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Artifact 667faaf14a69a5683ac383acdc8d942cf32c3f93:


/*
** 2014 May 31
**
** The author disclaims copyright to this source code.  In place of
** 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.
**
******************************************************************************
**
*/



#include "fts5Int.h"
#include "fts5parse.h"

/*
** All token types in the generated fts5parse.h file are greater than 0.
*/
#define FTS5_EOF 0

#define FTS5_LARGEST_INT64  (0xffffffff|(((i64)0x7fffffff)<<32))

typedef struct Fts5ExprTerm Fts5ExprTerm;

/*
** Functions generated by lemon from fts5parse.y.
*/
void *sqlite3Fts5ParserAlloc(void *(*mallocProc)(u64));
void sqlite3Fts5ParserFree(void*, void (*freeProc)(void*));
void sqlite3Fts5Parser(void*, int, Fts5Token, Fts5Parse*);

struct Fts5Expr {
  Fts5Index *pIndex;
  Fts5ExprNode *pRoot;
  int bDesc;                      /* Iterate in descending rowid order */
  int nPhrase;                    /* Number of phrases in expression */
  Fts5ExprPhrase **apExprPhrase;  /* Pointers to phrase objects */
};

/*
** eType:
**   Expression node type. Always one of:
**
**       FTS5_AND                 (nChild, apChild valid)
**       FTS5_OR                  (nChild, apChild valid)
**       FTS5_NOT                 (nChild, apChild valid)
**       FTS5_STRING              (pNear valid)
**       FTS5_TERM                (pNear valid)
*/
struct Fts5ExprNode {
  int eType;                      /* Node type */
  int bEof;                       /* True at EOF */
  int bNomatch;                   /* True if entry is not a match */

  i64 iRowid;                     /* Current rowid */
  Fts5ExprNearset *pNear;         /* For FTS5_STRING - cluster of phrases */

  /* Child nodes. For a NOT node, this array always contains 2 entries. For 
  ** AND or OR nodes, it contains 2 or more entries.  */
  int nChild;                     /* Number of child nodes */
  Fts5ExprNode *apChild[1];       /* Array of child nodes */
};

#define Fts5NodeIsString(p) ((p)->eType==FTS5_TERM || (p)->eType==FTS5_STRING)

/*
** An instance of the following structure represents a single search term
** or term prefix.
*/
struct Fts5ExprTerm {
  int bPrefix;                    /* True for a prefix term */
  char *zTerm;                    /* nul-terminated term */
  Fts5IndexIter *pIter;           /* Iterator for this term */
  Fts5ExprTerm *pSynonym;         /* Pointer to first in list of synonyms */
};

/*
** A phrase. One or more terms that must appear in a contiguous sequence
** within a document for it to match.
*/
struct Fts5ExprPhrase {
  Fts5ExprNode *pNode;            /* FTS5_STRING node this phrase is part of */
  Fts5Buffer poslist;             /* Current position list */
  int nTerm;                      /* Number of entries in aTerm[] */
  Fts5ExprTerm aTerm[1];          /* Terms that make up this phrase */
};

/*
** If a NEAR() clump may only match a specific set of columns, then
** Fts5ExprNearset.pColset points to an object of the following type.
** Each entry in the aiCol[] array
*/
struct Fts5ExprColset {
  int nCol;
  int aiCol[1];
};

/*
** One or more phrases that must appear within a certain token distance of
** each other within each matching document.
*/
struct Fts5ExprNearset {
  int nNear;                      /* NEAR parameter */
  Fts5ExprColset *pColset;        /* Columns to search (NULL -> all columns) */
  int nPhrase;                    /* Number of entries in aPhrase[] array */
  Fts5ExprPhrase *apPhrase[1];    /* Array of phrase pointers */
};


/*
** Parse context.
*/
struct Fts5Parse {
  Fts5Config *pConfig;
  char *zErr;
  int rc;
  int nPhrase;                    /* Size of apPhrase array */
  Fts5ExprPhrase **apPhrase;      /* Array of all phrases */
  Fts5ExprNode *pExpr;            /* Result of a successful parse */
};

void sqlite3Fts5ParseError(Fts5Parse *pParse, const char *zFmt, ...){
  va_list ap;
  va_start(ap, zFmt);
  if( pParse->rc==SQLITE_OK ){
    pParse->zErr = sqlite3_vmprintf(zFmt, ap);
    pParse->rc = SQLITE_ERROR;
  }
  va_end(ap);
}

static int fts5ExprIsspace(char t){
  return t==' ' || t=='\t' || t=='\n' || t=='\r';
}

/*
** Read the first token from the nul-terminated string at *pz.
*/
static int fts5ExprGetToken(
  Fts5Parse *pParse, 
  const char **pz,                /* IN/OUT: Pointer into buffer */
  Fts5Token *pToken
){
  const char *z = *pz;
  int tok;

  /* Skip past any whitespace */
  while( fts5ExprIsspace(*z) ) z++;

  pToken->p = z;
  pToken->n = 1;
  switch( *z ){
    case '(':  tok = FTS5_LP;    break;
    case ')':  tok = FTS5_RP;    break;
    case '{':  tok = FTS5_LCP;   break;
    case '}':  tok = FTS5_RCP;   break;
    case ':':  tok = FTS5_COLON; break;
    case ',':  tok = FTS5_COMMA; break;
    case '+':  tok = FTS5_PLUS;  break;
    case '*':  tok = FTS5_STAR;  break;
    case '\0': tok = FTS5_EOF;   break;

    case '"': {
      const char *z2;
      tok = FTS5_STRING;

      for(z2=&z[1]; 1; z2++){
        if( z2[0]=='"' ){
          z2++;
          if( z2[0]!='"' ) break;
        }
        if( z2[0]=='\0' ){
          sqlite3Fts5ParseError(pParse, "unterminated string");
          return FTS5_EOF;
        }
      }
      pToken->n = (z2 - z);
      break;
    }

    default: {
      const char *z2;
      if( sqlite3Fts5IsBareword(z[0])==0 ){
        sqlite3Fts5ParseError(pParse, "fts5: syntax error near \"%.1s\"", z);
        return FTS5_EOF;
      }
      tok = FTS5_STRING;
      for(z2=&z[1]; sqlite3Fts5IsBareword(*z2); z2++);
      pToken->n = (z2 - z);
      if( pToken->n==2 && memcmp(pToken->p, "OR", 2)==0 )  tok = FTS5_OR;
      if( pToken->n==3 && memcmp(pToken->p, "NOT", 3)==0 ) tok = FTS5_NOT;
      if( pToken->n==3 && memcmp(pToken->p, "AND", 3)==0 ) tok = FTS5_AND;
      break;
    }
  }

  *pz = &pToken->p[pToken->n];
  return tok;
}

static void *fts5ParseAlloc(u64 t){ return sqlite3_malloc((int)t); }
static void fts5ParseFree(void *p){ sqlite3_free(p); }

int sqlite3Fts5ExprNew(
  Fts5Config *pConfig,            /* FTS5 Configuration */
  const char *zExpr,              /* Expression text */
  Fts5Expr **ppNew, 
  char **pzErr
){
  Fts5Parse sParse;
  Fts5Token token;
  const char *z = zExpr;
  int t;                          /* Next token type */
  void *pEngine;
  Fts5Expr *pNew;

  *ppNew = 0;
  *pzErr = 0;
  memset(&sParse, 0, sizeof(sParse));
  pEngine = sqlite3Fts5ParserAlloc(fts5ParseAlloc);
  if( pEngine==0 ){ return SQLITE_NOMEM; }
  sParse.pConfig = pConfig;

  do {
    t = fts5ExprGetToken(&sParse, &z, &token);
    sqlite3Fts5Parser(pEngine, t, token, &sParse);
  }while( sParse.rc==SQLITE_OK && t!=FTS5_EOF );
  sqlite3Fts5ParserFree(pEngine, fts5ParseFree);

  assert( sParse.rc!=SQLITE_OK || sParse.zErr==0 );
  if( sParse.rc==SQLITE_OK ){
    *ppNew = pNew = sqlite3_malloc(sizeof(Fts5Expr));
    if( pNew==0 ){
      sParse.rc = SQLITE_NOMEM;
      sqlite3Fts5ParseNodeFree(sParse.pExpr);
    }else{
      pNew->pRoot = sParse.pExpr;
      pNew->pIndex = 0;
      pNew->apExprPhrase = sParse.apPhrase;
      pNew->nPhrase = sParse.nPhrase;
      sParse.apPhrase = 0;
    }
  }

  sqlite3_free(sParse.apPhrase);
  *pzErr = sParse.zErr;
  return sParse.rc;
}

/*
** Free the expression node object passed as the only argument.
*/
void sqlite3Fts5ParseNodeFree(Fts5ExprNode *p){
  if( p ){
    int i;
    for(i=0; i<p->nChild; i++){
      sqlite3Fts5ParseNodeFree(p->apChild[i]);
    }
    sqlite3Fts5ParseNearsetFree(p->pNear);
    sqlite3_free(p);
  }
}

/*
** Free the expression object passed as the only argument.
*/
void sqlite3Fts5ExprFree(Fts5Expr *p){
  if( p ){
    sqlite3Fts5ParseNodeFree(p->pRoot);
    sqlite3_free(p->apExprPhrase);
    sqlite3_free(p);
  }
}

static int fts5ExprColsetTest(Fts5ExprColset *pColset, int iCol){
  int i;
  for(i=0; i<pColset->nCol; i++){
    if( pColset->aiCol[i]==iCol ) return 1;
  }
  return 0;
}

