor is
** pointing to.  Begin reading the payload at "offset" and read
** a total of "amt" bytes.  Put the result in zBuf.
**
** This routine does not make a distinction between key and data.
** It just reads bytes from the payload area.
*/
static int getPayload(
  BtCursor *pCur,      /* Cursor pointing to entry to read from */
  int offset,          /* Begin reading this far into payload */
  int amt,             /* Read this many bytes */
  unsigned char *pBuf, /* Write the bytes into this buffer */ 
  int skipKey          /* offset begins at data if this is true */
){
  unsigned char *aPayload;
  Pgno nextPage;
  int rc;
  MemPage *pPage;
  Btree *pBt;
  u64 nData, nKey;
  int maxLocal, ovflSize;

  assert( pCur!=0 && pCur->pPage!=0 );
  pBt = pCur->pBt;
  pPage = pCur->pPage;
  assert( pCur->idx>=0 && pCur->idx<pPage->nCell );

  aPayload = pPage->aCell[pCur->idx];
  aPayload += 2;  /* Skip the next cell index */
  if( pPage->leaf ){
    aPayload += 4;  /* Skip the child pointer */
  }
  if( pPage->zeroData ){
    nData = 0;
  }else{
    aPayload += getVarint(aPayload, &nData);
  }
  aPayload += getVarInt(aPayload, &nKey);
  if( pPage->intKey ){
    nKey = 0;
  }
  assert( offset>=0 );
  if( skipKey ){
    offset += nKey;
  }
  if( offset+amt > nKey+nData ){
    sqlite SQLITE_ERROR;
  }
  maxLocal = pBt->maxLocal
  if( offset<maxLocal ){
    int a = amt;
    if( a+offset>maxLocal ){

      a = maxLocal - offset;
    }
    memcpy(zBuf, &aPayload[offset], a);
    if( a==amt ){
      return SQLITE_OK;
    }
    offset = 0;
    zBuf += a;
    amt -= a;
  }else{
    offset -= maxLocal;
  }
  if( amt>0 ){
    nextPage = get4bytes(&aPayload[maxLocal]);
  }
  ovflSize = pBt->pageSize - 4;
  while( amt>0 && nextPage ){

    rc = sqlitepager_get(pBt->pPager, nextPage, (void**)&aPayload);
    if( rc!=0 ){
      return rc;
    }
    nextPage = get4bytes(aPayload);
    if( offset<ovflSize ){
      int a = amt;
      if( a + offset > ovflSize ){
        a = ovflSize - offset;
      }
      memcpy(zBuf, &aPayload[offset], a);
      offset = 0;
      amt -= a;
      zBuf += a;
    }else{
      offset -= ovflSize;
    }
    sqlitepager_unref(aPayload);
  }
  if( amt>0 ){
    return SQLITE_CORRUPT;
  }
  return SQLITE_OK;
}

/*
** Read part of the key associated with cursor pCur.  Exactly
** "amt" bytes will be transfered into zBuf[].  The transfer
** begins at "offset".

**
** Return SQLITE_OK on success or an error code if anything goes
** wrong.  An error is returned if "offset+amt" is larger than
** the available payload.




*/
int sqlite3BtreeKey(BtCursor *pCur, int offset, int amt, void *pBuf){
  MemPage *pPage;

  assert( amt>=0 );
  assert( offset>=0 );
  assert( pCur->pPage!=0 );
  pPage = pCur->pPage;
  if( pCur->idx >= pPage->nCell || pPage->intKey ){
    assert( amt==0 );
    return SQLITE_OK;
  }

  return getPayload(pCur, offset, amt, (unsigned char*)pBuf, 0);
}

/*
** Return a pointer to the key of record that cursor pCur
** is point to if the entire key is in contiguous memory.
** If the key is split up among multiple tables, return 0.
** If pCur is not pointing to a valid entry return 0.
**
** The pointer returned is ephemeral.  The key may move
** or be destroyed on the next call to any Btree routine.
**
** This routine is used to do quick key comparisons in the
** common case where the entire key fits in the payload area
** of a cell and does not overflow onto secondary pages.
*/
void *sqlite3BtreeKeyFetch(BtCursor *pCur){
  unsigned char *aPayload;
  MemPage *pPage;
  Btree *pBt;
  u64 nData, nKey;

  assert( pCur!=0 && pCur->pPage!=0 );
  pBt = pCur->pBt;
  pPage = pCur->pPage;
  assert( pCur->idx>=0 && pCur->idx<pPage->nCell );
  aPayload = pPage->aCell[pCur->idx];
  aPayload += 2;  /* Skip the next cell index */
  if( pPage->leaf ){
    aPayload += 4;  /* Skip the child pointer */
  }
  if( !pPage->zeroData ){
    aPayload += getVarint(aPayload, &nData);
  }
  aPayload += getVarInt(aPayload, &nKey);
  if( pPage->intKey || nKey>pBt->maxLocal ){
    return 0;
  }
  return aPayload;
}


/*
** Set *pSize to the number of bytes of data in the entry the
** cursor currently points to.  Always return SQLITE_OK.
** Failure is not possible.  If the cursor is not currently
** pointing to an entry (which can happen, for example, if
** the database is empty) then *pSize is set to 0.
*/
int sqlite3BtreeDataSize(BtCursor *pCur, u32 *pSize){

  MemPage *pPage;

  pPage = pCur->pPage;
  assert( pPage!=0 );
  if( pCur->idx >= pPage->nCell || pPage->zeroData ){
    *pSize = 0;
  }else{
    unsigned char *cell;
    u64 size;
    cell = pPage->aCell[pCur->idx];

    cell += 2;   /* Skip the offset to the next cell */
    if( pPage->leaf ){
      cell += 4;  /* Skip the child pointer */
    }
    getVarint(data, size);
    assert( (size & 0x00000000ffffffff)==size );
    *pSize = size;
  }
  return SQLITE_OK;
}

/*
** Read part of the data associated with cursor pCur.  Exactly
** "amt" bytes will be transfered into zBuf[].  The transfer
** begins at "offset".
**
** Return SQLITE_OK on success or an error code if anything goes
** wrong.  An error is returned if "offset+amt" is larger than
** the available payload.
*/
int sqlite3BtreeData(BtCursor *pCur, u32 offset, u32 amt, void *pBuf){

  MemPage *pPage;

  assert( amt>=0 );
  assert( offset>=0 );
  assert( pCur->pPage!=0 );
  pPage = pCur->pPage;
  if( pCur->idx >= pPage->nCell ){
    return 0;
  }
  pCell = pPage->apCell[pCur->idx];

  return getPayload(pCur, offset, amt, pBuf, 1);

}

/*



















































































** Move the cursor down to a new child page.  The newPgno argument is the
** page number of the child page in the byte order of the disk image.
*/
static int moveToChild(BtCursor *pCur, u32 newPgno){
  int rc;
  MemPage *pNewPage;
  MemPage *pOldPage;
  unsigned char *aData;
  Btree *pBt = pCur->pBt;

  rc = getPage(pBt, newPgno, &pNewPage);

  if( rc ) return rc;

  rc = initPage(pNewPage, pCur->pPage);
  if( rc ) return rc;




  pNewPage->idxParent = pCur->idx;
  pOldPage = pCur->pPage;
  pOldPage->idxShift = 0;

  releasePage(pOldPage);
  pCur->pPage = pNewPage;
  pCur->idx = 0;
  if( pNewPage->nCell<1 ){
    return SQLITE_CORRUPT;
  }
  return SQLITE_OK;
}
................................................................................
** the largest cell index.
*/
static void moveToParent(BtCursor *pCur){
  Pgno oldPgno;
  MemPage *pParent;
  MemPage *pPage;
  int idxParent;

  pPage = pCur->pPage;
  assert( pPage!=0 );
  pParent = pPage->pParent;
  assert( pParent!=0 );
  idxParent = pPage->idxParent;
  sqlitepager_ref(pParent->aData);
  oldPgno = pPage->pgno;
  releasePage(pPage);
  pCur->pPage = pParent;
  assert( pParent->idxShift==0 );
  if( pParent->idxShift==0 ){
    pCur->idx = idxParent;
#ifndef NDEBUG  
    /* Verify that pCur->idx is the correct index to point back to the child
    ** page we just came from 
    */

    if( pCur->idx<pParent->nCell ){

      assert( get4Byte(&pParent->aCell[idxParent][2])==oldPgno );
    }else{

      assert( get4Byte(&pParent->aData[pParent->hdrOffset+6])==oldPgno );
    }
#endif
  }else{
    /* The MemPage.idxShift flag indicates that cell indices might have 
    ** changed since idxParent was set and hence idxParent might be out
    ** of date.  So recompute the parent cell index by scanning all cells
    ** and locating the one that points to the child we just came from.
    */
    int i;
    pCur->idx = pParent->nCell;

    for(i=0; i<pParent->nCell; i++){

      if( get4byte(&pParent->aCell[i][2])==oldPgno ){
        pCur->idx = i;
        break;
      }
    }
  }
}

/*
** Move the cursor to the root page
*/
static int moveToRoot(BtCursor *pCur){
  MemPage *pRoot;
  int rc;
  Btree *pBt = pCur->pBt;

  rc = sqlitepager_get(pBt->pPager, pCur->pgnoRoot, &pRoot);
  if( rc ) return rc;
  rc = initPage(pRoot, 0);
  if( rc ) return rc;
  releasePage(pCur->pPage);
  pCur->pPage = pRoot;
  pCur->idx = 0;
  return SQLITE_OK;
}

/*
** Move the cursor down to the left-most leaf entry beneath the
** entry to which it is currently pointing.
*/
static int moveToLeftmost(BtCursor *pCur){
  Pgno pgno;
  int rc;
  MemPage *pPage;


  while( !(pPage = pCur->pPage)->leaf ){
    assert( pCur->idx>=0 && pCur->idx<pPage->nPage );
    pgno = get4byte(pPage->aCell[pCur->idx][2]);
    rc = moveToChild(pCur, pgno);
    if( rc ) return rc;
  }
  return SQLITE_OK;
}

/*
................................................................................
** between moveToLeftmost() and moveToRightmost().  moveToLeftmost()
** finds the left-most entry beneath the *entry* whereas moveToRightmost()
** finds the right-most entry beneath the *page*.
*/
static int moveToRightmost(BtCursor *pCur){
  Pgno pgno;
  int rc;
  MemPage *pPage;


  while( !(pPage = pCur->pPage)->leaf ){
    pgno = get4byte(&pPage->aData[pPage->hdrOffset+6]);
    pCur->idx = pPage->nCell;
    rc = moveToChild(pCur, pgno);
    if( rc ) return rc;
  }
  pCur->idx = pPage->nCell - 1;
  return SQLITE_OK;
}

/* Move the cursor to the first entry in the table.  Return SQLITE_OK
** on success.  Set *pRes to 0 if the cursor actually points to something
** or set *pRes to 1 if the table is empty.
*/
int sqlite3BtreeFirst(BtCursor *pCur, int *pRes){
  int rc;
  if( pCur->pPage==0 ) return SQLITE_ABORT;
  rc = moveToRoot(pCur);
  if( rc ) return rc;
  if( pCur->pPage->nCell==0 ){
    *pRes = 1;
    return SQLITE_OK;
................................................................................
  return rc;
}

/* Move the cursor to the last entry in the table.  Return SQLITE_OK
** on success.  Set *pRes to 0 if the cursor actually points to something
** or set *pRes to 1 if the table is empty.
*/
int sqlite3BtreeLast(BtCursor *pCur, int *pRes){
  int rc;
  if( pCur->pPage==0 ) return SQLITE_ABORT;
  rc = moveToRoot(pCur);
  if( rc ) return rc;
  assert( pCur->pPage->isInit );
  if( pCur->pPage->nCell==0 ){
    *pRes = 1;
................................................................................
  }
  *pRes = 0;
  rc = moveToRightmost(pCur);
  pCur->eSkip = SKIP_NONE;
  return rc;
}

/* Move the cursor so that it points to an entry near pKey/nKey.
** Return a success code.
**
** For INTKEY tables, only the nKey parameter is used.  pKey is
** ignored.  For other tables, nKey is the number of bytes of data
** in nKey.  The comparison function specified when the cursor was
** created is used to compare keys.
**
** If an exact match is not found, then the cursor is always
** left pointing at a leaf page which would hold the entry if it
** were present.  The cursor might point to an entry that comes
** before or after the key.
**
** The result of comparing the key with the entry to which the
................................................................................
**
**     *pRes==0     The cursor is left pointing at an entry that
**                  exactly matches pKey.
**
**     *pRes>0      The cursor is left pointing at an entry that
**                  is larger than pKey.
*/

int sqlite3BtreeMoveto(BtCursor *pCur, const void *pKey, u64 nKey, int *pRes){
  int rc;
  if( pCur->pPage==0 ) return SQLITE_ABORT;
  pCur->eSkip = SKIP_NONE;
  rc = moveToRoot(pCur);
  if( rc ) return rc;
  for(;;){
    int lwr, upr;
    Pgno chldPg;
    MemPage *pPage = pCur->pPage;
    int c = -1;  /* pRes return if table is empty must be -1 */
    lwr = 0;
    upr = pPage->nCell-1;
    while( lwr<=upr ){
      void *pCellKey;
      u64 nCellKey;
      pCur->idx = (lwr+upr)/2;

      nCellKey = sqlite3BtreeKeySize(pCur, &nCellKey);
      if( pPage->intKey ){
        if( nCellKey<nKey ){
          c = -1;
        }else if( nCellKey>nKey ){
          c = +1;
        }else{
          c = 0;
        }
      }else if( (pCellKey = sqlite3BtreeKeyFetch(pCur))!=0 ){
        c = pCur->xCompare(pCur->pArg, nCellKey, pCellKey, nKey, pKey);
      }else{
        pCellKey = sqliteMalloc( nCellKey );
        if( pCellKey==0 ) return SQLITE_NOMEM;
        rc = sqlite3BtreeKey(pCur, 0, nCellKey, pCellKey);
        c = pCur->xCompare(pCur->pArg, nCellKey, pCellKey, nKey, pKey);
        sqliteFree(pCellKey);
        if( rc ) return rc;
      }
      if( c==0 ){
        pCur->iMatch = c;
        if( pRes ) *pRes = 0;
        return SQLITE_OK;
      }
      if( c<0 ){
        lwr = pCur->idx+1;
      }else{
        upr = pCur->idx-1;
      }
    }
    assert( lwr==upr+1 );
    assert( pPage->isInit );
    if( pPage->leaf ){
      chldpg = 0;
    }else if( lwr>=pPage->nCell ){

      chldPg = get4byte(&pPage->aData[pPage->hdrOffset+6]);
    }else{

      chldPg = get4byte(&pPage->aCell[lwr][2]);
    }
    if( chldPg==0 ){
      pCur->iMatch = c;
      if( pRes ) *pRes = c;
      return SQLITE_OK;
    }
    pCur->idx = lwr;
................................................................................

/*
** Advance the cursor to the next entry in the database.  If
** successful then set *pRes=0.  If the cursor
** was already pointing to the last entry in the database before
** this routine was called, then set *pRes=1.
*/
int sqlite3BtreeNext(BtCursor *pCur, int *pRes){
  int rc;
  MemPage *pPage = pCur->pPage;
  assert( pRes!=0 );
  if( pPage==0 ){
    *pRes = 1;
    return SQLITE_ABORT;
  }
................................................................................
    pCur->eSkip = SKIP_NONE;
    *pRes = 0;
    return SQLITE_OK;
  }
  pCur->eSkip = SKIP_NONE;
  pCur->idx++;
  if( pCur->idx>=pPage->nCell ){
    if( !pPage->left ){
      rc = moveToChild(pCur, get4byte(&pPage->aData[pPage->hdrOffset+6]);
      if( rc ) return rc;
      rc = moveToLeftmost(pCur);
      *pRes = 0;
      return rc;
    }
    do{
      if( pPage->pParent==0 ){
................................................................................
      moveToParent(pCur);
      pPage = pCur->pPage;
    }while( pCur->idx>=pPage->nCell );
    *pRes = 0;
    return SQLITE_OK;
  }
  *pRes = 0;
  if( pPage->leaf ){
    return SQLITE_OK;
  }
  rc = moveToLeftmost(pCur);
  return rc;
}

/*
** Step the cursor to the back to the previous entry in the database.  If
** successful then set *pRes=0.  If the cursor
** was already pointing to the first entry in the database before
** this routine was called, then set *pRes=1.
*/
int sqlite3BtreePrevious(BtCursor *pCur, int *pRes){
  int rc;
  Pgno pgno;
  MemPage *pPage;
  pPage = pCur->pPage;
  if( pPage==0 ){
    *pRes = 1;
    return SQLITE_ABORT;
................................................................................
  if( pCur->eSkip==SKIP_PREV ){
    pCur->eSkip = SKIP_NONE;
    *pRes = 0;
    return SQLITE_OK;
  }
  pCur->eSkip = SKIP_NONE;
  assert( pCur->idx>=0 );
  if( !pPage->left ){
    pgno = get4byte(&pPage->aCell[pCur->idx][2]);
    rc = moveToChild(pCur, pgno);
    if( rc ) return rc;
    rc = moveToRightmost(pCur);
  }else{
    while( pCur->idx==0 ){
      if( pPage->pParent==0 ){
        if( pRes ) *pRes = 1;
................................................................................
**
** If the "nearby" parameter is not 0, then a (feeble) effort is made to 
** locate a page close to the page number "nearby".  This can be used in an
** attempt to keep related pages close to each other in the database file,
** which in turn can make database access faster.
*/
static int allocatePage(Btree *pBt, MemPage **ppPage, Pgno *pPgno, Pgno nearby){
  u32 pn;
  MemPage *pPage1;
  MemPage *pPage;
  int rc;


  int n;     /* Number of pages on the freelist */
  int k;     /* Number of leaves on the trunk of the freelist */

  pPage1 = pBt->pPage1;
  n = get4byte(&pPage1->aData[36]);
  if( n>0 ){
    /* There exists pages on the freelist.  Reuse one of those pages. */
    MemPage *pTrunk;
    rc = sqlitepager_write(pPage1->aData);
    if( rc ) return rc;



    put4byte(&pPage1->aData[36], n-1);
    rc = getPage(pBt, get4byte(&pPage1->aData[32]), &pTrunk);
    if( rc ) return rc;
    rc = sqlitepager_write(pTrunk->aData);
    if( rc ){

      releasePage(pTrunk);
      return rc;
    }

    k = get4byte(&pTrunk->aData[4]);
    if( k==0 ){


      /* The trunk has no leaves.  So extract the trunk page itself and
      ** use it as the newly allocated page */
      *pPgno = get4byte(pPage1->aData[32]);
      memcpy(&pPage1->aData[32], &pTrunk->aData[0], 4);
      *ppPage = pTrunk;
    }else{
      /* Extract a leaf from the trunk */
      int closest;

      unsigned char *aData = pTrunk->aData;
      if( nearby>0 ){
        int i, dist;
        closest = 0;

        dist = get4byte(&aData[8]) - nearby;
        if( dist<0 ) dist = -dist;
        for(i=1; i<n; i++){

          int d2 = get4byte(&aData[8+i*4]) - nearby;
          if( d2<0 ) d2 = -d2;
          if( d2<dist ) closest = i;
        }
      }else{
        closest = 0;
      }
      put4byte(&aData[4], n-1);
      *pPgno = get4data(&aData[8+closest*4]);
      memcpy(&aData[8+closest*4], &aData[4+closest*n], 4);
      rc = getPage(pBt, *pPgno, ppPage);
      releasePage(pTrunk);
      if( rc==SQLITE_OK ){
        sqlitepager_dont_rollback(*ppPage);
        rc = sqlitepager_write((*ppPage)->aData);
      }
    }
  }else{
    /* There are no pages on the freelist, so create a new page at the
    ** end of the file */
    *pPgno = sqlitepager_pagecount(pBt->pPager) + 1;
    rc = getPage(pBt, *pPgno, ppPage);
    if( rc ) return rc;
    rc = sqlitepager_write((*ppPage)->aData);
  }
  return rc;
}

