** 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 1.611 2009/06/03 17:26:18 danielk1977 Exp $
**
** This file implements a external (disk-based) database using BTrees.
** See the header comment on "btreeInt.h" for additional information.
** Including a description of file format and an overview of operation.
*/
#include "btreeInt.h"

................................................................................
    pPage->cellOffset = cellOffset = hdr + 12 - 4*pPage->leaf;
    top = get2byte(&data[hdr+5]);
    pPage->nCell = get2byte(&data[hdr+3]);
    if( pPage->nCell>MX_CELL(pBt) ){
      /* To many cells for a single page.  The page must be corrupt */
      return SQLITE_CORRUPT_BKPT;
    }
  































    /* Compute the total free space on the page */
    pc = get2byte(&data[hdr+1]);
    nFree = data[hdr+7] + top;
    while( pc>0 ){
      u16 next, size;
      if( pc>usableSize-4 ){
        /* Free block is off the page */

** 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 1.612 2009/06/03 21:04:36 drh Exp $
**
** This file implements a external (disk-based) database using BTrees.
** See the header comment on "btreeInt.h" for additional information.
** Including a description of file format and an overview of operation.
*/
#include "btreeInt.h"

................................................................................
    pPage->cellOffset = cellOffset = hdr + 12 - 4*pPage->leaf;
    top = get2byte(&data[hdr+5]);
    pPage->nCell = get2byte(&data[hdr+3]);
    if( pPage->nCell>MX_CELL(pBt) ){
      /* To many cells for a single page.  The page must be corrupt */
      return SQLITE_CORRUPT_BKPT;
    }

    /* A malformed database page might cause use to read past the end
    ** of page when parsing a cell.  
    **
    ** The following block of code checks early to see if a cell extends
    ** past the end of a page boundary and causes SQLITE_CORRUPT to be 
    ** returned if it does.
    */
#if defined(SQLITE_OVERREAD_CHECK) || 1
    {
      int iCellFirst;   /* First allowable cell index */
      int iCellLast;    /* Last possible cell index */
      int i;            /* Index into the cell pointer array */
      int sz;           /* Size of a cell */

      iCellFirst = cellOffset + 2*pPage->nCell;
      iCellLast = usableSize - 4;
      if( !pPage->leaf ) iCellLast--;
      for(i=0; i<pPage->nCell; i++){
        pc = get2byte(&data[cellOffset+i*2]);
        if( pc<iCellFirst || pc>iCellLast ){
          return SQLITE_CORRUPT_BKPT;
        }
        sz = cellSizePtr(pPage, &data[pc]);
        if( pc+sz>usableSize ){
          return SQLITE_CORRUPT_BKPT;
        }
      }
    }  
#endif


    /* Compute the total free space on the page */
    pc = get2byte(&data[hdr+1]);
    nFree = data[hdr+7] + top;
    while( pc>0 ){
      u16 next, size;
      if( pc>usableSize-4 ){
        /* Free block is off the page */

**
** This file implements the default page cache implementation (the
** sqlite3_pcache interface). It also contains part of the implementation
** of the SQLITE_CONFIG_PAGECACHE and sqlite3_release_memory() features.
** If the default page cache implementation is overriden, then neither of
** these two features are available.
**
** @(#) $Id: pcache1.c,v 1.15 2009/05/22 11:12:23 drh Exp $
*/

#include "sqliteInt.h"

typedef struct PCache1 PCache1;
typedef struct PgHdr1 PgHdr1;
typedef struct PgFreeslot PgFreeslot;
................................................................................

  unsigned int iMaxKey;               /* Largest key seen since xTruncate() */
};

/*
** Each cache entry is represented by an instance of the following 
** structure. A buffer of PgHdr1.pCache->szPage bytes is allocated 
** directly after the structure in memory (see the PGHDR1_TO_PAGE() 
** macro below).
*/
struct PgHdr1 {
  unsigned int iKey;             /* Key value (page number) */
  PgHdr1 *pNext;                 /* Next in hash table chain */
  PCache1 *pCache;               /* Cache that currently owns this page */
  PgHdr1 *pLruNext;              /* Next in LRU list of unpinned pages */
................................................................................
** alias "pcache1". This ensures that the WSD emulation is used when
** compiling for systems that do not support real WSD.
*/
#define pcache1 (GLOBAL(struct PCacheGlobal, pcache1_g))

/*
** When a PgHdr1 structure is allocated, the associated PCache1.szPage
** bytes of data are located directly after it in memory (i.e. the total
** size of the allocation is sizeof(PgHdr1)+PCache1.szPage byte). The
** PGHDR1_TO_PAGE() macro takes a pointer to a PgHdr1 structure as
** an argument and returns a pointer to the associated block of szPage
** bytes. The PAGE_TO_PGHDR1() macro does the opposite: its argument is
** a pointer to a block of szPage bytes of data and the return value is
** a pointer to the associated PgHdr1 structure.
**
**   assert( PGHDR1_TO_PAGE(PAGE_TO_PGHDR1(X))==X );
*/
#define PGHDR1_TO_PAGE(p) (void *)(&((unsigned char *)p)[sizeof(PgHdr1)])
#define PAGE_TO_PGHDR1(p) (PgHdr1 *)(&((unsigned char *)p)[-1*(int)sizeof(PgHdr1)])