/*
** Argument pTerm must be a synonym iterator. Return the current rowid
** that it points to.
*/
static i64 fts5ExprSynonymRowid(Fts5ExprTerm *pTerm, int bDesc, int *pbEof){
  i64 iRet = 0;
  int bRetValid = 0;
  Fts5ExprTerm *p;

  assert( pTerm->pSynonym );
  assert( bDesc==0 || bDesc==1 );
  for(p=pTerm; p; p=p->pSynonym){
    if( 0==sqlite3Fts5IterEof(p->pIter) ){
      i64 iRowid = sqlite3Fts5IterRowid(p->pIter);
      if( bRetValid==0 || (bDesc!=(iRowid<iRet)) ){
        iRet = iRowid;
        bRetValid = 1;
      }
    }
  }

  if( pbEof && bRetValid==0 ) *pbEof = 1;
  return iRet;
}

/*
** Argument pTerm must be a synonym iterator.
*/
static int fts5ExprSynonymPoslist(
  Fts5ExprTerm *pTerm, 
  i64 iRowid,
  int *pbDel,                     /* OUT: Caller should sqlite3_free(*pa) */
  u8 **pa, int *pn
){
  Fts5PoslistReader aStatic[4];
  Fts5PoslistReader *aIter = aStatic;
  int nIter = 0;
  int nAlloc = 4;
  int rc = SQLITE_OK;
  Fts5ExprTerm *p;

  assert( pTerm->pSynonym );
  for(p=pTerm; p; p=p->pSynonym){
    Fts5IndexIter *pIter = p->pIter;
    if( sqlite3Fts5IterEof(pIter)==0 && sqlite3Fts5IterRowid(pIter)==iRowid ){
      const u8 *a;
      int n;
      i64 dummy;
      rc = sqlite3Fts5IterPoslist(pIter, &a, &n, &dummy);
      if( rc!=SQLITE_OK ) goto synonym_poslist_out;
      if( nIter==nAlloc ){
        int nByte = sizeof(Fts5PoslistReader) * nAlloc * 2;
        Fts5PoslistReader *aNew = (Fts5PoslistReader*)sqlite3_malloc(nByte);
        if( aNew==0 ){
          rc = SQLITE_NOMEM;
          goto synonym_poslist_out;
        }
        memcpy(aNew, aIter, sizeof(Fts5PoslistReader) * nIter);
        nAlloc = nAlloc*2;
        if( aIter!=aStatic ) sqlite3_free(aIter);
        aIter = aNew;
      }
      sqlite3Fts5PoslistReaderInit(-1, a, n, &aIter[nIter]);
      assert( aIter[nIter].bEof==0 );
      nIter++;
    }
  }

  assert( *pbDel==0 );
  if( nIter==1 ){
    *pa = (u8*)aIter[0].a;
    *pn = aIter[0].n;
  }else{
    Fts5PoslistWriter writer = {0};
    Fts5Buffer buf = {0,0,0};
    i64 iPrev = -1;
    while( 1 ){
      int i;
      i64 iMin = FTS5_LARGEST_INT64;
      for(i=0; i<nIter; i++){
        if( aIter[i].bEof==0 ){
          if( aIter[i].iPos==iPrev ){
            if( sqlite3Fts5PoslistReaderNext(&aIter[i]) ) continue;
          }
          if( aIter[i].iPos<iMin ){
            iMin = aIter[i].iPos;
          }
        }
      }
      if( iMin==FTS5_LARGEST_INT64 || rc!=SQLITE_OK ) break;
      rc = sqlite3Fts5PoslistWriterAppend(&buf, &writer, iMin);
      iPrev = iMin;
    }
    if( rc ){
      sqlite3_free(buf.p);
    }else{
      *pa = buf.p;
      *pn = buf.n;
      *pbDel = 1;
    }
  }

 synonym_poslist_out:
  if( aIter!=aStatic ) sqlite3_free(aIter);
  return rc;
}


/*
** All individual term iterators in pPhrase are guaranteed to be valid and
** pointing to the same rowid when this function is called. This function 
** checks if the current rowid really is a match, and if so populates
** the pPhrase->poslist buffer accordingly. Output parameter *pbMatch
** is set to true if this is really a match, or false otherwise.
**
** SQLITE_OK is returned if an error occurs, or an SQLite error code 
** otherwise. It is not considered an error code if the current rowid is 
** not a match.
*/
static int fts5ExprPhraseIsMatch(
  Fts5ExprNode *pNode,            /* Node pPhrase belongs to */
  Fts5ExprColset *pColset,        /* Restrict matches to these columns */
  Fts5ExprPhrase *pPhrase,        /* Phrase object to initialize */
  int *pbMatch                    /* OUT: Set to true if really a match */
){
  Fts5PoslistWriter writer = {0};
  Fts5PoslistReader aStatic[4];
  Fts5PoslistReader *aIter = aStatic;
  int i;
  int rc = SQLITE_OK;
  int iCol = -1;
  
  if( pColset && pColset->nCol==1 ){
    iCol = pColset->aiCol[0];
    pColset = 0;
  }

  fts5BufferZero(&pPhrase->poslist);

  /* If the aStatic[] array is not large enough, allocate a large array
  ** using sqlite3_malloc(). This approach could be improved upon. */
  if( pPhrase->nTerm>(sizeof(aStatic) / sizeof(aStatic[0])) ){
    int nByte = sizeof(Fts5PoslistReader) * pPhrase->nTerm;
    aIter = (Fts5PoslistReader*)sqlite3_malloc(nByte);
    if( !aIter ) return SQLITE_NOMEM;
  }
  memset(aIter, 0, sizeof(Fts5PoslistReader) * pPhrase->nTerm);

  /* Initialize a term iterator for each term in the phrase */
  for(i=0; i<pPhrase->nTerm; i++){
    Fts5ExprTerm *pTerm = &pPhrase->aTerm[i];
    i64 dummy;
    int n = 0;
    int bFlag = 0;
    const u8 *a = 0;
    if( pTerm->pSynonym ){
      rc = fts5ExprSynonymPoslist(pTerm, pNode->iRowid, &bFlag, (u8**)&a, &n);
    }else{
      rc = sqlite3Fts5IterPoslist(pTerm->pIter, &a, &n, &dummy);
    }
    if( rc!=SQLITE_OK ) goto ismatch_out;
    sqlite3Fts5PoslistReaderInit(iCol, a, n, &aIter[i]);
    aIter[i].bFlag = bFlag;
    if( aIter[i].bEof ) goto ismatch_out;
  }

  while( 1 ){
    int bMatch;
    i64 iPos = aIter[0].iPos;
    do {
      bMatch = 1;
      for(i=0; i<pPhrase->nTerm; i++){
        Fts5PoslistReader *pPos = &aIter[i];
        i64 iAdj = iPos + i;
        if( pPos->iPos!=iAdj ){
          bMatch = 0;
          while( pPos->iPos<iAdj ){
            if( sqlite3Fts5PoslistReaderNext(pPos) ) goto ismatch_out;
          }
          if( pPos->iPos>iAdj ) iPos = pPos->iPos-i;
        }
      }
    }while( bMatch==0 );

    if( pColset==0 || fts5ExprColsetTest(pColset, FTS5_POS2COLUMN(iPos)) ){
      /* Append position iPos to the output */
      rc = sqlite3Fts5PoslistWriterAppend(&pPhrase->poslist, &writer, iPos);
      if( rc!=SQLITE_OK ) goto ismatch_out;
    }

    for(i=0; i<pPhrase->nTerm; i++){
      if( sqlite3Fts5PoslistReaderNext(&aIter[i]) ) goto ismatch_out;
    }
  }

 ismatch_out:
  *pbMatch = (pPhrase->poslist.n>0);
  for(i=0; i<pPhrase->nTerm; i++){
    if( aIter[i].bFlag ) sqlite3_free((u8*)aIter[i].a);
  }
  if( aIter!=aStatic ) sqlite3_free(aIter);
  return rc;
}

typedef struct Fts5LookaheadReader Fts5LookaheadReader;
struct Fts5LookaheadReader {
  const u8 *a;                    /* Buffer containing position list */
  int n;                          /* Size of buffer a[] in bytes */
  int i;                          /* Current offset in position list */
  i64 iPos;                       /* Current position */
  i64 iLookahead;                 /* Next position */
};

#define FTS5_LOOKAHEAD_EOF (((i64)1) << 62)

static int fts5LookaheadReaderNext(Fts5LookaheadReader *p){
  p->iPos = p->iLookahead;
  if( sqlite3Fts5PoslistNext64(p->a, p->n, &p->i, &p->iLookahead) ){
    p->iLookahead = FTS5_LOOKAHEAD_EOF;
  }
  return (p->iPos==FTS5_LOOKAHEAD_EOF);
}

static int fts5LookaheadReaderInit(
  const u8 *a, int n,             /* Buffer to read position list from */
  Fts5LookaheadReader *p          /* Iterator object to initialize */
){
  memset(p, 0, sizeof(Fts5LookaheadReader));
  p->a = a;
  p->n = n;
  fts5LookaheadReaderNext(p);
  return fts5LookaheadReaderNext(p);
}

#if 0
static int fts5LookaheadReaderEof(Fts5LookaheadReader *p){
  return (p->iPos==FTS5_LOOKAHEAD_EOF);
}
#endif

typedef struct Fts5NearTrimmer Fts5NearTrimmer;
struct Fts5NearTrimmer {
  Fts5LookaheadReader reader;     /* Input iterator */
  Fts5PoslistWriter writer;       /* Writer context */
  Fts5Buffer *pOut;               /* Output poslist */
};

/*
** The near-set object passed as the first argument contains more than
** one phrase. All phrases currently point to the same row. The
** Fts5ExprPhrase.poslist buffers are populated accordingly. This function
** tests if the current row contains instances of each phrase sufficiently
** close together to meet the NEAR constraint. Non-zero is returned if it
** does, or zero otherwise.
**
** If in/out parameter (*pRc) is set to other than SQLITE_OK when this
** function is called, it is a no-op. Or, if an error (e.g. SQLITE_NOMEM)
** occurs within this function (*pRc) is set accordingly before returning.
** The return value is undefined in both these cases.
** 
** If no error occurs and non-zero (a match) is returned, the position-list
** of each phrase object is edited to contain only those entries that
** meet the constraint before returning.
*/
static int fts5ExprNearIsMatch(int *pRc, Fts5ExprNearset *pNear){
  Fts5NearTrimmer aStatic[4];
  Fts5NearTrimmer *a = aStatic;
  Fts5ExprPhrase **apPhrase = pNear->apPhrase;

  int i;
  int rc = *pRc;
  int bMatch;

  assert( pNear->nPhrase>1 );

  /* If the aStatic[] array is not large enough, allocate a large array
  ** using sqlite3_malloc(). This approach could be improved upon. */
  if( pNear->nPhrase>(sizeof(aStatic) / sizeof(aStatic[0])) ){
    int nByte = sizeof(Fts5NearTrimmer) * pNear->nPhrase;
    a = (Fts5NearTrimmer*)sqlite3Fts5MallocZero(&rc, nByte);
  }else{
    memset(aStatic, 0, sizeof(aStatic));
  }
  if( rc!=SQLITE_OK ){
    *pRc = rc;
    return 0;
  }

  /* Initialize a lookahead iterator for each phrase. After passing the
  ** buffer and buffer size to the lookaside-reader init function, zero
  ** the phrase poslist buffer. The new poslist for the phrase (containing
  ** the same entries as the original with some entries removed on account 
  ** of the NEAR constraint) is written over the original even as it is
  ** being read. This is safe as the entries for the new poslist are a
  ** subset of the old, so it is not possible for data yet to be read to
  ** be overwritten.  */
  for(i=0; i<pNear->nPhrase; i++){
    Fts5Buffer *pPoslist = &apPhrase[i]->poslist;
    fts5LookaheadReaderInit(pPoslist->p, pPoslist->n, &a[i].reader);
    pPoslist->n = 0;
    a[i].pOut = pPoslist;
  }

  while( 1 ){
    int iAdv;
    i64 iMin;
    i64 iMax;