/*
** Add a page of the database file to the freelist.
**
** sqlitepager_unref() is NOT called for pPage.
*/
static int freePage(MemPage *pPage){
  Btree *pBt = pPage->pBt;
  MemPage *pPage1 = pBt->pPage1;
  int rc, n, k;

  /* Prepare the page for freeing */
  assert( pPage->pgno>1 );
  pPage->isInit = 0;
  releasePage(pPage->pParent);
  pPage->pParent = 0;

  /* Increment the free page count on page1 */
  rc = sqlitepager_write(pPage1->aData);
  if( rc ) return rc;
  n = get4byte(&pPage1->aData[36]);
  put4byte(&pPage1->aData[36], n+1);

  if( n==0 ){
    /* This is the first free page */
    memset(pPage->aData, 0, 8);
    put4byte(pPage1->aData[32], pPage->pgno);
  }else{
    /* Other free pages already exist.  Retrive the first trunk page
    ** of the freelist and find out how many leaves it has. */
    MemPage *pTrunk
    rc = getPage(pBt, get4byte(pPage1->aData[32], &pTrunk);
    if( rc ) return rc;
    k = get4byte(&pTrunk->aData[4]);
    if( k==pBt->pageSize/4 - 8 ){
      /* The trunk is full.  Turn the page being freed into a new
      ** trunk page with no leaves. */
      rc = sqlitepager_write(pPage->aData);
      if( rc ) return rc;
      put4byte(pPage->aData, pTrunk->pgno);
      put4byte(&pPage->aData[4], 0);
      put4byte(&pPage1->aData[32], pPage->pgno);
    }else{
      /* Add the newly freed page as a leaf on the current trunk */
      rc = sqlitepager_write(pTrunk->aData);
      if( rc ) return rc;
      put4byte(&pTrunk->aData[4], k+1);
      put4byte(&pTrunk->aData[8+k*4], pPage->pgno);
      sqlitepager_dont_write(pBt->pPager, pPage->pgno);
    }
    releasePage(pTrunk);
  }
  return rc;
}

/*
** Free any overflow pages associated with the given Cell.
*/
static int clearCell(MemPage *pPage, unsigned char *pCell){
  Btree *pBt = pPage->pBt;
  int rc, n;
  u64 nData, nKey;
  Pgno ovflPgno;

  parseCellHeader(pPage, pCell, &nData, &nKey, &n);
  nPayload = nData;
  if( !pPage->intKey ){
    nPayload += nKey;
  }
  if( nPayload<=pBt->maxLocal ){
    return;  /* There are no overflow pages.  Return without doing anything */
  }
  ovflPgno = get4byte(&pCell[n+pBt->maxLocal]);
  while( ovflPgno!=0 ){
    MemPage *pOvfl;
    rc = getPage(pBt, ovflPgno, &pOvfl);
    if( rc ) return rc;
    ovflPgno = get4byte(pOvfl->aData);
    rc = freePage(pBt, pOvfl, ovfl);
    if( rc ) return rc;
    sqlitepager_unref(pOvfl->aData);









  }
  return SQLITE_OK;
}

/*
** Compute the number of bytes required by a cell header.  If the *pHeader
** argument is not NULL, fill it in with the bytes of the header.
*/
static int makeCellHeader(
  MemPage *pPage,          /* The page that will contain the cell */
  u64 nKey,                /* Size of key, or the key value if intKey */
  int nData,               /* Size of data.  Ignored for zerodata */
  unsigned char *pHeader   /* Write header bytes here */
){
  int n = 2;
  if( !pPage->leaf ) n += 4;
  if( !pPage->zeroData ){
    n += putVarint(&pHeader[n], nData);
  }
  n += putVarint(&pHeader[n], nKey);
  return n;
}

/*
** Fill in the payload section of a cell into the space provided.  If
** the payload will not completely fit in the cell, allocate additional
** overflow pages and fill them in.
*/
static int fillInCell(
  MemPage *pPage,                /* The page that contains the cell */
  unsigned char *pCell,          /* Pointer to start of payload area */
  int nHeader,                   /* Number of bytes in the cell header */
  const void *pKey, u64 nKey,    /* The key */
  const void *pData,int nData    /* The data */
){
  int nPayload;
  const void *pSrc;
  int nSrc, nSrc2;
  int spaceLeft;
  MemPage *pOvfl = 0;
  unsigned char *pPrior;
  unsigned char *pPayload;
  Btree *pBt = pPage->pBt;
  Pgno pgnoOvfl = 0;

  nPayload = nData;
  if( pPage->intKey ){
    pSrc = pData;
    nSrc = nData;
    nSrc2 = 0;
  }else{
    nPayload += nKey;
    pSrc = pKey;
    nSrc = nKey;
  }
  spaceLeft = pBt->maxLocal;
  pPayload = &pCell[nHeader];
  pPrior = &pPayload[pBt->maxLocal];

  while( nPayload>0 ){
    if( spaceLeft==0 ){
      rc =  allocatePage(pBt, &pOvfl, &pgnoOvfl, pgnoOvfl);
      if( rc ){
        clearCell(pPage, pCell);
        return rc;
      }
      put4byte(pPrior, pgnoOvfl);
      pPrior = pOvfl->aData;
      put4byte(pPrior, 0);
      pPayload = &pOvfl->aData[4];
      spaceLeft = pBt->pageSize - 4;
    }
    n = nPayload;
    if( n>spaceLeft ) n = spaceLeft;
    if( n>nSrc ) n = nSrc;
    memcpy(pPayload, pSrc, n);
    nPayload -= n;

    nSrc -= n;
    spaceLeft -= n;
    if( nSrc==0 ){
      nSrc = nData;
      pSrc = pData;


    }
    if( pOvfl && (spaceLeft==0 || nPayload==0) ){
      releasePage(pOvfl);
    }



  }
  return SQLITE_OK;
}

/*
** Change the MemPage.pParent pointer on the page whose number is
** given in the second argument so that MemPage.pParent holds the
................................................................................

/*
** Insert a new record into the BTree.  The key is given by (pKey,nKey)
** and the data is given by (pData,nData).  The cursor is used only to
** define what database the record should be inserted into.  The cursor
** is left pointing at the new record.
*/
int sqlite3BtreeInsert(
  BtCursor *pCur,                /* Insert data into the table of this cursor */
  const void *pKey, int nKey,    /* The key of the new record */
  const void *pData, int nData   /* The data of the new record */
){
  Cell newCell;
  int rc;
  int loc;
................................................................................
  assert( !pBt->readOnly );
  if( !pCur->wrFlag ){
    return SQLITE_PERM;   /* Cursor not open for writing */
  }
  if( checkReadLocks(pCur) ){
    return SQLITE_LOCKED; /* The table pCur points to has a read lock */
  }
  rc = sqlite3BtreeMoveto(pCur, pKey, nKey, &loc);
  if( rc ) return rc;
  pPage = pCur->pPage;
  assert( pPage->isInit );
  rc = sqlitepager_write(pPage);
  if( rc ) return rc;
  rc = fillInCell(pBt, &newCell, pKey, nKey, pData, nData);
  if( rc ) return rc;
................................................................................
** sqliteBtreeNext() after a delete and the cursor will be left
** pointing to the first entry after the deleted entry.  Similarly,
** pCur->eSkip is set to SKIP_PREV is the cursor is left pointing to
** the entry prior to the deleted entry so that a subsequent call to
** sqliteBtreePrevious() will always leave the cursor pointing at the
** entry immediately before the one that was deleted.
*/
int sqlite3BtreeDelete(BtCursor *pCur){
  MemPage *pPage = pCur->pPage;
  Cell *pCell;
  int rc;
  Pgno pgnoChild;
  Btree *pBt = pCur->pBt;

  assert( pPage->isInit );
................................................................................
    ** to be a leaf so we can use it.
    */
    BtCursor leafCur;
    Cell *pNext;
    int szNext;
    int notUsed;
    getTempCursor(pCur, &leafCur);
    rc = sqlite3BtreeNext(&leafCur, &notUsed);
    if( rc!=SQLITE_OK ){
      if( rc!=SQLITE_NOMEM ) rc = SQLITE_CORRUPT;
      return rc;
    }
    rc = sqlitepager_write(leafCur.pPage);
    if( rc ) return rc;
    dropCell(pBt, pPage, pCur->idx, cellSize(pBt, pCell));
................................................................................
**
** In the current implementation, BTree tables and BTree indices are the 
** the same.  In the future, we may change this so that BTree tables
** are restricted to having a 4-byte integer key and arbitrary data and
** BTree indices are restricted to having an arbitrary key and no data.
** But for now, this routine also serves to create indices.
*/
int sqlite3BtreeCreateTable(Btree *pBt, int *piTable, int flags){
  MemPage *pRoot;
  Pgno pgnoRoot;
  int rc;
  if( !pBt->inTrans ){
    /* Must start a transaction first */
    return pBt->readOnly ? SQLITE_READONLY : SQLITE_ERROR;
  }
................................................................................
  sqlitepager_unref(pPage);
  return rc;
}

/*
** Delete all information from a single table in the database.
*/
int sqlite3BtreeClearTable(Btree *pBt, int iTable){
  int rc;
  BtCursor *pCur;
  if( !pBt->inTrans ){
    return pBt->readOnly ? SQLITE_READONLY : SQLITE_ERROR;
  }
  for(pCur=pBt->pCursor; pCur; pCur=pCur->pNext){
    if( pCur->pgnoRoot==(Pgno)iTable ){
      if( pCur->wrFlag==0 ) return SQLITE_LOCKED;
      moveToRoot(pCur);
    }
  }
  rc = clearDatabasePage(pBt, (Pgno)iTable, 0);
  if( rc ){
    sqlite3BtreeRollback(pBt);
  }
  return rc;
}

/*
** Erase all information in a table and add the root of the table to
** the freelist.  Except, the root of the principle table (the one on
** page 2) is never added to the freelist.
*/
int sqlite3BtreeDropTable(Btree *pBt, int iTable){
  int rc;
  MemPage *pPage;
  BtCursor *pCur;
  if( !pBt->inTrans ){
    return pBt->readOnly ? SQLITE_READONLY : SQLITE_ERROR;
  }
  for(pCur=pBt->pCursor; pCur; pCur=pCur->pNext){
    if( pCur->pgnoRoot==(Pgno)iTable ){
      return SQLITE_LOCKED;  /* Cannot drop a table that has a cursor */
    }
  }
  rc = sqlitepager_get(pBt->pPager, (Pgno)iTable, (void**)&pPage);
  if( rc ) return rc;
  rc = sqlite3BtreeClearTable(pBt, iTable);
  if( rc ) return rc;
  if( iTable>2 ){
    rc = freePage(pBt, pPage, iTable);
  }else{
    zeroPage(pBt, pPage);
  }
  sqlitepager_unref(pPage);
................................................................................
  return rc;
}
#endif

/*
** Read the meta-information out of a database file.
*/
int sqlite3BtreeGetMeta(Btree *pBt, int idx, u32 *pMeta){

  int rc;
  int i;

  rc = sqlitepager_get(pBt->pPager, 1, (void**)&pP1);
  if( rc ) return rc;
  aMeta[0] = SWAB32(pBt, pP1->nFree);
  for(i=0; i<sizeof(pP1->aMeta)/sizeof(pP1->aMeta[0]); i++){
................................................................................
  sqlitepager_unref(pP1);
  return SQLITE_OK;
}

/*
** Write meta-information back into the database.
*/
int sqlite3BtreeUpdateMeta(Btree *pBt, int idx, u32 iMeta){
  PageOne *pP1;
  int rc, i;
  if( !pBt->inTrans ){
    return pBt->readOnly ? SQLITE_READONLY : SQLITE_ERROR;
  }
  pP1 = pBt->page1;
  rc = sqlitepager_write(pP1);
................................................................................
}
#endif

/*
** Return the pager associated with a BTree.  This routine is used for
** testing and debugging only.
*/
Pager *sqlite3BtreePager(Btree *pBt){
  return pBt->pPager;
}

/*
** This structure is passed around through all the sanity checking routines
** in order to keep track of some global state information.
*/
................................................................................
** a table.  nRoot is the number of entries in aRoot.
**
** If everything checks out, this routine returns NULL.  If something is
** amiss, an error message is written into memory obtained from malloc()
** and a pointer to that error message is returned.  The calling function
** is responsible for freeing the error message when it is done.
*/
char *sqlite3BtreeIntegrityCheck(Btree *pBt, int *aRoot, int nRoot){
  int i;
  int nRef;
  IntegrityCk sCheck;

  nRef = *sqlitepager_stats(pBt->pPager);
  if( lockBtree(pBt)!=SQLITE_OK ){
    return sqliteStrDup("Unable to acquire a read lock on the database");
................................................................................
  sqliteFree(sCheck.anRef);
  return sCheck.zErrMsg;
}

/*
** Return the full pathname of the underlying database file.
*/
const char *sqlite3BtreeGetFilename(Btree *pBt){
  assert( pBt->pPager!=0 );
  return sqlitepager_filename(pBt->pPager);
}

/*
** Copy the complete content of pBtFrom into pBtTo.  A transaction
** must be active for both files.
**
** The size of file pBtFrom may be reduced by this operation.
** If anything goes wrong, the transaction on pBtFrom is rolled back.
*/
int sqlite3BtreeCopyFile(Btree *pBtTo, Btree *pBtFrom){
  int rc = SQLITE_OK;
  Pgno i, nPage, nToPage;

  if( !pBtTo->inTrans || !pBtFrom->inTrans ) return SQLITE_ERROR;
  if( pBtTo->needSwab!=pBtFrom->needSwab ) return SQLITE_ERROR;
  if( pBtTo->pCursor ) return SQLITE_BUSY;
  memcpy(pBtTo->page1, pBtFrom->page1, SQLITE_USABLE_SIZE);
................................................................................
    sqlitepager_unref(pPage);
    sqlitepager_dont_write(pBtTo->pPager, i);
  }
  if( !rc && nPage<nToPage ){
    rc = sqlitepager_truncate(pBtTo->pPager, nPage);
  }
  if( rc ){
    sqlite3BtreeRollback(pBtTo);
  }
  return rc;  
}

**    May you share freely, never taking more than you give.
**
*************************************************************************
** This header file defines the interface that the sqlite B-Tree file
** subsystem.  See comments in the source code for a detailed description
** of what each interface routine does.
**
** @(#) $Id: btree.h,v 1.36 2004/02/10 02:57:59 drh Exp $
*/
#ifndef _BTREE_H_
#define _BTREE_H_

/*
** Forward declarations of structure
*/
typedef struct Btree Btree;
typedef struct BtCursor BtCursor;
typedef struct BtOps BtOps;
typedef struct BtCursorOps BtCursorOps;




/*
** An instance of the following structure contains pointers to all
** methods against an open BTree.  Alternative BTree implementations
** (examples: file based versus in-memory) can be created by substituting
** different methods.  Users of the BTree cannot tell the difference.
**
** In C++ we could do this by defining a virtual base class and then
** creating subclasses for each different implementation.  But this is
** C not C++ so we have to be a little more explicit.
*/







struct BtOps {
    int (*Close)(Btree*);
    int (*SetCacheSize)(Btree*, int);
    int (*SetSafetyLevel)(Btree*, int);
    int (*BeginTrans)(Btree*);
    int (*Commit)(Btree*);
    int (*Rollback)(Btree*);

    int (*BeginCkpt)(Btree*);
    int (*CommitCkpt)(Btree*);
    int (*RollbackCkpt)(Btree*);
    int (*CreateTable)(Btree*, int*);
    int (*CreateIndex)(Btree*, int*);

    int (*DropTable)(Btree*, int);
    int (*ClearTable)(Btree*, int);
    int (*Cursor)(Btree*, int iTable, int wrFlag, BtCursor **ppCur);
    int (*GetMeta)(Btree*, int*);
    int (*UpdateMeta)(Btree*, int*);
    char *(*IntegrityCheck)(Btree*, int*, int);

    const char *(*GetFilename)(Btree*);
    int (*Copyfile)(Btree*,Btree*);
    struct Pager *(*Pager)(Btree*);
#ifdef SQLITE_TEST
    int (*PageDump)(Btree*, int, int);
#endif
};



/*
** An instance of this structure defines all of the methods that can
** be executed against a cursor.
*/
struct BtCursorOps {
    int (*Moveto)(BtCursor*, const void *pKey, int nKey, int *pRes);
    int (*Delete)(BtCursor*);
    int (*Insert)(BtCursor*, const void *pKey, int nKey,
                             const void *pData, int nData);
    int (*First)(BtCursor*, int *pRes);
    int (*Last)(BtCursor*, int *pRes);
    int (*Next)(BtCursor*, int *pRes);
    int (*Previous)(BtCursor*, int *pRes);



    int (*KeySize)(BtCursor*, int *pSize);
    int (*Key)(BtCursor*, int offset, int amt, char *zBuf);
    int (*KeyCompare)(BtCursor*, const void *pKey, int nKey,
                                 int nIgnore, int *pRes);
    int (*DataSize)(BtCursor*, int *pSize);
    int (*Data)(BtCursor*, int offset, int amt, char *zBuf);
    int (*CloseCursor)(BtCursor*);
#ifdef SQLITE_TEST
    int (*CursorDump)(BtCursor*, int*);
#endif
};

/*
** The number of 4-byte "meta" values contained on the first page of each
** database file.
*/
#define SQLITE_N_BTREE_META 10

int sqliteBtreeOpen(const char *zFilename, int mode, int nPg, Btree **ppBtree);
int sqliteRbtreeOpen(const char *zFilename, int mode, int nPg, Btree **ppBtree);

#define btOps(pBt) (*((BtOps **)(pBt)))
#define btCOps(pCur) (*((BtCursorOps **)(pCur)))

#define sqliteBtreeClose(pBt)              (btOps(pBt)->Close(pBt))
#define sqliteBtreeSetCacheSize(pBt, sz)   (btOps(pBt)->SetCacheSize(pBt, sz))
#define sqliteBtreeSetSafetyLevel(pBt, sl) (btOps(pBt)->SetSafetyLevel(pBt, sl))
#define sqliteBtreeBeginTrans(pBt)         (btOps(pBt)->BeginTrans(pBt))
#define sqliteBtreeCommit(pBt)             (btOps(pBt)->Commit(pBt))
#define sqliteBtreeRollback(pBt)           (btOps(pBt)->Rollback(pBt))
#define sqliteBtreeBeginCkpt(pBt)          (btOps(pBt)->BeginCkpt(pBt))
#define sqliteBtreeCommitCkpt(pBt)         (btOps(pBt)->CommitCkpt(pBt))
#define sqliteBtreeRollbackCkpt(pBt)       (btOps(pBt)->RollbackCkpt(pBt))
#define sqliteBtreeCreateTable(pBt,piTable)\
                (btOps(pBt)->CreateTable(pBt,piTable))
#define sqliteBtreeCreateIndex(pBt, piIndex)\
                (btOps(pBt)->CreateIndex(pBt, piIndex))
#define sqliteBtreeDropTable(pBt, iTable) (btOps(pBt)->DropTable(pBt, iTable))
#define sqliteBtreeClearTable(pBt, iTable)\
                (btOps(pBt)->ClearTable(pBt, iTable))
#define sqliteBtreeCursor(pBt, iTable, wrFlag, ppCur)\
                (btOps(pBt)->Cursor(pBt, iTable, wrFlag, ppCur))
#define sqliteBtreeMoveto(pCur, pKey, nKey, pRes)\
                (btCOps(pCur)->Moveto(pCur, pKey, nKey, pRes))
#define sqliteBtreeDelete(pCur)           (btCOps(pCur)->Delete(pCur))
#define sqliteBtreeInsert(pCur, pKey, nKey, pData, nData) \
                (btCOps(pCur)->Insert(pCur, pKey, nKey, pData, nData))
#define sqliteBtreeFirst(pCur, pRes)      (btCOps(pCur)->First(pCur, pRes))
#define sqliteBtreeLast(pCur, pRes)       (btCOps(pCur)->Last(pCur, pRes))
#define sqliteBtreeNext(pCur, pRes)       (btCOps(pCur)->Next(pCur, pRes))
#define sqliteBtreePrevious(pCur, pRes)   (btCOps(pCur)->Previous(pCur, pRes))
#define sqliteBtreeKeySize(pCur, pSize)   (btCOps(pCur)->KeySize(pCur, pSize) )
#define sqliteBtreeKey(pCur, offset, amt, zBuf)\
                (btCOps(pCur)->Key(pCur, offset, amt, zBuf))
#define sqliteBtreeKeyCompare(pCur, pKey, nKey, nIgnore, pRes)\
                (btCOps(pCur)->KeyCompare(pCur, pKey, nKey, nIgnore, pRes))
#define sqliteBtreeDataSize(pCur, pSize)  (btCOps(pCur)->DataSize(pCur, pSize))
#define sqliteBtreeData(pCur, offset, amt, zBuf)\
                (btCOps(pCur)->Data(pCur, offset, amt, zBuf))
#define sqliteBtreeCloseCursor(pCur)      (btCOps(pCur)->CloseCursor(pCur))
#define sqliteBtreeGetMeta(pBt, aMeta)    (btOps(pBt)->GetMeta(pBt, aMeta))
#define sqliteBtreeUpdateMeta(pBt, aMeta) (btOps(pBt)->UpdateMeta(pBt, aMeta))
#define sqliteBtreeIntegrityCheck(pBt, aRoot, nRoot)\
                (btOps(pBt)->IntegrityCheck(pBt, aRoot, nRoot))
#define sqliteBtreeGetFilename(pBt)       (btOps(pBt)->GetFilename(pBt))
#define sqliteBtreeCopyFile(pBt1, pBt2)   (btOps(pBt1)->Copyfile(pBt1, pBt2))
#define sqliteBtreePager(pBt)             (btOps(pBt)->Pager(pBt))

#ifdef SQLITE_TEST
#define sqliteBtreePageDump(pBt, pgno, recursive)\
                (btOps(pBt)->PageDump(pBt, pgno, recursive))
#define sqliteBtreeCursorDump(pCur, aResult)\
                (btCOps(pCur)->CursorDump(pCur, aResult))
int btree_native_byte_order;
#endif /* SQLITE_TEST */


#endif /* _BTREE_H_ */

**    May you share freely, never taking more than you give.
**
*************************************************************************
** This header file defines the interface that the sqlite B-Tree file
** subsystem.  See comments in the source code for a detailed description
** of what each interface routine does.
**
** @(#) $Id: btree.h,v 1.37 2004/04/26 14:10:21 drh Exp $
*/
#ifndef _BTREE_H_
#define _BTREE_H_

/*
** Forward declarations of structure
*/
typedef struct Btree Btree;
typedef struct BtCursor BtCursor;




int sqlite3BtreeOpen(const char *zFilename, Btree **, int nCache, int flags);

/* The flags parameter to sqlite3BtreeOpen can be the bitwise or of the
** following values.







