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#include "chess.h"
#include "data.h"
/* last modified 12/21/09 */
/*
*******************************************************************************
* *
* Drawn() is used to answer the question "is this position a hopeless draw?"*
* Several considerations are included in making this decision, but the most *
* basic one is simply the remaining material for each side. If either side *
* has pawns, it's not a draw. With no pawns, equal material is a draw. *
* Otherwise, the superior side must have enough material to be able to force*
* a mate. *
* *
* Drawn() has 0 possible return values: *
* *
* 0: Game is not a draw by rule or drawish in nature. *
* *
* 1: Game is a "technical draw" where material is even with no pawns and *
* the search is also returning draw scores as the best outcome. *
* *
* 2: Game is an "actual draw" by FIDE rules, such as KB vs K, where mate *
* can't be forced, even with worst possible play by one side. *
* *
*******************************************************************************
*/
int Drawn(TREE * RESTRICT tree, int value) {
/*
************************************************************
* *
* If either side has pawns, the game is not a draw for *
* lack of material. *
* *
************************************************************
*/
if (TotalPieces(white, pawn) || TotalPieces(black, pawn))
return (0);
/*
************************************************************
* *
* If the score suggests a mate has been found, this is *
* not a draw. *
* *
************************************************************
*/
if (Abs(value) > MATE - 1024)
return (0);
/*
************************************************************
* *
* If neither side has pawns, and one side has some sort *
* of material superiority, then determine if the winning *
* side has enough material to win. *
* *
************************************************************
*/
if (TotalPieces(white, occupied) + TotalPieces(black, occupied) < 4)
return (2);
if (TotalPieces(white, occupied) < 5 && TotalPieces(black, occupied) < 5)
return (1);
if (TotalPieces(white, occupied) == 5 || TotalPieces(white, occupied) > 6)
return (0);
if (TotalPieces(black, occupied) == 5 || TotalPieces(black, occupied) > 6)
return (0);
if ((TotalPieces(white, occupied) == 6 && !Bishops(white) && Material > 0)
|| (TotalPieces(black, occupied) == 6 && !Bishops(black) &&
Material < 0))
return (1);
/*
************************************************************
* *
* The search result must indicate a draw also, otherwise *
* it could be a tactical win or loss, so we will skip *
* calling an equal material (no pawns) position a draw *
* to make sure there is no mate that the search sees. *
* *
* If neither side has pawns, then one side must have *
* some sort of material superiority, otherwise it is a *
* draw. *
* *
************************************************************
*/
if (value != DrawScore(wtm))
return (0);
if (TotalPieces(white, occupied) == TotalPieces(black, occupied))
return (1);
return (0);
}
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