SQLite

** arrays of registers using the collation sequences and other comparison
** parameters specified by pOrderBy. 
**
** If the two arrays are not equal, the contents of regNew is copied to 
** regOld and control falls through. Otherwise, if the contents of the arrays
** are equal, an OP_Goto is executed. The address of the OP_Goto is returned.
*/
static void windowIfNewPeer(
  Parse *pParse,
  ExprList *pOrderBy,
  int regNew,                     /* First in array of new values */
  int regOld,                     /* First in array of old values */
  int addr                        /* Jump here */
){
  Vdbe *v = sqlite3GetVdbe(pParse);

  if( pOrderBy ){
    int nVal = pOrderBy->nExpr;
    KeyInfo *pKeyInfo = sqlite3KeyInfoFromExprList(pParse, pOrderBy, 0, 0);
    sqlite3VdbeAddOp3(v, OP_Compare, regOld, regNew, nVal);
    sqlite3VdbeAppendP4(v, (void*)pKeyInfo, P4_KEYINFO);
    sqlite3VdbeAddOp3(v, OP_Jump, 
      sqlite3VdbeCurrentAddr(v)+1, addr, sqlite3VdbeCurrentAddr(v)+1
    );
    VdbeCoverageEqNe(v);
    sqlite3VdbeAddOp3(v, OP_Copy, regNew, regOld, nVal-1);
  }else{
    sqlite3VdbeAddOp2(v, OP_Goto, 0, addr);
  }

}

typedef struct WindowCodeArg WindowCodeArg;
typedef struct WindowCsrAndReg WindowCsrAndReg;
struct WindowCsrAndReg {
  int csr;
  int reg;

  }

  if( bPeer ){
    int addr;
    int nReg = (pMWin->pOrderBy ? pMWin->pOrderBy->nExpr : 0);
    int regTmp = (nReg ? sqlite3GetTempRange(pParse, nReg) : 0);
    windowReadPeerValues(p, csr, regTmp);
    windowIfNewPeer(pParse, pMWin->pOrderBy, regTmp, reg, addrContinue);

    sqlite3ReleaseTempRange(pParse, regTmp, nReg);
  }

  if( addrNextRange ){
    sqlite3VdbeAddOp2(v, OP_Goto, 0, addrNextRange);
  }
  sqlite3VdbeResolveLabel(v, lblDone);

**
**     ... loop started by sqlite3WhereBegin() ...
**       if( new partition ){
**         Gosub flush
**       }
**       Insert new row into eph table.
**       if( first row of partition ){
**         Rewind(csrEnd) ; Rewind(csrStart) ; Rewind(csrCurrent)


**         regEnd = <expr2>
**         regStart = <expr1>
**       }else{
**         if( (regEnd--)<=0 ){
**           AGGSTEP
**         }
**         RETURN_ROW

**
**     ... loop started by sqlite3WhereBegin() ...
**     if( new partition ){
**       Gosub flush
**     }
**     Insert new row into eph table.
**     if( first row of partition ){
**       Rewind(csrEnd) ; Rewind(csrStart) ; Rewind(csrCurrent)


**       regEnd = <expr2>
**       regStart = regEnd - <expr1>
**     }else{
**       AGGSTEP
**       if( (regEnd--)<=0 ){
**         RETURN_ROW
**       }

**
**     ... loop started by sqlite3WhereBegin() ...
**     if( new partition ){
**       Gosub flush
**     }
**     Insert new row into eph table.
**     if( first row of partition ){
**       Rewind(csrEnd) ; Rewind(csrStart) ; Rewind(csrCurrent)


