SQLite

**   Then, for each level from 0 to nMax:
**
**     + number of input segments in ongoing merge.
**     + total number of segments in level.
**     + for each segment from oldest to newest:
**         + segment id (always > 0)
**         + b-tree height (1 -> root is leaf, 2 -> root is parent of leaf etc.)
**         + first leaf page number (often 1, always greater than 0)
**         + final leaf page number
**
** 2. The Averages Record:
**
**   A single record within the %_data table. The data is a list of varints.
**   The first value is the number of rows in the index. Then, for each column
**   from left to right, the total number of tokens in the column for all 

      sqlite3_free(p->apHash);
    }
    sqlite3_free(p->zDataTbl);
    sqlite3_free(p);
  }
  return rc;
}

/*
** Argument p points to a buffer containing utf-8 text that is n bytes in 
** size. Return the number of bytes in the nChar character prefix of the
** buffer, or 0 if there are less than nChar characters in total.
*/
static int fts5IndexCharlenToBytelen(const char *p, int nByte, int nChar){
  int n = 0;
  int i;
  for(i=0; i<nChar; i++){
    if( n>=nByte ) return 0;      /* Input contains fewer than nChar chars */
    if( (unsigned char)p[n++]>=0xc0 ){
      while( (p[n] & 0xc0)==0x80 ) n++;
    }
  }
  return n;
}

/*
** pIn is a UTF-8 encoded string, nIn bytes in size. Return the number of
** unicode characters in the string.
*/
int fts5IndexCharlen(const char *pIn, int nIn){
  int nChar = 0;            
  int i = 0;
  while( i<nIn ){
    if( (unsigned char)pIn[i++]>=0xc0 ){
      while( i<nIn && (pIn[i] & 0xc0)==0x80 ) i++;
    }
    nChar++;
  }
  return nChar;
}

/*
** Calculate and return a checksum that is the XOR of the index entry
** checksum of all entries that would be generated by the token specified
** by the final 5 arguments.
*/
u64 sqlite3Fts5IndexCksum(
  Fts5Config *pConfig,            /* Configuration object */
  i64 iRowid,                     /* Document term appears in */
  int iCol,                       /* Column term appears in */
  int iPos,                       /* Position term appears in */
  const char *pTerm, int nTerm    /* Term at iPos */
){
  u64 ret = 0;                    /* Return value */
  int iIdx;                       /* For iterating through indexes */

  ret = fts5IndexEntryCksum(iRowid, iCol, iPos, pTerm, nTerm);

  for(iIdx=0; iIdx<pConfig->nPrefix; iIdx++){
    int nByte = fts5IndexCharlenToBytelen(pTerm, nTerm, pConfig->aPrefix[iIdx]);
    if( nByte ){
      ret ^= fts5IndexEntryCksum(iRowid, iCol, iPos, pTerm, nByte);
    }
  }

  return ret;
}

/*

    }
  }

  /* Add the new token to the main terms hash table. And to each of the
  ** prefix hash tables that it is large enough for. */
  fts5AddTermToHash(p, 0, iCol, iPos, pToken, nToken);
  for(i=0; i<pConfig->nPrefix; i++){
    int nByte = fts5IndexCharlenToBytelen(pToken, nToken, pConfig->aPrefix[i]);
    if( nByte ){
      fts5AddTermToHash(p, i+1, iCol, iPos, pToken, nByte);
    }
  }

  return fts5IndexReturn(p);
}

/*

  Fts5IndexIter **ppIter          /* OUT: New iterator object */
){
  Fts5IndexIter *pRet;
  int iIdx = 0;

  if( flags & FTS5INDEX_QUERY_PREFIX ){
    Fts5Config *pConfig = p->pConfig;
    int nChar = fts5IndexCharlen(pToken, nToken);
    for(iIdx=1; iIdx<=pConfig->nPrefix; iIdx++){
      if( pConfig->aPrefix[iIdx-1]==nChar ) break;
    }
    if( iIdx>pConfig->nPrefix ){
      iIdx = -1;
    }
  }

  pRet = (Fts5IndexIter*)sqlite3Fts5MallocZero(&p->rc, sizeof(Fts5IndexIter));

    sqlite3_result_text(pCtx, (const char*)s.p, s.n, SQLITE_TRANSIENT);
  }else{
    sqlite3_result_error_code(pCtx, rc);
  }
  fts5BufferFree(&s);
}