*/
#define BTREE_OMIT_JOURNAL  1  /* Do not use journal.  No argument */
#define BTREE_MEMORY        2  /* In-memory DB.  No argument */

int sqlite3BtreeClose(Btree*);
int sqlite3BtreeSetCacheSize(Btree*,int);
int sqlite3BtreeSetSafetyLevel(Btree*,int);
int sqlite3BtreeBeginTrans(Btree*);
int sqlite3BtreeCommit(Btree*);
int sqlite3BtreeRollback(Btree*);
int sqlite3BtreeBeginStmt(Btree*);
int sqlite3BtreeCommitStmt(Btree*);
int sqlite3BtreeRollbackStmt(Btree*);
int sqlite3BtreeCreateTable(Btree*, int*, int flags);


/* The flags parameter to sqlite3BtreeCreateTable can be the bitwise OR
** of the following flags:
*/
#define BTREE_INTKEY     1      /* Table has only 64-bit integer keys */
#define BTREE_ZERODATA   2      /* Table has keys only - no data */

int sqlite3BtreeDropTable(Btree*, int);
int sqlite3BtreeClearTable(Btree*, int);

int sqlite3BtreeGetMeta(Btree*, int idx, u32 *pValue);
int sqlite3BtreeUpdateMeta(Btree*, int idx, u32 value);


int sqlite3BtreeCursor(
  Btree*,                              /* BTree containing table to open */
  int iTable,                          /* Index of root page */
  int wrFlag,                          /* 1 for writing.  0 for read-only */
  int(*)(void*,int,const void*,int,const void*),  /* Key comparison function */
  void*,                               /* First argument to compare function */

  BtCursor **ppCursor                  /* Returned cursor */
);


int sqlite3BtreeCursorClose(BtCursor*);



int sqlite3BtreeMoveto(BtCursor*, const void *pKey, u64 nKey, int *pRes);
int sqlite3BtreeDelete(BtCursor*);
int sqlite3BtreeInsert(BtCursor*, const void *pKey, u64 nKey,
                                  const void *pData, int nData);
int sqlite3BtreeFirst(BtCursor*, int *pRes);
int sqlite3BtreeLast(BtCursor*, int *pRes);
int sqlite3BtreeNext(BtCursor*, int *pRes);
int sqlite3BtreePrevious(BtCursor*, int *pRes);
int sqlite3BtreeKeySize(BtCursor*, u64 *pSize);
int sqlite3BtreeKey(BtCursor*, u32 offset, u32 amt, void*);
void *sqlite3BtreeKeyFetch(BtCursor*);
int sqlite3BtreeDataSize(BtCursor*, u32 *pSize);
int sqlite3BtreeData(BtCursor*, u32 offset, u32 amt, void*);











































































#endif /* _BTREE_H_ */

*/
int Md5_Init(Tcl_Interp *interp){
  Tcl_CreateCommand(interp, "md5", (Tcl_CmdProc*)md5_cmd, 0, 0);
  Tcl_CreateCommand(interp, "md5file", (Tcl_CmdProc*)md5file_cmd, 0, 0);
  return TCL_OK;
}


/*
** During testing, the special md5sum() aggregate function is available.
** inside SQLite.  The following routines implement that function.
*/
static void md5step(sqlite_func *context, int argc, const char **argv){
  MD5Context *p;
  int i;
................................................................................
  MD5Final(digest,p);
  DigestToBase16(digest, zBuf);
  sqlite_set_result_string(context, zBuf, strlen(zBuf));
}
void Md5_Register(sqlite *db){
  sqlite_create_aggregate(db, "md5sum", -1, md5step, md5finalize, 0);
}

*/
int Md5_Init(Tcl_Interp *interp){
  Tcl_CreateCommand(interp, "md5", (Tcl_CmdProc*)md5_cmd, 0, 0);
  Tcl_CreateCommand(interp, "md5file", (Tcl_CmdProc*)md5file_cmd, 0, 0);
  return TCL_OK;
}

#if 0
/*
** During testing, the special md5sum() aggregate function is available.
** inside SQLite.  The following routines implement that function.
*/
static void md5step(sqlite_func *context, int argc, const char **argv){
  MD5Context *p;
  int i;
................................................................................
  MD5Final(digest,p);
  DigestToBase16(digest, zBuf);
  sqlite_set_result_string(context, zBuf, strlen(zBuf));
}
void Md5_Register(sqlite *db){
  sqlite_create_aggregate(db, "md5sum", -1, md5step, md5finalize, 0);
}
#endif

** The pager is used to access a database disk file.  It implements
** atomic commit and rollback through the use of a journal file that
** is separate from the database file.  The pager also implements file
** locking to prevent two processes from writing the same database
** file simultaneously, or one process from reading the database while
** another is writing.
**
** @(#) $Id: pager.c,v 1.101 2004/02/25 02:20:41 drh Exp $
*/
#include "os.h"         /* Must be first to enable large file support */
#include "sqliteInt.h"
#include "pager.h"
#include <assert.h>
#include <string.h>

................................................................................


/*
** Each in-memory image of a page begins with the following header.
** This header is only visible to this pager module.  The client
** code that calls pager sees only the data that follows the header.
**
** Client code should call sqlitepager_write() on a page prior to making
** any modifications to that page.  The first time sqlitepager_write()
** is called, the original page contents are written into the rollback
** journal and PgHdr.inJournal and PgHdr.needSync are set.  Later, once
** the journal page has made it onto the disk surface, PgHdr.needSync
** is cleared.  The modified page cannot be written back into the original
** database file until the journal pages has been synced to disk and the
** PgHdr.needSync has been cleared.
**
** The PgHdr.dirty flag is set when sqlitepager_write() is called and
** is cleared again when the page content is written back to the original
** database file.
*/
typedef struct PgHdr PgHdr;
struct PgHdr {
  Pager *pPager;                 /* The pager to which this page belongs */
  Pgno pgno;                     /* The page number for this page */
................................................................................
#define JOURNAL_PG_SZ(X) \
   (SQLITE_PAGE_SIZE + sizeof(Pgno) + ((X)>=3)*sizeof(u32))

/*
** Enable reference count tracking here:
*/
#ifdef SQLITE_TEST
  int pager_refinfo_enable = 0;
  static void pager_refinfo(PgHdr *p){
    static int cnt = 0;
    if( !pager_refinfo_enable ) return;
    printf(
       "REFCNT: %4d addr=0x%08x nRef=%d\n",
       p->pgno, (int)PGHDR_TO_DATA(p), p->nRef
    );
    cnt++;   /* Something to set a breakpoint on */
  }
# define REFINFO(X)  pager_refinfo(X)
................................................................................
}

/*
** Add or remove a page from the list of all pages that are in the
** checkpoint journal.
**
** The Pager keeps a separate list of pages that are currently in
** the checkpoint journal.  This helps the sqlitepager_ckpt_commit()
** routine run MUCH faster for the common case where there are many
** pages in memory but only a few are in the checkpoint journal.
*/
static void page_add_to_ckpt_list(PgHdr *pPg){
  Pager *pPager = pPg->pPager;
  if( pPg->inCkpt ) return;
  assert( pPg->pPrevCkpt==0 && pPg->pNextCkpt==0 );
  pPg->pPrevCkpt = 0;
  if( pPager->pCkpt ){
    pPager->pCkpt->pPrevCkpt = pPg;
  }
  pPg->pNextCkpt = pPager->pCkpt;
  pPager->pCkpt = pPg;
  pPg->inCkpt = 1;
}
static void page_remove_from_ckpt_list(PgHdr *pPg){
  if( !pPg->inCkpt ) return;
  if( pPg->pPrevCkpt ){
    assert( pPg->pPrevCkpt->pNextCkpt==pPg );
    pPg->pPrevCkpt->pNextCkpt = pPg->pNextCkpt;
  }else{
    assert( pPg->pPager->pCkpt==pPg );
    pPg->pPager->pCkpt = pPg->pNextCkpt;
................................................................................
  pPager->pFirst = 0;
  pPager->pFirstSynced = 0;
  pPager->pLast = 0;
  pPager->pAll = 0;
  memset(pPager->aHash, 0, sizeof(pPager->aHash));
  pPager->nPage = 0;
  if( pPager->state>=SQLITE_WRITELOCK ){
    sqlitepager_rollback(pPager);
  }
  sqliteOsUnlock(&pPager->fd);
  pPager->state = SQLITE_UNLOCK;
  pPager->dbSize = -1;
  pPager->nRef = 0;
  assert( pPager->journalOpen==0 );
}
................................................................................
** This might give a performance improvement on windows where opening
** a file is an expensive operation.
*/
static int pager_unwritelock(Pager *pPager){
  int rc;
  PgHdr *pPg;
  if( pPager->state<SQLITE_WRITELOCK ) return SQLITE_OK;
  sqlitepager_ckpt_commit(pPager);
  if( pPager->ckptOpen ){
    sqliteOsClose(&pPager->cpfd);
    pPager->ckptOpen = 0;
  }
  if( pPager->journalOpen ){
    sqliteOsClose(&pPager->jfd);
    pPager->journalOpen = 0;
................................................................................
**         the checkpoint is stored in pPager->ckptSize, not in the
**         journal file itself.
**
**    (2)  In addition to playing back the checkpoint journal, also
**         playback all pages of the transaction journal beginning
**         at offset pPager->ckptJSize.
*/
static int pager_ckpt_playback(Pager *pPager){
  off_t szJ;               /* Size of the full journal */
  int nRec;                /* Number of Records */
  int i;                   /* Loop counter */
  int rc;

  /* Truncate the database back to its original size.
  */
................................................................................
  ** database file.  Note that the checkpoint journal always uses format
  ** 2 instead of format 3 since it does not need to be concerned with
  ** power failures corrupting the journal and can thus omit the checksums.
  */
  for(i=nRec-1; i>=0; i--){
    rc = pager_playback_one_page(pPager, &pPager->cpfd, 2);
    assert( rc!=SQLITE_DONE );
    if( rc!=SQLITE_OK ) goto end_ckpt_playback;
  }

  /* Figure out how many pages need to be copied out of the transaction
  ** journal.
  */
  rc = sqliteOsSeek(&pPager->jfd, pPager->ckptJSize);
  if( rc!=SQLITE_OK ){
    goto end_ckpt_playback;
  }
  rc = sqliteOsFileSize(&pPager->jfd, &szJ);
  if( rc!=SQLITE_OK ){
    goto end_ckpt_playback;
  }
  nRec = (szJ - pPager->ckptJSize)/JOURNAL_PG_SZ(journal_format);
  for(i=nRec-1; i>=0; i--){
    rc = pager_playback_one_page(pPager, &pPager->jfd, journal_format);
    if( rc!=SQLITE_OK ){
      assert( rc!=SQLITE_DONE );
      goto end_ckpt_playback;
    }
  }
  
end_ckpt_playback:
  if( rc!=SQLITE_OK ){
    pPager->errMask |= PAGER_ERR_CORRUPT;
    rc = SQLITE_CORRUPT;
  }
  return rc;
}

................................................................................
** The maximum number is the absolute value of the mxPage parameter.
** If mxPage is negative, the noSync flag is also set.  noSync bypasses
** calls to sqliteOsSync().  The pager runs much faster with noSync on,
** but if the operating system crashes or there is an abrupt power 
** failure, the database file might be left in an inconsistent and
** unrepairable state.  
*/
void sqlitepager_set_cachesize(Pager *pPager, int mxPage){
  if( mxPage>=0 ){
    pPager->noSync = pPager->tempFile;
    if( pPager->noSync==0 ) pPager->needSync = 0;
  }else{
    pPager->noSync = 1;
    mxPage = -mxPage;
  }
................................................................................
**              single disk sector is atomic, then this mode provides
**              assurance that the journal will not be corrupted to the
**              point of causing damage to the database during rollback.
**
** Numeric values associated with these states are OFF==1, NORMAL=2,
** and FULL=3.
*/
void sqlitepager_set_safety_level(Pager *pPager, int level){
  pPager->noSync =  level==1 || pPager->tempFile;
  pPager->fullSync = level==3 && !pPager->tempFile;
  if( pPager->noSync==0 ) pPager->needSync = 0;
}

/*
** Open a temporary file.  Write the name of the file into zName
................................................................................
** (zName must be at least SQLITE_TEMPNAME_SIZE bytes long.)  Write
** the file descriptor into *fd.  Return SQLITE_OK on success or some
** other error code if we fail.
**
** The OS will automatically delete the temporary file when it is
** closed.
*/
static int sqlitepager_opentemp(char *zFile, OsFile *fd){
  int cnt = 8;
  int rc;
  do{
    cnt--;
    sqliteOsTempFileName(zFile);
    rc = sqliteOsOpenExclusive(zFile, fd, 1);
  }while( cnt>0 && rc!=SQLITE_OK );
  return rc;
}

/*
** Create a new page cache and put a pointer to the page cache in *ppPager.
** The file to be cached need not exist.  The file is not locked until
** the first call to sqlitepager_get() and is only held open until the
** last page is released using sqlitepager_unref().
**
** If zFilename is NULL then a randomly-named temporary file is created
** and used as the file to be cached.  The file will be deleted
** automatically when it is closed.
*/
int sqlitepager_open(
  Pager **ppPager,         /* Return the Pager structure here */
  const char *zFilename,   /* Name of the database file to open */
  int mxPage,              /* Max number of in-memory cache pages */
  int nExtra,              /* Extra bytes append to each in-memory page */
  int useJournal           /* TRUE to use a rollback journal on this file */
){
  Pager *pPager;
................................................................................
    return SQLITE_NOMEM;
  }
  if( zFilename && zFilename[0] ){
    zFullPathname = sqliteOsFullPathname(zFilename);
    rc = sqliteOsOpenReadWrite(zFullPathname, &fd, &readOnly);
    tempFile = 0;
  }else{
    rc = sqlitepager_opentemp(zTemp, &fd);
    zFilename = zTemp;
    zFullPathname = sqliteOsFullPathname(zFilename);
    tempFile = 1;
  }
  if( sqlite_malloc_failed ){
    return SQLITE_NOMEM;
  }
................................................................................
}

/*
** Set the destructor for this pager.  If not NULL, the destructor is called
** when the reference count on each page reaches zero.  The destructor can
** be used to clean up information in the extra segment appended to each page.
**
** The destructor is not called as a result sqlitepager_close().  
** Destructors are only called by sqlitepager_unref().
*/
void sqlitepager_set_destructor(Pager *pPager, void (*xDesc)(void*)){
  pPager->xDestructor = xDesc;
}

/*
** Return the total number of pages in the disk file associated with
** pPager.
*/
int sqlitepager_pagecount(Pager *pPager){
  off_t n;
  assert( pPager!=0 );
  if( pPager->dbSize>=0 ){
    return pPager->dbSize;
  }
  if( sqliteOsFileSize(&pPager->fd, &n)!=SQLITE_OK ){
    pPager->errMask |= PAGER_ERR_DISK;
................................................................................
** Forward declaration
*/
static int syncJournal(Pager*);

/*
** Truncate the file to the number of pages specified.
*/
int sqlitepager_truncate(Pager *pPager, Pgno nPage){
  int rc;
  if( pPager->dbSize<0 ){
    sqlitepager_pagecount(pPager);
  }
  if( pPager->errMask!=0 ){
    rc = pager_errcode(pPager);
    return rc;
  }
  if( nPage>=(unsigned)pPager->dbSize ){
    return SQLITE_OK;
................................................................................
**
** If a transaction was in progress when this routine is called, that
** transaction is rolled back.  All outstanding pages are invalidated
** and their memory is freed.  Any attempt to use a page associated
** with this page cache after this function returns will likely
** result in a coredump.
*/
int sqlitepager_close(Pager *pPager){
  PgHdr *pPg, *pNext;
  switch( pPager->state ){
    case SQLITE_WRITELOCK: {
      sqlitepager_rollback(pPager);
      sqliteOsUnlock(&pPager->fd);
      assert( pPager->journalOpen==0 );
      break;
    }
    case SQLITE_READLOCK: {
      sqliteOsUnlock(&pPager->fd);
      break;
................................................................................
  sqliteFree(pPager);
  return SQLITE_OK;
}

/*
** Return the page number for the given page data.
*/
Pgno sqlitepager_pagenumber(void *pData){
  PgHdr *p = DATA_TO_PGHDR(pData);
  return p->pgno;
}

/*
** Increment the reference count for a page.  If the page is
** currently on the freelist (the reference count is zero) then
................................................................................
  REFINFO(pPg);
}

/*
** Increment the reference count for a page.  The input pointer is
** a reference to the page data.
*/
int sqlitepager_ref(void *pData){
  PgHdr *pPg = DATA_TO_PGHDR(pData);
  page_ref(pPg);
  return SQLITE_OK;
}

/*
** Sync the journal.  In other words, make sure all the pages that have
................................................................................
** read occurs and the memory image of the page is initialized to
** all zeros.  The extra data appended to a page is always initialized
** to zeros the first time a page is loaded into memory.
**
** The acquisition might fail for several reasons.  In all cases,
** an appropriate error code is returned and *ppPage is set to NULL.
**
** See also sqlitepager_lookup().  Both this routine and _lookup() attempt
** to find a page in the in-memory cache first.  If the page is not already
** in memory, this routine goes to disk to read it in whereas _lookup()
** just returns 0.  This routine acquires a read-lock the first time it
** has to go to disk, and could also playback an old journal if necessary.
** Since _lookup() never goes to disk, it never has to deal with locks
** or journal files.
*/
int sqlitepager_get(Pager *pPager, Pgno pgno, void **ppPage){
  PgHdr *pPg;
  int rc;