**       regStart = <expr1>
**     }else{
**       AGGSTEP
**     }
**   }
**   flush:
**     AGGSTEP
**     while( 1 ){
**       if( (regStart--)<=0 ){
**         AGGINVERSE
**         if( eof ) break
**       }
**       RETURN_ROW
**     }
**     while( !eof csrCurrent ){
**       RETURN_ROW
**     }
**
** Also requiring special handling are the cases:
**
**   ROWS BETWEEN <expr1> PRECEDING AND <expr2> PRECEDING
**   ROWS BETWEEN <expr1> FOLLOWING AND <expr2> FOLLOWING
**
** when (expr1 < expr2). This is detected at runtime, not by this function.
** To handle this case, the pseudo-code programs depicted above are modified
** slightly to be:
**
**     ... loop started by sqlite3WhereBegin() ...
**     if( new partition ){
**       Gosub flush
**     }
**     Insert new row into eph table.
**     if( first row of partition ){
**       Rewind(csrEnd) ; Rewind(csrStart) ; Rewind(csrCurrent)
**       regEnd = <expr2>
**       regStart = <expr1>
**       if( regEnd < regStart ){
**         RETURN_ROW
**         delete eph table contents
**         continue
**       }
**     ...
**
** The new "continue" statement in the above jumps to the next iteration
** of the outer loop - the one started by sqlite3WhereBegin().
**
** The various GROUPS cases are implemented using the same patterns as
** ROWS. The VM code is modified slightly so that:
**
**   1. The else branch in the main loop is only taken if the row just
**      added to the ephemeral table is the start of a new group. In
**      other words, it becomes:
**
**         ... loop started by sqlite3WhereBegin() ...
**         if( new partition ){
**           Gosub flush
**         }
**         Insert new row into eph table.
**         if( first row of partition ){
**           Rewind(csrEnd) ; Rewind(csrStart) ; Rewind(csrCurrent)
**           regEnd = <expr2>
**           regStart = <expr1>
**         }else if( new group ){
**           ... 
**         }
**       }
**
**   2. Instead of processing a single row, each RETURN_ROW, AGGSTEP or 
**      AGGINVERSE step processes the current row of the relevant cursor and
**      all subsequent rows belonging to the same group.
**
** RANGE window frames are a little different again. As for GROUPS, the 
** main loop runs once per group only. And RETURN_ROW, AGGSTEP and AGGINVERSE
** deal in groups instead of rows. As for ROWS and GROUPS, there are three
** basic cases:
**
**   RANGE BETWEEN <expr1> PRECEDING AND <expr2> FOLLOWING
**
**     ... loop started by sqlite3WhereBegin() ...
**       if( new partition ){
**         Gosub flush
**       }
**       Insert new row into eph table.
**       if( first row of partition ){
**         Rewind(csrEnd) ; Rewind(csrStart) ; Rewind(csrCurrent)
**         regEnd = <expr2>
**         regStart = <expr1>
**       }else{
**         AGGSTEP
**         while( (csrCurrent.key + regEnd) < csrEnd.key ){
**           RETURN_ROW
**           while( csrStart.key + regStart) < csrCurrent.key ){
**             AGGINVERSE
**           }
**         }
**       }
**     }
**     flush:
**       AGGSTEP
**       while( 1 ){
**         RETURN ROW
**         if( csrCurrent is EOF ) break;
**           while( csrStart.key + regStart) < csrCurrent.key ){
**             AGGINVERSE
**           }
**         }
**       }
**
** In the above notation, "csr.key" means the current value of the ORDER BY 
** expression (there is only ever 1 for a RANGE that uses an <expr> FOLLOWING
** or <expr PRECEDING) read from cursor csr.
**
**   RANGE BETWEEN <expr1> PRECEDING AND <expr2> PRECEDING
**
**     ... loop started by sqlite3WhereBegin() ...
**       if( new partition ){
**         Gosub flush
**       }
**       Insert new row into eph table.
**       if( first row of partition ){
**         Rewind(csrEnd) ; Rewind(csrStart) ; Rewind(csrCurrent)
**         regEnd = <expr2>
**         regStart = <expr1>
**       }else{
**         while( (csrEnd.key + regEnd) <= csrCurrent.key ){
**           AGGSTEP
**         }
**         RETURN_ROW
**         while( (csrStart.key + regStart) < csrCurrent.key ){
**           AGGINVERSE
**         }
**       }
**     }
**     flush:
**       while( (csrEnd.key + regEnd) <= csrCurrent.key ){
**         AGGSTEP
**       }
**       RETURN_ROW
**
**   RANGE BETWEEN <expr1> FOLLOWING AND <expr2> FOLLOWING
**
**     ... loop started by sqlite3WhereBegin() ...
**       if( new partition ){
**         Gosub flush
**       }
**       Insert new row into eph table.
**       if( first row of partition ){
**         Rewind(csrEnd) ; Rewind(csrStart) ; Rewind(csrCurrent)
**         regEnd = <expr2>
**         regStart = <expr1>
**       }else{
**         AGGSTEP
**         while( (csrCurrent.key + regEnd) < csrEnd.key ){
**           while( (csrCurrent.key + regStart) > csrStart.key ){
**             AGGINVERSE
**           }
**           RETURN_ROW
**         }
**       }
**     }
**     flush:
**       AGGSTEP
**       while( 1 ){
**         while( (csrCurrent.key + regStart) > csrStart.key ){
**           AGGINVERSE
**           if( eof ) break "while( 1 )" loop.
**         }
**         RETURN_ROW
**       }
**       while( !eof csrCurrent ){
**         RETURN_ROW
**       }
**
*/
void sqlite3WindowCodeStep(
  Parse *pParse,                  /* Parse context */
  Select *p,                      /* Rewritten SELECT statement */
  WhereInfo *pWInfo,              /* Context returned by sqlite3WhereBegin() */
  int regGosub,                   /* Register for OP_Gosub */
  int addrGosub                   /* OP_Gosub here to return each row */
){
  Window *pMWin = p->pWin;
  ExprList *pOrderBy = pMWin->pOrderBy;
  Vdbe *v = sqlite3GetVdbe(pParse);
  int regFlushPart;               /* Register for "Gosub flush_partition" */
  int csrWrite;                   /* Cursor used to write to eph. table */
  int csrInput = p->pSrc->a[0].iCursor;     /* Cursor of sub-select */
  int nInput = p->pSrc->a[0].pTab->nCol;    /* Number of cols returned by sub */
  int iInput;                               /* To iterate through sub cols */

