SQLite

  int iMin;                 /* Index in a[] of entry with minimum score */
  int nSample;              /* Current number of samples */
  int iGet;                 /* Index of current sample accessed by stat_get() */
  Stat4Sample *a;           /* Array of mxSample Stat4Sample objects */
};

/*
** Implementation of the stat_init(C,N,S) SQL function. The three parameters
** are the number of rows in the table or index (C), the number of columns
** in the index (N) and the number of samples to accumulate (S).
**
** This routine allocates the Stat4Accum object in heap memory. The return 
** value is a pointer to the the Stat4Accum object encoded as a blob (i.e. 
** the size of the blob is sizeof(void*) bytes). 
*/
static void statInit(
  sqlite3_context *context,

  int nCol;                       /* Number of columns in index being sampled */
  int n;                          /* Bytes of space to allocate */
  int i;                          /* Used to iterate through p->aSample[] */

  /* Decode the three function arguments */
  UNUSED_PARAMETER(argc);
  nRow = (tRowcnt)sqlite3_value_int64(argv[0]);
  mxSample = sqlite3_value_int(argv[2]);
  nCol = sqlite3_value_int(argv[1]);
  assert( nCol>1 );               /* >1 because it includes the rowid column */

  /* Allocate the space required for the Stat4Accum object */
  n = sizeof(*p) 
    + sizeof(tRowcnt)*nCol                    /* Stat4Accum.anEq */
    + sizeof(tRowcnt)*nCol                    /* Stat4Accum.anLt */

    p->aBest[i].iCol = i;
  }

  /* Return a pointer to the allocated object to the caller */
  sqlite3_result_blob(context, p, sizeof(p), sqlite3_free);
}
static const FuncDef statInitFuncdef = {
  3,               /* nArg */
  SQLITE_UTF8,     /* iPrefEnc */
  0,               /* flags */
  0,               /* pUserData */
  0,               /* pNext */
  statInit,        /* xFunc */
  0,               /* xStep */
  0,               /* xFinalize */

    ** 
    **     * the number of rows in the index,
    **     * the number of columns in the index including the rowid,
    **     * the recommended number of samples for the stat3/stat4 table.
    */
    sqlite3VdbeAddOp2(v, OP_Count, iIdxCur, regStat4+1);
    sqlite3VdbeAddOp2(v, OP_Integer, nCol+1, regStat4+2);
    sqlite3VdbeAddOp2(v, OP_Integer, SQLITE_STAT4_SAMPLES, regStat4+3);
    sqlite3VdbeAddOp3(v, OP_Function, 0, regStat4+1, regStat4);
    sqlite3VdbeChangeP4(v, -1, (char*)&statInitFuncdef, P4_FUNCDEF);
    sqlite3VdbeChangeP5(v, 3);

    /* Implementation of the following:
    **
    **   Rewind csr
    **   if eof(csr) goto end_of_scan;
    **   regChng = 0
    **   goto next_push_0;