X-Git-Url: https://git.sesse.net/?p=stockfish;a=blobdiff_plain;f=src%2Fendgame.cpp;h=94967c25eac588043e0730eabc2c0da5a4a16745;hp=635ff4085382ad07f4d2ecc67a7fbcfacb615695;hb=5f12069cbfc882fdf989d04618ad9c33e603c419;hpb=3cddb0c0765e7a4ecd66806d92b72e1faddac4c4 diff --git a/src/endgame.cpp b/src/endgame.cpp index 635ff408..94967c25 100644 --- a/src/endgame.cpp +++ b/src/endgame.cpp @@ -1,7 +1,7 @@ /* Stockfish, a UCI chess playing engine derived from Glaurung 2.1 Copyright (C) 2004-2008 Tord Romstad (Glaurung author) - Copyright (C) 2008-2013 Marco Costalba, Joona Kiiski, Tord Romstad + Copyright (C) 2008-2014 Marco Costalba, Joona Kiiski, Tord Romstad Stockfish is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by @@ -65,10 +65,24 @@ namespace { } #endif - // Get the material key of a Position out of the given endgame key code - // like "KBPKN". The trick here is to first forge an ad-hoc fen string - // and then let a Position object to do the work for us. Note that the - // fen string could correspond to an illegal position. + // Map the square as if strongSide is white and strongSide's only pawn + // is on the left half of the board. + Square normalize(const Position& pos, Color strongSide, Square sq) { + + assert(pos.count(strongSide) == 1); + + if (file_of(pos.list(strongSide)[0]) >= FILE_E) + sq = Square(sq ^ 7); // Mirror SQ_H1 -> SQ_A1 + + if (strongSide == BLACK) + sq = ~sq; + + return sq; + } + + // Get the material key of Position out of the given endgame key code + // like "KBPKN". The trick here is to first forge an ad-hoc FEN string + // and then let a Position object do the work for us. Key key(const string& code, Color c) { assert(code.length() > 0 && code.length() < 8); @@ -79,8 +93,8 @@ namespace { std::transform(sides[c].begin(), sides[c].end(), sides[c].begin(), tolower); - string fen = sides[0] + char('0' + int(8 - code.length())) - + sides[1] + "/8/8/8/8/8/8/8 w - - 0 10"; + string fen = sides[0] + char(8 - sides[0].length() + '0') + "/8/8/8/8/8/8/" + + sides[1] + char(8 - sides[1].length() + '0') + " w - - 0 10"; return Position(fen, false, NULL).material_key(); } @@ -103,7 +117,6 @@ Endgames::Endgames() { add("KRKN"); add("KQKP"); add("KQKR"); - add("KBBKN"); add("KNPK"); add("KNPKB"); @@ -130,7 +143,7 @@ void Endgames::add(const string& code) { /// Mate with KX vs K. This function is used to evaluate positions with -/// King and plenty of material vs a lone king. It simply gives the +/// king and plenty of material vs a lone king. It simply gives the /// attacking side a bonus for driving the defending king towards the edge /// of the board, and for keeping the distance between the two kings small. template<> @@ -172,13 +185,13 @@ Value Endgame::operator()(const Position& pos) const { Square loserKSq = pos.king_square(weakSide); Square bishopSq = pos.list(strongSide)[0]; - // kbnk_mate_table() tries to drive toward corners A1 or H8, - // if we have a bishop that cannot reach the above squares we - // mirror the kings so to drive enemy toward corners A8 or H1. + // kbnk_mate_table() tries to drive toward corners A1 or H8. If we have a + // bishop that cannot reach the above squares, we flip the kings in order + // to drive the enemy toward corners A8 or H1. if (opposite_colors(bishopSq, SQ_A1)) { - winnerKSq = mirror(winnerKSq); - loserKSq = mirror(loserKSq); + winnerKSq = ~winnerKSq; + loserKSq = ~loserKSq; } Value result = VALUE_KNOWN_WIN @@ -196,25 +209,12 @@ Value Endgame::operator()(const Position& pos) const { assert(verify_material(pos, strongSide, VALUE_ZERO, 1)); assert(verify_material(pos, weakSide, VALUE_ZERO, 0)); - Square wksq = pos.king_square(strongSide); - Square bksq = pos.king_square(weakSide); - Square psq = pos.list(strongSide)[0]; - Color