    /* This block advances the phrase iterators until they point to a set of
    ** entries that together comprise a match.  */
    iMax = a[0].reader.iPos;
    do {
      bMatch = 1;
      for(i=0; i<pNear->nPhrase; i++){
        Fts5LookaheadReader *pPos = &a[i].reader;
        iMin = iMax - pNear->apPhrase[i]->nTerm - pNear->nNear;
        if( pPos->iPos<iMin || pPos->iPos>iMax ){
          bMatch = 0;
          while( pPos->iPos<iMin ){
            if( fts5LookaheadReaderNext(pPos) ) goto ismatch_out;
          }
          if( pPos->iPos>iMax ) iMax = pPos->iPos;
        }
      }
    }while( bMatch==0 );

    /* Add an entry to each output position list */
    for(i=0; i<pNear->nPhrase; i++){
      i64 iPos = a[i].reader.iPos;
      Fts5PoslistWriter *pWriter = &a[i].writer;
      if( a[i].pOut->n==0 || iPos!=pWriter->iPrev ){
        sqlite3Fts5PoslistWriterAppend(a[i].pOut, pWriter, iPos);
      }
    }

    iAdv = 0;
    iMin = a[0].reader.iLookahead;
    for(i=0; i<pNear->nPhrase; i++){
      if( a[i].reader.iLookahead < iMin ){
        iMin = a[i].reader.iLookahead;
        iAdv = i;
      }
    }
    if( fts5LookaheadReaderNext(&a[iAdv].reader) ) goto ismatch_out;
  }

  ismatch_out: {
    int bRet = a[0].pOut->n>0;
    *pRc = rc;
    if( a!=aStatic ) sqlite3_free(a);
    return bRet;
  }
}

/*
** Advance the first term iterator in the first phrase of pNear. Set output
** variable *pbEof to true if it reaches EOF or if an error occurs.
**
** Return SQLITE_OK if successful, or an SQLite error code if an error
** occurs.
*/
static int fts5ExprNearAdvanceFirst(
  Fts5Expr *pExpr,                /* Expression pPhrase belongs to */
  Fts5ExprNode *pNode,            /* FTS5_STRING or FTS5_TERM node */
  int bFromValid,
  i64 iFrom 
){
  Fts5ExprTerm *pTerm = &pNode->pNear->apPhrase[0]->aTerm[0];
  int rc = SQLITE_OK;

  if( pTerm->pSynonym ){
    int bEof = 1;
    Fts5ExprTerm *p;

    /* Find the firstest rowid any synonym points to. */
    i64 iRowid = fts5ExprSynonymRowid(pTerm, pExpr->bDesc, 0);

    /* Advance each iterator that currently points to iRowid. Or, if iFrom
    ** is valid - each iterator that points to a rowid before iFrom.  */
    for(p=pTerm; p; p=p->pSynonym){
      if( sqlite3Fts5IterEof(p->pIter)==0 ){
        i64 ii = sqlite3Fts5IterRowid(p->pIter);
        if( ii==iRowid 
         || (bFromValid && ii!=iFrom && (ii>iFrom)==pExpr->bDesc) 
        ){
          if( bFromValid ){
            rc = sqlite3Fts5IterNextFrom(p->pIter, iFrom);
          }else{
            rc = sqlite3Fts5IterNext(p->pIter);
          }
          if( rc!=SQLITE_OK ) break;
          if( sqlite3Fts5IterEof(p->pIter)==0 ){
            bEof = 0;
          }
        }else{
          bEof = 0;
        }
      }
    }

    /* Set the EOF flag if either all synonym iterators are at EOF or an
    ** error has occurred.  */
    pNode->bEof = (rc || bEof);
  }else{
    Fts5IndexIter *pIter = pTerm->pIter;

    assert( Fts5NodeIsString(pNode) );
    if( bFromValid ){
      rc = sqlite3Fts5IterNextFrom(pIter, iFrom);
    }else{
      rc = sqlite3Fts5IterNext(pIter);
    }

    pNode->bEof = (rc || sqlite3Fts5IterEof(pIter));
  }

  return rc;
}

/*
** Advance iterator pIter until it points to a value equal to or laster
** than the initial value of *piLast. If this means the iterator points
** to a value laster than *piLast, update *piLast to the new lastest value.
**
** If the iterator reaches EOF, set *pbEof to true before returning. If
** an error occurs, set *pRc to an error code. If either *pbEof or *pRc
** are set, return a non-zero value. Otherwise, return zero.
*/
static int fts5ExprAdvanceto(
  Fts5IndexIter *pIter,           /* Iterator to advance */
  int bDesc,                      /* True if iterator is "rowid DESC" */
  i64 *piLast,                    /* IN/OUT: Lastest rowid seen so far */
  int *pRc,                       /* OUT: Error code */
  int *pbEof                      /* OUT: Set to true if EOF */
){
  i64 iLast = *piLast;
  i64 iRowid;

  iRowid = sqlite3Fts5IterRowid(pIter);
  if( (bDesc==0 && iLast>iRowid) || (bDesc && iLast<iRowid) ){
    int rc = sqlite3Fts5IterNextFrom(pIter, iLast);
    if( rc || sqlite3Fts5IterEof(pIter) ){
      *pRc = rc;
      *pbEof = 1;
      return 1;
    }
    iRowid = sqlite3Fts5IterRowid(pIter);
    assert( (bDesc==0 && iRowid>=iLast) || (bDesc==1 && iRowid<=iLast) );
  }
  *piLast = iRowid;

  return 0;
}

static int fts5ExprSynonymAdvanceto(
  Fts5ExprTerm *pTerm,            /* Term iterator to advance */
  int bDesc,                      /* True if iterator is "rowid DESC" */
  i64 *piLast,                    /* IN/OUT: Lastest rowid seen so far */
  int *pRc                        /* OUT: Error code */
){
  int rc = SQLITE_OK;
  i64 iLast = *piLast;
  Fts5ExprTerm *p;
  int bEof = 0;

  for(p=pTerm; rc==SQLITE_OK && p; p=p->pSynonym){
    if( sqlite3Fts5IterEof(p->pIter)==0 ){
      i64 iRowid = sqlite3Fts5IterRowid(p->pIter);
      if( (bDesc==0 && iLast>iRowid) || (bDesc && iLast<iRowid) ){
        rc = sqlite3Fts5IterNextFrom(p->pIter, iLast);
      }
    }
  }

  if( rc!=SQLITE_OK ){
    *pRc = rc;
    bEof = 1;
  }else{
    *piLast = fts5ExprSynonymRowid(pTerm, bDesc, &bEof);
  }
  return bEof;
}

/*
** IN/OUT parameter (*pa) points to a position list n bytes in size. If
** the position list contains entries for column iCol, then (*pa) is set
** to point to the sub-position-list for that column and the number of
** bytes in it returned. Or, if the argument position list does not
** contain any entries for column iCol, return 0.
*/
static int fts5ExprExtractCol(
  const u8 **pa,                  /* IN/OUT: Pointer to poslist */
  int n,                          /* IN: Size of poslist in bytes */
  int iCol                        /* Column to extract from poslist */
){
  int iCurrent = 0;
  const u8 *p = *pa;
  const u8 *pEnd = &p[n];         /* One byte past end of position list */
  u8 prev = 0;

  while( iCol!=iCurrent ){
    /* Advance pointer p until it points to pEnd or an 0x01 byte that is
    ** not part of a varint */
    while( (prev & 0x80) || *p!=0x01 ){
      prev = *p++;
      if( p==pEnd ) return 0;
    }
    *pa = p++;
    p += fts5GetVarint32(p, iCurrent);
  }

  /* Advance pointer p until it points to pEnd or an 0x01 byte that is
  ** not part of a varint */
  assert( (prev & 0x80)==0 );
  while( p<pEnd && ((prev & 0x80) || *p!=0x01) ){
    prev = *p++;
  }
  return p - (*pa);
}

static int fts5ExprExtractColset (
  Fts5ExprColset *pColset,        /* Colset to filter on */
  const u8 *pPos, int nPos,       /* Position list */
  Fts5Buffer *pBuf                /* Output buffer */
){
  int rc = SQLITE_OK;
  int i;

  fts5BufferZero(pBuf);
  for(i=0; i<pColset->nCol; i++){
    const u8 *pSub = pPos;
    int nSub = fts5ExprExtractCol(&pSub, nPos, pColset->aiCol[i]);
    if( nSub ){
      fts5BufferAppendBlob(&rc, pBuf, nSub, pSub);
    }
  }
  return rc;
}

static int fts5ExprNearTest(
  int *pRc,
  Fts5Expr *pExpr,                /* Expression that pNear is a part of */
  Fts5ExprNode *pNode             /* The "NEAR" node (FTS5_STRING) */
){
  Fts5ExprNearset *pNear = pNode->pNear;
  int rc = *pRc;
  int i;

  /* Check that each phrase in the nearset matches the current row.
  ** Populate the pPhrase->poslist buffers at the same time. If any
  ** phrase is not a match, break out of the loop early.  */
  for(i=0; rc==SQLITE_OK && i<pNear->nPhrase; i++){
    Fts5ExprPhrase *pPhrase = pNear->apPhrase[i];
    if( pPhrase->nTerm>1 || pPhrase->aTerm[0].pSynonym || pNear->pColset ){
      int bMatch = 0;
      rc = fts5ExprPhraseIsMatch(pNode, pNear->pColset, pPhrase, &bMatch);
      if( bMatch==0 ) break;
    }else{
      rc = sqlite3Fts5IterPoslistBuffer(
          pPhrase->aTerm[0].pIter, &pPhrase->poslist
      );
    }
  }

  *pRc = rc;
  if( i==pNear->nPhrase && (i==1 || fts5ExprNearIsMatch(pRc, pNear)) ){
    return 1;
  }

  return 0;
}

static int fts5ExprTokenTest(
  Fts5Expr *pExpr,                /* Expression that pNear is a part of */
  Fts5ExprNode *pNode             /* The "NEAR" node (FTS5_TERM) */
){
  /* As this "NEAR" object is actually a single phrase that consists 
  ** of a single term only, grab pointers into the poslist managed by the
  ** fts5_index.c iterator object. This is much faster than synthesizing 
  ** a new poslist the way we have to for more complicated phrase or NEAR
  ** expressions.  */
  Fts5ExprNearset *pNear = pNode->pNear;
  Fts5ExprPhrase *pPhrase = pNear->apPhrase[0];
  Fts5IndexIter *pIter = pPhrase->aTerm[0].pIter;
  Fts5ExprColset *pColset = pNear->pColset;
  const u8 *pPos;
  int nPos;
  int rc;

  assert( pNode->eType==FTS5_TERM );
  assert( pNear->nPhrase==1 && pPhrase->nTerm==1 );
  assert( pPhrase->aTerm[0].pSynonym==0 );

  rc = sqlite3Fts5IterPoslist(pIter, &pPos, &nPos, &pNode->iRowid);