  int addrIfNot;                  /* Address of OP_IfNot */
  int addrGosubFlush;             /* Address of OP_Gosub to flush: */
  int addrInteger;                /* Address of OP_Integer */

  int addrEmpty = 0;              /* Address of OP_Rewind in flush: */

  int regStart = 0;               /* Value of <expr> PRECEDING */
  int regEnd = 0;                 /* Value of <expr> FOLLOWING */
  int regNew;                     /* Array of registers holding new input row */
  int regRecord;                  /* regNew array in record form */
  int regRowid;                   /* Rowid for regRecord in eph table */
  int regNewPeer = 0;             /* Peer values for new row (part of regNew) */
  int regPeer = 0;                /* Peer values for current row */
  WindowCodeArg s;                /* Context object for sub-routines */
  int lblWhereEnd;                /* Label just before sqlite3WhereEnd() code */

  assert( pMWin->eStart==TK_PRECEDING || pMWin->eStart==TK_CURRENT 
       || pMWin->eStart==TK_FOLLOWING || pMWin->eStart==TK_UNBOUNDED 
  );
  assert( pMWin->eEnd==TK_FOLLOWING || pMWin->eEnd==TK_CURRENT 
       || pMWin->eEnd==TK_UNBOUNDED || pMWin->eEnd==TK_PRECEDING 
  );

  lblWhereEnd = sqlite3VdbeMakeLabel(pParse);


  /* Fill in the context object */
  memset(&s, 0, sizeof(WindowCodeArg));
  s.pParse = pParse;
  s.pMWin = pMWin;
  s.pVdbe = v;
  s.regGosub = regGosub;

  if( pMWin->eStart==pMWin->eEnd && regStart && regEnd ){
    int op = ((pMWin->eStart==TK_FOLLOWING) ? OP_Ge : OP_Le);
    int addrGe = sqlite3VdbeAddOp3(v, op, regStart, 0, regEnd);
    windowAggFinal(pParse, pMWin, 0);
    sqlite3VdbeAddOp2(v, OP_Rewind, s.current.csr, 1);
    windowReturnOneRow(pParse, pMWin, regGosub, addrGosub);
    sqlite3VdbeAddOp1(v, OP_ResetSorter, s.current.csr);
    sqlite3VdbeAddOp2(v, OP_Goto, 0, lblWhereEnd);
    sqlite3VdbeJumpHere(v, addrGe);
  }
  if( pMWin->eStart==TK_FOLLOWING && pMWin->eType!=TK_RANGE && regEnd ){
    assert( pMWin->eEnd==TK_FOLLOWING );
    sqlite3VdbeAddOp3(v, OP_Subtract, regStart, regEnd, regStart);
  }

