SQLite

    char *zNew = sqlite3_realloc(pStr->z, nAlloc);
    if( !zNew ){
      return SQLITE_NOMEM;
    }
    pStr->z = zNew;
    pStr->nAlloc = nAlloc;
  }
  assert( pStr->z!=0 && (pStr->nAlloc >= pStr->n+nAppend+1) );

  /* Append the data to the string buffer. */
  memcpy(&pStr->z[pStr->n], zAppend, nAppend);
  pStr->n += nAppend;
  pStr->z[pStr->n] = '\0';

  return SQLITE_OK;

    ** following block advances it to point one byte past the end of
    ** the same offset list. */
    while( 1 ){
  
      /* The following line of code (and the "p++" below the while() loop) is
      ** normally all that is required to move pointer p to the desired 
      ** position. The exception is if this node is being loaded from disk
      ** incrementally and pointer "p" now points to the first byte past
      ** the populated part of pReader->aNode[].
      */
      while( *p | c ) c = *p++ & 0x80;
      assert( *p==0 );
  
      if( pReader->pBlob==0 || p<&pReader->aNode[pReader->nPopulate] ) break;
      rc = fts3SegReaderIncrRead(pReader);

      */
      for(i=0; i<nMerge; i++){
        fts3SegReaderFirstDocid(p, apSegment[i]);
      }
      fts3SegReaderSort(apSegment, nMerge, nMerge, xCmp);
      while( apSegment[0]->pOffsetList ){
        int j;                    /* Number of segments that share a docid */
        char *pList = 0;
        int nList = 0;
        int nByte;
        sqlite3_int64 iDocid = apSegment[0]->iDocid;
        fts3SegReaderNextDocid(p, apSegment[0], &pList, &nList);
        j = 1;
        while( j<nMerge
            && apSegment[j]->pOffsetList
            && apSegment[j]->iDocid==iDocid

  }
  pCur->eState = CURSOR_INVALID;
  rc = btreeMoveto(pCur, pCur->pKey, pCur->nKey, 0, &pCur->skipNext);
  if( rc==SQLITE_OK ){
    sqlite3_free(pCur->pKey);
    pCur->pKey = 0;
    assert( pCur->eState==CURSOR_VALID || pCur->eState==CURSOR_INVALID );
    if( pCur->skipNext && pCur->eState==CURSOR_VALID ){
      pCur->eState = CURSOR_SKIPNEXT;
    }
  }
  return rc;
}

#define restoreCursorPosition(p) \
  (p->eState>=CURSOR_REQUIRESEEK ? \
         btreeRestoreCursorPosition(p) : \

  int rc;

  rc = restoreCursorPosition(pCur);
  if( rc ){
    *pHasMoved = 1;
    return rc;
  }
  if( pCur->eState!=CURSOR_VALID || NEVER(pCur->skipNext!=0) ){
    *pHasMoved = 1;
  }else{
    *pHasMoved = 0;
  }
  return SQLITE_OK;
}

*/
int sqlite3BtreeNext(BtCursor *pCur, int *pRes){
  int rc;
  int idx;
  MemPage *pPage;

  assert( cursorHoldsMutex(pCur) );
  assert( pRes!=0 );
  assert( pCur->skipNext==0 || pCur->eState!=CURSOR_VALID );
  if( pCur->eState!=CURSOR_VALID ){
    rc = restoreCursorPosition(pCur);
    if( rc!=SQLITE_OK ){
      *pRes = 0;
      return rc;
    }

    if( CURSOR_INVALID==pCur->eState ){
      *pRes = 1;
      return SQLITE_OK;
    }
    if( pCur->skipNext ){
      assert( pCur->eState==CURSOR_VALID || pCur->eState==CURSOR_SKIPNEXT );
      pCur->eState = CURSOR_VALID;
      if( pCur->skipNext>0 ){
        pCur->skipNext = 0;
        *pRes = 0;
        return SQLITE_OK;
      }
      pCur->skipNext = 0;
    }
  }

  pPage = pCur->apPage[pCur->iPage];
  idx = ++pCur->aiIdx[pCur->iPage];
  assert( pPage->isInit );