  /* If the term may match any column, then this must be a match. 
  ** Return immediately in this case. Otherwise, try to find the
  ** part of the poslist that corresponds to the required column.
  ** If it can be found, return. If it cannot, the next iteration
  ** of the loop will test the next rowid in the database for this
  ** term.  */
  if( pColset==0 ){
    assert( pPhrase->poslist.nSpace==0 );
    pPhrase->poslist.p = (u8*)pPos;
    pPhrase->poslist.n = nPos;
  }else if( pColset->nCol==1 ){
    assert( pPhrase->poslist.nSpace==0 );
    pPhrase->poslist.n = fts5ExprExtractCol(&pPos, nPos, pColset->aiCol[0]);
    pPhrase->poslist.p = (u8*)pPos;
  }else if( rc==SQLITE_OK ){
    rc = fts5ExprExtractColset(pColset, pPos, nPos, &pPhrase->poslist);
  }

  pNode->bNomatch = (pPhrase->poslist.n==0);
  return rc;
}

/*
** All individual term iterators in pNear are guaranteed to be valid when
** this function is called. This function checks if all term iterators
** point to the same rowid, and if not, advances them until they do.
** If an EOF is reached before this happens, *pbEof is set to true before
** returning.
**
** SQLITE_OK is returned if an error occurs, or an SQLite error code 
** otherwise. It is not considered an error code if an iterator reaches
** EOF.
*/
static int fts5ExprNearNextMatch(
  Fts5Expr *pExpr,                /* Expression pPhrase belongs to */
  Fts5ExprNode *pNode
){
  Fts5ExprNearset *pNear = pNode->pNear;
  Fts5ExprPhrase *pLeft = pNear->apPhrase[0];
  int rc = SQLITE_OK;
  i64 iLast;                      /* Lastest rowid any iterator points to */
  int i, j;                       /* Phrase and token index, respectively */
  int bMatch;                     /* True if all terms are at the same rowid */
  const int bDesc = pExpr->bDesc;

  /* Check that this node should not be FTS5_TERM */
  assert( pNear->nPhrase>1 
       || pNear->apPhrase[0]->nTerm>1 
       || pNear->apPhrase[0]->aTerm[0].pSynonym
  );

  /* Initialize iLast, the "lastest" rowid any iterator points to. If the
  ** iterator skips through rowids in the default ascending order, this means
  ** the maximum rowid. Or, if the iterator is "ORDER BY rowid DESC", then it
  ** means the minimum rowid.  */
  if( pLeft->aTerm[0].pSynonym ){
    iLast = fts5ExprSynonymRowid(&pLeft->aTerm[0], bDesc, 0);
  }else{
    iLast = sqlite3Fts5IterRowid(pLeft->aTerm[0].pIter);
  }

  do {
    bMatch = 1;
    for(i=0; i<pNear->nPhrase; i++){
      Fts5ExprPhrase *pPhrase = pNear->apPhrase[i];
      for(j=0; j<pPhrase->nTerm; j++){
        Fts5ExprTerm *pTerm = &pPhrase->aTerm[j];
        if( pTerm->pSynonym ){
          i64 iRowid = fts5ExprSynonymRowid(pTerm, bDesc, 0);
          if( iRowid==iLast ) continue;
          bMatch = 0;
          if( fts5ExprSynonymAdvanceto(pTerm, bDesc, &iLast, &rc) ){
            pNode->bEof = 1;
            return rc;
          }
        }else{
          Fts5IndexIter *pIter = pPhrase->aTerm[j].pIter;
          i64 iRowid = sqlite3Fts5IterRowid(pIter);
          if( iRowid==iLast ) continue;
          bMatch = 0;
          if( fts5ExprAdvanceto(pIter, bDesc, &iLast, &rc, &pNode->bEof) ){
            return rc;
          }
        }
      }
    }
  }while( bMatch==0 );

  pNode->iRowid = iLast;
  pNode->bNomatch = (0==fts5ExprNearTest(&rc, pExpr, pNode));

  return rc;
}

/*
** Initialize all term iterators in the pNear object. If any term is found
** to match no documents at all, return immediately without initializing any
** further iterators.
*/
static int fts5ExprNearInitAll(
  Fts5Expr *pExpr,
  Fts5ExprNode *pNode
){
  Fts5ExprNearset *pNear = pNode->pNear;
  int i, j;
  int rc = SQLITE_OK;

  for(i=0; rc==SQLITE_OK && i<pNear->nPhrase; i++){
    Fts5ExprPhrase *pPhrase = pNear->apPhrase[i];
    for(j=0; j<pPhrase->nTerm; j++){
      Fts5ExprTerm *pTerm = &pPhrase->aTerm[j];
      Fts5ExprTerm *p;
      int bEof = 1;

      for(p=pTerm; p && rc==SQLITE_OK; p=p->pSynonym){
        if( p->pIter ){
          sqlite3Fts5IterClose(p->pIter);
          p->pIter = 0;
        }
        rc = sqlite3Fts5IndexQuery(
            pExpr->pIndex, p->zTerm, strlen(p->zTerm),
            (pTerm->bPrefix ? FTS5INDEX_QUERY_PREFIX : 0) |
            (pExpr->bDesc ? FTS5INDEX_QUERY_DESC : 0),
            &p->pIter
        );
        assert( rc==SQLITE_OK || p->pIter==0 );
        if( p->pIter && 0==sqlite3Fts5IterEof(p->pIter) ){
          bEof = 0;
        }
      }

      if( bEof ){
        pNode->bEof = 1;
        return rc;
      }
    }
  }

  return rc;
}

/* fts5ExprNodeNext() calls fts5ExprNodeNextMatch(). And vice-versa. */
static int fts5ExprNodeNextMatch(Fts5Expr*, Fts5ExprNode*);


/*
** If pExpr is an ASC iterator, this function returns a value with the
** same sign as:
**
**   (iLhs - iRhs)
**
** Otherwise, if this is a DESC iterator, the opposite is returned:
**
**   (iRhs - iLhs)
*/
static int fts5RowidCmp(
  Fts5Expr *pExpr,
  i64 iLhs,
  i64 iRhs
){
  assert( pExpr->bDesc==0 || pExpr->bDesc==1 );
  if( pExpr->bDesc==0 ){
    if( iLhs<iRhs ) return -1;
    return (iLhs > iRhs);
  }else{
    if( iLhs>iRhs ) return -1;
    return (iLhs < iRhs);
  }
}

static void fts5ExprSetEof(Fts5ExprNode *pNode){
  int i;
  pNode->bEof = 1;
  for(i=0; i<pNode->nChild; i++){
    fts5ExprSetEof(pNode->apChild[i]);
  }
}

static void fts5ExprNodeZeroPoslist(Fts5ExprNode *pNode){
  if( pNode->eType==FTS5_STRING || pNode->eType==FTS5_TERM ){
    Fts5ExprNearset *pNear = pNode->pNear;
    int i;
    for(i=0; i<pNear->nPhrase; i++){
      Fts5ExprPhrase *pPhrase = pNear->apPhrase[i];
      pPhrase->poslist.n = 0;
    }
  }else{
    int i;
    for(i=0; i<pNode->nChild; i++){
      fts5ExprNodeZeroPoslist(pNode->apChild[i]);
    }
  }
}


static int fts5ExprNodeNext(Fts5Expr*, Fts5ExprNode*, int, i64);

/*
** Argument pNode is an FTS5_AND node.
*/
static int fts5ExprAndNextRowid(
  Fts5Expr *pExpr,                /* Expression pPhrase belongs to */
  Fts5ExprNode *pAnd              /* FTS5_AND node to advance */
){
  int iChild;
  i64 iLast = pAnd->iRowid;
  int rc = SQLITE_OK;
  int bMatch;

  assert( pAnd->bEof==0 );
  do {
    pAnd->bNomatch = 0;
    bMatch = 1;
    for(iChild=0; iChild<pAnd->nChild; iChild++){
      Fts5ExprNode *pChild = pAnd->apChild[iChild];
      if( 0 && pChild->eType==FTS5_STRING ){
        /* TODO */
      }else{
        int cmp = fts5RowidCmp(pExpr, iLast, pChild->iRowid);
        if( cmp>0 ){
          /* Advance pChild until it points to iLast or laster */
          rc = fts5ExprNodeNext(pExpr, pChild, 1, iLast);
          if( rc!=SQLITE_OK ) return rc;
        }
      }

      /* If the child node is now at EOF, so is the parent AND node. Otherwise,
      ** the child node is guaranteed to have advanced at least as far as
      ** rowid iLast. So if it is not at exactly iLast, pChild->iRowid is the
      ** new lastest rowid seen so far.  */
      assert( pChild->bEof || fts5RowidCmp(pExpr, iLast, pChild->iRowid)<=0 );
      if( pChild->bEof ){
        fts5ExprSetEof(pAnd);
        bMatch = 1;
        break;
      }else if( iLast!=pChild->iRowid ){
        bMatch = 0;
        iLast = pChild->iRowid;
      }

      if( pChild->bNomatch ){
        pAnd->bNomatch = 1;
      }
    }
  }while( bMatch==0 );

  if( pAnd->bNomatch && pAnd!=pExpr->pRoot ){
    fts5ExprNodeZeroPoslist(pAnd);
  }
  pAnd->iRowid = iLast;
  return SQLITE_OK;
}


/*
** Compare the values currently indicated by the two nodes as follows:
**
**    res = (*p1) - (*p2)
**
** Nodes that point to values that come later in the iteration order are
** considered to be larger. Nodes at EOF are the largest of all.
**
** This means that if the iteration order is ASC, then numerically larger
** rowids are considered larger. Or if it is the default DESC, numerically
** smaller rowids are larger.
*/
static int fts5NodeCompare(
  Fts5Expr *pExpr,
  Fts5ExprNode *p1, 
  Fts5ExprNode *p2
){
  if( p2->bEof ) return -1;
  if( p1->bEof ) return +1;
  return fts5RowidCmp(pExpr, p1->iRowid, p2->iRowid);
}