/*
** Macros to enter and leave the global LRU mutex.
*/
#define pcache1EnterMutex() sqlite3_mutex_enter(pcache1.mutex)
#define pcache1LeaveMutex() sqlite3_mutex_leave(pcache1.mutex)

................................................................................
}

/*
** Allocate a new page object initially associated with cache pCache.
*/
static PgHdr1 *pcache1AllocPage(PCache1 *pCache){
  int nByte = sizeof(PgHdr1) + pCache->szPage;
  PgHdr1 *p = (PgHdr1 *)pcache1Alloc(nByte);

  if( p ){

    if( pCache->bPurgeable ){
      pcache1.nCurrentPage++;
    }


  }
  return p;
}

/*
** Free a page object allocated by pcache1AllocPage().
*/
static void pcache1FreePage(PgHdr1 *p){
  if( p ){
    if( p->pCache->bPurgeable ){
      pcache1.nCurrentPage--;
    }
    pcache1Free(p);
  }
}

/*
** Malloc function used by SQLite to obtain space from the buffer configured
** using sqlite3_config(SQLITE_CONFIG_PAGECACHE) option. If no such buffer
** exists, this function falls back to sqlite3Malloc().
................................................................................
  */
  if( !pPage ){
    pPage = pcache1AllocPage(pCache);
  }

  if( pPage ){
    unsigned int h = iKey % pCache->nHash;
    *(void **)(PGHDR1_TO_PAGE(pPage)) = 0;
    pCache->nPage++;
    pPage->iKey = iKey;
    pPage->pNext = pCache->apHash[h];
    pPage->pCache = pCache;
    pPage->pLruPrev = 0;
    pPage->pLruNext = 0;

    pCache->apHash[h] = pPage;
  }

fetch_out:
  if( pPage && iKey>pCache->iMaxKey ){
    pCache->iMaxKey = iKey;
  }
................................................................................
/*
** Implementation of the sqlite3_pcache.xUnpin method.
**
** Mark a page as unpinned (eligible for asynchronous recycling).
*/
static void pcache1Unpin(sqlite3_pcache *p, void *pPg, int reuseUnlikely){
  PCache1 *pCache = (PCache1 *)p;
  PgHdr1 *pPage = PAGE_TO_PGHDR1(pPg);


  pcache1EnterMutex();

  /* It is an error to call this function if the page is already 
  ** part of the global LRU list.
  */
  assert( pPage->pLruPrev==0 && pPage->pLruNext==0 );
  assert( pcache1.pLruHead!=pPage && pcache1.pLruTail!=pPage );
................................................................................
static void pcache1Rekey(
  sqlite3_pcache *p,
  void *pPg,
  unsigned int iOld,
  unsigned int iNew
){
  PCache1 *pCache = (PCache1 *)p;
  PgHdr1 *pPage = PAGE_TO_PGHDR1(pPg);
  PgHdr1 **pp;
  unsigned int h; 
  assert( pPage->iKey==iOld );


  pcache1EnterMutex();

  h = iOld%pCache->nHash;
  pp = &pCache->apHash[h];
  while( (*pp)!=pPage ){
    pp = &(*pp)->pNext;
................................................................................
*/
int sqlite3PcacheReleaseMemory(int nReq){
  int nFree = 0;
  if( pcache1.pStart==0 ){
    PgHdr1 *p;
    pcache1EnterMutex();
    while( (nReq<0 || nFree<nReq) && (p=pcache1.pLruTail) ){
      nFree += sqlite3MallocSize(p);
      pcache1PinPage(p);
      pcache1RemoveFromHash(p);
      pcache1FreePage(p);
    }
    pcache1LeaveMutex();
  }
  return nFree;

**
** This file implements the default page cache implementation (the
** sqlite3_pcache interface). It also contains part of the implementation
** of the SQLITE_CONFIG_PAGECACHE and sqlite3_release_memory() features.
** If the default page cache implementation is overriden, then neither of
** these two features are available.
**
** @(#) $Id: pcache1.c,v 1.16 2009/06/03 21:04:36 drh Exp $
*/

#include "sqliteInt.h"

typedef struct PCache1 PCache1;
typedef struct PgHdr1 PgHdr1;
typedef struct PgFreeslot PgFreeslot;
................................................................................

  unsigned int iMaxKey;               /* Largest key seen since xTruncate() */
};

/*
** Each cache entry is represented by an instance of the following 
** structure. A buffer of PgHdr1.pCache->szPage bytes is allocated 
** directly before this structure in memory (see the PGHDR1_TO_PAGE() 
** macro below).
*/
struct PgHdr1 {
  unsigned int iKey;             /* Key value (page number) */
  PgHdr1 *pNext;                 /* Next in hash table chain */
  PCache1 *pCache;               /* Cache that currently owns this page */
  PgHdr1 *pLruNext;              /* Next in LRU list of unpinned pages */
................................................................................
** alias "pcache1". This ensures that the WSD emulation is used when
** compiling for systems that do not support real WSD.
*/
#define pcache1 (GLOBAL(struct PCacheGlobal, pcache1_g))