  /* Make sure we have not hit any critical errors.
  */ 
  assert( pPager!=0 );
  assert( pgno!=0 );
................................................................................
      ** on the journal file then fsync the journal file.  This is a
      ** very slow operation, so we work hard to avoid it.  But sometimes
      ** it can't be helped.
      */
      if( pPg==0 ){
        int rc = syncJournal(pPager);
        if( rc!=0 ){
          sqlitepager_rollback(pPager);
          return SQLITE_IOERR;
        }
        pPg = pPager->pFirst;
      }
      assert( pPg->nRef==0 );

      /* Write the page to the database file if it is dirty.
      */
      if( pPg->dirty ){
        assert( pPg->needSync==0 );
        pPg->pDirty = 0;
        rc = pager_write_pagelist( pPg );
        if( rc!=SQLITE_OK ){
          sqlitepager_rollback(pPager);
          return SQLITE_IOERR;
        }
      }
      assert( pPg->dirty==0 );

      /* If the page we are recycling is marked as alwaysRollback, then
      ** set the global alwaysRollback flag, thus disabling the
................................................................................
      pPg->needSync = 0;
    }else{
      pPg->inJournal = 0;
      pPg->needSync = 0;
    }
    if( pPager->aInCkpt && (int)pgno<=pPager->ckptSize
             && (pPager->aInCkpt[pgno/8] & (1<<(pgno&7)))!=0 ){
      page_add_to_ckpt_list(pPg);
    }else{
      page_remove_from_ckpt_list(pPg);
    }
    pPg->dirty = 0;
    pPg->nRef = 1;
    REFINFO(pPg);
    pPager->nRef++;
    h = pager_hash(pgno);
    pPg->pNextHash = pPager->aHash[h];
................................................................................
    if( pPg->pNextHash ){
      assert( pPg->pNextHash->pPrevHash==0 );
      pPg->pNextHash->pPrevHash = pPg;
    }
    if( pPager->nExtra>0 ){
      memset(PGHDR_TO_EXTRA(pPg), 0, pPager->nExtra);
    }
    if( pPager->dbSize<0 ) sqlitepager_pagecount(pPager);
    if( pPager->errMask!=0 ){
      sqlitepager_unref(PGHDR_TO_DATA(pPg));
      rc = pager_errcode(pPager);
      return rc;
    }
    if( pPager->dbSize<(int)pgno ){
      memset(PGHDR_TO_DATA(pPg), 0, SQLITE_PAGE_SIZE);
    }else{
      int rc;
................................................................................
      rc = sqliteOsRead(&pPager->fd, PGHDR_TO_DATA(pPg), SQLITE_PAGE_SIZE);
      TRACE2("FETCH %d\n", pPg->pgno);
      CODEC(pPager, PGHDR_TO_DATA(pPg), pPg->pgno, 3);
      if( rc!=SQLITE_OK ){
        off_t fileSize;
        if( sqliteOsFileSize(&pPager->fd,&fileSize)!=SQLITE_OK
               || fileSize>=pgno*SQLITE_PAGE_SIZE ){
          sqlitepager_unref(PGHDR_TO_DATA(pPg));
          return rc;
        }else{
          memset(PGHDR_TO_DATA(pPg), 0, SQLITE_PAGE_SIZE);
        }
      }
    }
  }else{
................................................................................
}

/*
** Acquire a page if it is already in the in-memory cache.  Do
** not read the page from disk.  Return a pointer to the page,
** or 0 if the page is not in cache.
**
** See also sqlitepager_get().  The difference between this routine
** and sqlitepager_get() is that _get() will go to the disk and read
** in the page if the page is not already in cache.  This routine
** returns NULL if the page is not in cache or if a disk I/O error 
** has ever happened.
*/
void *sqlitepager_lookup(Pager *pPager, Pgno pgno){
  PgHdr *pPg;

  assert( pPager!=0 );
  assert( pgno!=0 );
  if( pPager->errMask & ~(PAGER_ERR_FULL) ){
    return 0;
  }
................................................................................
** Release a page.
**
** If the number of references to the page drop to zero, then the
** page is added to the LRU list.  When all references to all pages
** are released, a rollback occurs and the lock on the database is
** removed.
*/
int sqlitepager_unref(void *pData){
  PgHdr *pPg;

  /* Decrement the reference count for this page
  */
  pPg = DATA_TO_PGHDR(pData);
  assert( pPg->nRef>0 );
  pPg->nRef--;
................................................................................
** write lock if anything goes wrong.
*/
static int pager_open_journal(Pager *pPager){
  int rc;
  assert( pPager->state==SQLITE_WRITELOCK );
  assert( pPager->journalOpen==0 );
  assert( pPager->useJournal );
  sqlitepager_pagecount(pPager);
  pPager->aInJournal = sqliteMalloc( pPager->dbSize/8 + 1 );
  if( pPager->aInJournal==0 ){
    sqliteOsReadLock(&pPager->fd);
    pPager->state = SQLITE_READLOCK;
    return SQLITE_NOMEM;
  }
  rc = sqliteOsOpenExclusive(pPager->zJournal, &pPager->jfd,pPager->tempFile);
................................................................................
    assert( journal_format==JOURNAL_FORMAT_1 );
    rc = sqliteOsWrite(&pPager->jfd, aJournalMagic1, sizeof(aJournalMagic1));
  }
  if( rc==SQLITE_OK ){
    rc = write32bits(&pPager->jfd, pPager->dbSize);
  }
  if( pPager->ckptAutoopen && rc==SQLITE_OK ){
    rc = sqlitepager_ckpt_begin(pPager);
  }
  if( rc!=SQLITE_OK ){
    rc = pager_unwritelock(pPager);
    if( rc==SQLITE_OK ){
      rc = SQLITE_FULL;
    }
  }
................................................................................
  return rc;  
}

/*
** Acquire a write-lock on the database.  The lock is removed when
** the any of the following happen:
**
**   *  sqlitepager_commit() is called.
**   *  sqlitepager_rollback() is called.
**   *  sqlitepager_close() is called.
**   *  sqlitepager_unref() is called to on every outstanding page.
**
** The parameter to this routine is a pointer to any open page of the
** database file.  Nothing changes about the page - it is used merely
** to acquire a pointer to the Pager structure and as proof that there
** is already a read-lock on the database.
**
** A journal file is opened if this is not a temporary file.  For
** temporary files, the opening of the journal file is deferred until
** there is an actual need to write to the journal.
**
** If the database is already write-locked, this routine is a no-op.
*/
int sqlitepager_begin(void *pData){
  PgHdr *pPg = DATA_TO_PGHDR(pData);
  Pager *pPager = pPg->pPager;
  int rc = SQLITE_OK;
  assert( pPg->nRef>0 );
  assert( pPager->state!=SQLITE_UNLOCK );
  if( pPager->state==SQLITE_READLOCK ){
    assert( pPager->aInJournal==0 );
................................................................................
** lock could not be acquired, this routine returns SQLITE_BUSY.  The
** calling routine must check for that return value and be careful not to
** change any page data until this routine returns SQLITE_OK.
**
** If the journal file could not be written because the disk is full,
** then this routine returns SQLITE_FULL and does an immediate rollback.
** All subsequent write attempts also return SQLITE_FULL until there
** is a call to sqlitepager_commit() or sqlitepager_rollback() to
** reset.
*/
int sqlitepager_write(void *pData){
  PgHdr *pPg = DATA_TO_PGHDR(pData);
  Pager *pPager = pPg->pPager;
  int rc = SQLITE_OK;

  /* Check for errors
  */
  if( pPager->errMask ){ 
................................................................................
  ** written to the transaction journal or the ckeckpoint journal
  ** or both.
  **
  ** First check to see that the transaction journal exists and
  ** create it if it does not.
  */
  assert( pPager->state!=SQLITE_UNLOCK );
  rc = sqlitepager_begin(pData);
  if( rc!=SQLITE_OK ){
    return rc;
  }
  assert( pPager->state==SQLITE_WRITELOCK );
  if( !pPager->journalOpen && pPager->useJournal ){
    rc = pager_open_journal(pPager);
    if( rc!=SQLITE_OK ) return rc;
................................................................................
      rc = sqliteOsWrite(&pPager->jfd, &((char*)pData)[-4], szPg);
      TRACE3("JOURNAL %d %d\n", pPg->pgno, pPg->needSync);
      CODEC(pPager, pData, pPg->pgno, 0);
      if( journal_format>=JOURNAL_FORMAT_3 ){
        *(u32*)PGHDR_TO_EXTRA(pPg) = saved;
      }
      if( rc!=SQLITE_OK ){
        sqlitepager_rollback(pPager);
        pPager->errMask |= PAGER_ERR_FULL;
        return rc;
      }
      pPager->nRec++;
      assert( pPager->aInJournal!=0 );
      pPager->aInJournal[pPg->pgno/8] |= 1<<(pPg->pgno&7);
      pPg->needSync = !pPager->noSync;
      pPg->inJournal = 1;
      if( pPager->ckptInUse ){
        pPager->aInCkpt[pPg->pgno/8] |= 1<<(pPg->pgno&7);
        page_add_to_ckpt_list(pPg);
      }
    }else{
      pPg->needSync = !pPager->journalStarted && !pPager->noSync;
      TRACE3("APPEND %d %d\n", pPg->pgno, pPg->needSync);
    }
    if( pPg->needSync ){
      pPager->needSync = 1;
................................................................................
    assert( pPg->inJournal || (int)pPg->pgno>pPager->origDbSize );
    store32bits(pPg->pgno, pPg, -4);
    CODEC(pPager, pData, pPg->pgno, 7);
    rc = sqliteOsWrite(&pPager->cpfd, &((char*)pData)[-4], SQLITE_PAGE_SIZE+4);
    TRACE2("CKPT-JOURNAL %d\n", pPg->pgno);
    CODEC(pPager, pData, pPg->pgno, 0);
    if( rc!=SQLITE_OK ){
      sqlitepager_rollback(pPager);
      pPager->errMask |= PAGER_ERR_FULL;
      return rc;
    }
    pPager->ckptNRec++;
    assert( pPager->aInCkpt!=0 );
    pPager->aInCkpt[pPg->pgno/8] |= 1<<(pPg->pgno&7);
    page_add_to_ckpt_list(pPg);
  }

  /* Update the database size and return.
  */
  if( pPager->dbSize<(int)pPg->pgno ){
    pPager->dbSize = pPg->pgno;
  }
  return rc;
}

/*
** Return TRUE if the page given in the argument was previously passed
** to sqlitepager_write().  In other words, return TRUE if it is ok
** to change the content of the page.
*/
int sqlitepager_iswriteable(void *pData){
  PgHdr *pPg = DATA_TO_PGHDR(pData);
  return pPg->dirty;
}

/*
** Replace the content of a single page with the information in the third
** argument.
*/
int sqlitepager_overwrite(Pager *pPager, Pgno pgno, void *pData){
  void *pPage;
  int rc;

  rc = sqlitepager_get(pPager, pgno, &pPage);
  if( rc==SQLITE_OK ){
    rc = sqlitepager_write(pPage);
    if( rc==SQLITE_OK ){
      memcpy(pPage, pData, SQLITE_PAGE_SIZE);
    }
    sqlitepager_unref(pPage);
  }
  return rc;
}

/*
** A call to this routine tells the pager that it is not necessary to
** write the information on page "pgno" back to the disk, even though
................................................................................
** that page might be marked as dirty.
**
** The overlying software layer calls this routine when all of the data
** on the given page is unused.  The pager marks the page as clean so
** that it does not get written to disk.
**
** Tests show that this optimization, together with the
** sqlitepager_dont_rollback() below, more than double the speed
** of large INSERT operations and quadruple the speed of large DELETEs.
**
** When this routine is called, set the alwaysRollback flag to true.
** Subsequent calls to sqlitepager_dont_rollback() for the same page
** will thereafter be ignored.  This is necessary to avoid a problem
** where a page with data is added to the freelist during one part of
** a transaction then removed from the freelist during a later part
** of the same transaction and reused for some other purpose.  When it
** is first added to the freelist, this routine is called.  When reused,
** the dont_rollback() routine is called.  But because the page contains
** critical data, we still need to be sure it gets rolled back in spite
** of the dont_rollback() call.
*/
void sqlitepager_dont_write(Pager *pPager, Pgno pgno){
  PgHdr *pPg;

  pPg = pager_lookup(pPager, pgno);
  pPg->alwaysRollback = 1;
  if( pPg && pPg->dirty ){
    if( pPager->dbSize==(int)pPg->pgno && pPager->origDbSize<pPager->dbSize ){
      /* If this pages is the last page in the file and the file has grown
................................................................................

/*
** A call to this routine tells the pager that if a rollback occurs,
** it is not necessary to restore the data on the given page.  This
** means that the pager does not have to record the given page in the
** rollback journal.
*/
void sqlitepager_dont_rollback(void *pData){
  PgHdr *pPg = DATA_TO_PGHDR(pData);
  Pager *pPager = pPg->pPager;

  if( pPager->state!=SQLITE_WRITELOCK || pPager->journalOpen==0 ) return;
  if( pPg->alwaysRollback || pPager->alwaysRollback ) return;
  if( !pPg->inJournal && (int)pPg->pgno <= pPager->origDbSize ){
    assert( pPager->aInJournal!=0 );
    pPager->aInJournal[pPg->pgno/8] |= 1<<(pPg->pgno&7);
    pPg->inJournal = 1;
    if( pPager->ckptInUse ){
      pPager->aInCkpt[pPg->pgno/8] |= 1<<(pPg->pgno&7);
      page_add_to_ckpt_list(pPg);
    }
    TRACE2("DONT_ROLLBACK %d\n", pPg->pgno);
  }
  if( pPager->ckptInUse && !pPg->inCkpt && (int)pPg->pgno<=pPager->ckptSize ){
    assert( pPg->inJournal || (int)pPg->pgno>pPager->origDbSize );
    assert( pPager->aInCkpt!=0 );
    pPager->aInCkpt[pPg->pgno/8] |= 1<<(pPg->pgno&7);
    page_add_to_ckpt_list(pPg);
  }
}

/*
** Commit all changes to the database and release the write lock.
**
** If the commit fails for any reason, a rollback attempt is made
** and an error code is returned.  If the commit worked, SQLITE_OK
** is returned.
*/
int sqlitepager_commit(Pager *pPager){
  int rc;
  PgHdr *pPg;

  if( pPager->errMask==PAGER_ERR_FULL ){
    rc = sqlitepager_rollback(pPager);
    if( rc==SQLITE_OK ){
      rc = SQLITE_FULL;
    }
    return rc;
  }
  if( pPager->errMask!=0 ){
    rc = pager_errcode(pPager);
................................................................................
  rc = pager_unwritelock(pPager);
  pPager->dbSize = -1;
  return rc;

  /* Jump here if anything goes wrong during the commit process.
  */
commit_abort:
  rc = sqlitepager_rollback(pPager);
  if( rc==SQLITE_OK ){
    rc = SQLITE_FULL;
  }
  return rc;
}

/*
................................................................................
** This routine cannot fail unless some other process is not following
** the correct locking protocol (SQLITE_PROTOCOL) or unless some other
** process is writing trash into the journal file (SQLITE_CORRUPT) or
** unless a prior malloc() failed (SQLITE_NOMEM).  Appropriate error
** codes are returned for all these occasions.  Otherwise,
** SQLITE_OK is returned.
*/
int sqlitepager_rollback(Pager *pPager){
  int rc;
  TRACE1("ROLLBACK\n");
  if( !pPager->dirtyFile || !pPager->journalOpen ){
    rc = pager_unwritelock(pPager);
    pPager->dbSize = -1;
    return rc;
  }
................................................................................
  return rc;
}

/*
** Return TRUE if the database file is opened read-only.  Return FALSE
** if the database is (in theory) writable.
*/
int sqlitepager_isreadonly(Pager *pPager){
  return pPager->readOnly;
}

/*
** This routine is used for testing and analysis only.
*/
int *sqlitepager_stats(Pager *pPager){
  static int a[9];
  a[0] = pPager->nRef;
  a[1] = pPager->nPage;
  a[2] = pPager->mxPage;
  a[3] = pPager->dbSize;
  a[4] = pPager->state;
  a[5] = pPager->errMask;
................................................................................
/*
** Set the checkpoint.
**
** This routine should be called with the transaction journal already
** open.  A new checkpoint journal is created that can be used to rollback
** changes of a single SQL command within a larger transaction.
*/
int sqlitepager_ckpt_begin(Pager *pPager){
  int rc;
  char zTemp[SQLITE_TEMPNAME_SIZE];
  if( !pPager->journalOpen ){
    pPager->ckptAutoopen = 1;
    return SQLITE_OK;
  }
  assert( pPager->journalOpen );
................................................................................
  assert( pPager->ckptJSize == 
    pPager->nRec*JOURNAL_PG_SZ(journal_format)+JOURNAL_HDR_SZ(journal_format) );
#endif
  pPager->ckptJSize = pPager->nRec*JOURNAL_PG_SZ(journal_format)
                         + JOURNAL_HDR_SZ(journal_format);
  pPager->ckptSize = pPager->dbSize;
  if( !pPager->ckptOpen ){
    rc = sqlitepager_opentemp(zTemp, &pPager->cpfd);
    if( rc ) goto ckpt_begin_failed;
    pPager->ckptOpen = 1;
    pPager->ckptNRec = 0;
  }
  pPager->ckptInUse = 1;
  return SQLITE_OK;
 
................................................................................
  }
  return rc;
}

/*
** Commit a checkpoint.
*/
int sqlitepager_ckpt_commit(Pager *pPager){
  if( pPager->ckptInUse ){
    PgHdr *pPg, *pNext;
    sqliteOsSeek(&pPager->cpfd, 0);
    /* sqliteOsTruncate(&pPager->cpfd, 0); */
    pPager->ckptNRec = 0;
    pPager->ckptInUse = 0;
    sqliteFree( pPager->aInCkpt );
................................................................................
  pPager->ckptAutoopen = 0;
  return SQLITE_OK;
}

/*
** Rollback a checkpoint.
*/
int sqlitepager_ckpt_rollback(Pager *pPager){
  int rc;
  if( pPager->ckptInUse ){
    rc = pager_ckpt_playback(pPager);
    sqlitepager_ckpt_commit(pPager);
  }else{
    rc = SQLITE_OK;
  }
  pPager->ckptAutoopen = 0;
  return rc;
}

/*
** Return the full pathname of the database file.
*/
const char *sqlitepager_filename(Pager *pPager){
  return pPager->zFilename;
}

/*
** Set the codec for this pager
*/
void sqlitepager_set_codec(
  Pager *pPager,
  void (*xCodec)(void*,void*,Pgno,int),
  void *pCodecArg
){
  pPager->xCodec = xCodec;
  pPager->pCodecArg = pCodecArg;
}

#ifdef SQLITE_TEST
/*
** Print a listing of all referenced pages and their ref count.
*/
void sqlitepager_refdump(Pager *pPager){
  PgHdr *pPg;
  for(pPg=pPager->pAll; pPg; pPg=pPg->pNextAll){
    if( pPg->nRef<=0 ) continue;
    printf("PAGE %3d addr=0x%08x nRef=%d\n", 
       pPg->pgno, (int)PGHDR_TO_DATA(pPg), pPg->nRef);
  }
}
#endif

** The pager is used to access a database disk file.  It implements
** atomic commit and rollback through the use of a journal file that
** is separate from the database file.  The pager also implements file
** locking to prevent two processes from writing the same database
** file simultaneously, or one process from reading the database while
** another is writing.
**
** @(#) $Id: pager.c,v 1.102 2004/04/26 14:10:21 drh Exp $
*/
#include "os.h"         /* Must be first to enable large file support */
#include "sqliteInt.h"
#include "pager.h"
#include <assert.h>
#include <string.h>

................................................................................


