SQLite

}

/*
** Return a section of the pPage->aData to the freelist.
** The first byte of the new free block is pPage->aData[iStart]
** and the size of the block is iSize bytes.
**
** Adjacent freeblocks are coalesced.
**
** Note that even though the freeblock list was checked by btreeInitPage(),
** that routine will not detect overlap between cells or freeblocks.  Nor
** does it detect cells or freeblocks that encrouch into the reserved bytes
** at the end of the page.  So do additional corruption checks inside this
** routine and return SQLITE_CORRUPT if any problems are found.
*/
static int freeSpace(MemPage *pPage, u16 iStart, u16 iSize){
  u16 iPtr;                             /* Address of pointer to next freeblock */
  u16 iFreeBlk;                         /* Address of the next freeblock */
  u8 hdr;                               /* Page header size.  0 or 100 */
  u8 nFrag = 0;                         /* Reduction in fragmentation */
  u16 iOrigSize = iSize;                /* Original value of iSize */
  u32 iLast = pPage->pBt->usableSize-4; /* Largest possible freeblock offset */
  u32 iEnd = iStart + iSize;            /* First byte past the iStart buffer */
  unsigned char *data = pPage->aData;   /* Page content */

  assert( pPage->pBt!=0 );
  assert( sqlite3PagerIswriteable(pPage->pDbPage) );
  assert( iStart>=pPage->hdrOffset+6+pPage->childPtrSize );
  assert( iEnd <= pPage->pBt->usableSize );
  assert( sqlite3_mutex_held(pPage->pBt->mutex) );
  assert( iSize>=4 );   /* Minimum cell size is 4 */
  assert( iStart<=iLast );


  /* Overwrite deleted information with zeros when the secure_delete
  ** option is enabled */
  if( pPage->pBt->btsFlags & BTS_SECURE_DELETE ){
    memset(&data[iStart], 0, iSize);
  }

  /* The list of freeblocks must be in ascending order.  Find the 






  ** spot on the list where iStart should be inserted.
  */
  hdr = pPage->hdrOffset;
  iPtr = hdr + 1;


  while( (iFreeBlk = get2byte(&data[iPtr]))>0 && iFreeBlk<iStart ){
    if( iFreeBlk<iPtr+4 ) return SQLITE_CORRUPT_BKPT;


    iPtr = iFreeBlk;
  }
  if( iFreeBlk>iLast ) return SQLITE_CORRUPT_BKPT;


  assert( iFreeBlk>iPtr || iFreeBlk==0 );





  /* At this point:


  **    iFreeBlk:   First freeblock after iStart, or zero if none
  **    iPtr:       The address of a pointer iFreeBlk
  **
  ** Check to see if iFreeBlk should be coalesced onto the end of iStart.
  */
  if( iFreeBlk && iEnd+3>=iFreeBlk ){
    nFrag = iFreeBlk - iEnd;
    if( iEnd>iFreeBlk ) return SQLITE_CORRUPT_BKPT;
    iEnd = iFreeBlk + get2byte(&data[iFreeBlk+2]);
    iSize = iEnd - iStart;
    iFreeBlk = get2byte(&data[iFreeBlk]);
  }

  /* If iPtr is another freeblock (that is, if iPtr is not the freelist pointer
  ** in the page header) then check to see if iStart should be coalesced 
  ** onto the end of iPtr.
  */
  if( iPtr>hdr+1 ){
    int iPtrEnd = iPtr + get2byte(&data[iPtr+2]);
    if( iPtrEnd+3>=iStart ){
      if( iPtrEnd>iStart ) return SQLITE_CORRUPT_BKPT;
      nFrag += iStart - iPtrEnd;
      iSize = iEnd - iPtr;
      iStart = iPtr;
    }
  }
  if( nFrag>data[hdr+7] ) return SQLITE_CORRUPT_BKPT;

  data[hdr+7] -= nFrag;
  if( iPtr==hdr+1 && iStart==get2byte(&data[hdr+5]) ){
    /* The new freeblock is at the beginning of the cell content area,
    ** so just extend the cell content area rather than create another
    ** freelist entry */
    put2byte(&data[hdr+1], iFreeBlk);

    put2byte(&data[hdr+5], iEnd);
  }else{



    /* Insert the new freeblock into the freelist */



    put2byte(&data[iPtr], iStart);

    put2byte(&data[iStart], iFreeBlk);
    put2byte(&data[iStart+2], iSize);
  }
  pPage->nFree += iOrigSize;
  return SQLITE_OK;
}

/*
** Decode the flags byte (the first byte of the header) for a page
** and initialize fields of the MemPage structure accordingly.
**