SQLite

      if( addrIf ) sqlite3VdbeJumpHere(v, addrIf);
    }
  }
}

typedef struct WindowCodeArg WindowCodeArg;
typedef struct WindowCsrAndReg WindowCsrAndReg;

/*
** See comments above struct WindowCodeArg.
*/
struct WindowCsrAndReg {
  int csr;                        /* Cursor number */
  int reg;                        /* First in array of peer values */
};

/*
** A single instance of this structure is allocated on the stack by 
** sqlite3WindowCodeStep() and a pointer to it passed to the various helper
** routines. This is to reduce the number of arguments required by each
** helper function.
**
** regArg:
**   Each window function requires an accumulator register (just as an
**   ordinary aggregate function does). This variable is set to the first
**   in an array of accumulator registers - one for each window function
**   in the WindowCodeArg.pMWin list.
**
** eDelete:
**   The window functions implementation sometimes caches the input rows
**   that it processes in a temporary table. If it is not zero, this
**   variable indicates when rows may be removed from the temp table (in
**   order to reduce memory requirements - it would always be safe just
**   to leave them there). Possible values for eDelete are:
**
**      WINDOW_RETURN_ROW:
**        An input row can be discarded after it is returned to the caller.
**
**      WINDOW_AGGINVERSE:
**        An input row can be discarded after the window functions xInverse()
**        callbacks have been invoked in it.
**
**      WINDOW_AGGSTEP:
**        An input row can be discarded after the window functions xStep()
**        callbacks have been invoked in it.
**
** start,current,end
**   Consider a window-frame similar to the following:
**
**     (ORDER BY a, b GROUPS BETWEEN 2 PRECEDING AND 2 FOLLOWING)
**
**   The windows functions implmentation caches the input rows in a temp
**   table, sorted by "a, b" (it actually populates the cache lazily, and
**   aggressively removes rows once they are no longer required, but that's
**   a mere detail). It keeps three cursors open on the temp table. One
**   (current) that points to the next row to return to the query engine
**   once its window function values have been calculated. Another (end)
**   points to the next row to call the xStep() method of each window function
**   on (so that it is 2 groups ahead of current). And a third (start) that
**   points to the next row to call the xInverse() method of each window
**   function on.
**
**   Each cursor (start, current and end) consists of a VDBE cursor
**   (WindowCsrAndReg.csr) and an array of registers (starting at
**   WindowCodeArg.reg) that always contains a copy of the peer values 
**   read from the corresponding cursor.
**
**   Depending on the window-frame in question, all three cursors may not
**   be required. In this case both WindowCodeArg.csr and reg are set to
**   0.
*/
struct WindowCodeArg {
  Parse *pParse;             /* Parse context */
  Window *pMWin;             /* First in list of functions being processed */
  Vdbe *pVdbe;               /* VDBE object */

  int addrGosub;             /* OP_Gosub to this address to return one row */
  int regGosub;              /* Register used with OP_Gosub(addrGosub) */
  int regArg;                /* First in array of accumulator registers */
  int eDelete;               /* See above */

  WindowCsrAndReg start;
  WindowCsrAndReg current;
  WindowCsrAndReg end;
};

/*

*/
static void windowCodeRangeTest(
  WindowCodeArg *p, 
  int op,                          /* OP_Ge, OP_Gt, or OP_Le */
  int csr1,                        /* Cursor number for cursor 1 */
  int regVal,                      /* Register containing non-negative number */
  int csr2,                        /* Cursor number for cursor 2 */
  int lbl                         /* Jump destination if condition is true */
){
  Parse *pParse = p->pParse;
  Vdbe *v = sqlite3GetVdbe(pParse);
  ExprList *pOrderBy = p->pMWin->pOrderBy;  /* ORDER BY clause for window */
  int reg1 = sqlite3GetTempReg(pParse);     /* Reg. for csr1.peerVal+regVal */
  int reg2 = sqlite3GetTempReg(pParse);     /* Reg. for csr2.peerVal */
  int regString = ++pParse->nMem;           /* Reg. for constant value '' */
  int arith = OP_Add;                       /* OP_Add or OP_Subtract */
  int addrGe;                               /* Jump destination */

  assert( op==OP_Ge || op==OP_Gt || op==OP_Le );
  assert( pOrderBy && pOrderBy->nExpr==1 );
  if( pOrderBy->a[0].sortFlags & KEYINFO_ORDER_DESC ){
    switch( op ){