SQLite

    }
  }

  *piPage = p->iPrior = iRet;
  return (iRet==0xFFFFFFFF);
}

/*
** This function merges two sorted lists into a single sorted list.
*/
static void walMerge(
  u32 *aContent,                  /* Pages in wal */
  ht_slot *aLeft,                 /* IN: Left hand input list */
  int nLeft,                      /* IN: Elements in array *paLeft */
  ht_slot **paRight,              /* IN/OUT: Right hand input list */
  int *pnRight,                   /* IN/OUT: Elements in *paRight */
  ht_slot *aTmp                   /* Temporary buffer */
){
  int iLeft = 0;                  /* Current index in aLeft */
  int iRight = 0;                 /* Current index in aRight */
  int iOut = 0;                   /* Current index in output buffer */
  int nRight = *pnRight;
  ht_slot *aRight = *paRight;

  assert( nLeft>0 && nRight>0 );
  while( iRight<nRight || iLeft<nLeft ){
    ht_slot logpage;
    Pgno dbpage;

    if( (iLeft<nLeft) 
     && (iRight>=nRight || aContent[aLeft[iLeft]]<aContent[aRight[iRight]])
    ){
      logpage = aLeft[iLeft++];
    }else{
      logpage = aRight[iRight++];
    }
    dbpage = aContent[logpage];

    aTmp[iOut++] = logpage;
    if( iLeft<nLeft && aContent[aLeft[iLeft]]==dbpage ) iLeft++;

    assert( iLeft>=nLeft || aContent[aLeft[iLeft]]>dbpage );
    assert( iRight>=nRight || aContent[aRight[iRight]]>dbpage );
  }

  *paRight = aLeft;
  *pnRight = iOut;
  memcpy(aLeft, aTmp, sizeof(aTmp[0])*iOut);
}

/*
** Sort the elements in list aList, removing any duplicates.
*/
static void walMergesort(
  u32 *aContent,                  /* Pages in wal */
  ht_slot *aBuffer,               /* Buffer of at least *pnList items to use */
  ht_slot *aList,                 /* IN/OUT: List to sort */
  int *pnList                     /* IN/OUT: Number of elements in aList[] */
){
  struct Sublist {
    int nList;                    /* Number of elements in aList */
    ht_slot *aList;               /* Pointer to sub-list content */
  };

  const int nList = *pnList;      /* Size of input list */
  int nMerge;                     /* Number of elements in list aMerge */
  ht_slot *aMerge;                /* List to be merged */
  int iList;                      /* Index into input list */
  int iSub;                       /* Index into aSub array */
  struct Sublist aSub[13];        /* Array of sub-lists */




  memset(aSub, 0, sizeof(aSub));
  assert( nList<=HASHTABLE_NPAGE && nList>0 );
  assert( HASHTABLE_NPAGE==(1<<(ArraySize(aSub)-1)) );



  for(iList=0; iList<nList; iList++){
    nMerge = 1;
    aMerge = &aList[iList];
    for(iSub=0; iList & (1<<iSub); iSub++){
      struct Sublist *p = &aSub[iSub];
      assert( p->aList && p->nList<=(1<<iSub) );
      walMerge(aContent, p->aList, p->nList, &aMerge, &nMerge, aBuffer);
    }



    aSub[iSub].aList = aMerge;

    aSub[iSub].nList = nMerge;
  }


  for(iSub++; iSub<ArraySize(aSub); iSub++){
    if( nList & (1<<iSub) ){
      struct Sublist *p = &aSub[iSub];
      assert( p->nList<=(2<<iSub) );
      walMerge(aContent, p->aList, p->nList, &aMerge, &nMerge, aBuffer);
    }


  }
  assert( aMerge==aList );
  *pnList = nMerge;


#ifdef SQLITE_DEBUG
  {
    int i;
    for(i=1; i<*pnList; i++){
      assert( aContent[aList[i]] > aContent[aList[i-1]] );
    }

  WalIterator *pIter = 0;         /* Wal iterator context */
  u32 iDbpage = 0;                /* Next database page to write */
  u32 iFrame = 0;                 /* Wal frame containing data for iDbpage */
  u32 mxSafeFrame;                /* Max frame that can be backfilled */
  int i;                          /* Loop counter */
  volatile WalCkptInfo *pInfo;    /* The checkpoint status information */

  if( pWal->hdr.mxFrame==0 ) return SQLITE_OK;

  /* Allocate the iterator */
  rc = walIteratorInit(pWal, &pIter);
  if( rc!=SQLITE_OK ){
    goto walcheckpoint_out;
  }
  assert( pIter );

  /*** TODO:  Move this test out to the caller.  Make it an assert() here ***/
  if( pWal->hdr.szPage!=nBuf ){
    rc = SQLITE_CORRUPT_BKPT;
    goto walcheckpoint_out;
  }