  /* If the database file is corrupt, it is possible for the value of idx 
  ** to be invalid here. This can only occur if a second cursor modifies
  ** the page while cursor pCur is holding a reference to it. Which can
  ** only happen if the database is corrupt in such a way as to link the
  ** page into more than one b-tree structure. */
  testcase( idx>pPage->nCell );

  pCur->info.nSize = 0;
  pCur->validNKey = 0;
  if( idx>=pPage->nCell ){
    if( !pPage->leaf ){
      rc = moveToChild(pCur, get4byte(&pPage->aData[pPage->hdrOffset+8]));
      if( rc ){
        *pRes = 0;
        return rc;
      }
      rc = moveToLeftmost(pCur);
      *pRes = 0;
      return rc;
    }
    do{
      if( pCur->iPage==0 ){
        *pRes = 1;

** this routine was called, then set *pRes=1.
*/
int sqlite3BtreePrevious(BtCursor *pCur, int *pRes){
  int rc;
  MemPage *pPage;

  assert( cursorHoldsMutex(pCur) );
  assert( pRes!=0 );
  assert( pCur->skipNext==0 || pCur->eState!=CURSOR_VALID );
  pCur->atLast = 0;
  if( pCur->eState!=CURSOR_VALID ){
    if( ALWAYS(pCur->eState>=CURSOR_REQUIRESEEK) ){
      rc = btreeRestoreCursorPosition(pCur);
      if( rc!=SQLITE_OK ){
        *pRes = 0;
        return rc;
      }

    }
    if( CURSOR_INVALID==pCur->eState ){
      *pRes = 1;
      return SQLITE_OK;
    }
    if( pCur->skipNext ){
      assert( pCur->eState==CURSOR_VALID || pCur->eState==CURSOR_SKIPNEXT );
      pCur->eState = CURSOR_VALID;
      if( pCur->skipNext<0 ){
        pCur->skipNext = 0;
        *pRes = 0;
        return SQLITE_OK;
      }
      pCur->skipNext = 0;
    }
  }

  pPage = pCur->apPage[pCur->iPage];
  assert( pPage->isInit );
  if( !pPage->leaf ){
    int idx = pCur->aiIdx[pCur->iPage];
    rc = moveToChild(pCur, get4byte(findCell(pPage, idx)));
    if( rc ){
      *pRes = 0;
      return rc;
    }
    rc = moveToRightmost(pCur);
  }else{
    while( pCur->aiIdx[pCur->iPage]==0 ){
      if( pCur->iPage==0 ){
        pCur->eState = CURSOR_INVALID;

  u16 aiIdx[BTCURSOR_MAX_DEPTH];        /* Current index in apPage[i] */
  MemPage *apPage[BTCURSOR_MAX_DEPTH];  /* Pages from root to current page */
};

/*
** Potential values for BtCursor.eState.
**



** CURSOR_INVALID:
**   Cursor does not point to a valid entry. This can happen (for example) 
**   because the table is empty or because BtreeCursorFirst() has not been
**   called.
**
** CURSOR_VALID:
**   Cursor points to a valid entry. getPayload() etc. may be called.
**
** CURSOR_SKIPNEXT:
**   Cursor is valid except that the Cursor.skipNext field is non-zero
**   indicating that the next sqlite3BtreeNext() or sqlite3BtreePrevious()
**   operation should be a no-op.
**
** CURSOR_REQUIRESEEK:
**   The table that this cursor was opened on still exists, but has been 
**   modified since the cursor was last used. The cursor position is saved
**   in variables BtCursor.pKey and BtCursor.nKey. When a cursor is in 
**   this state, restoreCursorPosition() can be called to attempt to
**   seek the cursor to the saved position.
**
** CURSOR_FAULT:
**   A unrecoverable error (an I/O error or a malloc failure) has occurred
**   on a different connection that shares the BtShared cache with this
**   cursor.  The error has left the cache in an inconsistent state.
**   Do nothing else with this cursor.  Any attempt to use the cursor
**   should return the error code stored in BtCursor.skip
*/
#define CURSOR_INVALID           0
#define CURSOR_VALID             1
#define CURSOR_SKIPNEXT          2
#define CURSOR_REQUIRESEEK       3
#define CURSOR_FAULT             4

/* 
** The database page the PENDING_BYTE occupies. This page is never used.
*/
# define PENDING_BYTE_PAGE(pBt) PAGER_MJ_PGNO(pBt)