us = pos.side_to_move(); - - if (strongSide == BLACK) - { - wksq = ~wksq; - bksq = ~bksq; - psq = ~psq; - us = ~us; - } + // Assume strongSide is white and the pawn is on files A-D + Square wksq = normalize(pos, strongSide, pos.king_square(strongSide)); + Square bksq = normalize(pos, strongSide, pos.king_square(weakSide)); + Square psq = normalize(pos, strongSide, pos.list(strongSide)[0]); - if (file_of(psq) >= FILE_E) - { - wksq = mirror(wksq); - bksq = mirror(bksq); - psq = mirror(psq); - } + Color us = strongSide == pos.side_to_move() ? WHITE : BLACK; if (!Bitbases::probe_kpk(wksq, psq, bksq, us)) return VALUE_DRAW; @@ -235,20 +235,12 @@ Value Endgame::operator()(const Position& pos) const { assert(verify_material(pos, strongSide, RookValueMg, 0)); assert(verify_material(pos, weakSide, VALUE_ZERO, 1)); - Square wksq = pos.king_square(strongSide); - Square bksq = pos.king_square(weakSide); - Square rsq = pos.list(strongSide)[0]; - Square psq = pos.list(weakSide)[0]; - - if (strongSide == BLACK) - { - wksq = ~wksq; - bksq = ~bksq; - rsq = ~rsq; - psq = ~psq; - } + Square wksq = relative_square(strongSide, pos.king_square(strongSide)); + Square bksq = relative_square(strongSide, pos.king_square(weakSide)); + Square rsq = relative_square(strongSide, pos.list(strongSide)[0]); + Square psq = relative_square(strongSide, pos.list(weakSide)[0]); - Square queeningSq = file_of(psq) | RANK_1; + Square queeningSq = make_square(file_of(psq), RANK_1); Value result; // If the stronger side's king is in front of the pawn, it's a win @@ -292,7 +284,7 @@ Value Endgame::operator()(const Position& pos) const { } -/// KR vs KN. The attacking side has slightly better winning chances than +/// KR vs KN. The attacking side has slightly better winning chances than /// in KR vs KB, particularly if the king and the knight are far apart. template<> Value Endgame::operator()(const Position& pos) const { @@ -307,9 +299,10 @@ Value Endgame::operator()(const Position& pos) const { } -/// KQ vs KP. In general, a win for the stronger side, however, there are a few -/// important exceptions. Pawn on 7th rank, A,C,F or H file, with king next can -/// be a draw, so we scale down to distance between kings only. +/// KQ vs KP. In general, this is a win for the stronger side, but there are a +/// few important exceptions. A pawn on 7th rank and on the A,C,F or H files +/// with a king positioned next to it can be a draw, so in that case, we only +/// use the distance between the kings. template<> Value Endgame::operator()(const Position& pos) const { @@ -333,9 +326,8 @@ Value Endgame::operator()(const Position& pos) const { /// KQ vs KR. This is almost identical to KX vs K: We give the attacking /// king a bonus for having the kings close together, and for forcing the -/// defending king towards the edge. If we also take care to avoid null move -/// for the defending side in the search, this is usually sufficient to be -/// able to win KQ vs KR. +/// defending king towards the edge. If we also take care to avoid null move for +/// the defending side in the search, this is usually sufficient to win KQ vs KR. template<> Value Endgame::operator()(const Position& pos) const { @@ -354,35 +346,11 @@ Value Endgame::operator()(const Position& pos) const { } -/// KBB vs KN. This is almost always a win. We try to push enemy king to a corner -/// and away from his knight. For a reference of this difficult endgame see: -/// en.wikipedia.org/wiki/Chess_endgame#Effect_of_tablebases_on_endgame_theory - -template<> -Value Endgame::operator()(const Position& pos) const { - - assert(verify_material(pos, strongSide, 2 * BishopValueMg, 0)); - assert(verify_material(pos, weakSide, KnightValueMg, 0)); - - Square winnerKSq = pos.king_square(strongSide); - Square loserKSq = pos.king_square(weakSide); - Square knightSq = pos.list(weakSide)[0]; - - Value result = VALUE_KNOWN_WIN - + PushToCorners[loserKSq] - + PushClose[square_distance(winnerKSq, loserKSq)] - + PushAway[square_distance(loserKSq, knightSq)]; - - return strongSide == pos.side_to_move() ? result : -result; -} - - /// Some cases of trivial draws template<> Value Endgame::operator()(const Position&) const { return VALUE_DRAW; } -template<> Value Endgame::operator()(const Position&) const { return VALUE_DRAW; } -/// K, bishop and one or more pawns vs K. It checks for draws with rook pawns and +/// KB and one or more pawns vs K. It checks for draws with rook pawns and /// a bishop of the wrong color. If such a draw is detected, SCALE_FACTOR_DRAW /// is returned. If not, the return value is SCALE_FACTOR_NONE, i.e. no scaling /// will be used. @@ -403,7 +371,7 @@ ScaleFactor Endgame::operator()(const Position& pos) const { && !(pawns & ~file_bb(pawnFile))) { Square bishopSq = pos.list(strongSide)[0]; - Square queeningSq = relative_square(strongSide, pawnFile | RANK_8); + Square queeningSq = relative_square(strongSide, make_square(pawnFile, RANK_8)); Square kingSq = pos.king_square(weakSide); if ( opposite_colors(queeningSq, bishopSq) @@ -411,20 +379,20 @@ ScaleFactor Endgame::operator()(const Position& pos) const { return SCALE_FACTOR_DRAW; } - // All pawns on same B or G file? Then potential draw + // If all the pawns are on the same B or G file, then it's potentially a draw if ( (pawnFile == FILE_B || pawnFile == FILE_G) && !(pos.pieces(PAWN) & ~file_bb(pawnFile)) && pos.non_pawn_material(weakSide) == 0 && pos.count(weakSide) >= 1) { - // Get weakSide pawn that is closest to home rank + // Get weakSide pawn that is closest to the home rank Square weakPawnSq = backmost_sq(weakSide, pos.pieces(weakSide, PAWN)); Square strongKingSq = pos.king_square(strongSide); Square weakKingSq = pos.king_square(weakSide); Square bishopSq = pos.list(strongSide)[0]; - // Potential for a draw if our pawn is blocked on the 7th rank + // There's potential for a draw if our pawn is blocked on the 7th rank, // the bishop cannot attack it or they only have one pawn left if ( relative_rank(strongSide, weakPawnSq) == RANK_7 && (pos.pieces(strongSide, PAWN) & (weakPawnSq + pawn_push(weakSide))) @@ -433,7 +401,7 @@ ScaleFactor Endgame::operator()(const Position& pos) const { int strongKingDist = square_distance(weakPawnSq, strongKingSq); int weakKingDist = square_distance(weakPawnSq, weakKingSq); - // Draw if the weak king is on it's back two ranks, within 2 + // It's a draw if the weak king is on its back two ranks, within 2 // squares of the blocking pawn and the strong king is not // closer. (I think this rule only fails in practically // unreachable positions such as 5k1K/6p1/6P1/8/8/3B4/8/8 w @@ -450,8 +418,8 @@ ScaleFactor Endgame::operator()(const Position& pos) const { } -/// K and queen vs K, rook and one or more pawns. It tests for fortress draws with -/// a rook on the third rank defended by a pawn. +/// KQ vs KR and one or more pawns. It tests for fortress draws with a rook on +/// the third rank defended by a pawn. template<> ScaleFactor Endgame::operator()(const Position& pos) const { @@ -474,47 +442,28 @@ ScaleFactor Endgame::operator()(const Position& pos) const { } -/// K, rook and one pawn vs K and a rook. This function knows a handful of the -/// most important classes of drawn positions, but is far from perfect. It would -/// probably be a good idea to add more knowledge in the future. +/// KRP vs KR. This function knows a handful of the most important classes of +/// drawn positions, but is far from perfect. It would probably be a good