  if( pMWin->eStart!=TK_UNBOUNDED ){
    sqlite3VdbeAddOp2(v, OP_Rewind, s.start.csr, 1);
  }
  sqlite3VdbeAddOp2(v, OP_Rewind, s.current.csr, 1);
  sqlite3VdbeAddOp2(v, OP_Rewind, s.end.csr, 1);
  if( regPeer && pOrderBy ){
    sqlite3VdbeAddOp3(v, OP_Copy, regNewPeer, regPeer, pOrderBy->nExpr-1);
    sqlite3VdbeAddOp3(v, OP_Copy, regPeer, s.start.reg, pOrderBy->nExpr-1);
    sqlite3VdbeAddOp3(v, OP_Copy, regPeer, s.current.reg, pOrderBy->nExpr-1);
    sqlite3VdbeAddOp3(v, OP_Copy, regPeer, s.end.reg, pOrderBy->nExpr-1);
  }

  sqlite3VdbeAddOp2(v, OP_Integer, 0, pMWin->regFirst);
  sqlite3VdbeAddOp2(v, OP_Goto, 0, lblWhereEnd);

  /* Begin generating SECOND_ROW_CODE */
  VdbeModuleComment((pParse->pVdbe, "Begin WindowCodeStep.SECOND_ROW"));
  sqlite3VdbeJumpHere(v, addrIfNot);
  if( regPeer ){
    windowIfNewPeer(pParse, pOrderBy, regNewPeer, regPeer, lblWhereEnd);
  }
  if( pMWin->eStart==TK_FOLLOWING ){
    windowCodeOp(&s, WINDOW_AGGSTEP, 0, 0);
    if( pMWin->eEnd!=TK_UNBOUNDED ){
      if( pMWin->eType==TK_RANGE ){
        int lbl = sqlite3VdbeMakeLabel(pParse);
        int addrNext = sqlite3VdbeCurrentAddr(v);

        if( regEnd ) addr = sqlite3VdbeAddOp3(v, OP_IfPos, regEnd, 0, 1);
        windowCodeOp(&s, WINDOW_RETURN_ROW, 0, 0);
        windowCodeOp(&s, WINDOW_AGGINVERSE, regStart, 0);
        if( regEnd ) sqlite3VdbeJumpHere(v, addr);
      }
    }
  }



  VdbeModuleComment((pParse->pVdbe, "End WindowCodeStep.SECOND_ROW"));

  /* End of the main input loop */
  sqlite3VdbeResolveLabel(v, lblWhereEnd);

  sqlite3WhereEnd(pWInfo);

  /* Fall through */
  if( pMWin->pPartition ){
    addrInteger = sqlite3VdbeAddOp2(v, OP_Integer, 0, regFlushPart);
    sqlite3VdbeJumpHere(v, addrGosubFlush);
  }

    windowCodeOp(&s, WINDOW_AGGSTEP, 0, 0);
    addrStart = sqlite3VdbeCurrentAddr(v);
    addrBreak = windowCodeOp(&s, WINDOW_RETURN_ROW, 0, 1);
    windowCodeOp(&s, WINDOW_AGGINVERSE, regStart, 0);
    sqlite3VdbeAddOp2(v, OP_Goto, 0, addrStart);
    sqlite3VdbeJumpHere(v, addrBreak);
  }

  sqlite3VdbeJumpHere(v, addrEmpty);

  sqlite3VdbeAddOp1(v, OP_ResetSorter, s.current.csr);
  sqlite3VdbeAddOp2(v, OP_Integer, 1, pMWin->regFirst);
  VdbeModuleComment((pParse->pVdbe, "End WindowCodeStep.FLUSH"));
  if( pMWin->pPartition ){
    sqlite3VdbeChangeP1(v, addrInteger, sqlite3VdbeCurrentAddr(v));
    sqlite3VdbeAddOp1(v, OP_Return, regFlushPart);
  }
}

#endif /* SQLITE_OMIT_WINDOWFUNC */