/*

    case TK_UPLUS: {
      rc = sqlite3ExprIsInteger(p->pLeft, pValue);
      break;
    }
    case TK_UMINUS: {
      int v;
      if( sqlite3ExprIsInteger(p->pLeft, &v) ){
        assert( v!=-2147483648 );
        *pValue = -v;
        rc = 1;
      }
      break;
    }
    default: break;
  }

  )){
    goto fetch_out;
  }

  if( pCache->nPage>=pCache->nHash && pcache1ResizeHash(pCache) ){
    goto fetch_out;
  }
  assert( pCache->nHash>0 && pCache->apHash );

  /* Step 4. Try to recycle a page. */
  if( pCache->bPurgeable && pGroup->pLruTail && (
         (pCache->nPage+1>=pCache->nMax)
      || pGroup->nCurrentPage>=pGroup->nMaxPage
      || pcache1UnderMemoryPressure(pCache)
  )){

      /* Need to check for batch mode here to so we can avoid printing
      ** informational messages (like from process_sqliterc) before 
      ** we do the actual processing of arguments later in a second pass.
      */
      stdin_is_interactive = 0;
    }else if( strcmp(z,"-heap")==0 ){
#if defined(SQLITE_ENABLE_MEMSYS3) || defined(SQLITE_ENABLE_MEMSYS5)

      const char *zSize;
      sqlite3_int64 szHeap;

      zSize = cmdline_option_value(argc, argv, ++i);
      szHeap = integerValue(zSize);
      if( szHeap>0x7fff0000 ) szHeap = 0x7fff0000;
      sqlite3_config(SQLITE_CONFIG_HEAP, malloc((int)szHeap), (int)szHeap, 64);

  p->pResultSet = 0;
  db->busyHandler.nBusy = 0;
  CHECK_FOR_INTERRUPT;
  sqlite3VdbeIOTraceSql(p);
#ifndef SQLITE_OMIT_PROGRESS_CALLBACK
  if( db->xProgress ){
    assert( 0 < db->nProgressOps );
    nProgressLimit = (unsigned)p->aCounter[SQLITE_STMTSTATUS_VM_STEP];
    if( nProgressLimit==0 ){
      nProgressLimit = db->nProgressOps;
    }else{
      nProgressLimit %= (unsigned)db->nProgressOps;
    }
  }
#endif

  /* The output cell may already have a buffer allocated. Move
  ** the pointer to ctx.s so in case the user-function can use
  ** the already allocated buffer instead of allocating a new one.
  */
  sqlite3VdbeMemMove(&ctx.s, pOut);
  MemSetTypeFlag(&ctx.s, MEM_Null);

  ctx.fErrorOrAux = 0;
  if( ctx.pFunc->flags & SQLITE_FUNC_NEEDCOLL ){
    assert( pOp>aOp );
    assert( pOp[-1].p4type==P4_COLLSEQ );
    assert( pOp[-1].opcode==OP_CollSeq );
    ctx.pColl = pOp[-1].p4.pColl;
  }
  db->lastRowid = lastRowid;
  (*ctx.pFunc->xFunc)(&ctx, n, apVal); /* IMP: R-24505-23230 */
  lastRowid = db->lastRowid;






  if( db->mallocFailed ){
    /* Even though a malloc() has failed, the implementation of the
    ** user function may have called an sqlite3_result_XXX() function
    ** to return a value. The following call releases any resources
    ** associated with such a value.
    */
    sqlite3VdbeMemRelease(&ctx.s);
    goto no_mem;
  }

  /* If the function returned an error, throw an exception */
  if( ctx.fErrorOrAux ){
    if( ctx.isError ){
      sqlite3SetString(&p->zErrMsg, db, "%s", sqlite3_value_text(&ctx.s));
      rc = ctx.isError;
    }
    sqlite3VdbeDeleteAuxData(p, pc, pOp->p1);
  }