/*
** Each in-memory image of a page begins with the following header.
** This header is only visible to this pager module.  The client
** code that calls pager sees only the data that follows the header.
**
** Client code should call sqlite3pager_write() on a page prior to making
** any modifications to that page.  The first time sqlite3pager_write()
** is called, the original page contents are written into the rollback
** journal and PgHdr.inJournal and PgHdr.needSync are set.  Later, once
** the journal page has made it onto the disk surface, PgHdr.needSync
** is cleared.  The modified page cannot be written back into the original
** database file until the journal pages has been synced to disk and the
** PgHdr.needSync has been cleared.
**
** The PgHdr.dirty flag is set when sqlite3pager_write() is called and
** is cleared again when the page content is written back to the original
** database file.
*/
typedef struct PgHdr PgHdr;
struct PgHdr {
  Pager *pPager;                 /* The pager to which this page belongs */
  Pgno pgno;                     /* The page number for this page */
................................................................................
#define JOURNAL_PG_SZ(X) \
   (SQLITE_PAGE_SIZE + sizeof(Pgno) + ((X)>=3)*sizeof(u32))

/*
** Enable reference count tracking here:
*/
#ifdef SQLITE_TEST
  int pager3_refinfo_enable = 0;
  static void pager_refinfo(PgHdr *p){
    static int cnt = 0;
    if( !pager3_refinfo_enable ) return;
    printf(
       "REFCNT: %4d addr=0x%08x nRef=%d\n",
       p->pgno, (int)PGHDR_TO_DATA(p), p->nRef
    );
    cnt++;   /* Something to set a breakpoint on */
  }
# define REFINFO(X)  pager_refinfo(X)
................................................................................
}

/*
** Add or remove a page from the list of all pages that are in the
** checkpoint journal.
**
** The Pager keeps a separate list of pages that are currently in
** the checkpoint journal.  This helps the sqlite3pager_stmt_commit()
** routine run MUCH faster for the common case where there are many
** pages in memory but only a few are in the checkpoint journal.
*/
static void page_add_to_stmt_list(PgHdr *pPg){
  Pager *pPager = pPg->pPager;
  if( pPg->inCkpt ) return;
  assert( pPg->pPrevCkpt==0 && pPg->pNextCkpt==0 );
  pPg->pPrevCkpt = 0;
  if( pPager->pCkpt ){
    pPager->pCkpt->pPrevCkpt = pPg;
  }
  pPg->pNextCkpt = pPager->pCkpt;
  pPager->pCkpt = pPg;
  pPg->inCkpt = 1;
}
static void page_remove_from_stmt_list(PgHdr *pPg){
  if( !pPg->inCkpt ) return;
  if( pPg->pPrevCkpt ){
    assert( pPg->pPrevCkpt->pNextCkpt==pPg );
    pPg->pPrevCkpt->pNextCkpt = pPg->pNextCkpt;
  }else{
    assert( pPg->pPager->pCkpt==pPg );
    pPg->pPager->pCkpt = pPg->pNextCkpt;
................................................................................
  pPager->pFirst = 0;
  pPager->pFirstSynced = 0;
  pPager->pLast = 0;
  pPager->pAll = 0;
  memset(pPager->aHash, 0, sizeof(pPager->aHash));
  pPager->nPage = 0;
  if( pPager->state>=SQLITE_WRITELOCK ){
    sqlite3pager_rollback(pPager);
  }
  sqliteOsUnlock(&pPager->fd);
  pPager->state = SQLITE_UNLOCK;
  pPager->dbSize = -1;
  pPager->nRef = 0;
  assert( pPager->journalOpen==0 );
}
................................................................................
** This might give a performance improvement on windows where opening
** a file is an expensive operation.
*/
static int pager_unwritelock(Pager *pPager){
  int rc;
  PgHdr *pPg;
  if( pPager->state<SQLITE_WRITELOCK ) return SQLITE_OK;
  sqlite3pager_stmt_commit(pPager);
  if( pPager->ckptOpen ){
    sqliteOsClose(&pPager->cpfd);
    pPager->ckptOpen = 0;
  }
  if( pPager->journalOpen ){
    sqliteOsClose(&pPager->jfd);
    pPager->journalOpen = 0;
................................................................................
**         the checkpoint is stored in pPager->ckptSize, not in the
**         journal file itself.
**
**    (2)  In addition to playing back the checkpoint journal, also
**         playback all pages of the transaction journal beginning
**         at offset pPager->ckptJSize.
*/
static int pager_stmt_playback(Pager *pPager){
  off_t szJ;               /* Size of the full journal */
  int nRec;                /* Number of Records */
  int i;                   /* Loop counter */
  int rc;

  /* Truncate the database back to its original size.
  */
................................................................................
  ** database file.  Note that the checkpoint journal always uses format
  ** 2 instead of format 3 since it does not need to be concerned with
  ** power failures corrupting the journal and can thus omit the checksums.
  */
  for(i=nRec-1; i>=0; i--){
    rc = pager_playback_one_page(pPager, &pPager->cpfd, 2);
    assert( rc!=SQLITE_DONE );
    if( rc!=SQLITE_OK ) goto end_stmt_playback;
  }

  /* Figure out how many pages need to be copied out of the transaction
  ** journal.
  */
  rc = sqliteOsSeek(&pPager->jfd, pPager->ckptJSize);
  if( rc!=SQLITE_OK ){
    goto end_stmt_playback;
  }
  rc = sqliteOsFileSize(&pPager->jfd, &szJ);
  if( rc!=SQLITE_OK ){
    goto end_stmt_playback;
  }
  nRec = (szJ - pPager->ckptJSize)/JOURNAL_PG_SZ(journal_format);
  for(i=nRec-1; i>=0; i--){
    rc = pager_playback_one_page(pPager, &pPager->jfd, journal_format);
    if( rc!=SQLITE_OK ){
      assert( rc!=SQLITE_DONE );
      goto end_stmt_playback;
    }
  }
  
end_stmt_playback:
  if( rc!=SQLITE_OK ){
    pPager->errMask |= PAGER_ERR_CORRUPT;
    rc = SQLITE_CORRUPT;
  }
  return rc;
}

................................................................................
** The maximum number is the absolute value of the mxPage parameter.
** If mxPage is negative, the noSync flag is also set.  noSync bypasses
** calls to sqliteOsSync().  The pager runs much faster with noSync on,
** but if the operating system crashes or there is an abrupt power 
** failure, the database file might be left in an inconsistent and
** unrepairable state.  
*/
void sqlite3pager_set_cachesize(Pager *pPager, int mxPage){
  if( mxPage>=0 ){
    pPager->noSync = pPager->tempFile;
    if( pPager->noSync==0 ) pPager->needSync = 0;
  }else{
    pPager->noSync = 1;
    mxPage = -mxPage;
  }
................................................................................
**              single disk sector is atomic, then this mode provides
**              assurance that the journal will not be corrupted to the
**              point of causing damage to the database during rollback.
**
** Numeric values associated with these states are OFF==1, NORMAL=2,
** and FULL=3.
*/
void sqlite3pager_set_safety_level(Pager *pPager, int level){
  pPager->noSync =  level==1 || pPager->tempFile;
  pPager->fullSync = level==3 && !pPager->tempFile;
  if( pPager->noSync==0 ) pPager->needSync = 0;
}

/*
** Open a temporary file.  Write the name of the file into zName
................................................................................
** (zName must be at least SQLITE_TEMPNAME_SIZE bytes long.)  Write
** the file descriptor into *fd.  Return SQLITE_OK on success or some
** other error code if we fail.
**
** The OS will automatically delete the temporary file when it is
** closed.
*/
static int sqlite3pager_opentemp(char *zFile, OsFile *fd){
  int cnt = 8;
  int rc;
  do{
    cnt--;
    sqliteOsTempFileName(zFile);
    rc = sqliteOsOpenExclusive(zFile, fd, 1);
  }while( cnt>0 && rc!=SQLITE_OK );
  return rc;
}

/*
** Create a new page cache and put a pointer to the page cache in *ppPager.
** The file to be cached need not exist.  The file is not locked until
** the first call to sqlite3pager_get() and is only held open until the
** last page is released using sqlite3pager_unref().
**
** If zFilename is NULL then a randomly-named temporary file is created
** and used as the file to be cached.  The file will be deleted
** automatically when it is closed.
*/
int sqlite3pager_open(
  Pager **ppPager,         /* Return the Pager structure here */
  const char *zFilename,   /* Name of the database file to open */
  int mxPage,              /* Max number of in-memory cache pages */
  int nExtra,              /* Extra bytes append to each in-memory page */
  int useJournal           /* TRUE to use a rollback journal on this file */
){
  Pager *pPager;
................................................................................
    return SQLITE_NOMEM;
  }
  if( zFilename && zFilename[0] ){
    zFullPathname = sqliteOsFullPathname(zFilename);
    rc = sqliteOsOpenReadWrite(zFullPathname, &fd, &readOnly);
    tempFile = 0;
  }else{
    rc = sqlite3pager_opentemp(zTemp, &fd);
    zFilename = zTemp;
    zFullPathname = sqliteOsFullPathname(zFilename);
    tempFile = 1;
  }
  if( sqlite_malloc_failed ){
    return SQLITE_NOMEM;
  }
................................................................................
}

/*
** Set the destructor for this pager.  If not NULL, the destructor is called
** when the reference count on each page reaches zero.  The destructor can
** be used to clean up information in the extra segment appended to each page.
**
** The destructor is not called as a result sqlite3pager_close().  
** Destructors are only called by sqlite3pager_unref().
*/
void sqlite3pager_set_destructor(Pager *pPager, void (*xDesc)(void*)){
  pPager->xDestructor = xDesc;
}

/*
** Return the total number of pages in the disk file associated with
** pPager.
*/
int sqlite3pager_pagecount(Pager *pPager){
  off_t n;
  assert( pPager!=0 );
  if( pPager->dbSize>=0 ){
    return pPager->dbSize;
  }
  if( sqliteOsFileSize(&pPager->fd, &n)!=SQLITE_OK ){
    pPager->errMask |= PAGER_ERR_DISK;
................................................................................
** Forward declaration
*/
static int syncJournal(Pager*);

/*
** Truncate the file to the number of pages specified.
*/
int sqlite3pager_truncate(Pager *pPager, Pgno nPage){
  int rc;
  if( pPager->dbSize<0 ){
    sqlite3pager_pagecount(pPager);
  }
  if( pPager->errMask!=0 ){
    rc = pager_errcode(pPager);
    return rc;
  }
  if( nPage>=(unsigned)pPager->dbSize ){
    return SQLITE_OK;
................................................................................
**
** If a transaction was in progress when this routine is called, that
** transaction is rolled back.  All outstanding pages are invalidated
** and their memory is freed.  Any attempt to use a page associated
** with this page cache after this function returns will likely
** result in a coredump.
*/
int sqlite3pager_close(Pager *pPager){
  PgHdr *pPg, *pNext;
  switch( pPager->state ){
    case SQLITE_WRITELOCK: {
      sqlite3pager_rollback(pPager);
      sqliteOsUnlock(&pPager->fd);
      assert( pPager->journalOpen==0 );
      break;
    }
    case SQLITE_READLOCK: {
      sqliteOsUnlock(&pPager->fd);
      break;
................................................................................
  sqliteFree(pPager);
  return SQLITE_OK;
}

/*
** Return the page number for the given page data.
*/
Pgno sqlite3pager_pagenumber(void *pData){
  PgHdr *p = DATA_TO_PGHDR(pData);
  return p->pgno;
}

/*
** Increment the reference count for a page.  If the page is
** currently on the freelist (the reference count is zero) then
................................................................................
  REFINFO(pPg);
}

/*
** Increment the reference count for a page.  The input pointer is
** a reference to the page data.
*/
int sqlite3pager_ref(void *pData){
  PgHdr *pPg = DATA_TO_PGHDR(pData);
  page_ref(pPg);
  return SQLITE_OK;
}

/*
** Sync the journal.  In other words, make sure all the pages that have
................................................................................
** read occurs and the memory image of the page is initialized to
** all zeros.  The extra data appended to a page is always initialized
** to zeros the first time a page is loaded into memory.
**
** The acquisition might fail for several reasons.  In all cases,
** an appropriate error code is returned and *ppPage is set to NULL.
**
** See also sqlite3pager_lookup().  Both this routine and _lookup() attempt
** to find a page in the in-memory cache first.  If the page is not already
** in memory, this routine goes to disk to read it in whereas _lookup()
** just returns 0.  This routine acquires a read-lock the first time it
** has to go to disk, and could also playback an old journal if necessary.
** Since _lookup() never goes to disk, it never has to deal with locks
** or journal files.
*/
int sqlite3pager_get(Pager *pPager, Pgno pgno, void **ppPage){
  PgHdr *pPg;
  int rc;

  /* Make sure we have not hit any critical errors.
  */ 
  assert( pPager!=0 );
  assert( pgno!=0 );
................................................................................
      ** on the journal file then fsync the journal file.  This is a
      ** very slow operation, so we work hard to avoid it.  But sometimes
      ** it can't be helped.
      */
      if( pPg==0 ){
        int rc = syncJournal(pPager);
        if( rc!=0 ){
          sqlite3pager_rollback(pPager);
          return SQLITE_IOERR;
        }
        pPg = pPager->pFirst;
      }
      assert( pPg->nRef==0 );

      /* Write the page to the database file if it is dirty.
      */
      if( pPg->dirty ){
        assert( pPg->needSync==0 );
        pPg->pDirty = 0;
        rc = pager_write_pagelist( pPg );
        if( rc!=SQLITE_OK ){
          sqlite3pager_rollback(pPager);
          return SQLITE_IOERR;
        }
      }
      assert( pPg->dirty==0 );

      /* If the page we are recycling is marked as alwaysRollback, then
      ** set the global alwaysRollback flag, thus disabling the
................................................................................
      pPg->needSync = 0;
    }else{
      pPg->inJournal = 0;
      pPg->needSync = 0;
    }
    if( pPager->aInCkpt && (int)pgno<=pPager->ckptSize
             && (pPager->aInCkpt[pgno/8] & (1<<(pgno&7)))!=0 ){
      page_add_to_stmt_list(pPg);
    }else{
      page_remove_from_stmt_list(pPg);
    }
    pPg->dirty = 0;
    pPg->nRef = 1;
    REFINFO(pPg);
    pPager->nRef++;
    h = pager_hash(pgno);
    pPg->pNextHash = pPager->aHash[h];
................................................................................
    if( pPg->pNextHash ){
      assert( pPg->pNextHash->pPrevHash==0 );
      pPg->pNextHash->pPrevHash = pPg;
    }
    if( pPager->nExtra>0 ){
      memset(PGHDR_TO_EXTRA(pPg), 0, pPager->nExtra);
    }
    if( pPager->dbSize<0 ) sqlite3pager_pagecount(pPager);
    if( pPager->errMask!=0 ){
      sqlite3pager_unref(PGHDR_TO_DATA(pPg));
      rc = pager_errcode(pPager);
      return rc;
    }
    if( pPager->dbSize<(int)pgno ){
      memset(PGHDR_TO_DATA(pPg), 0, SQLITE_PAGE_SIZE);
    }else{
      int rc;
................................................................................
      rc = sqliteOsRead(&pPager->fd, PGHDR_TO_DATA(pPg), SQLITE_PAGE_SIZE);
      TRACE2("FETCH %d\n", pPg->pgno);
      CODEC(pPager, PGHDR_TO_DATA(pPg), pPg->pgno, 3);
      if( rc!=SQLITE_OK ){
        off_t fileSize;
        if( sqliteOsFileSize(&pPager->fd,&fileSize)!=SQLITE_OK
               || fileSize>=pgno*SQLITE_PAGE_SIZE ){
          sqlite3pager_unref(PGHDR_TO_DATA(pPg));
          return rc;
        }else{
          memset(PGHDR_TO_DATA(pPg), 0, SQLITE_PAGE_SIZE);
        }
      }
    }
  }else{
................................................................................
}

/*
** Acquire a page if it is already in the in-memory cache.  Do
** not read the page from disk.  Return a pointer to the page,
** or 0 if the page is not in cache.
**
** See also sqlite3pager_get().  The difference between this routine
** and sqlite3pager_get() is that _get() will go to the disk and read
** in the page if the page is not already in cache.  This routine
** returns NULL if the page is not in cache or if a disk I/O error 
** has ever happened.
*/
void *sqlite3pager_lookup(Pager *pPager, Pgno pgno){
  PgHdr *pPg;

  assert( pPager!=0 );
  assert( pgno!=0 );
  if( pPager->errMask & ~(PAGER_ERR_FULL) ){
    return 0;
  }
................................................................................
** Release a page.
**
** If the number of references to the page drop to zero, then the
** page is added to the LRU list.  When all references to all pages
** are released, a rollback occurs and the lock on the database is
** removed.
*/
int sqlite3pager_unref(void *pData){
  PgHdr *pPg;

  /* Decrement the reference count for this page
  */
  pPg = DATA_TO_PGHDR(pData);
  assert( pPg->nRef>0 );
  pPg->nRef--;
................................................................................
** write lock if anything goes wrong.
*/
static int pager_open_journal(Pager *pPager){
  int rc;
  assert( pPager->state==SQLITE_WRITELOCK );
  assert( pPager->journalOpen==0 );
  assert( pPager->useJournal );
  sqlite3pager_pagecount(pPager);
  pPager->aInJournal = sqliteMalloc( pPager->dbSize/8 + 1 );
  if( pPager->aInJournal==0 ){
    sqliteOsReadLock(&pPager->fd);
    pPager->state = SQLITE_READLOCK;
    return SQLITE_NOMEM;
  }
  rc = sqliteOsOpenExclusive(pPager->zJournal, &pPager->jfd,pPager->tempFile);
................................................................................
    assert( journal_format==JOURNAL_FORMAT_1 );
    rc = sqliteOsWrite(&pPager->jfd, aJournalMagic1, sizeof(aJournalMagic1));
  }
  if( rc==SQLITE_OK ){
    rc = write32bits(&pPager->jfd, pPager->dbSize);
  }
  if( pPager->ckptAutoopen && rc==SQLITE_OK ){
    rc = sqlite3pager_stmt_begin(pPager);
  }
  if( rc!=SQLITE_OK ){
    rc = pager_unwritelock(pPager);
    if( rc==SQLITE_OK ){
      rc = SQLITE_FULL;
    }
  }
................................................................................
  return rc;  
}

/*
** Acquire a write-lock on the database.  The lock is removed when
** the any of the following happen:
**
**   *  sqlite3pager_commit() is called.
**   *  sqlite3pager_rollback() is called.
**   *  sqlite3pager_close() is called.
**   *  sqlite3pager_unref() is called to on every outstanding page.
**
** The parameter to this routine is a pointer to any open page of the
** database file.  Nothing changes about the page - it is used merely
** to acquire a pointer to the Pager structure and as proof that there
** is already a read-lock on the database.
**
** A journal file is opened if this is not a temporary file.  For
** temporary files, the opening of the journal file is deferred until
** there is an actual need to write to the journal.
**
** If the database is already write-locked, this routine is a no-op.
*/
int sqlite3pager_begin(void *pData){
  PgHdr *pPg = DATA_TO_PGHDR(pData);
  Pager *pPager = pPg->pPager;
  int rc = SQLITE_OK;
  assert( pPg->nRef>0 );
  assert( pPager->state!=SQLITE_UNLOCK );
  if( pPager->state==SQLITE_READLOCK ){
    assert( pPager->aInJournal==0 );
................................................................................
** lock could not be acquired, this routine returns SQLITE_BUSY.  The
** calling routine must check for that return value and be careful not to
** change any page data until this routine returns SQLITE_OK.
**
** If the journal file could not be written because the disk is full,
** then this routine returns SQLITE_FULL and does an immediate rollback.
** All subsequent write attempts also return SQLITE_FULL until there
** is a call to sqlite3pager_commit() or sqlite3pager_rollback() to
** reset.
*/
int sqlite3pager_write(void *pData){
  PgHdr *pPg = DATA_TO_PGHDR(pData);
  Pager *pPager = pPg->pPager;
  int rc = SQLITE_OK;