/*
** The implementation of user-defined scalar function fts5_rowid().
*/
static void fts5RowidFunction(
  sqlite3_context *pCtx,          /* Function call context */
  int nArg,                       /* Number of args (always 2) */
  sqlite3_value **apVal           /* Function arguments */
){
  const char *zArg;
  if( nArg==0 ){
    sqlite3_result_error(pCtx, "should be: fts5_rowid(subject, ....)", -1);
  }else{
    zArg = (const char*)sqlite3_value_text(apVal[0]);
    if( 0==sqlite3_stricmp(zArg, "segment") ){
      i64 iRowid;
      int idx, segid, height, pgno;
      if( nArg!=5 ){
        sqlite3_result_error(pCtx, 
            "should be: fts5_rowid('segment', idx, segid, height, pgno))", -1
        );
      }else{
        idx = sqlite3_value_int(apVal[1]);
        segid = sqlite3_value_int(apVal[2]);
        height = sqlite3_value_int(apVal[3]);
        pgno = sqlite3_value_int(apVal[4]);
        iRowid = FTS5_SEGMENT_ROWID(idx, segid, height, pgno);
        sqlite3_result_int64(pCtx, iRowid);
      }
    }else if( 0==sqlite3_stricmp(zArg, "start-of-index") ){
      i64 iRowid;
      int idx;
      if( nArg!=2 ){
        sqlite3_result_error(pCtx, 
            "should be: fts5_rowid('start-of-index', idx)", -1
        );
      }else{
        idx = sqlite3_value_int(apVal[1]);
        iRowid = FTS5_SEGMENT_ROWID(idx, 1, 0, 0);
        sqlite3_result_int64(pCtx, iRowid);
      }
    }else {
      sqlite3_result_error(pCtx, 
        "first arg to fts5_rowid() must be 'segment' "
        "or 'start-of-index' ..."
        , -1
      );
    }
  }
}

/*
** This is called as part of registering the FTS5 module with database
** connection db. It registers several user-defined scalar functions useful
** with FTS5.
**
** If successful, SQLITE_OK is returned. If an error occurs, some other
** SQLite error code is returned instead.
*/
int sqlite3Fts5IndexInit(sqlite3 *db){
  int rc = sqlite3_create_function(
      db, "fts5_decode", 2, SQLITE_UTF8, 0, fts5DecodeFunction, 0, 0
  );
  if( rc==SQLITE_OK ){
    rc = sqlite3_create_function(
        db, "fts5_rowid", -1, SQLITE_UTF8, 0, fts5RowidFunction, 0, 0
    );
  }
  return rc;
}

# 2015 Jan 13
#
# 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.
#
#***********************************************************************
#
#

source [file join [file dirname [info script]] fts5_common.tcl]
set testprefix fts5prefix


#-------------------------------------------------------------------------
# Check that prefix indexes really do index n-character prefixes, not 
# n-byte prefixes. Use the ascii tokenizer so as not to be confused by
# diacritic removal.
#
do_execsql_test 1.0 { 
  CREATE VIRTUAL TABLE t1 USING fts5(x, tokenize = ascii, prefix = 2) 
}

do_test 1.2 {
  foreach {rowid string} {
    1 "\xCA\xCB\xCC\xCD"
    2 "\u1234\u5678\u4321\u8765"
  } {
    execsql { INSERT INTO t1(rowid, x) VALUES($rowid, $string) }
  }
} {}

do_execsql_test 1.1.2 {
  INSERT INTO t1(t1) VALUES('integrity-check');
}

#db eval { select fts5_decode(id, block) AS d FROM t1_data; } { puts $d }

foreach o {1 2} {
  if {$o==2} breakpoint
  foreach {tn q res} {
    1 "SELECT rowid FROM t1 WHERE t1 MATCH '\xCA\xCB*'" 1
    2 "SELECT rowid FROM t1 WHERE t1 MATCH '\u1234\u5678*'" 2
  } {
    do_execsql_test 1.$o.$tn $q $res
  }

  execsql {
    DELETE FROM t1_data WHERE 
    rowid>=fts5_rowid('start-of-index', 0) AND 
    rowid<fts5_rowid('start-of-index', 1);
  }
}


finish_test