SQLite

  p++;
  *pp = p;

  sqlite3Fts3GetVarint(p, &iVal);
  *pVal = iVal;
}

/*
** As long as *pp has not reached its end (pEnd), then do the same
** as fts3GetDeltaVarint(): read a single varint and add it to *pVal.
** But if we have reached the end of the varint, just set *pp=0 and
** leave *pVal unchanged.
*/
static void fts3GetDeltaVarint2(char **pp, char *pEnd, sqlite3_int64 *pVal){
  if( *pp>=pEnd ){
    *pp = 0;
  }else{
    fts3GetDeltaVarint(pp, pVal);
  }
}

/*
** The xDisconnect() virtual table method.
*/
static int fts3DisconnectMethod(sqlite3_vtab *pVtab){
  Fts3Table *p = (Fts3Table *)pVtab;
  int i;

      res = 0;
    }

    return res;
  }
}

/*
** Values that may be used as the first parameter to fts3DoclistMerge().
*/
#define MERGE_NOT        2        /* D + D -> D */
#define MERGE_AND        3        /* D + D -> D */
#define MERGE_OR         4        /* D + D -> D */
#define MERGE_PHRASE     6        /* P + P -> D */
#define MERGE_NEAR       8        /* P + P -> D */

#define MERGE_POS_OR     5        /* P + P -> P */
#define MERGE_POS_PHRASE 7        /* P + P -> P */
#define MERGE_POS_NEAR   9        /* P + P -> P */

/*
** Merge the two doclists passed in buffer a1 (size n1 bytes) and a2
** (size n2 bytes). The output is written to pre-allocated buffer aBuffer,
** which is guaranteed to be large enough to hold the results. The number
** of bytes written to aBuffer is stored in *pnBuffer before returning.
**
** If successful, SQLITE_OK is returned. Otherwise, if a malloc error
** occurs while allocating a temporary buffer as part of the merge operation,
** SQLITE_NOMEM is returned.
*/
static int fts3DoclistMerge(
  int mergetype,                  /* One of the MERGE_XXX constants */
  int nParam1,                    /* Used by MERGE_NEAR and MERGE_POS_NEAR */
  int nParam2,                    /* Used by MERGE_NEAR and MERGE_POS_NEAR */
  char *aBuffer,                  /* Pre-allocated output buffer */
  int *pnBuffer,                  /* OUT: Bytes written to aBuffer */
  char *a1,                       /* Buffer containing first doclist */
  int n1,                         /* Size of buffer a1 */
  char *a2,                       /* Buffer containing second doclist */
  int n2,                         /* Size of buffer a2 */
  int *pnDoc                      /* OUT: Number of docids in output */
){
  sqlite3_int64 i1 = 0;
  sqlite3_int64 i2 = 0;
  sqlite3_int64 iPrev = 0;

  char *p = aBuffer;
  char *p1 = a1;
  char *p2 = a2;
  char *pEnd1 = &a1[n1];
  char *pEnd2 = &a2[n2];
  int nDoc = 0;

  assert( mergetype==MERGE_OR     || mergetype==MERGE_POS_OR 
       || mergetype==MERGE_AND    || mergetype==MERGE_NOT
       || mergetype==MERGE_PHRASE || mergetype==MERGE_POS_PHRASE
       || mergetype==MERGE_NEAR   || mergetype==MERGE_POS_NEAR
  );
  assert( mergetype==MERGE_POS_PHRASE || mergetype==MERGE_POS_NEAR );

  if( !aBuffer ){
    *pnBuffer = 0;
    return SQLITE_NOMEM;
  }

  /* Read the first docid from each doclist */
  fts3GetDeltaVarint2(&p1, pEnd1, &i1);
  fts3GetDeltaVarint2(&p2, pEnd2, &i2);

  switch( mergetype ){
    case MERGE_OR:
    case MERGE_POS_OR:
      while( p1 || p2 ){
        if( p2 && p1 && i1==i2 ){
          fts3PutDeltaVarint(&p, &iPrev, i1);
          if( mergetype==MERGE_POS_OR ) fts3PoslistMerge(&p, &p1, &p2);
          fts3GetDeltaVarint2(&p1, pEnd1, &i1);
          fts3GetDeltaVarint2(&p2, pEnd2, &i2);
        }else if( !p2 || (p1 && i1<i2) ){
          fts3PutDeltaVarint(&p, &iPrev, i1);
          if( mergetype==MERGE_POS_OR ) fts3PoslistCopy(&p, &p1);
          fts3GetDeltaVarint2(&p1, pEnd1, &i1);
        }else{
          fts3PutDeltaVarint(&p, &iPrev, i2);
          if( mergetype==MERGE_POS_OR ) fts3PoslistCopy(&p, &p2);
          fts3GetDeltaVarint2(&p2, pEnd2, &i2);
        }
      }
      break;

    case MERGE_AND:
      while( p1 && p2 ){
        if( i1==i2 ){
          fts3PutDeltaVarint(&p, &iPrev, i1);
          fts3GetDeltaVarint2(&p1, pEnd1, &i1);
          fts3GetDeltaVarint2(&p2, pEnd2, &i2);
          nDoc++;
        }else if( i1<i2 ){
          fts3GetDeltaVarint2(&p1, pEnd1, &i1);
        }else{
          fts3GetDeltaVarint2(&p2, pEnd2, &i2);
        }
      }
      break;

    case MERGE_NOT:
      while( p1 ){
        if( p2 && i1==i2 ){
          fts3GetDeltaVarint2(&p1, pEnd1, &i1);
          fts3GetDeltaVarint2(&p2, pEnd2, &i2);
        }else if( !p2 || i1<i2 ){
          fts3PutDeltaVarint(&p, &iPrev, i1);
          fts3GetDeltaVarint2(&p1, pEnd1, &i1);
        }else{
          fts3GetDeltaVarint2(&p2, pEnd2, &i2);
        }
      }
      break;