  /* Check for errors
  */
  if( pPager->errMask ){ 
................................................................................
  ** written to the transaction journal or the ckeckpoint journal
  ** or both.
  **
  ** First check to see that the transaction journal exists and
  ** create it if it does not.
  */
  assert( pPager->state!=SQLITE_UNLOCK );
  rc = sqlite3pager_begin(pData);
  if( rc!=SQLITE_OK ){
    return rc;
  }
  assert( pPager->state==SQLITE_WRITELOCK );
  if( !pPager->journalOpen && pPager->useJournal ){
    rc = pager_open_journal(pPager);
    if( rc!=SQLITE_OK ) return rc;
................................................................................
      rc = sqliteOsWrite(&pPager->jfd, &((char*)pData)[-4], szPg);
      TRACE3("JOURNAL %d %d\n", pPg->pgno, pPg->needSync);
      CODEC(pPager, pData, pPg->pgno, 0);
      if( journal_format>=JOURNAL_FORMAT_3 ){
        *(u32*)PGHDR_TO_EXTRA(pPg) = saved;
      }
      if( rc!=SQLITE_OK ){
        sqlite3pager_rollback(pPager);
        pPager->errMask |= PAGER_ERR_FULL;
        return rc;
      }
      pPager->nRec++;
      assert( pPager->aInJournal!=0 );
      pPager->aInJournal[pPg->pgno/8] |= 1<<(pPg->pgno&7);
      pPg->needSync = !pPager->noSync;
      pPg->inJournal = 1;
      if( pPager->ckptInUse ){
        pPager->aInCkpt[pPg->pgno/8] |= 1<<(pPg->pgno&7);
        page_add_to_stmt_list(pPg);
      }
    }else{
      pPg->needSync = !pPager->journalStarted && !pPager->noSync;
      TRACE3("APPEND %d %d\n", pPg->pgno, pPg->needSync);
    }
    if( pPg->needSync ){
      pPager->needSync = 1;
................................................................................
    assert( pPg->inJournal || (int)pPg->pgno>pPager->origDbSize );
    store32bits(pPg->pgno, pPg, -4);
    CODEC(pPager, pData, pPg->pgno, 7);
    rc = sqliteOsWrite(&pPager->cpfd, &((char*)pData)[-4], SQLITE_PAGE_SIZE+4);
    TRACE2("CKPT-JOURNAL %d\n", pPg->pgno);
    CODEC(pPager, pData, pPg->pgno, 0);
    if( rc!=SQLITE_OK ){
      sqlite3pager_rollback(pPager);
      pPager->errMask |= PAGER_ERR_FULL;
      return rc;
    }
    pPager->ckptNRec++;
    assert( pPager->aInCkpt!=0 );
    pPager->aInCkpt[pPg->pgno/8] |= 1<<(pPg->pgno&7);
    page_add_to_stmt_list(pPg);
  }

  /* Update the database size and return.
  */
  if( pPager->dbSize<(int)pPg->pgno ){
    pPager->dbSize = pPg->pgno;
  }
  return rc;
}

/*
** Return TRUE if the page given in the argument was previously passed
** to sqlite3pager_write().  In other words, return TRUE if it is ok
** to change the content of the page.
*/
int sqlite3pager_iswriteable(void *pData){
  PgHdr *pPg = DATA_TO_PGHDR(pData);
  return pPg->dirty;
}

/*
** Replace the content of a single page with the information in the third
** argument.
*/
int sqlite3pager_overwrite(Pager *pPager, Pgno pgno, void *pData){
  void *pPage;
  int rc;

  rc = sqlite3pager_get(pPager, pgno, &pPage);
  if( rc==SQLITE_OK ){
    rc = sqlite3pager_write(pPage);
    if( rc==SQLITE_OK ){
      memcpy(pPage, pData, SQLITE_PAGE_SIZE);
    }
    sqlite3pager_unref(pPage);
  }
  return rc;
}

/*
** A call to this routine tells the pager that it is not necessary to
** write the information on page "pgno" back to the disk, even though
................................................................................
** that page might be marked as dirty.
**
** The overlying software layer calls this routine when all of the data
** on the given page is unused.  The pager marks the page as clean so
** that it does not get written to disk.
**
** Tests show that this optimization, together with the
** sqlite3pager_dont_rollback() below, more than double the speed
** of large INSERT operations and quadruple the speed of large DELETEs.
**
** When this routine is called, set the alwaysRollback flag to true.
** Subsequent calls to sqlite3pager_dont_rollback() for the same page
** will thereafter be ignored.  This is necessary to avoid a problem
** where a page with data is added to the freelist during one part of
** a transaction then removed from the freelist during a later part
** of the same transaction and reused for some other purpose.  When it
** is first added to the freelist, this routine is called.  When reused,
** the dont_rollback() routine is called.  But because the page contains
** critical data, we still need to be sure it gets rolled back in spite
** of the dont_rollback() call.
*/
void sqlite3pager_dont_write(Pager *pPager, Pgno pgno){
  PgHdr *pPg;

  pPg = pager_lookup(pPager, pgno);
  pPg->alwaysRollback = 1;
  if( pPg && pPg->dirty ){
    if( pPager->dbSize==(int)pPg->pgno && pPager->origDbSize<pPager->dbSize ){
      /* If this pages is the last page in the file and the file has grown
................................................................................

/*
** A call to this routine tells the pager that if a rollback occurs,
** it is not necessary to restore the data on the given page.  This
** means that the pager does not have to record the given page in the
** rollback journal.
*/
void sqlite3pager_dont_rollback(void *pData){
  PgHdr *pPg = DATA_TO_PGHDR(pData);
  Pager *pPager = pPg->pPager;

  if( pPager->state!=SQLITE_WRITELOCK || pPager->journalOpen==0 ) return;
  if( pPg->alwaysRollback || pPager->alwaysRollback ) return;
  if( !pPg->inJournal && (int)pPg->pgno <= pPager->origDbSize ){
    assert( pPager->aInJournal!=0 );
    pPager->aInJournal[pPg->pgno/8] |= 1<<(pPg->pgno&7);
    pPg->inJournal = 1;
    if( pPager->ckptInUse ){
      pPager->aInCkpt[pPg->pgno/8] |= 1<<(pPg->pgno&7);
      page_add_to_stmt_list(pPg);
    }
    TRACE2("DONT_ROLLBACK %d\n", pPg->pgno);
  }
  if( pPager->ckptInUse && !pPg->inCkpt && (int)pPg->pgno<=pPager->ckptSize ){
    assert( pPg->inJournal || (int)pPg->pgno>pPager->origDbSize );
    assert( pPager->aInCkpt!=0 );
    pPager->aInCkpt[pPg->pgno/8] |= 1<<(pPg->pgno&7);
    page_add_to_stmt_list(pPg);
  }
}

/*
** Commit all changes to the database and release the write lock.
**
** If the commit fails for any reason, a rollback attempt is made
** and an error code is returned.  If the commit worked, SQLITE_OK
** is returned.
*/
int sqlite3pager_commit(Pager *pPager){
  int rc;
  PgHdr *pPg;

  if( pPager->errMask==PAGER_ERR_FULL ){
    rc = sqlite3pager_rollback(pPager);
    if( rc==SQLITE_OK ){
      rc = SQLITE_FULL;
    }
    return rc;
  }
  if( pPager->errMask!=0 ){
    rc = pager_errcode(pPager);
................................................................................
  rc = pager_unwritelock(pPager);
  pPager->dbSize = -1;
  return rc;

  /* Jump here if anything goes wrong during the commit process.
  */
commit_abort:
  rc = sqlite3pager_rollback(pPager);
  if( rc==SQLITE_OK ){
    rc = SQLITE_FULL;
  }
  return rc;
}

/*
................................................................................
** This routine cannot fail unless some other process is not following
** the correct locking protocol (SQLITE_PROTOCOL) or unless some other
** process is writing trash into the journal file (SQLITE_CORRUPT) or
** unless a prior malloc() failed (SQLITE_NOMEM).  Appropriate error
** codes are returned for all these occasions.  Otherwise,
** SQLITE_OK is returned.
*/
int sqlite3pager_rollback(Pager *pPager){
  int rc;
  TRACE1("ROLLBACK\n");
  if( !pPager->dirtyFile || !pPager->journalOpen ){
    rc = pager_unwritelock(pPager);
    pPager->dbSize = -1;
    return rc;
  }
................................................................................
  return rc;
}

/*
** Return TRUE if the database file is opened read-only.  Return FALSE
** if the database is (in theory) writable.
*/
int sqlite3pager_isreadonly(Pager *pPager){
  return pPager->readOnly;
}

/*
** This routine is used for testing and analysis only.
*/
int *sqlite3pager_stats(Pager *pPager){
  static int a[9];
  a[0] = pPager->nRef;
  a[1] = pPager->nPage;
  a[2] = pPager->mxPage;
  a[3] = pPager->dbSize;
  a[4] = pPager->state;
  a[5] = pPager->errMask;
................................................................................
/*
** Set the checkpoint.
**
** This routine should be called with the transaction journal already
** open.  A new checkpoint journal is created that can be used to rollback
** changes of a single SQL command within a larger transaction.
*/
int sqlite3pager_stmt_begin(Pager *pPager){
  int rc;
  char zTemp[SQLITE_TEMPNAME_SIZE];
  if( !pPager->journalOpen ){
    pPager->ckptAutoopen = 1;
    return SQLITE_OK;
  }
  assert( pPager->journalOpen );
................................................................................
  assert( pPager->ckptJSize == 
    pPager->nRec*JOURNAL_PG_SZ(journal_format)+JOURNAL_HDR_SZ(journal_format) );
#endif
  pPager->ckptJSize = pPager->nRec*JOURNAL_PG_SZ(journal_format)
                         + JOURNAL_HDR_SZ(journal_format);
  pPager->ckptSize = pPager->dbSize;
  if( !pPager->ckptOpen ){
    rc = sqlite3pager_opentemp(zTemp, &pPager->cpfd);
    if( rc ) goto ckpt_begin_failed;
    pPager->ckptOpen = 1;
    pPager->ckptNRec = 0;
  }
  pPager->ckptInUse = 1;
  return SQLITE_OK;
 
................................................................................
  }
  return rc;
}

/*
** Commit a checkpoint.
*/
int sqlite3pager_stmt_commit(Pager *pPager){
  if( pPager->ckptInUse ){
    PgHdr *pPg, *pNext;
    sqliteOsSeek(&pPager->cpfd, 0);
    /* sqliteOsTruncate(&pPager->cpfd, 0); */
    pPager->ckptNRec = 0;
    pPager->ckptInUse = 0;
    sqliteFree( pPager->aInCkpt );
................................................................................
  pPager->ckptAutoopen = 0;
  return SQLITE_OK;
}

/*
** Rollback a checkpoint.
*/
int sqlite3pager_stmt_rollback(Pager *pPager){
  int rc;
  if( pPager->ckptInUse ){
    rc = pager_stmt_playback(pPager);
    sqlite3pager_stmt_commit(pPager);
  }else{
    rc = SQLITE_OK;
  }
  pPager->ckptAutoopen = 0;
  return rc;
}

/*
** Return the full pathname of the database file.
*/
const char *sqlite3pager_filename(Pager *pPager){
  return pPager->zFilename;
}

/*
** Set the codec for this pager
*/
void sqlite3pager_set_codec(
  Pager *pPager,
  void (*xCodec)(void*,void*,Pgno,int),
  void *pCodecArg
){
  pPager->xCodec = xCodec;
  pPager->pCodecArg = pCodecArg;
}

#ifdef SQLITE_TEST
/*
** Print a listing of all referenced pages and their ref count.
*/
void sqlite3pager_refdump(Pager *pPager){
  PgHdr *pPg;
  for(pPg=pPager->pAll; pPg; pPg=pPg->pNextAll){
    if( pPg->nRef<=0 ) continue;
    printf("PAGE %3d addr=0x%08x nRef=%d\n", 
       pPg->pgno, (int)PGHDR_TO_DATA(pPg), pPg->nRef);
  }
}
#endif

**    May you share freely, never taking more than you give.
**
*************************************************************************
** This header file defines the interface that the sqlite page cache
** subsystem.  The page cache subsystem reads and writes a file a page
** at a time and provides a journal for rollback.
**
** @(#) $Id: pager.h,v 1.26 2004/02/11 02:18:07 drh Exp $
*/

/*
** The size of one page
**
** You can change this value to another (reasonable) value you want.
** It need not be a power of two, though the interface to the disk
................................................................................
** The total number of usable bytes stored on disk for each page.
** The usable bytes come at the beginning of the page and the reserve
** bytes come at the end.
*/
#define SQLITE_USABLE_SIZE (SQLITE_PAGE_SIZE-SQLITE_PAGE_RESERVE)

/*
** Maximum number of pages in one database.  (This is a limitation of
** imposed by 4GB files size limits.)
*/
#define SQLITE_MAX_PAGE 1073741823

/*
** The type used to represent a page number.  The first page in a file
** is called page 1.  0 is used to represent "not a page".
*/
................................................................................
*/
typedef struct Pager Pager;

/*
** See source code comments for a detailed description of the following
** routines:
*/
int sqlitepager_open(Pager **ppPager, const char *zFilename,
                     int nPage, int nExtra, int useJournal);
void sqlitepager_set_destructor(Pager*, void(*)(void*));
void sqlitepager_set_cachesize(Pager*, int);
int sqlitepager_close(Pager *pPager);
int sqlitepager_get(Pager *pPager, Pgno pgno, void **ppPage);
void *sqlitepager_lookup(Pager *pPager, Pgno pgno);
int sqlitepager_ref(void*);
int sqlitepager_unref(void*);
Pgno sqlitepager_pagenumber(void*);
int sqlitepager_write(void*);
int sqlitepager_iswriteable(void*);
int sqlitepager_overwrite(Pager *pPager, Pgno pgno, void*);
int sqlitepager_pagecount(Pager*);
int sqlitepager_truncate(Pager*,Pgno);
int sqlitepager_begin(void*);
int sqlitepager_commit(Pager*);
int sqlitepager_rollback(Pager*);
int sqlitepager_isreadonly(Pager*);
int sqlitepager_ckpt_begin(Pager*);
int sqlitepager_ckpt_commit(Pager*);
int sqlitepager_ckpt_rollback(Pager*);
void sqlitepager_dont_rollback(void*);
void sqlitepager_dont_write(Pager*, Pgno);
int *sqlitepager_stats(Pager*);
void sqlitepager_set_safety_level(Pager*,int);
const char *sqlitepager_filename(Pager*);
int sqlitepager_rename(Pager*, const char *zNewName);
void sqlitepager_set_codec(Pager*,void(*)(void*,void*,Pgno,int),void*);

#ifdef SQLITE_TEST
void sqlitepager_refdump(Pager*);
int pager_refinfo_enable;
int journal_format;
#endif

**    May you share freely, never taking more than you give.
**
*************************************************************************
** This header file defines the interface that the sqlite page cache
** subsystem.  The page cache subsystem reads and writes a file a page
** at a time and provides a journal for rollback.
**
** @(#) $Id: pager.h,v 1.27 2004/04/26 14:10:22 drh Exp $
*/

/*
** The size of one page
**
** You can change this value to another (reasonable) value you want.
** It need not be a power of two, though the interface to the disk
................................................................................
** The total number of usable bytes stored on disk for each page.
** The usable bytes come at the beginning of the page and the reserve
** bytes come at the end.
*/
#define SQLITE_USABLE_SIZE (SQLITE_PAGE_SIZE-SQLITE_PAGE_RESERVE)

/*
** Maximum number of pages in one database.

*/
#define SQLITE_MAX_PAGE 1073741823

/*
** The type used to represent a page number.  The first page in a file
** is called page 1.  0 is used to represent "not a page".
*/
................................................................................
*/
typedef struct Pager Pager;

/*
** See source code comments for a detailed description of the following
** routines:
*/
int sqlite3pager_open(Pager **ppPager, const char *zFilename,
                     int nPage, int nExtra, int useJournal);
void sqlite3pager_set_destructor(Pager*, void(*)(void*));
void sqlite3pager_set_cachesize(Pager*, int);
int sqlite3pager_close(Pager *pPager);
int sqlite3pager_get(Pager *pPager, Pgno pgno, void **ppPage);
void *sqlite3pager_lookup(Pager *pPager, Pgno pgno);
int sqlite3pager_ref(void*);
int sqlite3pager_unref(void*);
Pgno sqlite3pager_pagenumber(void*);
int sqlite3pager_write(void*);
int sqlite3pager_iswriteable(void*);
int sqlite3pager_overwrite(Pager *pPager, Pgno pgno, void*);
int sqlite3pager_pagecount(Pager*);
int sqlite3pager_truncate(Pager*,Pgno);
int sqlite3pager_begin(void*);
int sqlite3pager_commit(Pager*);
int sqlite3pager_rollback(Pager*);
int sqlite3pager_isreadonly(Pager*);
int sqlite3pager_stmt_begin(Pager*);
int sqlite3pager_stmt_commit(Pager*);
int sqlite3pager_stmt_rollback(Pager*);
void sqlite3pager_dont_rollback(void*);
void sqlite3pager_dont_write(Pager*, Pgno);
int *sqlite3pager_stats(Pager*);
void sqlite3pager_set_safety_level(Pager*,int);
const char *sqlite3pager_filename(Pager*);
int sqlite3pager_rename(Pager*, const char *zNewName);
void sqlite3pager_set_codec(Pager*,void(*)(void*,void*,Pgno,int),void*);

#ifdef SQLITE_TEST
void sqlite3pager_refdump(Pager*);
int pager3_refinfo_enable;

#endif

**    May you do good and not evil.
**    May you find forgiveness for yourself and forgive others.
**    May you share freely, never taking more than you give.
**
*************************************************************************
** Internal interface definitions for SQLite.
**
** @(#) $Id: sqliteInt.h,v 1.220 2004/02/25 13:47:33 drh Exp $
*/
#include "config.h"
#include "sqlite.h"
#include "hash.h"
#include "parse.h"
#include "btree.h"
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <assert.h>

/*
** The maximum number of in-memory pages to use for the main database
................................................................................
/*
** Integers of known sizes.  These typedefs might change for architectures
** where the sizes very.  Preprocessor macros are available so that the
** types can be conveniently redefined at compile-type.  Like this:
**
**         cc '-DUINTPTR_TYPE=long long int' ...
*/



#ifndef UINT32_TYPE
# define UINT32_TYPE unsigned int
#endif
#ifndef UINT16_TYPE
# define UINT16_TYPE unsigned short int
#endif
#ifndef UINT8_TYPE
................................................................................
#ifndef INTPTR_TYPE
# if SQLITE_PTR_SZ==4
#   define INTPTR_TYPE int
# else
#   define INTPTR_TYPE long long
# endif
#endif

typedef UINT32_TYPE u32;           /* 4-byte unsigned integer */
typedef UINT16_TYPE u16;           /* 2-byte unsigned integer */
typedef UINT8_TYPE u8;             /* 1-byte unsigned integer */
typedef UINT8_TYPE i8;             /* 1-byte signed integer */
typedef INTPTR_TYPE ptr;           /* Big enough to hold a pointer */
typedef unsigned INTPTR_TYPE uptr; /* Big enough to hold a pointer */

/*
** Defer sourcing vdbe.h until after the "u8" typedef is defined.
*/
#include "vdbe.h"


/*
** Most C compilers these days recognize "long double", don't they?
** Just in case we encounter one that does not, we will create a macro
** for long double so that it can be easily changed to just "double".
*/
#ifndef LONGDOUBLE_TYPE

**    May you do good and not evil.
**    May you find forgiveness for yourself and forgive others.
**    May you share freely, never taking more than you give.
**
*************************************************************************
** Internal interface definitions for SQLite.
**
** @(#) $Id: sqliteInt.h,v 1.221 2004/04/26 14:10:22 drh Exp $
*/
#include "config.h"
#include "sqlite.h"
#include "hash.h"
#include "parse.h"