idea +/// to add more knowledge in the future. /// /// It would also be nice to rewrite the actual code for this function, -/// which is mostly copied from Glaurung 1.x, and not very pretty. +/// which is mostly copied from Glaurung 1.x, and isn't very pretty. template<> ScaleFactor Endgame::operator()(const Position& pos) const { assert(verify_material(pos, strongSide, RookValueMg, 1)); assert(verify_material(pos, weakSide, RookValueMg, 0)); - Square wksq = pos.king_square(strongSide); - Square bksq = pos.king_square(weakSide); - Square wrsq = pos.list(strongSide)[0]; - Square wpsq = pos.list(strongSide)[0]; - Square brsq = pos.list(weakSide)[0]; - - // Orient the board in such a way that the stronger side is white, and the - // pawn is on the left half of the board. - if (strongSide == BLACK) - { - wksq = ~wksq; - wrsq = ~wrsq; - wpsq = ~wpsq; - bksq = ~bksq; - brsq = ~brsq; - } - - if (file_of(wpsq) > FILE_D) - { - wksq = mirror(wksq); - wrsq = mirror(wrsq); - wpsq = mirror(wpsq); - bksq = mirror(bksq); - brsq = mirror(brsq); - } + // Assume strongSide is white and the pawn is on files A-D + Square wksq = normalize(pos, strongSide, pos.king_square(strongSide)); + Square bksq = normalize(pos, strongSide, pos.king_square(weakSide)); + Square wrsq = normalize(pos, strongSide, pos.list(strongSide)[0]); + Square wpsq = normalize(pos, strongSide, pos.list(strongSide)[0]); + Square brsq = normalize(pos, strongSide, pos.list(weakSide)[0]); File f = file_of(wpsq); Rank r = rank_of(wpsq); - Square queeningSq = f | RANK_8; + Square queeningSq = make_square(f, RANK_8); int tempo = (pos.side_to_move() == strongSide); // If the pawn is not too far advanced and the defending king defends the @@ -580,7 +529,7 @@ ScaleFactor Endgame::operator()(const Position& pos) const { - 8 * square_distance(wpsq, queeningSq) - 2 * square_distance(wksq, queeningSq)); - // If the pawn is not far advanced, and the defending king is somewhere in + // If the pawn is not far advanced and the defending king is somewhere in // the pawn's path, it's probably a draw. if (r <= RANK_4 && bksq > wpsq) { @@ -637,9 +586,8 @@ ScaleFactor Endgame::operator()(const Position& pos) const { return SCALE_FACTOR_NONE; } -/// K, rook and two pawns vs K, rook and one pawn. There is only a single -/// pattern: If the stronger side has no passed pawns and the defending king -/// is actively placed, the position is drawish. +/// KRPP vs KRP. There is just a single rule: if the stronger side has no passed +/// pawns and the defending king is actively placed, the position is drawish. template<> ScaleFactor Endgame::operator()(const Position& pos) const { @@ -686,8 +634,8 @@ ScaleFactor Endgame::operator()(const Position& pos) const { Bitboard pawns = pos.pieces(strongSide, PAWN); Square psq = pos.list(strongSide)[0]; - // If all pawns are ahead of the king, all pawns are on a single - // rook file and the king is within one file of the pawns then draw. + // If all pawns are ahead of the king, on a single rook file and + // the king is within one file of the pawns, it's a draw. if ( !(pawns & ~in_front_bb(weakSide, rank_of(ksq))) && !((pawns & ~FileABB) && (pawns & ~FileHBB)) && file_distance(ksq, psq) <= 1) @@ -697,10 +645,10 @@ ScaleFactor Endgame::operator()(const Position& pos) const { } -/// K, bishop and a pawn vs K and a bishop. There are two rules: If the defending -/// king is somewhere along the path of the pawn, and the square of the king is -/// not of the same color as the stronger side's bishop, it's a draw. If the two -/// bishops have opposite color, it's almost always a draw. +/// KBP vs KB. There are two rules: if the defending king is somewhere along the +/// path of the pawn, and the square of the king is not