/*
** Advance node iterator pNode, part of expression pExpr. If argument
** bFromValid is zero, then pNode is advanced exactly once. Or, if argument
** bFromValid is non-zero, then pNode is advanced until it is at or past
** rowid value iFrom. Whether "past" means "less than" or "greater than"
** depends on whether this is an ASC or DESC iterator.
*/
static int fts5ExprNodeNext(
  Fts5Expr *pExpr, 
  Fts5ExprNode *pNode,
  int bFromValid,
  i64 iFrom
){
  int rc = SQLITE_OK;

  if( pNode->bEof==0 ){
    switch( pNode->eType ){
      case FTS5_STRING: {
        rc = fts5ExprNearAdvanceFirst(pExpr, pNode, bFromValid, iFrom);
        break;
      };

      case FTS5_TERM: {
        Fts5IndexIter *pIter = pNode->pNear->apPhrase[0]->aTerm[0].pIter;
        if( bFromValid ){
          rc = sqlite3Fts5IterNextFrom(pIter, iFrom);
        }else{
          rc = sqlite3Fts5IterNext(pIter);
        }
        if( rc==SQLITE_OK && sqlite3Fts5IterEof(pIter)==0 ){
          assert( rc==SQLITE_OK );
          rc = fts5ExprTokenTest(pExpr, pNode);
        }else{
          pNode->bEof = 1;
        }
        return rc;
      };

      case FTS5_AND: {
        Fts5ExprNode *pLeft = pNode->apChild[0];
        rc = fts5ExprNodeNext(pExpr, pLeft, bFromValid, iFrom);
        break;
      }

      case FTS5_OR: {
        int i;
        i64 iLast = pNode->iRowid;

        for(i=0; rc==SQLITE_OK && i<pNode->nChild; i++){
          Fts5ExprNode *p1 = pNode->apChild[i];
          assert( p1->bEof || fts5RowidCmp(pExpr, p1->iRowid, iLast)>=0 );
          if( p1->bEof==0 ){
            if( (p1->iRowid==iLast) 
             || (bFromValid && fts5RowidCmp(pExpr, p1->iRowid, iFrom)<0)
            ){
              rc = fts5ExprNodeNext(pExpr, p1, bFromValid, iFrom);
            }
          }
        }

        break;
      }

      default: assert( pNode->eType==FTS5_NOT ); {
        assert( pNode->nChild==2 );
        rc = fts5ExprNodeNext(pExpr, pNode->apChild[0], bFromValid, iFrom);
        break;
      }
    }

    if( rc==SQLITE_OK ){
      rc = fts5ExprNodeNextMatch(pExpr, pNode);
    }
  }

  /* Assert that if bFromValid was true, either:
  **
  **   a) an error occurred, or
  **   b) the node is now at EOF, or
  **   c) the node is now at or past rowid iFrom.
  */
  assert( bFromValid==0 
      || rc!=SQLITE_OK                                                  /* a */
      || pNode->bEof                                                    /* b */
      || pNode->iRowid==iFrom || pExpr->bDesc==(pNode->iRowid<iFrom)    /* c */
  );

  return rc;
}


/*
** If pNode currently points to a match, this function returns SQLITE_OK
** without modifying it. Otherwise, pNode is advanced until it does point
** to a match or EOF is reached.
*/
static int fts5ExprNodeNextMatch(
  Fts5Expr *pExpr,                /* Expression of which pNode is a part */
  Fts5ExprNode *pNode             /* Expression node to test */
){
  int rc = SQLITE_OK;
  if( pNode->bEof==0 ){
    switch( pNode->eType ){

      case FTS5_STRING: {
        /* Advance the iterators until they all point to the same rowid */
        rc = fts5ExprNearNextMatch(pExpr, pNode);
        break;
      }

      case FTS5_TERM: {
        rc = fts5ExprTokenTest(pExpr, pNode);
        break;
      }

      case FTS5_AND: {
        rc = fts5ExprAndNextRowid(pExpr, pNode);
        break;
      }

      case FTS5_OR: {
        Fts5ExprNode *pNext = pNode->apChild[0];
        int i;

        for(i=1; i<pNode->nChild; i++){
          Fts5ExprNode *pChild = pNode->apChild[i];
          int cmp = fts5NodeCompare(pExpr, pNext, pChild);
          if( cmp>0 || (cmp==0 && pChild->bNomatch==0) ){
            pNext = pChild;
          }
        }
        pNode->iRowid = pNext->iRowid;
        pNode->bEof = pNext->bEof;
        pNode->bNomatch = pNext->bNomatch;
        break;
      }

      default: assert( pNode->eType==FTS5_NOT ); {
        Fts5ExprNode *p1 = pNode->apChild[0];
        Fts5ExprNode *p2 = pNode->apChild[1];
        assert( pNode->nChild==2 );

        while( rc==SQLITE_OK && p1->bEof==0 ){
          int cmp = fts5NodeCompare(pExpr, p1, p2);
          if( cmp>0 ){
            rc = fts5ExprNodeNext(pExpr, p2, 1, p1->iRowid);
            cmp = fts5NodeCompare(pExpr, p1, p2);
          }
          assert( rc!=SQLITE_OK || cmp<=0 );
          if( cmp || p2->bNomatch ) break;
          rc = fts5ExprNodeNext(pExpr, p1, 0, 0);
        }
        pNode->bEof = p1->bEof;
        pNode->iRowid = p1->iRowid;
        break;
      }
    }
  }
  return rc;
}

 
/*
** Set node pNode, which is part of expression pExpr, to point to the first
** match. If there are no matches, set the Node.bEof flag to indicate EOF.
**
** Return an SQLite error code if an error occurs, or SQLITE_OK otherwise.
** It is not an error if there are no matches.
*/
static int fts5ExprNodeFirst(Fts5Expr *pExpr, Fts5ExprNode *pNode){
  int rc = SQLITE_OK;
  pNode->bEof = 0;

  if( Fts5NodeIsString(pNode) ){
    /* Initialize all term iterators in the NEAR object. */
    rc = fts5ExprNearInitAll(pExpr, pNode);
  }else{
    int i;
    for(i=0; i<pNode->nChild && rc==SQLITE_OK; i++){
      rc = fts5ExprNodeFirst(pExpr, pNode->apChild[i]);
    }
    pNode->iRowid = pNode->apChild[0]->iRowid;
  }

  if( rc==SQLITE_OK ){
    rc = fts5ExprNodeNextMatch(pExpr, pNode);
  }
  return rc;
}


/*
** Begin iterating through the set of documents in index pIdx matched by
** the MATCH expression passed as the first argument. If the "bDesc" 
** parameter is passed a non-zero value, iteration is in descending rowid 
** order. Or, if it is zero, in ascending order.
**
** If iterating in ascending rowid order (bDesc==0), the first document
** visited is that with the smallest rowid that is larger than or equal
** to parameter iFirst. Or, if iterating in ascending order (bDesc==1),
** then the first document visited must have a rowid smaller than or
** equal to iFirst.
**
** Return SQLITE_OK if successful, or an SQLite error code otherwise. It
** is not considered an error if the query does not match any documents.
*/
int sqlite3Fts5ExprFirst(Fts5Expr *p, Fts5Index *pIdx, i64 iFirst, int bDesc){
  Fts5ExprNode *pRoot = p->pRoot;
  int rc = SQLITE_OK;
  if( pRoot ){
    p->pIndex = pIdx;
    p->bDesc = bDesc;
    rc = fts5ExprNodeFirst(p, pRoot);

    /* If not at EOF but the current rowid occurs earlier than iFirst in
    ** the iteration order, move to document iFirst or later. */
    if( pRoot->bEof==0 && fts5RowidCmp(p, pRoot->iRowid, iFirst)<0 ){
      rc = fts5ExprNodeNext(p, pRoot, 1, iFirst);
    }

    /* If the iterator is not at a real match, skip forward until it is. */
    while( pRoot->bNomatch && rc==SQLITE_OK && pRoot->bEof==0 ){
      rc = fts5ExprNodeNext(p, pRoot, 0, 0);
    }
  }
  return rc;
}

/*
** Move to the next document 
**
** Return SQLITE_OK if successful, or an SQLite error code otherwise. It
** is not considered an error if the query does not match any documents.
*/
int sqlite3Fts5ExprNext(Fts5Expr *p, i64 iLast){
  int rc;
  Fts5ExprNode *pRoot = p->pRoot;
  do {
    rc = fts5ExprNodeNext(p, pRoot, 0, 0);
  }while( pRoot->bNomatch && pRoot->bEof==0 && rc==SQLITE_OK );
  if( fts5RowidCmp(p, pRoot->iRowid, iLast)>0 ){
    pRoot->bEof = 1;
  }
  return rc;
}

int sqlite3Fts5ExprEof(Fts5Expr *p){
  return (p->pRoot==0 || p->pRoot->bEof);
}

i64 sqlite3Fts5ExprRowid(Fts5Expr *p){
  return p->pRoot->iRowid;
}

static int fts5ParseStringFromToken(Fts5Token *pToken, char **pz){
  int rc = SQLITE_OK;
  *pz = sqlite3Fts5Strndup(&rc, pToken->p, pToken->n);
  return rc;
}

/*
** Free the phrase object passed as the only argument.
*/
static void fts5ExprPhraseFree(Fts5ExprPhrase *pPhrase){
  if( pPhrase ){
    int i;
    for(i=0; i<pPhrase->nTerm; i++){
      Fts5ExprTerm *pSyn;
      Fts5ExprTerm *pNext;
      Fts5ExprTerm *pTerm = &pPhrase->aTerm[i];
      sqlite3_free(pTerm->zTerm);
      sqlite3Fts5IterClose(pTerm->pIter);

      for(pSyn=pTerm->pSynonym; pSyn; pSyn=pNext){
        pNext = pSyn->pSynonym;
        sqlite3Fts5IterClose(pSyn->pIter);
        sqlite3_free(pSyn);
      }
    }
    if( pPhrase->poslist.nSpace>0 ) fts5BufferFree(&pPhrase->poslist);
    sqlite3_free(pPhrase);
  }
}