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <assert.h>

/*
** The maximum number of in-memory pages to use for the main database
................................................................................
/*
** Integers of known sizes.  These typedefs might change for architectures
** where the sizes very.  Preprocessor macros are available so that the
** types can be conveniently redefined at compile-type.  Like this:
**
**         cc '-DUINTPTR_TYPE=long long int' ...
*/
#ifndef UINT64_TYPE
# define UINT64_TYPE unsigned long long int
#endif
#ifndef UINT32_TYPE
# define UINT32_TYPE unsigned int
#endif
#ifndef UINT16_TYPE
# define UINT16_TYPE unsigned short int
#endif
#ifndef UINT8_TYPE
................................................................................
#ifndef INTPTR_TYPE
# if SQLITE_PTR_SZ==4
#   define INTPTR_TYPE int
# else
#   define INTPTR_TYPE long long
# endif
#endif
typedef UINT64_TYPE u64;           /* 8-byte unsigned integer */
typedef UINT32_TYPE u32;           /* 4-byte unsigned integer */
typedef UINT16_TYPE u16;           /* 2-byte unsigned integer */
typedef UINT8_TYPE u8;             /* 1-byte unsigned integer */
typedef UINT8_TYPE i8;             /* 1-byte signed integer */
typedef INTPTR_TYPE ptr;           /* Big enough to hold a pointer */
typedef unsigned INTPTR_TYPE uptr; /* Big enough to hold a pointer */

/*
** Defer sourcing vdbe.h until after the "u8" typedef is defined.
*/
#include "vdbe.h"
#include "btree.h"

/*
** Most C compilers these days recognize "long double", don't they?
** Just in case we encounter one that does not, we will create a macro
** for long double so that it can be easily changed to just "double".
*/
#ifndef LONGDOUBLE_TYPE

**    May you do good and not evil.
**    May you find forgiveness for yourself and forgive others.
**    May you share freely, never taking more than you give.
**
*************************************************************************
** A TCL Interface to SQLite
**
** $Id: tclsqlite.c,v 1.59 2004/02/25 22:51:06 rdc Exp $
*/
#ifndef NO_TCL     /* Omit this whole file if TCL is unavailable */

#include "sqliteInt.h"
#include "tcl.h"
#include <stdlib.h>
#include <string.h>
#include <assert.h>


/*
** If TCL uses UTF-8 and SQLite is configured to use iso8859, then we
** have to do a translation when going between the two.  Set the 
** UTF_TRANSLATION_NEEDED macro to indicate that we need to do
** this translation.  
*/
#if defined(TCL_UTF_MAX) && !defined(SQLITE_UTF8)
................................................................................
}
int Sqlite_SafeInit(Tcl_Interp *interp){
  return TCL_OK;
}
int Tclsqlite_SafeInit(Tcl_Interp *interp){
  return TCL_OK;
}


#if 0
/*
** If compiled using mktclapp, this routine runs to initialize
** everything.
*/
int Et_AppInit(Tcl_Interp *interp){
................................................................................
;

#define TCLSH_MAIN main   /* Needed to fake out mktclapp */
int TCLSH_MAIN(int argc, char **argv){
  Tcl_Interp *interp;
  Tcl_FindExecutable(argv[0]);
  interp = Tcl_CreateInterp();
  Sqlite_Init(interp);
#ifdef SQLITE_TEST
  {
    extern int Sqlitetest1_Init(Tcl_Interp*);
    extern int Sqlitetest2_Init(Tcl_Interp*);
    extern int Sqlitetest3_Init(Tcl_Interp*);
    extern int Sqlitetest4_Init(Tcl_Interp*);
    extern int Md5_Init(Tcl_Interp*);
    Sqlitetest1_Init(interp);
    Sqlitetest2_Init(interp);
    Sqlitetest3_Init(interp);
    Sqlitetest4_Init(interp);
    Md5_Init(interp);
  }
#endif
  if( argc>=2 ){
    int i;
    Tcl_SetVar(interp,"argv0",argv[1],TCL_GLOBAL_ONLY);
    Tcl_SetVar(interp,"argv", "", TCL_GLOBAL_ONLY);

**    May you do good and not evil.
**    May you find forgiveness for yourself and forgive others.
**    May you share freely, never taking more than you give.
**
*************************************************************************
** A TCL Interface to SQLite
**
** $Id: tclsqlite.c,v 1.60 2004/04/26 14:10:22 drh Exp $
*/
#ifndef NO_TCL     /* Omit this whole file if TCL is unavailable */

#include "sqliteInt.h"
#include "tcl.h"
#include <stdlib.h>
#include <string.h>
#include <assert.h>

#if 0
/*
** If TCL uses UTF-8 and SQLite is configured to use iso8859, then we
** have to do a translation when going between the two.  Set the 
** UTF_TRANSLATION_NEEDED macro to indicate that we need to do
** this translation.  
*/
#if defined(TCL_UTF_MAX) && !defined(SQLITE_UTF8)
................................................................................
}
int Sqlite_SafeInit(Tcl_Interp *interp){
  return TCL_OK;
}
int Tclsqlite_SafeInit(Tcl_Interp *interp){
  return TCL_OK;
}
#endif

#if 0
/*
** If compiled using mktclapp, this routine runs to initialize
** everything.
*/
int Et_AppInit(Tcl_Interp *interp){
................................................................................
;

#define TCLSH_MAIN main   /* Needed to fake out mktclapp */
int TCLSH_MAIN(int argc, char **argv){
  Tcl_Interp *interp;
  Tcl_FindExecutable(argv[0]);
  interp = Tcl_CreateInterp();
  /* Sqlite_Init(interp); */
#ifdef SQLITE_TEST
  {
    extern int Sqlitetest1_Init(Tcl_Interp*);
    extern int Sqlitetest2_Init(Tcl_Interp*);
    extern int Sqlitetest3_Init(Tcl_Interp*);
    extern int Sqlitetest4_Init(Tcl_Interp*);
    extern int Md5_Init(Tcl_Interp*);
    /* Sqlitetest1_Init(interp); */
    Sqlitetest2_Init(interp);
    /* Sqlitetest3_Init(interp); */
    /* Sqlitetest4_Init(interp); */
    Md5_Init(interp);
  }
#endif
  if( argc>=2 ){
    int i;
    Tcl_SetVar(interp,"argv0",argv[1],TCL_GLOBAL_ONLY);
    Tcl_SetVar(interp,"argv", "", TCL_GLOBAL_ONLY);

**    May you share freely, never taking more than you give.
**
*************************************************************************
** Code for testing the pager.c module in SQLite.  This code
** is not included in the SQLite library.  It is used for automated
** testing of the SQLite library.
**
** $Id: test2.c,v 1.16 2004/02/10 01:54:28 drh Exp $
*/
#include "os.h"
#include "sqliteInt.h"
#include "pager.h"
#include "tcl.h"
#include <stdlib.h>
#include <string.h>
................................................................................
  char zBuf[100];
  if( argc!=3 ){
    Tcl_AppendResult(interp, "wrong # args: should be \"", argv[0],
       " FILENAME N-PAGE\"", 0);
    return TCL_ERROR;
  }
  if( Tcl_GetInt(interp, argv[2], &nPage) ) return TCL_ERROR;
  rc = sqlitepager_open(&pPager, argv[1], nPage, 0, 1);
  if( rc!=SQLITE_OK ){
    Tcl_AppendResult(interp, errorName(rc), 0);
    return TCL_ERROR;
  }
  sprintf(zBuf,"0x%x",(int)pPager);
  Tcl_AppendResult(interp, zBuf, 0);
  return TCL_OK;
................................................................................
  int rc;
  if( argc!=2 ){
    Tcl_AppendResult(interp, "wrong # args: should be \"", argv[0],
       " ID\"", 0);
    return TCL_ERROR;
  }
  if( Tcl_GetInt(interp, argv[1], (int*)&pPager) ) return TCL_ERROR;
  rc = sqlitepager_close(pPager);
  if( rc!=SQLITE_OK ){
    Tcl_AppendResult(interp, errorName(rc), 0);
    return TCL_ERROR;
  }
  return TCL_OK;
}

................................................................................
  int rc;
  if( argc!=2 ){
    Tcl_AppendResult(interp, "wrong # args: should be \"", argv[0],
       " ID\"", 0);
    return TCL_ERROR;
  }
  if( Tcl_GetInt(interp, argv[1], (int*)&pPager) ) return TCL_ERROR;
  rc = sqlitepager_rollback(pPager);
  if( rc!=SQLITE_OK ){
    Tcl_AppendResult(interp, errorName(rc), 0);
    return TCL_ERROR;
  }
  return TCL_OK;
}

................................................................................
  int rc;
  if( argc!=2 ){
    Tcl_AppendResult(interp, "wrong # args: should be \"", argv[0],
       " ID\"", 0);
    return TCL_ERROR;
  }
  if( Tcl_GetInt(interp, argv[1], (int*)&pPager) ) return TCL_ERROR;
  rc = sqlitepager_commit(pPager);



























  if( rc!=SQLITE_OK ){
    Tcl_AppendResult(interp, errorName(rc), 0);
    return TCL_ERROR;
  }
  return TCL_OK;
}

/*
** Usage:   pager_ckpt_begin ID
**
** Start a new checkpoint.
*/
static int pager_ckpt_begin(
  void *NotUsed,
  Tcl_Interp *interp,    /* The TCL interpreter that invoked this command */
  int argc,              /* Number of arguments */
  const char **argv      /* Text of each argument */
){
  Pager *pPager;
  int rc;
  if( argc!=2 ){
    Tcl_AppendResult(interp, "wrong # args: should be \"", argv[0],
       " ID\"", 0);
    return TCL_ERROR;
  }
  if( Tcl_GetInt(interp, argv[1], (int*)&pPager) ) return TCL_ERROR;
  rc = sqlitepager_ckpt_begin(pPager);
  if( rc!=SQLITE_OK ){
    Tcl_AppendResult(interp, errorName(rc), 0);
    return TCL_ERROR;
  }
  return TCL_OK;
}

/*
** Usage:   pager_ckpt_rollback ID
**
** Rollback changes to a checkpoint
*/
static int pager_ckpt_rollback(
  void *NotUsed,
  Tcl_Interp *interp,    /* The TCL interpreter that invoked this command */
  int argc,              /* Number of arguments */
  const char **argv      /* Text of each argument */
){
  Pager *pPager;
  int rc;
  if( argc!=2 ){
    Tcl_AppendResult(interp, "wrong # args: should be \"", argv[0],
       " ID\"", 0);
    return TCL_ERROR;
  }
  if( Tcl_GetInt(interp, argv[1], (int*)&pPager) ) return TCL_ERROR;
  rc = sqlitepager_ckpt_rollback(pPager);
  if( rc!=SQLITE_OK ){
    Tcl_AppendResult(interp, errorName(rc), 0);
    return TCL_ERROR;
  }
  return TCL_OK;
}

/*
** Usage:   pager_ckpt_commit ID
**
** Commit changes to a checkpoint
*/
static int pager_ckpt_commit(
  void *NotUsed,
  Tcl_Interp *interp,    /* The TCL interpreter that invoked this command */
  int argc,              /* Number of arguments */
  const char **argv      /* Text of each argument */
){
  Pager *pPager;
  int rc;
  if( argc!=2 ){
    Tcl_AppendResult(interp, "wrong # args: should be \"", argv[0],
       " ID\"", 0);
    return TCL_ERROR;
  }
  if( Tcl_GetInt(interp, argv[1], (int*)&pPager) ) return TCL_ERROR;
  rc = sqlitepager_ckpt_commit(pPager);
  if( rc!=SQLITE_OK ){
    Tcl_AppendResult(interp, errorName(rc), 0);
    return TCL_ERROR;
  }
  return TCL_OK;
}

................................................................................
  int i, *a;
  if( argc!=2 ){
    Tcl_AppendResult(interp, "wrong # args: should be \"", argv[0],
       " ID\"", 0);
    return TCL_ERROR;
  }
  if( Tcl_GetInt(interp, argv[1], (int*)&pPager) ) return TCL_ERROR;
  a = sqlitepager_stats(pPager);
  for(i=0; i<9; i++){
    static char *zName[] = {
      "ref", "page", "max", "size", "state", "err",
      "hit", "miss", "ovfl",
    };
    char zBuf[100];
    Tcl_AppendElement(interp, zName[i]);
................................................................................
  char zBuf[100];
  if( argc!=2 ){
    Tcl_AppendResult(interp, "wrong # args: should be \"", argv[0],
       " ID\"", 0);
    return TCL_ERROR;
  }
  if( Tcl_GetInt(interp, argv[1], (int*)&pPager) ) return TCL_ERROR;
  sprintf(zBuf,"%d",sqlitepager_pagecount(pPager));
  Tcl_AppendResult(interp, zBuf, 0);
  return TCL_OK;
}

/*
** Usage:   page_get ID PGNO
**
................................................................................
  if( argc!=3 ){
    Tcl_AppendResult(interp, "wrong # args: should be \"", argv[0],
       " ID PGNO\"", 0);
    return TCL_ERROR;
  }
  if( Tcl_GetInt(interp, argv[1], (int*)&pPager) ) return TCL_ERROR;
  if( Tcl_GetInt(interp, argv[2], &pgno) ) return TCL_ERROR;
  rc = sqlitepager_get(pPager, pgno, &pPage);
  if( rc!=SQLITE_OK ){
    Tcl_AppendResult(interp, errorName(rc), 0);
    return TCL_ERROR;
  }
  sprintf(zBuf,"0x%x",(int)pPage);
  Tcl_AppendResult(interp, zBuf, 0);
  return TCL_OK;
................................................................................
  if( argc!=3 ){
    Tcl_AppendResult(interp, "wrong # args: should be \"", argv[0],
       " ID PGNO\"", 0);
    return TCL_ERROR;
  }
  if( Tcl_GetInt(interp, argv[1], (int*)&pPager) ) return TCL_ERROR;
  if( Tcl_GetInt(interp, argv[2], &pgno) ) return TCL_ERROR;
  pPage = sqlitepager_lookup(pPager, pgno);
  if( pPage ){
    sprintf(zBuf,"0x%x",(int)pPage);
    Tcl_AppendResult(interp, zBuf, 0);
  }
  return TCL_OK;
}

................................................................................
  int rc;
  if( argc!=2 ){
    Tcl_AppendResult(interp, "wrong # args: should be \"", argv[0],
       " PAGE\"", 0);
    return TCL_ERROR;
  }
  if( Tcl_GetInt(interp, argv[1], (int*)&pPage) ) return TCL_ERROR;
  rc = sqlitepager_unref(pPage);
  if( rc!=SQLITE_OK ){
    Tcl_AppendResult(interp, errorName(rc), 0);
    return TCL_ERROR;
  }
  return TCL_OK;
}

................................................................................
  void *pPage;
  if( argc!=2 ){
    Tcl_AppendResult(interp, "wrong # args: should be \"", argv[0],
       " PAGE\"", 0);
    return TCL_ERROR;
  }
  if( Tcl_GetInt(interp, argv[1], (int*)&pPage) ) return TCL_ERROR;
  sprintf(zBuf, "%d", sqlitepager_pagenumber(pPage));
  Tcl_AppendResult(interp, zBuf, 0);
  return TCL_OK;
}

/*
** Usage:   page_write PAGE DATA
**
................................................................................
  int rc;
  if( argc!=3 ){
    Tcl_AppendResult(interp, "wrong # args: should be \"", argv[0],
       " PAGE DATA\"", 0);
    return TCL_ERROR;
  }
  if( Tcl_GetInt(interp, argv[1], (int*)&pPage) ) return TCL_ERROR;
  rc = sqlitepager_write(pPage);
  if( rc!=SQLITE_OK ){
    Tcl_AppendResult(interp, errorName(rc), 0);
    return TCL_ERROR;
  }
  strncpy((char*)pPage, argv[2], SQLITE_USABLE_SIZE-1);
  ((char*)pPage)[SQLITE_USABLE_SIZE-1] = 0;
  return TCL_OK;
................................................................................
    char *zName;
    Tcl_CmdProc *xProc;
  } aCmd[] = {
    { "pager_open",              (Tcl_CmdProc*)pager_open          },
    { "pager_close",             (Tcl_CmdProc*)pager_close         },
    { "pager_commit",            (Tcl_CmdProc*)pager_commit        },
    { "pager_rollback",          (Tcl_CmdProc*)pager_rollback      },
    { "pager_ckpt_begin",        (Tcl_CmdProc*)pager_ckpt_begin    },
    { "pager_ckpt_commit",       (Tcl_CmdProc*)pager_ckpt_commit   },
    { "pager_ckpt_rollback",     (Tcl_CmdProc*)pager_ckpt_rollback },
    { "pager_stats",             (Tcl_CmdProc*)pager_stats         },
    { "pager_pagecount",         (Tcl_CmdProc*)pager_pagecount     },
    { "page_get",                (Tcl_CmdProc*)page_get            },
    { "page_lookup",             (Tcl_CmdProc*)page_lookup         },
    { "page_unref",              (Tcl_CmdProc*)page_unref          },
    { "page_read",               (Tcl_CmdProc*)page_read           },
    { "page_write",              (Tcl_CmdProc*)page_write          },
................................................................................
  int i;
  for(i=0; i<sizeof(aCmd)/sizeof(aCmd[0]); i++){
    Tcl_CreateCommand(interp, aCmd[i].zName, aCmd[i].xProc, 0, 0);
  }
  Tcl_LinkVar(interp, "sqlite_io_error_pending",
     (char*)&sqlite_io_error_pending, TCL_LINK_INT);
#ifdef SQLITE_TEST


  Tcl_LinkVar(interp, "journal_format",
     (char*)&journal_format, TCL_LINK_INT);

#endif
  sprintf(zBuf, "%d", SQLITE_PAGE_SIZE);
  Tcl_SetVar(interp, "SQLITE_PAGE_SIZE", zBuf, TCL_GLOBAL_ONLY); 
  sprintf(zBuf, "%d", SQLITE_PAGE_RESERVE);
  Tcl_SetVar(interp, "SQLITE_PAGE_RESERVE", zBuf, TCL_GLOBAL_ONLY); 
  sprintf(zBuf, "%d", SQLITE_USABLE_SIZE);
  Tcl_SetVar(interp, "SQLITE_USABLE_SIZE", zBuf, TCL_GLOBAL_ONLY); 
  return TCL_OK;
}

**    May you share freely, never taking more than you give.
**
*************************************************************************
** Code for testing the pager.c module in SQLite.  This code
** is not included in the SQLite library.  It is used for automated
** testing of the SQLite library.
**
** $Id: test2.c,v 1.17 2004/04/26 14:10:22 drh Exp $
*/
#include "os.h"
#include "sqliteInt.h"
#include "pager.h"
#include "tcl.h"
#include <stdlib.h>
#include <string.h>
................................................................................
  char zBuf[100];
  if( argc!=3 ){
    Tcl_AppendResult(interp, "wrong # args: should be \"", argv[0],
       " FILENAME N-PAGE\"", 0);
    return TCL_ERROR;
  }
  if( Tcl_GetInt(interp, argv[2], &nPage) ) return TCL_ERROR;
  rc = sqlite3pager_open(&pPager, argv[1], nPage, 0, 1);
  if( rc!=SQLITE_OK ){
    Tcl_AppendResult(interp, errorName(rc), 0);
    return TCL_ERROR;
  }
  sprintf(zBuf,"0x%x",(int)pPager);
  Tcl_AppendResult(interp, zBuf, 0);
  return TCL_OK;
................................................................................
  int rc;
  if( argc!=2 ){
    Tcl_AppendResult(interp, "wrong # args: should be \"", argv[0],
       " ID\"", 0);
    return TCL_ERROR;
  }
  if( Tcl_GetInt(interp, argv[1], (int*)&pPager) ) return TCL_ERROR;
  rc = sqlite3pager_close(pPager);
  if( rc!=SQLITE_OK ){
    Tcl_AppendResult(interp, errorName(rc), 0);
    return TCL_ERROR;
  }
  return TCL_OK;
}

................................................................................
  int rc;
  if( argc!=2 ){
    Tcl_AppendResult(interp, "wrong # args: should be \"", argv[0],
       " ID\"", 0);
    return TCL_ERROR;
  }
  if( Tcl_GetInt(interp, argv[1], (int*)&pPager) ) return TCL_ERROR;
  rc = sqlite3pager_rollback(pPager);
  if( rc!=SQLITE_OK ){
    Tcl_AppendResult(interp, errorName(rc), 0);
    return TCL_ERROR;
  }
  return TCL_OK;
}