/*
** When a PgHdr1 structure is allocated, the associated PCache1.szPage
** bytes of data are located directly before it in memory (i.e. the total
** size of the allocation is sizeof(PgHdr1)+PCache1.szPage byte). The
** PGHDR1_TO_PAGE() macro takes a pointer to a PgHdr1 structure as
** an argument and returns a pointer to the associated block of szPage
** bytes. The PAGE_TO_PGHDR1() macro does the opposite: its argument is
** a pointer to a block of szPage bytes of data and the return value is
** a pointer to the associated PgHdr1 structure.
**
**   assert( PGHDR1_TO_PAGE(PAGE_TO_PGHDR1(pCache, X))==X );
*/
#define PGHDR1_TO_PAGE(p)    (void*)(((char*)p) - p->pCache->szPage)
#define PAGE_TO_PGHDR1(c, p) (PgHdr1*)(((char*)p) + c->szPage)

/*
** Macros to enter and leave the global LRU mutex.
*/
#define pcache1EnterMutex() sqlite3_mutex_enter(pcache1.mutex)
#define pcache1LeaveMutex() sqlite3_mutex_leave(pcache1.mutex)

................................................................................
}

/*
** Allocate a new page object initially associated with cache pCache.
*/
static PgHdr1 *pcache1AllocPage(PCache1 *pCache){
  int nByte = sizeof(PgHdr1) + pCache->szPage;
  void *pPg = pcache1Alloc(nByte);
  PgHdr1 *p;
  if( pPg ){
    p = PAGE_TO_PGHDR1(pCache, pPg);
    if( pCache->bPurgeable ){
      pcache1.nCurrentPage++;
    }
  }else{
    p = 0;
  }
  return p;
}

/*
** Free a page object allocated by pcache1AllocPage().
*/
static void pcache1FreePage(PgHdr1 *p){
  if( p ){
    if( p->pCache->bPurgeable ){
      pcache1.nCurrentPage--;
    }
    pcache1Free(PGHDR1_TO_PAGE(p));
  }
}

/*
** Malloc function used by SQLite to obtain space from the buffer configured
** using sqlite3_config(SQLITE_CONFIG_PAGECACHE) option. If no such buffer
** exists, this function falls back to sqlite3Malloc().
................................................................................
  */
  if( !pPage ){
    pPage = pcache1AllocPage(pCache);
  }

  if( pPage ){
    unsigned int h = iKey % pCache->nHash;

    pCache->nPage++;
    pPage->iKey = iKey;
    pPage->pNext = pCache->apHash[h];
    pPage->pCache = pCache;
    pPage->pLruPrev = 0;
    pPage->pLruNext = 0;
    *(void **)(PGHDR1_TO_PAGE(pPage)) = 0;
    pCache->apHash[h] = pPage;
  }

fetch_out:
  if( pPage && iKey>pCache->iMaxKey ){
    pCache->iMaxKey = iKey;
  }
................................................................................
/*
** Implementation of the sqlite3_pcache.xUnpin method.
**
** Mark a page as unpinned (eligible for asynchronous recycling).
*/
static void pcache1Unpin(sqlite3_pcache *p, void *pPg, int reuseUnlikely){
  PCache1 *pCache = (PCache1 *)p;
  PgHdr1 *pPage = PAGE_TO_PGHDR1(pCache, pPg);
 
  assert( pPage->pCache==pCache );
  pcache1EnterMutex();

  /* It is an error to call this function if the page is already 
  ** part of the global LRU list.
  */
  assert( pPage->pLruPrev==0 && pPage->pLruNext==0 );
  assert( pcache1.pLruHead!=pPage && pcache1.pLruTail!=pPage );
................................................................................
static void pcache1Rekey(
  sqlite3_pcache *p,
  void *pPg,
  unsigned int iOld,
  unsigned int iNew
){
  PCache1 *pCache = (PCache1 *)p;
  PgHdr1 *pPage = PAGE_TO_PGHDR1(pCache, pPg);
  PgHdr1 **pp;
  unsigned int h; 
  assert( pPage->iKey==iOld );
  assert( pPage->pCache==pCache );

  pcache1EnterMutex();

  h = iOld%pCache->nHash;
  pp = &pCache->apHash[h];
  while( (*pp)!=pPage ){
    pp = &(*pp)->pNext;
................................................................................
*/
int sqlite3PcacheReleaseMemory(int nReq){
  int nFree = 0;
  if( pcache1.pStart==0 ){
    PgHdr1 *p;
    pcache1EnterMutex();
    while( (nReq<0 || nFree<nReq) && (p=pcache1.pLruTail) ){
      nFree += sqlite3MallocSize(PGHDR1_TO_PAGE(p));
      pcache1PinPage(p);
      pcache1RemoveFromHash(p);
      pcache1FreePage(p);
    }
    pcache1LeaveMutex();
  }
  return nFree;