  /* Copy the result of the function into register P3 */
  sqlite3VdbeChangeEncoding(&ctx.s, encoding);
  sqlite3VdbeMemMove(pOut, &ctx.s);
  if( sqlite3VdbeMemTooBig(pOut) ){
    goto too_big;

        res = 1;  /* Results are not equal */
      }
    }else{
      /* SQLITE_NULLEQ is clear and at least one operand is NULL,
      ** then the result is always NULL.
      ** The jump is taken if the SQLITE_JUMPIFNULL bit is set.
      */
      if( pOp->p5 & SQLITE_JUMPIFNULL ){
        pc = pOp->p2-1;
      }else if( pOp->p5 & SQLITE_STOREP2 ){
        pOut = &aMem[pOp->p2];
        MemSetTypeFlag(pOut, MEM_Null);
        REGISTER_TRACE(pOp->p2, pOut);


      }
      break;
    }
  }else{
    /* Neither operand is NULL.  Do a comparison. */
    affinity = pOp->p5 & SQLITE_AFF_MASK;
    if( affinity ){

*/
case OP_SorterSort:    /* jump */
case OP_Sort: {        /* jump */
#ifdef SQLITE_TEST
  sqlite3_sort_count++;
  sqlite3_search_count--;
#endif
  p->aCounter[SQLITE_STMTSTATUS_SORT]++;
  /* Fall through into OP_Rewind */
}
/* Opcode: Rewind P1 P2 * * *
**
** The next use of the Rowid or Column or Next instruction for P1 
** will refer to the first entry in the database table or index.
** If the table or index is empty and P2>0, then jump immediately to P2.

case OP_SorterNext:    /* jump */
case OP_Prev:          /* jump */
case OP_Next: {        /* jump */
  VdbeCursor *pC;
  int res;

  assert( pOp->p1>=0 && pOp->p1<p->nCursor );
  assert( pOp->p5<ArraySize(p->aCounter) );
  pC = p->apCsr[pOp->p1];
  if( pC==0 ){
    break;  /* See ticket #2273 */
  }
  assert( pC->isSorter==(pOp->opcode==OP_SorterNext) );
  if( isSorter(pC) ){
    assert( pOp->opcode==OP_SorterNext );
    rc = sqlite3VdbeSorterNext(db, pC, &res);
  }else{
    /* res = 1; // Always initialized by the xAdvance() call */
    assert( pC->deferredMoveto==0 );
    assert( pC->pCursor );
    assert( pOp->opcode!=OP_Next || pOp->p4.xAdvance==sqlite3BtreeNext );
    assert( pOp->opcode!=OP_Prev || pOp->p4.xAdvance==sqlite3BtreePrevious );
    rc = pOp->p4.xAdvance(pC->pCursor, &res);
  }
  pC->nullRow = (u8)res;
  pC->cacheStatus = CACHE_STALE;
  if( res==0 ){
    pc = pOp->p2 - 1;
    p->aCounter[pOp->p5]++;
#ifdef SQLITE_TEST
    sqlite3_search_count++;
#endif
  }
  pC->rowidIsValid = 0;
  goto check_for_interrupt;
}

  /* This is the only way out of this procedure.  We have to
  ** release the mutexes on btrees that were acquired at the
  ** top. */
vdbe_return:
  db->lastRowid = lastRowid;
  testcase( nVmStep>0 );
  p->aCounter[SQLITE_STMTSTATUS_VM_STEP] += (int)nVmStep;
  sqlite3VdbeLeave(p);
  return rc;

  /* Jump to here if a string or blob larger than SQLITE_MAX_LENGTH
  ** is encountered.
  */
too_big:

** (Mem) which are only defined there.
*/
struct sqlite3_context {
  FuncDef *pFunc;       /* Pointer to function information.  MUST BE FIRST */
  Mem s;                /* The return value is stored here */
  Mem *pMem;            /* Memory cell used to store aggregate context */
  CollSeq *pColl;       /* Collating sequence */
  Vdbe *pVdbe;          /* The VM that owns this context */
  int iOp;              /* Instruction number of OP_Function */
  int isError;          /* Error code returned by the function. */
  u8 skipFlag;          /* Skip skip accumulator loading if true */
  u8 fErrorOrAux;       /* isError!=0 or pVdbe->pAuxData modified */

};