................................................................................
  int rc;
  if( argc!=2 ){
    Tcl_AppendResult(interp, "wrong # args: should be \"", argv[0],
       " ID\"", 0);
    return TCL_ERROR;
  }
  if( Tcl_GetInt(interp, argv[1], (int*)&pPager) ) return TCL_ERROR;
  rc = sqlite3pager_commit(pPager);
  if( rc!=SQLITE_OK ){
    Tcl_AppendResult(interp, errorName(rc), 0);
    return TCL_ERROR;
  }
  return TCL_OK;
}

/*
** Usage:   pager_stmt_begin ID
**
** Start a new checkpoint.
*/
static int pager_stmt_begin(
  void *NotUsed,
  Tcl_Interp *interp,    /* The TCL interpreter that invoked this command */
  int argc,              /* Number of arguments */
  const char **argv      /* Text of each argument */
){
  Pager *pPager;
  int rc;
  if( argc!=2 ){
    Tcl_AppendResult(interp, "wrong # args: should be \"", argv[0],
       " ID\"", 0);
    return TCL_ERROR;
  }
  if( Tcl_GetInt(interp, argv[1], (int*)&pPager) ) return TCL_ERROR;
  rc = sqlite3pager_stmt_begin(pPager);
  if( rc!=SQLITE_OK ){
    Tcl_AppendResult(interp, errorName(rc), 0);
    return TCL_ERROR;
  }
  return TCL_OK;
}

/*
** Usage:   pager_stmt_rollback ID
**
** Rollback changes to a checkpoint
*/
static int pager_stmt_rollback(
  void *NotUsed,
  Tcl_Interp *interp,    /* The TCL interpreter that invoked this command */
  int argc,              /* Number of arguments */
  const char **argv      /* Text of each argument */
){
  Pager *pPager;
  int rc;
  if( argc!=2 ){
    Tcl_AppendResult(interp, "wrong # args: should be \"", argv[0],
       " ID\"", 0);
    return TCL_ERROR;
  }
  if( Tcl_GetInt(interp, argv[1], (int*)&pPager) ) return TCL_ERROR;
  rc = sqlite3pager_stmt_rollback(pPager);
  if( rc!=SQLITE_OK ){
    Tcl_AppendResult(interp, errorName(rc), 0);
    return TCL_ERROR;
  }
  return TCL_OK;
}

/*
** Usage:   pager_stmt_commit ID
**
** Commit changes to a checkpoint
*/
static int pager_stmt_commit(
  void *NotUsed,
  Tcl_Interp *interp,    /* The TCL interpreter that invoked this command */
  int argc,              /* Number of arguments */
  const char **argv      /* Text of each argument */
){
  Pager *pPager;
  int rc;
  if( argc!=2 ){
    Tcl_AppendResult(interp, "wrong # args: should be \"", argv[0],
       " ID\"", 0);
    return TCL_ERROR;
  }
  if( Tcl_GetInt(interp, argv[1], (int*)&pPager) ) return TCL_ERROR;



























  rc = sqlite3pager_stmt_commit(pPager);
  if( rc!=SQLITE_OK ){
    Tcl_AppendResult(interp, errorName(rc), 0);
    return TCL_ERROR;
  }
  return TCL_OK;
}

................................................................................
  int i, *a;
  if( argc!=2 ){
    Tcl_AppendResult(interp, "wrong # args: should be \"", argv[0],
       " ID\"", 0);
    return TCL_ERROR;
  }
  if( Tcl_GetInt(interp, argv[1], (int*)&pPager) ) return TCL_ERROR;
  a = sqlite3pager_stats(pPager);
  for(i=0; i<9; i++){
    static char *zName[] = {
      "ref", "page", "max", "size", "state", "err",
      "hit", "miss", "ovfl",
    };
    char zBuf[100];
    Tcl_AppendElement(interp, zName[i]);
................................................................................
  char zBuf[100];
  if( argc!=2 ){
    Tcl_AppendResult(interp, "wrong # args: should be \"", argv[0],
       " ID\"", 0);
    return TCL_ERROR;
  }
  if( Tcl_GetInt(interp, argv[1], (int*)&pPager) ) return TCL_ERROR;
  sprintf(zBuf,"%d",sqlite3pager_pagecount(pPager));
  Tcl_AppendResult(interp, zBuf, 0);
  return TCL_OK;
}

/*
** Usage:   page_get ID PGNO
**
................................................................................
  if( argc!=3 ){
    Tcl_AppendResult(interp, "wrong # args: should be \"", argv[0],
       " ID PGNO\"", 0);
    return TCL_ERROR;
  }
  if( Tcl_GetInt(interp, argv[1], (int*)&pPager) ) return TCL_ERROR;
  if( Tcl_GetInt(interp, argv[2], &pgno) ) return TCL_ERROR;
  rc = sqlite3pager_get(pPager, pgno, &pPage);
  if( rc!=SQLITE_OK ){
    Tcl_AppendResult(interp, errorName(rc), 0);
    return TCL_ERROR;
  }
  sprintf(zBuf,"0x%x",(int)pPage);
  Tcl_AppendResult(interp, zBuf, 0);
  return TCL_OK;
................................................................................
  if( argc!=3 ){
    Tcl_AppendResult(interp, "wrong # args: should be \"", argv[0],
       " ID PGNO\"", 0);
    return TCL_ERROR;
  }
  if( Tcl_GetInt(interp, argv[1], (int*)&pPager) ) return TCL_ERROR;
  if( Tcl_GetInt(interp, argv[2], &pgno) ) return TCL_ERROR;
  pPage = sqlite3pager_lookup(pPager, pgno);
  if( pPage ){
    sprintf(zBuf,"0x%x",(int)pPage);
    Tcl_AppendResult(interp, zBuf, 0);
  }
  return TCL_OK;
}

................................................................................
  int rc;
  if( argc!=2 ){
    Tcl_AppendResult(interp, "wrong # args: should be \"", argv[0],
       " PAGE\"", 0);
    return TCL_ERROR;
  }
  if( Tcl_GetInt(interp, argv[1], (int*)&pPage) ) return TCL_ERROR;
  rc = sqlite3pager_unref(pPage);
  if( rc!=SQLITE_OK ){
    Tcl_AppendResult(interp, errorName(rc), 0);
    return TCL_ERROR;
  }
  return TCL_OK;
}

................................................................................
  void *pPage;
  if( argc!=2 ){
    Tcl_AppendResult(interp, "wrong # args: should be \"", argv[0],
       " PAGE\"", 0);
    return TCL_ERROR;
  }
  if( Tcl_GetInt(interp, argv[1], (int*)&pPage) ) return TCL_ERROR;
  sprintf(zBuf, "%d", sqlite3pager_pagenumber(pPage));
  Tcl_AppendResult(interp, zBuf, 0);
  return TCL_OK;
}

/*
** Usage:   page_write PAGE DATA
**
................................................................................
  int rc;
  if( argc!=3 ){
    Tcl_AppendResult(interp, "wrong # args: should be \"", argv[0],
       " PAGE DATA\"", 0);
    return TCL_ERROR;
  }
  if( Tcl_GetInt(interp, argv[1], (int*)&pPage) ) return TCL_ERROR;
  rc = sqlite3pager_write(pPage);
  if( rc!=SQLITE_OK ){
    Tcl_AppendResult(interp, errorName(rc), 0);
    return TCL_ERROR;
  }
  strncpy((char*)pPage, argv[2], SQLITE_USABLE_SIZE-1);
  ((char*)pPage)[SQLITE_USABLE_SIZE-1] = 0;
  return TCL_OK;
................................................................................
    char *zName;
    Tcl_CmdProc *xProc;
  } aCmd[] = {
    { "pager_open",              (Tcl_CmdProc*)pager_open          },
    { "pager_close",             (Tcl_CmdProc*)pager_close         },
    { "pager_commit",            (Tcl_CmdProc*)pager_commit        },
    { "pager_rollback",          (Tcl_CmdProc*)pager_rollback      },
    { "pager_stmt_begin",        (Tcl_CmdProc*)pager_stmt_begin    },
    { "pager_stmt_commit",       (Tcl_CmdProc*)pager_stmt_commit   },
    { "pager_stmt_rollback",     (Tcl_CmdProc*)pager_stmt_rollback },
    { "pager_stats",             (Tcl_CmdProc*)pager_stats         },
    { "pager_pagecount",         (Tcl_CmdProc*)pager_pagecount     },
    { "page_get",                (Tcl_CmdProc*)page_get            },
    { "page_lookup",             (Tcl_CmdProc*)page_lookup         },
    { "page_unref",              (Tcl_CmdProc*)page_unref          },
    { "page_read",               (Tcl_CmdProc*)page_read           },
    { "page_write",              (Tcl_CmdProc*)page_write          },
................................................................................
  int i;
  for(i=0; i<sizeof(aCmd)/sizeof(aCmd[0]); i++){
    Tcl_CreateCommand(interp, aCmd[i].zName, aCmd[i].xProc, 0, 0);
  }
  Tcl_LinkVar(interp, "sqlite_io_error_pending",
     (char*)&sqlite_io_error_pending, TCL_LINK_INT);
#ifdef SQLITE_TEST
  {
    extern int journal_format;
    Tcl_LinkVar(interp, "journal_format",
       (char*)&journal_format, TCL_LINK_INT);
  }
#endif
  sprintf(zBuf, "%d", SQLITE_PAGE_SIZE);
  Tcl_SetVar(interp, "SQLITE_PAGE_SIZE", zBuf, TCL_GLOBAL_ONLY); 
  sprintf(zBuf, "%d", SQLITE_PAGE_RESERVE);
  Tcl_SetVar(interp, "SQLITE_PAGE_RESERVE", zBuf, TCL_GLOBAL_ONLY); 
  sprintf(zBuf, "%d", SQLITE_USABLE_SIZE);
  Tcl_SetVar(interp, "SQLITE_USABLE_SIZE", zBuf, TCL_GLOBAL_ONLY); 
  return TCL_OK;
}

**
*************************************************************************
** Utility functions used throughout sqlite.
**
** This file contains functions for allocating memory, comparing
** strings, and stuff like that.
**
** $Id: util.c,v 1.74 2004/02/22 17:49:34 drh Exp $
*/
#include "sqliteInt.h"
#include <stdarg.h>
#include <ctype.h>

/*
** If malloc() ever fails, this global variable gets set to 1.
................................................................................
#if MEMORY_DEBUG>1
  fprintf(stderr,"string at 0x%x is %s\n", (int)*pz, *pz);
#endif
#endif
  va_end(ap);
}


/*
** Add an error message to pParse->zErrMsg and increment pParse->nErr.
** The following formatting characters are allowed:
**
**      %s      Insert a string
**      %z      A string that should be freed after use
**      %d      Insert an integer
................................................................................
  va_list ap;
  pParse->nErr++;
  sqliteFree(pParse->zErrMsg);
  va_start(ap, zFormat);
  pParse->zErrMsg = sqliteVMPrintf(zFormat, ap);
  va_end(ap);
}


/*
** Convert an SQL-style quoted string into a normal string by removing
** the quote characters.  The conversion is done in-place.  If the
** input does not begin with a quote character, then this routine
** is a no-op.
**

**
*************************************************************************
** Utility functions used throughout sqlite.
**
** This file contains functions for allocating memory, comparing
** strings, and stuff like that.
**
** $Id: util.c,v 1.75 2004/04/26 14:10:22 drh Exp $
*/
#include "sqliteInt.h"
#include <stdarg.h>
#include <ctype.h>

/*
** If malloc() ever fails, this global variable gets set to 1.
................................................................................
#if MEMORY_DEBUG>1
  fprintf(stderr,"string at 0x%x is %s\n", (int)*pz, *pz);
#endif
#endif
  va_end(ap);
}

#if 0
/*
** Add an error message to pParse->zErrMsg and increment pParse->nErr.
** The following formatting characters are allowed:
**
**      %s      Insert a string
**      %z      A string that should be freed after use
**      %d      Insert an integer
................................................................................
  va_list ap;
  pParse->nErr++;
  sqliteFree(pParse->zErrMsg);
  va_start(ap, zFormat);
  pParse->zErrMsg = sqliteVMPrintf(zFormat, ap);
  va_end(ap);
}
#endif

/*
** Convert an SQL-style quoted string into a normal string by removing
** the quote characters.  The conversion is done in-place.  If the
** input does not begin with a quote character, then this routine
** is a no-op.
**

#    May you find forgiveness for yourself and forgive others.
#    May you share freely, never taking more than you give.
#
#***********************************************************************
# This file implements regression tests for SQLite library.  The
# focus of this script is page cache subsystem.
#
# $Id: pager.test,v 1.14 2004/02/25 02:20:42 drh Exp $


set testdir [file dirname $argv0]
source $testdir/tester.tcl

if {[info commands pager_open]!=""} {
db close
................................................................................
  } {state 2}
  do_test pager-4.5.$i.2 {
    for {set j 2} {$j<=20} {incr j} {
      set gx [page_get $p1 $j]
      page_write $gx "Page-$j v$i"
      page_unref $gx
      if {$j==$i} {
        pager_ckpt_begin $p1
      }
    }
  } {}
  do_test pager-4.5.$i.3 {
    set res {}
    for {set j 2} {$j<=20} {incr j} {
      set gx [page_get $p1 $j]
................................................................................
  } {state 2}
  do_test pager-4.5.$i.6 {
    for {set j 2} {$j<=20} {incr j} {
      set gx [page_get $p1 $j]
      page_write $gx "Page-$j v$i"
      page_unref $gx
      if {$j==$i} {
        pager_ckpt_begin $p1
      }
    }
  } {}
  do_test pager-4.5.$i.7 {
    pager_ckpt_rollback $p1
    for {set j 2} {$j<=20} {incr j} {
      set gx [page_get $p1 $j]
      set value [page_read $gx]
      page_unref $gx
      if {$j<=$i || $i==1} {
        set shouldbe "Page-$j v$i"
      } else {
................................................................................
  } {}
  do_test pager-4.5.$i.8 {
    for {set j 2} {$j<=20} {incr j} {
      set gx [page_get $p1 $j]
      page_write $gx "Page-$j v$i"
      page_unref $gx
      if {$j==$i} {
        pager_ckpt_begin $p1
      }
    }
  } {}
  do_test pager-4.5.$i.9 {
    pager_ckpt_commit $p1
    for {set j 2} {$j<=20} {incr j} {
      set gx [page_get $p1 $j]
      set value [page_read $gx]
      page_unref $gx
      set shouldbe "Page-$j v$i"
      if {$value!=$shouldbe} {
        lappend res $value $shouldbe
................................................................................



  file delete -force ptf1.db

} ;# end if( not mem: and has pager_open command );


# Ticket #615: an assertion fault inside the pager.  It is a benign
# fault, but we might as well test for it.
#
do_test pager-5.1 {
  sqlite db test.db
  execsql {
    BEGIN;
    CREATE TABLE t1(x);
    PRAGMA synchronous=off;
    COMMIT;
  }
} {}


finish_test

#    May you find forgiveness for yourself and forgive others.
#    May you share freely, never taking more than you give.
#
#***********************************************************************
# This file implements regression tests for SQLite library.  The
# focus of this script is page cache subsystem.
#
# $Id: pager.test,v 1.15 2004/04/26 14:10:22 drh Exp $


set testdir [file dirname $argv0]
source $testdir/tester.tcl

if {[info commands pager_open]!=""} {
db close
................................................................................
  } {state 2}
  do_test pager-4.5.$i.2 {
    for {set j 2} {$j<=20} {incr j} {
      set gx [page_get $p1 $j]
      page_write $gx "Page-$j v$i"
      page_unref $gx
      if {$j==$i} {
        pager_stmt_begin $p1
      }
    }
  } {}
  do_test pager-4.5.$i.3 {
    set res {}
    for {set j 2} {$j<=20} {incr j} {
      set gx [page_get $p1 $j]
................................................................................
  } {state 2}
  do_test pager-4.5.$i.6 {
    for {set j 2} {$j<=20} {incr j} {
      set gx [page_get $p1 $j]
      page_write $gx "Page-$j v$i"
      page_unref $gx
      if {$j==$i} {
        pager_stmt_begin $p1
      }
    }
  } {}
  do_test pager-4.5.$i.7 {
    pager_stmt_rollback $p1
    for {set j 2} {$j<=20} {incr j} {
      set gx [page_get $p1 $j]
      set value [page_read $gx]
      page_unref $gx
      if {$j<=$i || $i==1} {
        set shouldbe "Page-$j v$i"
      } else {
................................................................................
  } {}
  do_test pager-4.5.$i.8 {
    for {set j 2} {$j<=20} {incr j} {
      set gx [page_get $p1 $j]
      page_write $gx "Page-$j v$i"
      page_unref $gx
      if {$j==$i} {
        pager_stmt_begin $p1
      }
    }
  } {}
  do_test pager-4.5.$i.9 {
    pager_stmt_commit $p1
    for {set j 2} {$j<=20} {incr j} {
      set gx [page_get $p1 $j]
      set value [page_read $gx]
      page_unref $gx
      set shouldbe "Page-$j v$i"
      if {$value!=$shouldbe} {
        lappend res $value $shouldbe
................................................................................



  file delete -force ptf1.db

} ;# end if( not mem: and has pager_open command );

if 0 {
# Ticket #615: an assertion fault inside the pager.  It is a benign
# fault, but we might as well test for it.
#
do_test pager-5.1 {
  sqlite db test.db
  execsql {
    BEGIN;
    CREATE TABLE t1(x);
    PRAGMA synchronous=off;
    COMMIT;
  }
} {}
}

finish_test

#    May you find forgiveness for yourself and forgive others.
#    May you share freely, never taking more than you give.
#
#***********************************************************************
# This file implements some common TCL routines used for regression
# testing the SQLite library
#
# $Id: tester.tcl,v 1.28 2004/02/14 01:39:50 drh Exp $


# Make sure tclsqlite was compiled correctly.  Abort now with an
# error message if not.
#
if {[sqlite -tcl-uses-utf]} {
  if {"\u1234"=="u1234"} {
    puts stderr "***** BUILD PROBLEM *****"
    puts stderr "$argv0 was linked against an older version"
................................................................................
catch {db close}
file delete -force test.db
file delete -force test.db-journal
sqlite db ./test.db
if {[info exists ::SETUP_SQL]} {
  db eval $::SETUP_SQL
}



# Abort early if this script has been run before.
#
if {[info exists nTest]} return

# Set the test counters to zero
#
................................................................................
  catch {db close}
  puts "$nErr errors out of $nTest tests"
  puts "Failures on these tests: $::failList"
  if {$nProb>0} {
    puts "$nProb probabilistic tests also failed, but this does"
    puts "not necessarily indicate a malfunction."
  }

  if {$sqlite_open_file_count} {
    puts "$sqlite_open_file_count files were left open"
    incr nErr

  }
  exit [expr {$nErr>0}]
}

# A procedure to execute SQL
#
proc execsql {sql {db db}} {

#    May you find forgiveness for yourself and forgive others.
#    May you share freely, never taking more than you give.
#
#***********************************************************************
# This file implements some common TCL routines used for regression
# testing the SQLite library
#
# $Id: tester.tcl,v 1.29 2004/04/26 14:10:22 drh Exp $

if 0 {
# Make sure tclsqlite was compiled correctly.  Abort now with an
# error message if not.
#
if {[sqlite -tcl-uses-utf]} {
  if {"\u1234"=="u1234"} {
    puts stderr "***** BUILD PROBLEM *****"
    puts stderr "$argv0 was linked against an older version"
................................................................................
catch {db close}
file delete -force test.db
file delete -force test.db-journal
sqlite db ./test.db
if {[info exists ::SETUP_SQL]} {
  db eval $::SETUP_SQL
}
}
proc db {args} {}

# Abort early if this script has been run before.
#
if {[info exists nTest]} return

# Set the test counters to zero
#
................................................................................
  catch {db close}
  puts "$nErr errors out of $nTest tests"
  puts "Failures on these tests: $::failList"
  if {$nProb>0} {
    puts "$nProb probabilistic tests also failed, but this does"
    puts "not necessarily indicate a malfunction."
  }
  if 0 {
  if {$sqlite_open_file_count} {
    puts "$sqlite_open_file_count files were left open"
    incr nErr
  }
  }
  exit [expr {$nErr>0}]
}

# A procedure to execute SQL
#
proc execsql {sql {db db}} {