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| 33 | pmbaty | 1 | #include "chess.h" |
| 2 | #include "data.h" |
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| 3 | /* last modified 12/21/09 */ |
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| 4 | /* |
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| 5 | ******************************************************************************* |
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| 6 | * * |
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| 7 | * Drawn() is used to answer the question "is this position a hopeless * |
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| 8 | * draw?" Several considerations are included in making this decision, but * |
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| 9 | * the most basic one is simply the remaining material for each side. If * |
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| 10 | * either side has pawns, it's not a draw. With no pawns, equal material is * |
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| 11 | * a draw. Otherwise, the superior side must have enough material to be * |
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| 12 | * able to force a mate. * |
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| 13 | * * |
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| 14 | * Drawn() has 0 possible return values: * |
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| 15 | * * |
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| 16 | * 0: Game is not a draw by rule or drawish in nature. * |
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| 17 | * * |
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| 18 | * 1: Game is a "technical draw" where material is even with no pawns and * |
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| 19 | * the search is also returning draw scores as the best outcome. * |
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| 20 | * * |
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| 21 | * 2: Game is an "actual draw" by FIDE rules, such as KB vs K, where mate * |
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| 22 | * can't be forced, even with worst possible play by one side. * |
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| 23 | * * |
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| 24 | ******************************************************************************* |
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| 25 | */ |
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| 26 | int Drawn(TREE * RESTRICT tree, int value) { |
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| 27 | /* |
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| 28 | ************************************************************ |
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| 29 | * * |
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| 30 | * If either side has pawns, the game is not a draw for * |
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| 31 | * lack of material. * |
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| 32 | * * |
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| 33 | ************************************************************ |
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| 34 | */ |
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| 35 | if (TotalPieces(white, pawn) || TotalPieces(black, pawn)) |
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| 36 | return 0; |
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| 37 | /* |
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| 38 | ************************************************************ |
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| 39 | * * |
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| 40 | * If the score suggests a mate has been found, this is * |
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| 41 | * not a draw. * |
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| 42 | * * |
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| 43 | ************************************************************ |
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| 44 | */ |
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| 45 | if (MateScore(value)) |
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| 46 | return 0; |
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| 47 | /* |
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| 48 | ************************************************************ |
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| 49 | * * |
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| 50 | * If neither side has pawns, and one side has some sort * |
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| 51 | * of material superiority, then determine if the winning * |
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| 52 | * side has enough material to win. * |
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| 53 | * * |
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| 54 | ************************************************************ |
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| 55 | */ |
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| 56 | if (TotalPieces(white, occupied) + TotalPieces(black, occupied) < 4) |
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| 57 | return 2; |
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| 58 | if (TotalPieces(white, occupied) < 5 && TotalPieces(black, occupied) < 5) |
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| 59 | return 1; |
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| 60 | if (TotalPieces(white, occupied) == 5 || TotalPieces(white, occupied) > 6) |
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| 61 | return 0; |
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| 62 | if (TotalPieces(black, occupied) == 5 || TotalPieces(black, occupied) > 6) |
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| 63 | return 0; |
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| 64 | if ((TotalPieces(white, occupied) == 6 && !Bishops(white) && Material > 0) |
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| 65 | || (TotalPieces(black, occupied) == 6 && !Bishops(black) |
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| 66 | && Material < 0)) |
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| 67 | return 1; |
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| 68 | /* |
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| 69 | ************************************************************ |
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| 70 | * * |
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| 71 | * The search result must indicate a draw also, otherwise * |
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| 72 | * it could be a tactical win or loss, so we will skip * |
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| 73 | * calling an equal material (no pawns) position a draw to * |
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| 74 | * make sure there is no mate that the search sees. * |
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| 75 | * * |
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| 76 | * If neither side has pawns, then one side must have some * |
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| 77 | * sort of material superiority, otherwise it is a draw. * |
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| 78 | * * |
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| 79 | ************************************************************ |
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| 80 | */ |
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| 81 | if (value != DrawScore(game_wtm)) |
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| 82 | return 0; |
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| 83 | if (TotalPieces(white, occupied) == TotalPieces(black, occupied)) |
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| 84 | return 1; |
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| 85 | return 0; |
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| 86 | } |