    case MERGE_POS_PHRASE:
    case MERGE_PHRASE: {
      char **ppPos = (mergetype==MERGE_PHRASE ? 0 : &p);
      while( p1 && p2 ){
        if( i1==i2 ){
          char *pSave = p;
          sqlite3_int64 iPrevSave = iPrev;
          fts3PutDeltaVarint(&p, &iPrev, i1);
          if( 0==fts3PoslistPhraseMerge(ppPos, nParam1, 0, 1, &p1, &p2) ){
            p = pSave;
            iPrev = iPrevSave;
          }else{
            nDoc++;
          }
          fts3GetDeltaVarint2(&p1, pEnd1, &i1);
          fts3GetDeltaVarint2(&p2, pEnd2, &i2);
        }else if( i1<i2 ){
          fts3PoslistCopy(0, &p1);
          fts3GetDeltaVarint2(&p1, pEnd1, &i1);
        }else{
          fts3PoslistCopy(0, &p2);
          fts3GetDeltaVarint2(&p2, pEnd2, &i2);
        }
      }
      break;
    }

    default: assert( mergetype==MERGE_POS_NEAR || mergetype==MERGE_NEAR ); {
      char *aTmp = 0;
      char **ppPos = 0;

      if( mergetype==MERGE_POS_NEAR ){
        ppPos = &p;
        aTmp = sqlite3_malloc(2*(n1+n2+1));
        if( !aTmp ){
          return SQLITE_NOMEM;
        }
      }

      while( p1 && p2 ){
        if( i1==i2 ){
          char *pSave = p;
          sqlite3_int64 iPrevSave = iPrev;
          fts3PutDeltaVarint(&p, &iPrev, i1);

          if( !fts3PoslistNearMerge(ppPos, aTmp, nParam1, nParam2, &p1, &p2) ){
            iPrev = iPrevSave;
            p = pSave;
          }

          fts3GetDeltaVarint2(&p1, pEnd1, &i1);
          fts3GetDeltaVarint2(&p2, pEnd2, &i2);
        }else if( i1<i2 ){
          fts3PoslistCopy(0, &p1);
          fts3GetDeltaVarint2(&p1, pEnd1, &i1);
        }else{
          fts3PoslistCopy(0, &p2);
          fts3GetDeltaVarint2(&p2, pEnd2, &i2);
        }
      }
      sqlite3_free(aTmp);
      break;
    }
  }

  if( pnDoc ) *pnDoc = nDoc;
  *pnBuffer = (int)(p-aBuffer);
  return SQLITE_OK;
}

/* 
** A pointer to an instance of this structure is used as the context 
** argument to sqlite3Fts3SegReaderIterate()
*/
typedef struct TermSelect TermSelect;
struct TermSelect {
  int isReqPos;

/*
** This function merges two doclists according to the requirements of a
** NEAR operator.
*/
static int fts3DoclistNearMerge(
  int bDescIdx,
  int mergetype,                  /* MERGE_POS_NEAR or MERGE_NEAR */
  int nNear,                      /* Parameter to NEAR operator */
  int nTokenLeft,                 /* Number of tokens in LHS phrase arg */
  char *aLeft,                    /* Doclist for LHS (incl. positions) */
  int nLeft,                      /* Size of LHS doclist in bytes */
  int nTokenRight,                /* As nTokenLeft */
  char *aRight,                   /* As aLeft */
  int nRight,                     /* As nRight */

** other doclists (except the aaOutput[0] one) and return SQLITE_OK.
**
** If an OOM error occurs, return SQLITE_NOMEM. In this case it is
** the responsibility of the caller to free any doclists left in the
** TermSelect.aaOutput[] array.
*/
static int fts3TermSelectMerge(Fts3Table *p, TermSelect *pTS){
  int mergetype = (pTS->isReqPos ? MERGE_POS_OR : MERGE_OR);
  char *aOut = 0;
  int nOut = 0;
  int i;

  /* Loop through the doclists in the aaOutput[] array. Merge them all
  ** into a single doclist.
  */

    pTS->anOutput[0] = nDoclist;
    if( pTS->aaOutput[0] ){
      memcpy(pTS->aaOutput[0], aDoclist, nDoclist);
    }else{
      return SQLITE_NOMEM;
    }
  }else{
    int mergetype = (pTS->isReqPos ? MERGE_POS_OR : MERGE_OR);
    char *aMerge = aDoclist;
    int nMerge = nDoclist;
    int iOut;

    for(iOut=0; iOut<SizeofArray(pTS->aaOutput); iOut++){
      if( pTS->aaOutput[iOut]==0 ){
        assert( iOut>0 );

      sqlite3_free(pRight->doclist.aAll);
      pRight->doclist.aAll = 0;
      pRight->doclist.nAll = 0;
    }else if( pRight->doclist.aAll ){
      char *aOut;                 /* Buffer in which to assemble new doclist */
      int nOut;                   /* Size of buffer aOut in bytes */
  
      *pRc = fts3DoclistNearMerge(bDescIdx, MERGE_POS_NEAR, nNear, 
      *pRc = fts3DoclistNearMerge(bDescIdx, nNear, 
          pLeft->nToken, pLeft->doclist.aAll, pLeft->doclist.nAll,
          pRight->nToken, pRight->doclist.aAll, pRight->doclist.nAll,
          &aOut, &nOut
      );
      sqlite3_free(pRight->doclist.aAll);
      pRight->doclist.aAll = aOut;
      pRight->doclist.nAll = nOut;