/*
** If argument pNear is NULL, then a new Fts5ExprNearset object is allocated
** and populated with pPhrase. Or, if pNear is not NULL, phrase pPhrase is
** appended to it and the results returned.
**
** If an OOM error occurs, both the pNear and pPhrase objects are freed and
** NULL returned.
*/
Fts5ExprNearset *sqlite3Fts5ParseNearset(
  Fts5Parse *pParse,              /* Parse context */
  Fts5ExprNearset *pNear,         /* Existing nearset, or NULL */
  Fts5ExprPhrase *pPhrase         /* Recently parsed phrase */
){
  const int SZALLOC = 8;
  Fts5ExprNearset *pRet = 0;

  if( pParse->rc==SQLITE_OK ){
    if( pPhrase==0 ){
      return pNear;
    }
    if( pNear==0 ){
      int nByte = sizeof(Fts5ExprNearset) + SZALLOC * sizeof(Fts5ExprPhrase*);
      pRet = sqlite3_malloc(nByte);
      if( pRet==0 ){
        pParse->rc = SQLITE_NOMEM;
      }else{
        memset(pRet, 0, nByte);
      }
    }else if( (pNear->nPhrase % SZALLOC)==0 ){
      int nNew = pNear->nPhrase + SZALLOC;
      int nByte = sizeof(Fts5ExprNearset) + nNew * sizeof(Fts5ExprPhrase*);

      pRet = (Fts5ExprNearset*)sqlite3_realloc(pNear, nByte);
      if( pRet==0 ){
        pParse->rc = SQLITE_NOMEM;
      }
    }else{
      pRet = pNear;
    }
  }

  if( pRet==0 ){
    assert( pParse->rc!=SQLITE_OK );
    sqlite3Fts5ParseNearsetFree(pNear);
    sqlite3Fts5ParsePhraseFree(pPhrase);
  }else{
    pRet->apPhrase[pRet->nPhrase++] = pPhrase;
  }
  return pRet;
}

typedef struct TokenCtx TokenCtx;
struct TokenCtx {
  Fts5ExprPhrase *pPhrase;
  int rc;
};

/*
** Callback for tokenizing terms used by ParseTerm().
*/
static int fts5ParseTokenize(
  void *pContext,                 /* Pointer to Fts5InsertCtx object */
  int tflags,                     /* Mask of FTS5_TOKEN_* flags */
  const char *pToken,             /* Buffer containing token */
  int nToken,                     /* Size of token in bytes */
  int iUnused1,                   /* Start offset of token */
  int iUnused2                    /* End offset of token */
){
  int rc = SQLITE_OK;
  const int SZALLOC = 8;
  TokenCtx *pCtx = (TokenCtx*)pContext;
  Fts5ExprPhrase *pPhrase = pCtx->pPhrase;

  /* If an error has already occurred, this is a no-op */
  if( pCtx->rc!=SQLITE_OK ) return pCtx->rc;

  assert( pPhrase==0 || pPhrase->nTerm>0 );
  if( pPhrase && (tflags & FTS5_TOKEN_COLOCATED) ){
    Fts5ExprTerm *pSyn;
    int nByte = sizeof(Fts5ExprTerm) + nToken+1;
    pSyn = (Fts5ExprTerm*)sqlite3_malloc(nByte);
    if( pSyn==0 ){
      rc = SQLITE_NOMEM;
    }else{
      memset(pSyn, 0, nByte);
      pSyn->zTerm = (char*)&pSyn[1];
      memcpy(pSyn->zTerm, pToken, nToken);
      pSyn->pSynonym = pPhrase->aTerm[pPhrase->nTerm-1].pSynonym;
      pPhrase->aTerm[pPhrase->nTerm-1].pSynonym = pSyn;
    }
  }else{
    Fts5ExprTerm *pTerm;
    if( pPhrase==0 || (pPhrase->nTerm % SZALLOC)==0 ){
      Fts5ExprPhrase *pNew;
      int nNew = SZALLOC + (pPhrase ? pPhrase->nTerm : 0);

      pNew = (Fts5ExprPhrase*)sqlite3_realloc(pPhrase, 
          sizeof(Fts5ExprPhrase) + sizeof(Fts5ExprTerm) * nNew
      );
      if( pNew==0 ){
        rc = SQLITE_NOMEM;
      }else{
        if( pPhrase==0 ) memset(pNew, 0, sizeof(Fts5ExprPhrase));
        pCtx->pPhrase = pPhrase = pNew;
        pNew->nTerm = nNew - SZALLOC;
      }
    }

    if( rc==SQLITE_OK ){
      pTerm = &pPhrase->aTerm[pPhrase->nTerm++];
      memset(pTerm, 0, sizeof(Fts5ExprTerm));
      pTerm->zTerm = sqlite3Fts5Strndup(&rc, pToken, nToken);
    }
  }

  pCtx->rc = rc;
  return rc;
}


/*
** Free the phrase object passed as the only argument.
*/
void sqlite3Fts5ParsePhraseFree(Fts5ExprPhrase *pPhrase){
  fts5ExprPhraseFree(pPhrase);
}

/*
** Free the phrase object passed as the second argument.
*/
void sqlite3Fts5ParseNearsetFree(Fts5ExprNearset *pNear){
  if( pNear ){
    int i;
    for(i=0; i<pNear->nPhrase; i++){
      fts5ExprPhraseFree(pNear->apPhrase[i]);
    }
    sqlite3_free(pNear->pColset);
    sqlite3_free(pNear);
  }
}

void sqlite3Fts5ParseFinished(Fts5Parse *pParse, Fts5ExprNode *p){
  assert( pParse->pExpr==0 );
  pParse->pExpr = p;
}

/*
** This function is called by the parser to process a string token. The
** string may or may not be quoted. In any case it is tokenized and a
** phrase object consisting of all tokens returned.
*/
Fts5ExprPhrase *sqlite3Fts5ParseTerm(
  Fts5Parse *pParse,              /* Parse context */
  Fts5ExprPhrase *pAppend,        /* Phrase to append to */
  Fts5Token *pToken,              /* String to tokenize */
  int bPrefix                     /* True if there is a trailing "*" */
){
  Fts5Config *pConfig = pParse->pConfig;
  TokenCtx sCtx;                  /* Context object passed to callback */
  int rc;                         /* Tokenize return code */
  char *z = 0;

  memset(&sCtx, 0, sizeof(TokenCtx));
  sCtx.pPhrase = pAppend;

  rc = fts5ParseStringFromToken(pToken, &z);
  if( rc==SQLITE_OK ){
    int flags = FTS5_TOKENIZE_QUERY | (bPrefix ? FTS5_TOKENIZE_QUERY : 0);
    int n;
    sqlite3Fts5Dequote(z);
    n = strlen(z);
    rc = sqlite3Fts5Tokenize(pConfig, flags, z, n, &sCtx, fts5ParseTokenize);
  }
  sqlite3_free(z);
  if( rc || (rc = sCtx.rc) ){
    pParse->rc = rc;
    fts5ExprPhraseFree(sCtx.pPhrase);
    sCtx.pPhrase = 0;
  }else if( sCtx.pPhrase ){

    if( pAppend==0 ){
      if( (pParse->nPhrase % 8)==0 ){
        int nByte = sizeof(Fts5ExprPhrase*) * (pParse->nPhrase + 8);
        Fts5ExprPhrase **apNew;
        apNew = (Fts5ExprPhrase**)sqlite3_realloc(pParse->apPhrase, nByte);
        if( apNew==0 ){
          pParse->rc = SQLITE_NOMEM;
          fts5ExprPhraseFree(sCtx.pPhrase);
          return 0;
        }
        pParse->apPhrase = apNew;
      }
      pParse->nPhrase++;
    }

    pParse->apPhrase[pParse->nPhrase-1] = sCtx.pPhrase;
    assert( sCtx.pPhrase->nTerm>0 );
    sCtx.pPhrase->aTerm[sCtx.pPhrase->nTerm-1].bPrefix = bPrefix;
  }

  return sCtx.pPhrase;
}

/*
** Create a new FTS5 expression by cloning phrase iPhrase of the
** expression passed as the second argument.
*/
int sqlite3Fts5ExprClonePhrase(
  Fts5Config *pConfig,
  Fts5Expr *pExpr, 
  int iPhrase, 
  Fts5Expr **ppNew
){
  int rc = SQLITE_OK;             /* Return code */
  Fts5ExprPhrase *pOrig;          /* The phrase extracted from pExpr */
  int i;                          /* Used to iterate through phrase terms */

  Fts5Expr *pNew = 0;             /* Expression to return via *ppNew */

  TokenCtx sCtx = {0,0};          /* Context object for fts5ParseTokenize */


  pOrig = pExpr->apExprPhrase[iPhrase];

  pNew = (Fts5Expr*)sqlite3Fts5MallocZero(&rc, sizeof(Fts5Expr));
  if( rc==SQLITE_OK ){
    pNew->apExprPhrase = (Fts5ExprPhrase**)sqlite3Fts5MallocZero(&rc, 
        sizeof(Fts5ExprPhrase*));
  }
  if( rc==SQLITE_OK ){
    pNew->pRoot = (Fts5ExprNode*)sqlite3Fts5MallocZero(&rc, 
        sizeof(Fts5ExprNode));
  }
  if( rc==SQLITE_OK ){
    pNew->pRoot->pNear = (Fts5ExprNearset*)sqlite3Fts5MallocZero(&rc, 
        sizeof(Fts5ExprNearset) + sizeof(Fts5ExprPhrase*));
  }

  for(i=0; rc==SQLITE_OK && i<pOrig->nTerm; i++){
    int tflags = 0;
    Fts5ExprTerm *p;
    for(p=&pOrig->aTerm[i]; p && rc==SQLITE_OK; p=p->pSynonym){
      const char *zTerm = p->zTerm;
      rc = fts5ParseTokenize((void*)&sCtx, tflags, zTerm, strlen(zTerm), 0, 0);
      tflags = FTS5_TOKEN_COLOCATED;
    }
    if( rc==SQLITE_OK ){
      sCtx.pPhrase->aTerm[i].bPrefix = pOrig->aTerm[i].bPrefix;
    }
  }

  if( rc==SQLITE_OK ){
    /* All the allocations succeeded. Put the expression object together. */
    pNew->pIndex = pExpr->pIndex;
    pNew->nPhrase = 1;
    pNew->apExprPhrase[0] = sCtx.pPhrase;
    pNew->pRoot->pNear->apPhrase[0] = sCtx.pPhrase;
    pNew->pRoot->pNear->nPhrase = 1;
    sCtx.pPhrase->pNode = pNew->pRoot;

    if( pOrig->nTerm==1 && pOrig->aTerm[0].pSynonym==0 ){
      pNew->pRoot->eType = FTS5_TERM;
    }else{
      pNew->pRoot->eType = FTS5_STRING;
    }
  }else{
    sqlite3Fts5ExprFree(pNew);
    fts5ExprPhraseFree(sCtx.pPhrase);
    pNew = 0;
  }