/*
** An Explain object accumulates indented output which is helpful
** in describing recursive data structures.
*/
struct Explain {

  bft bIsReader:1;        /* True for statements that read */
  bft isPrepareV2:1;      /* True if prepared with prepare_v2() */
  bft doingRerun:1;       /* True if rerunning after an auto-reprepare */
  int nChange;            /* Number of db changes made since last reset */
  yDbMask btreeMask;      /* Bitmask of db->aDb[] entries referenced */
  yDbMask lockMask;       /* Subset of btreeMask that requires a lock */
  int iStatement;         /* Statement number (or 0 if has not opened stmt) */
  u32 aCounter[5];        /* Counters used by sqlite3_stmt_status() */
#ifndef SQLITE_OMIT_TRACE
  i64 startTime;          /* Time when query started - used for profiling */
#endif
  i64 nFkConstraint;      /* Number of imm. FK constraints this VM */
  i64 nStmtDefCons;       /* Number of def. constraints when stmt started */
  i64 nStmtDefImmCons;    /* Number of def. imm constraints when stmt started */
  char *zSql;             /* Text of the SQL statement that generated this */

void sqlite3_result_double(sqlite3_context *pCtx, double rVal){
  assert( sqlite3_mutex_held(pCtx->s.db->mutex) );
  sqlite3VdbeMemSetDouble(&pCtx->s, rVal);
}
void sqlite3_result_error(sqlite3_context *pCtx, const char *z, int n){
  assert( sqlite3_mutex_held(pCtx->s.db->mutex) );
  pCtx->isError = SQLITE_ERROR;
  pCtx->fErrorOrAux = 1;
  sqlite3VdbeMemSetStr(&pCtx->s, z, n, SQLITE_UTF8, SQLITE_TRANSIENT);
}
#ifndef SQLITE_OMIT_UTF16
void sqlite3_result_error16(sqlite3_context *pCtx, const void *z, int n){
  assert( sqlite3_mutex_held(pCtx->s.db->mutex) );
  pCtx->isError = SQLITE_ERROR;
  pCtx->fErrorOrAux = 1;
  sqlite3VdbeMemSetStr(&pCtx->s, z, n, SQLITE_UTF16NATIVE, SQLITE_TRANSIENT);
}
#endif
void sqlite3_result_int(sqlite3_context *pCtx, int iVal){
  assert( sqlite3_mutex_held(pCtx->s.db->mutex) );
  sqlite3VdbeMemSetInt64(&pCtx->s, (i64)iVal);
}

}
void sqlite3_result_zeroblob(sqlite3_context *pCtx, int n){
  assert( sqlite3_mutex_held(pCtx->s.db->mutex) );
  sqlite3VdbeMemSetZeroBlob(&pCtx->s, n);
}
void sqlite3_result_error_code(sqlite3_context *pCtx, int errCode){
  pCtx->isError = errCode;
  pCtx->fErrorOrAux = 1;
  if( pCtx->s.flags & MEM_Null ){
    sqlite3VdbeMemSetStr(&pCtx->s, sqlite3ErrStr(errCode), -1, 
                         SQLITE_UTF8, SQLITE_STATIC);
  }
}

/* Force an SQLITE_TOOBIG error. */
void sqlite3_result_error_toobig(sqlite3_context *pCtx){
  assert( sqlite3_mutex_held(pCtx->s.db->mutex) );
  pCtx->isError = SQLITE_TOOBIG;
  pCtx->fErrorOrAux = 1;
  sqlite3VdbeMemSetStr(&pCtx->s, "string or blob too big", -1, 
                       SQLITE_UTF8, SQLITE_STATIC);
}

/* An SQLITE_NOMEM error. */
void sqlite3_result_error_nomem(sqlite3_context *pCtx){
  assert( sqlite3_mutex_held(pCtx->s.db->mutex) );
  sqlite3VdbeMemSetNull(&pCtx->s);
  pCtx->isError = SQLITE_NOMEM;
  pCtx->fErrorOrAux = 1;
  pCtx->s.db->mallocFailed = 1;
}

/*
** This function is called after a transaction has been committed. It 
** invokes callbacks registered with sqlite3_wal_hook() as required.
*/

  if( pAuxData==0 ){
    pAuxData = sqlite3DbMallocZero(pVdbe->db, sizeof(AuxData));
    if( !pAuxData ) goto failed;
    pAuxData->iOp = pCtx->iOp;
    pAuxData->iArg = iArg;
    pAuxData->pNext = pVdbe->pAuxData;
    pVdbe->pAuxData = pAuxData;
    if( pCtx->fErrorOrAux==0 ){
      pCtx->isError = 0;
      pCtx->fErrorOrAux = 1;
    }
  }else if( pAuxData->xDelete ){
    pAuxData->xDelete(pAuxData->pAux);
  }

  pAuxData->pAux = pAux;
  pAuxData->xDelete = xDelete;
  return;