  *ppNew = pNew;
  return rc;
}


/*
** Token pTok has appeared in a MATCH expression where the NEAR operator
** is expected. If token pTok does not contain "NEAR", store an error
** in the pParse object.
*/
void sqlite3Fts5ParseNear(Fts5Parse *pParse, Fts5Token *pTok){
  if( pTok->n!=4 || memcmp("NEAR", pTok->p, 4) ){
    sqlite3Fts5ParseError(
        pParse, "fts5: syntax error near \"%.*s\"", pTok->n, pTok->p
    );
  }
}

void sqlite3Fts5ParseSetDistance(
  Fts5Parse *pParse, 
  Fts5ExprNearset *pNear,
  Fts5Token *p
){
  int nNear = 0;
  int i;
  if( p->n ){
    for(i=0; i<p->n; i++){
      char c = (char)p->p[i];
      if( c<'0' || c>'9' ){
        sqlite3Fts5ParseError(
            pParse, "expected integer, got \"%.*s\"", p->n, p->p
        );
        return;
      }
      nNear = nNear * 10 + (p->p[i] - '0');
    }
  }else{
    nNear = FTS5_DEFAULT_NEARDIST;
  }
  pNear->nNear = nNear;
}

/*
** The second argument passed to this function may be NULL, or it may be
** an existing Fts5ExprColset object. This function returns a pointer to
** a new colset object containing the contents of (p) with new value column
** number iCol appended. 
**
** If an OOM error occurs, store an error code in pParse and return NULL.
** The old colset object (if any) is not freed in this case.
*/
static Fts5ExprColset *fts5ParseColset(
  Fts5Parse *pParse,              /* Store SQLITE_NOMEM here if required */
  Fts5ExprColset *p,              /* Existing colset object */
  int iCol                        /* New column to add to colset object */
){
  int nCol = p ? p->nCol : 0;     /* Num. columns already in colset object */
  Fts5ExprColset *pNew;           /* New colset object to return */

  assert( pParse->rc==SQLITE_OK );
  assert( iCol>=0 && iCol<pParse->pConfig->nCol );

  pNew = sqlite3_realloc(p, sizeof(Fts5ExprColset) + sizeof(int)*nCol);
  if( pNew==0 ){
    pParse->rc = SQLITE_NOMEM;
  }else{
    int *aiCol = pNew->aiCol;
    int i, j;
    for(i=0; i<nCol; i++){
      if( aiCol[i]==iCol ) return pNew;
      if( aiCol[i]>iCol ) break;
    }
    for(j=nCol; j>i; j--){
      aiCol[j] = aiCol[j-1];
    }
    aiCol[i] = iCol;
    pNew->nCol = nCol+1;

#ifndef NDEBUG
    /* Check that the array is in order and contains no duplicate entries. */
    for(i=1; i<pNew->nCol; i++) assert( pNew->aiCol[i]>pNew->aiCol[i-1] );
#endif
  }

  return pNew;
}

Fts5ExprColset *sqlite3Fts5ParseColset(
  Fts5Parse *pParse,              /* Store SQLITE_NOMEM here if required */
  Fts5ExprColset *pColset,        /* Existing colset object */
  Fts5Token *p
){
  Fts5ExprColset *pRet = 0;
  int iCol;
  char *z;                        /* Dequoted copy of token p */

  z = sqlite3Fts5Strndup(&pParse->rc, p->p, p->n);
  if( pParse->rc==SQLITE_OK ){
    Fts5Config *pConfig = pParse->pConfig;
    sqlite3Fts5Dequote(z);
    for(iCol=0; iCol<pConfig->nCol; iCol++){
      if( 0==sqlite3_stricmp(pConfig->azCol[iCol], z) ) break;
    }
    if( iCol==pConfig->nCol ){
      sqlite3Fts5ParseError(pParse, "no such column: %s", z);
    }else{
      pRet = fts5ParseColset(pParse, pColset, iCol);
    }
    sqlite3_free(z);
  }

  if( pRet==0 ){
    assert( pParse->rc!=SQLITE_OK );
    sqlite3_free(pColset);
  }

  return pRet;
}

void sqlite3Fts5ParseSetColset(
  Fts5Parse *pParse, 
  Fts5ExprNearset *pNear, 
  Fts5ExprColset *pColset 
){
  if( pNear ){
    pNear->pColset = pColset;
  }else{
    sqlite3_free(pColset);
  }
}

static void fts5ExprAddChildren(Fts5ExprNode *p, Fts5ExprNode *pSub){
  if( p->eType!=FTS5_NOT && pSub->eType==p->eType ){
    int nByte = sizeof(Fts5ExprNode*) * pSub->nChild;
    memcpy(&p->apChild[p->nChild], pSub->apChild, nByte);
    p->nChild += pSub->nChild;
    sqlite3_free(pSub);
  }else{
    p->apChild[p->nChild++] = pSub;
  }
}

/*
** Allocate and return a new expression object. If anything goes wrong (i.e.
** OOM error), leave an error code in pParse and return NULL.
*/
Fts5ExprNode *sqlite3Fts5ParseNode(
  Fts5Parse *pParse,              /* Parse context */
  int eType,                      /* FTS5_STRING, AND, OR or NOT */
  Fts5ExprNode *pLeft,            /* Left hand child expression */
  Fts5ExprNode *pRight,           /* Right hand child expression */
  Fts5ExprNearset *pNear          /* For STRING expressions, the near cluster */
){
  Fts5ExprNode *pRet = 0;

  if( pParse->rc==SQLITE_OK ){
    int nChild = 0;               /* Number of children of returned node */
    int nByte;                    /* Bytes of space to allocate for this node */
 
    assert( (eType!=FTS5_STRING && !pNear)
         || (eType==FTS5_STRING && !pLeft && !pRight)
    );
    if( eType==FTS5_STRING && pNear==0 ) return 0;
    if( eType!=FTS5_STRING && pLeft==0 ) return pRight;
    if( eType!=FTS5_STRING && pRight==0 ) return pLeft;

    if( eType==FTS5_NOT ){
      nChild = 2;
    }else if( eType==FTS5_AND || eType==FTS5_OR ){
      nChild = 2;
      if( pLeft->eType==eType ) nChild += pLeft->nChild-1;
      if( pRight->eType==eType ) nChild += pRight->nChild-1;
    }

    nByte = sizeof(Fts5ExprNode) + sizeof(Fts5ExprNode*)*(nChild-1);
    pRet = (Fts5ExprNode*)sqlite3Fts5MallocZero(&pParse->rc, nByte);

    if( pRet ){
      pRet->eType = eType;
      pRet->pNear = pNear;
      if( eType==FTS5_STRING ){
        int iPhrase;
        for(iPhrase=0; iPhrase<pNear->nPhrase; iPhrase++){
          pNear->apPhrase[iPhrase]->pNode = pRet;
        }
        if( pNear->nPhrase==1 
         && pNear->apPhrase[0]->nTerm==1 
         && pNear->apPhrase[0]->aTerm[0].pSynonym==0
        ){
          pRet->eType = FTS5_TERM;
        }
      }else{
        fts5ExprAddChildren(pRet, pLeft);
        fts5ExprAddChildren(pRet, pRight);
      }
    }
  }

  if( pRet==0 ){
    assert( pParse->rc!=SQLITE_OK );
    sqlite3Fts5ParseNodeFree(pLeft);
    sqlite3Fts5ParseNodeFree(pRight);
    sqlite3Fts5ParseNearsetFree(pNear);
  }
  return pRet;
}

static char *fts5ExprTermPrint(Fts5ExprTerm *pTerm){
  int nByte = 0;
  Fts5ExprTerm *p;
  char *zQuoted;

  /* Determine the maximum amount of space required. */
  for(p=pTerm; p; p=p->pSynonym){
    nByte += strlen(pTerm->zTerm) * 2 + 3 + 2;
  }
  zQuoted = sqlite3_malloc(nByte);

  if( zQuoted ){
    int i = 0;
    for(p=pTerm; p; p=p->pSynonym){
      char *zIn = p->zTerm;
      zQuoted[i++] = '"';
      while( *zIn ){
        if( *zIn=='"' ) zQuoted[i++] = '"';
        zQuoted[i++] = *zIn++;
      }
      zQuoted[i++] = '"';
      if( p->pSynonym ) zQuoted[i++] = '|';
    }
    if( pTerm->bPrefix ){
      zQuoted[i++] = ' ';
      zQuoted[i++] = '*';
    }
    zQuoted[i++] = '\0';
  }
  return zQuoted;
}

static char *fts5PrintfAppend(char *zApp, const char *zFmt, ...){
  char *zNew;
  va_list ap;
  va_start(ap, zFmt);
  zNew = sqlite3_vmprintf(zFmt, ap);
  va_end(ap);
  if( zApp && zNew ){
    char *zNew2 = sqlite3_mprintf("%s%s", zApp, zNew);
    sqlite3_free(zNew);
    zNew = zNew2;
  }
  sqlite3_free(zApp);
  return zNew;
}

/*
** Compose a tcl-readable representation of expression pExpr. Return a 
** pointer to a buffer containing that representation. It is the 
** responsibility of the caller to at some point free the buffer using 
** sqlite3_free().
*/
static char *fts5ExprPrintTcl(
  Fts5Config *pConfig, 
  const char *zNearsetCmd,
  Fts5ExprNode *pExpr
){
  char *zRet = 0;
  if( pExpr->eType==FTS5_STRING || pExpr->eType==FTS5_TERM ){
    Fts5ExprNearset *pNear = pExpr->pNear;
    int i; 
    int iTerm;

    zRet = fts5PrintfAppend(zRet, "%s ", zNearsetCmd);
    if( zRet==0 ) return 0;
    if( pNear->pColset ){
      int *aiCol = pNear->pColset->aiCol;
      int nCol = pNear->pColset->nCol;
      if( nCol==1 ){
        zRet = fts5PrintfAppend(zRet, "-col %d ", aiCol[0]);
      }else{
        zRet = fts5PrintfAppend(zRet, "-col {%d", aiCol[0]);
        for(i=1; i<pNear->pColset->nCol; i++){
          zRet = fts5PrintfAppend(zRet, " %d", aiCol[i]);
        }
        zRet = fts5PrintfAppend(zRet, "} ");
      }
      if( zRet==0 ) return 0;
    }

    if( pNear->nPhrase>1 ){
      zRet = fts5PrintfAppend(zRet, "-near %d ", pNear->nNear);
      if( zRet==0 ) return 0;
    }

    zRet = fts5PrintfAppend(zRet, "--");
    if( zRet==0 ) return 0;

    for(i=0; i<pNear->nPhrase; i++){
      Fts5ExprPhrase *pPhrase = pNear->apPhrase[i];

      zRet = fts5PrintfAppend(zRet, " {");
      for(iTerm=0; zRet && iTerm<pPhrase->nTerm; iTerm++){
        char *zTerm = pPhrase->aTerm[iTerm].zTerm;
        zRet = fts5PrintfAppend(zRet, "%s%s", iTerm==0?"":" ", zTerm);
      }

      if( zRet ) zRet = fts5PrintfAppend(zRet, "}");
      if( zRet==0 ) return 0;
    }

  }else{
    char const *zOp = 0;
    int i;
    switch( pExpr->eType ){
      case FTS5_AND: zOp = "AND"; break;
      case FTS5_NOT: zOp = "NOT"; break;
      default: 
        assert( pExpr->eType==FTS5_OR );
        zOp = "OR"; 
        break;
    }

    zRet = sqlite3_mprintf("%s", zOp);
    for(i=0; zRet && i<pExpr->nChild; i++){
      char *z = fts5ExprPrintTcl(pConfig, zNearsetCmd, pExpr->apChild[i]);
      if( !z ){
        sqlite3_free(zRet);
        zRet = 0;
      }else{
        zRet = fts5PrintfAppend(zRet, " [%z]", z);
      }
    }
  }

  return zRet;
}

static char *fts5ExprPrint(Fts5Config *pConfig, Fts5ExprNode *pExpr){
  char *zRet = 0;
  if( pExpr->eType==FTS5_STRING || pExpr->eType==FTS5_TERM ){
    Fts5ExprNearset *pNear = pExpr->pNear;
    int i; 
    int iTerm;

    if( pNear->pColset ){
      int iCol = pNear->pColset->aiCol[0];
      zRet = fts5PrintfAppend(zRet, "%s : ", pConfig->azCol[iCol]);
      if( zRet==0 ) return 0;
    }

    if( pNear->nPhrase>1 ){
      zRet = fts5PrintfAppend(zRet, "NEAR(");
      if( zRet==0 ) return 0;
    }

    for(i=0; i<pNear->nPhrase; i++){
      Fts5ExprPhrase *pPhrase = pNear->apPhrase[i];
      if( i!=0 ){
        zRet = fts5PrintfAppend(zRet, " ");
        if( zRet==0 ) return 0;
      }
      for(iTerm=0; iTerm<pPhrase->nTerm; iTerm++){
        char *zTerm = fts5ExprTermPrint(&pPhrase->aTerm[iTerm]);
        if( zTerm ){
          zRet = fts5PrintfAppend(zRet, "%s%s", iTerm==0?"":" + ", zTerm);
          sqlite3_free(zTerm);
        }
        if( zTerm==0 || zRet==0 ){
          sqlite3_free(zRet);
          return 0;
        }
      }
    }

    if( pNear->nPhrase>1 ){
      zRet = fts5PrintfAppend(zRet, ", %d)", pNear->nNear);
      if( zRet==0 ) return 0;
    }

  }else{
    char const *zOp = 0;
    int i;

    switch( pExpr->eType ){
      case FTS5_AND: zOp = " AND "; break;
      case FTS5_NOT: zOp = " NOT "; break;
      default:  
        assert( pExpr->eType==FTS5_OR );
        zOp = " OR "; 
        break;
    }

    for(i=0; i<pExpr->nChild; i++){
      char *z = fts5ExprPrint(pConfig, pExpr->apChild[i]);
      if( z==0 ){
        sqlite3_free(zRet);
        zRet = 0;
      }else{
        int e = pExpr->apChild[i]->eType;
        int b = (e!=FTS5_STRING && e!=FTS5_TERM);
        zRet = fts5PrintfAppend(zRet, "%s%s%z%s", 
            (i==0 ? "" : zOp),
            (b?"(":""), z, (b?")":"")
        );
      }
      if( zRet==0 ) break;
    }
  }

  return zRet;
}

/*
** The implementation of user-defined scalar functions fts5_expr() (bTcl==0)
** and fts5_expr_tcl() (bTcl!=0).
*/
static void fts5ExprFunction(
  sqlite3_context *pCtx,          /* Function call context */
  int nArg,                       /* Number of args */
  sqlite3_value **apVal,          /* Function arguments */
  int bTcl
){
  Fts5Global *pGlobal = (Fts5Global*)sqlite3_user_data(pCtx);
  sqlite3 *db = sqlite3_context_db_handle(pCtx);
  const char *zExpr = 0;
  char *zErr = 0;
  Fts5Expr *pExpr = 0;
  int rc;
  int i;

  const char **azConfig;          /* Array of arguments for Fts5Config */
  const char *zNearsetCmd = "nearset";
  int nConfig;                    /* Size of azConfig[] */
  Fts5Config *pConfig = 0;
  int iArg = 1;

  if( nArg<1 ){
    zErr = sqlite3_mprintf("wrong number of arguments to function %s",
        bTcl ? "fts5_expr_tcl" : "fts5_expr"
    );
    sqlite3_result_error(pCtx, zErr, -1);
    sqlite3_free(zErr);
    return;
  }

  if( bTcl && nArg>1 ){
    zNearsetCmd = (const char*)sqlite3_value_text(apVal[1]);
    iArg = 2;
  }

  nConfig = 3 + (nArg-iArg);
  azConfig = (const char**)sqlite3_malloc(sizeof(char*) * nConfig);
  if( azConfig==0 ){
    sqlite3_result_error_nomem(pCtx);
    return;
  }
  azConfig[0] = 0;
  azConfig[1] = "main";
  azConfig[2] = "tbl";
  for(i=3; iArg<nArg; iArg++){
    azConfig[i++] = (const char*)sqlite3_value_text(apVal[iArg]);
  }

  zExpr = (const char*)sqlite3_value_text(apVal[0]);

  rc = sqlite3Fts5ConfigParse(pGlobal, db, nConfig, azConfig, &pConfig, &zErr);
  if( rc==SQLITE_OK ){
    rc = sqlite3Fts5ExprNew(pConfig, zExpr, &pExpr, &zErr);
  }
  if( rc==SQLITE_OK ){
    char *zText;
    if( pExpr->pRoot==0 ){
      zText = sqlite3_mprintf("");
    }else if( bTcl ){
      zText = fts5ExprPrintTcl(pConfig, zNearsetCmd, pExpr->pRoot);
    }else{
      zText = fts5ExprPrint(pConfig, pExpr->pRoot);
    }
    if( zText==0 ){
      rc = SQLITE_NOMEM;
    }else{
      sqlite3_result_text(pCtx, zText, -1, SQLITE_TRANSIENT);
      sqlite3_free(zText);
    }
  }

  if( rc!=SQLITE_OK ){
    if( zErr ){
      sqlite3_result_error(pCtx, zErr, -1);
      sqlite3_free(zErr);
    }else{
      sqlite3_result_error_code(pCtx, rc);
    }
  }
  sqlite3_free((void *)azConfig);
  sqlite3Fts5ConfigFree(pConfig);
  sqlite3Fts5ExprFree(pExpr);
}

static void fts5ExprFunctionHr(
  sqlite3_context *pCtx,          /* Function call context */
  int nArg,                       /* Number of args */
  sqlite3_value **apVal           /* Function arguments */
){
  fts5ExprFunction(pCtx, nArg, apVal, 0);
}
static void fts5ExprFunctionTcl(
  sqlite3_context *pCtx,          /* Function call context */
  int nArg,                       /* Number of args */
  sqlite3_value **apVal           /* Function arguments */
){
  fts5ExprFunction(pCtx, nArg, apVal, 1);
}

/*
** The implementation of an SQLite user-defined-function that accepts a
** single integer as an argument. If the integer is an alpha-numeric 
** unicode code point, 1 is returned. Otherwise 0.
*/
static void fts5ExprIsAlnum(
  sqlite3_context *pCtx,          /* Function call context */
  int nArg,                       /* Number of args */
  sqlite3_value **apVal           /* Function arguments */
){
  int iCode;
  if( nArg!=1 ){
    sqlite3_result_error(pCtx, 
        "wrong number of arguments to function fts5_isalnum", -1
    );
    return;
  }
  iCode = sqlite3_value_int(apVal[0]);
  sqlite3_result_int(pCtx, sqlite3Fts5UnicodeIsalnum(iCode));
}

static void fts5ExprFold(
  sqlite3_context *pCtx,          /* Function call context */
  int nArg,                       /* Number of args */
  sqlite3_value **apVal           /* Function arguments */
){
  if( nArg!=1 && nArg!=2 ){
    sqlite3_result_error(pCtx, 
        "wrong number of arguments to function fts5_fold", -1
    );
  }else{
    int iCode;
    int bRemoveDiacritics = 0;
    iCode = sqlite3_value_int(apVal[0]);
    if( nArg==2 ) bRemoveDiacritics = sqlite3_value_int(apVal[1]);
    sqlite3_result_int(pCtx, sqlite3Fts5UnicodeFold(iCode, bRemoveDiacritics));
  }
}

/*
** This is called during initialization to register the fts5_expr() scalar
** UDF with the SQLite handle passed as the only argument.
*/
int sqlite3Fts5ExprInit(Fts5Global *pGlobal, sqlite3 *db){
  struct Fts5ExprFunc {
    const char *z;
    void (*x)(sqlite3_context*,int,sqlite3_value**);
  } aFunc[] = {
    { "fts5_expr",     fts5ExprFunctionHr },
    { "fts5_expr_tcl", fts5ExprFunctionTcl },
    { "fts5_isalnum",  fts5ExprIsAlnum },
    { "fts5_fold",     fts5ExprFold },
  };
  int i;
  int rc = SQLITE_OK;
  void *pCtx = (void*)pGlobal;

  for(i=0; rc==SQLITE_OK && i<(sizeof(aFunc) / sizeof(aFunc[0])); i++){
    struct Fts5ExprFunc *p = &aFunc[i];
    rc = sqlite3_create_function(db, p->z, -1, SQLITE_UTF8, pCtx, p->x, 0, 0);
  }

  return rc;
}

/*
** Return the number of phrases in expression pExpr.
*/
int sqlite3Fts5ExprPhraseCount(Fts5Expr *pExpr){
  return (pExpr ? pExpr->nPhrase : 0);
}

/*
** Return the number of terms in the iPhrase'th phrase in pExpr.
*/
int sqlite3Fts5ExprPhraseSize(Fts5Expr *pExpr, int iPhrase){
  if( iPhrase<0 || iPhrase>=pExpr->nPhrase ) return 0;
  return pExpr->apExprPhrase[iPhrase]->nTerm;
}

/*
** This function is used to access the current position list for phrase
** iPhrase.
*/
int sqlite3Fts5ExprPoslist(Fts5Expr *pExpr, int iPhrase, const u8 **pa){
  int nRet;
  Fts5ExprPhrase *pPhrase = pExpr->apExprPhrase[iPhrase];
  Fts5ExprNode *pNode = pPhrase->pNode;
  if( pNode->bEof==0 && pNode->iRowid==pExpr->pRoot->iRowid ){
    *pa = pPhrase->poslist.p;
    nRet = pPhrase->poslist.n;
  }else{
    *pa = 0;
    nRet = 0;
  }
  return nRet;
}