}

/*
** Return the value of a status counter for a prepared statement
*/
int sqlite3_stmt_status(sqlite3_stmt *pStmt, int op, int resetFlag){
  Vdbe *pVdbe = (Vdbe*)pStmt;
  u32 v = pVdbe->aCounter[op];
  if( resetFlag ) pVdbe->aCounter[op] = 0;
  return (int)v;
}

#ifdef SQLITE_ENABLE_PREUPDATE_HOOK
/*
** Allocate and populate an UnpackedRecord structure based on the serialized
** record in nKey/pKey. Return a pointer to the new UnpackedRecord structure
** if successful, or a NULL pointer if an OOM error is encountered.

  saved_nOut = pNew->nOut;
  pNew->rSetup = 0;
  rLogSize = estLog(whereCost(pProbe->aiRowEst[0]));
  for(; rc==SQLITE_OK && pTerm!=0; pTerm = whereScanNext(&scan)){
    int nIn = 0;
    if( pTerm->prereqRight & pNew->maskSelf ) continue;
#ifdef SQLITE_ENABLE_STAT3
    if( (pTerm->wtFlags & TERM_VNULL)!=0
     && (iCol<0 || pSrc->pTab->aCol[iCol].notNull)
    ){
      continue; /* skip IS NOT NULL constraints on a NOT NULL column */
    }
#endif
    pNew->wsFlags = saved_wsFlags;
    pNew->u.btree.nEq = saved_nEq;
    pNew->nLTerm = saved_nLTerm;
    if( whereLoopResize(db, pNew, pNew->nLTerm+1) ) break; /* OOM */

** the table is used by an index.  Only the first 63 columns are considered.
*/
static Bitmask columnsInIndex(Index *pIdx){
  Bitmask m = 0;
  int j;
  for(j=pIdx->nColumn-1; j>=0; j--){
    int x = pIdx->aiColumn[j];
    assert( x>=0 );
    testcase( x==BMS-1 );
    testcase( x==BMS-2 );
    if( x<BMS-1 ) m |= MASKBIT(x);
  }
  return m;
}

}
do_execsql_test 8.3 {
  INSERT INTO t12 VALUES('a d d a');
  SELECT mit(matchinfo(t12, 'x')) FROM t12 WHERE t12 MATCH 'a NEAR/1 d OR a';
} {
  {0 3 2 0 3 2 1 4 3} {1 3 2 1 3 2 1 4 3} {2 3 2 2 3 2 2 4 3}
}

do_execsql_test 9.1 {
  CREATE VIRTUAL TABLE ft2 USING fts4;
  INSERT INTO ft2 VALUES('a b c d e');
  INSERT INTO ft2 VALUES('f a b c d');
  SELECT snippet(ft2, '[', ']', '', -1, 1) FROM ft2 WHERE ft2 MATCH 'c';
} {{[c]} {[c]}}

finish_test

  COMMIT;
  ATTACH 'test2.db' AS aux1;
  CREATE TABLE aux1.t2(a INTEGER PRIMARY KEY, b, c, d);
  INSERT INTO t2 SELECT * FROM t1;
  DETACH aux1;
  PRAGMA cache_spill=ON;
} {}
sqlite3_release_memory
do_test pragma2-4.4 {
  db eval {
    BEGIN;
    UPDATE t1 SET c=c+1;
    PRAGMA lock_status;
  }
} {main exclusive temp unknown}  ;# EXCLUSIVE lock due to cache spill

  PRAGMA aux1.cache_size=50;
  BEGIN;
  UPDATE t2 SET c=c+1;
  PRAGMA lock_status;
} {main unlocked temp unknown aux1 reserved}
do_execsql_test pragma2-4.7 {
  COMMIT;
}
sqlite3_release_memory
do_execsql_test pragma2-4.8 {
  PRAGMA cache_spill=ON; -- Applies to all databases
  BEGIN;
  UPDATE t2 SET c=c-1;
  PRAGMA lock_status;
} {main unlocked temp unknown aux1 exclusive}
   

finish_test