of the same color as the +/// stronger side's bishop, it's a draw. If the two bishops have opposite color, +/// it's almost always a draw. template<> ScaleFactor Endgame::operator()(const Position& pos) const { @@ -750,8 +698,7 @@ ScaleFactor Endgame::operator()(const Position& pos) const { } -/// K, bishop and two pawns vs K and bishop. It detects a few basic draws with -/// opposite-colored bishops. +/// KBPP vs KB. It detects a few basic draws with opposite-colored bishops template<> ScaleFactor Endgame::operator()(const Position& pos) const { @@ -774,19 +721,19 @@ ScaleFactor Endgame::operator()(const Position& pos) const { if (relative_rank(strongSide, psq1) > relative_rank(strongSide, psq2)) { blockSq1 = psq1 + pawn_push(strongSide); - blockSq2 = file_of(psq2) | rank_of(psq1); + blockSq2 = make_square(file_of(psq2), rank_of(psq1)); } else { blockSq1 = psq2 + pawn_push(strongSide); - blockSq2 = file_of(psq1) | rank_of(psq2); + blockSq2 = make_square(file_of(psq1), rank_of(psq2)); } switch (file_distance(psq1, psq2)) { case 0: - // Both pawns are on the same file. Easy draw if defender firmly controls - // some square in the frontmost pawn's path. + // Both pawns are on the same file. It's an easy draw if the defender firmly + // controls some square in the frontmost pawn's path. if ( file_of(ksq) == file_of(blockSq1) && relative_rank(strongSide, ksq) >= relative_rank(strongSide, blockSq1) && opposite_colors(ksq, wbsq)) @@ -795,9 +742,9 @@ ScaleFactor Endgame::operator()(const Position& pos) const { return SCALE_FACTOR_NONE; case 1: - // Pawns on adjacent files. Draw if defender firmly controls the square - // in front of the frontmost pawn's path, and the square diagonally behind - // this square on the file of the other pawn. + // Pawns on adjacent files. It's a draw if the defender firmly controls the + // square in front of the frontmost pawn's path, and the square diagonally + // behind this square on the file of the other pawn. if ( ksq == blockSq1 && opposite_colors(ksq, wbsq) && ( bbsq == blockSq2 @@ -820,9 +767,9 @@ ScaleFactor Endgame::operator()(const Position& pos) const { } -/// K, bisop and a pawn vs K and knight. There is a single rule: If the defending -/// king is somewhere along the path of the pawn, and the square of the king is -/// not of the same color as the stronger side's bishop, it's a draw. +/// KBP vs KN. There is a single rule: If the defending king is somewhere along +/// the path of the pawn, and the square of the king is not of the same color as +/// the stronger side's bishop, it's a draw. template<> ScaleFactor Endgame::operator()(const Position& pos) const { @@ -843,32 +790,27 @@ ScaleFactor Endgame::operator()(const Position& pos) const { } -/// K, knight and a pawn vs K. There is a single rule: If the pawn is a rook pawn -/// on the 7th rank and the defending king prevents the pawn from advancing, the -/// position is drawn. +/// KNP vs K. There is a single rule: if the pawn is a rook pawn on the 7th rank +/// and the defending king prevents the pawn from advancing, the position is drawn. template<> ScaleFactor Endgame::operator()(const Position& pos) const { assert(verify_material(pos, strongSide, KnightValueMg, 1)); assert(verify_material(pos, weakSide, VALUE_ZERO, 0)); - Square pawnSq = pos.list(strongSide)[0]; - Square weakKingSq = pos.king_square(weakSide); - - if ( pawnSq == relative_square(strongSide, SQ_A7) - && square_distance(weakKingSq, relative_square(strongSide, SQ_A8)) <= 1) - return SCALE_FACTOR_DRAW; + // Assume strongSide is white and the pawn is on files A-D + Square pawnSq = normalize(pos, strongSide, pos.list(strongSide)[0]); + Square weakKingSq = normalize(pos, strongSide, pos.king_square(weakSide)); - if ( pawnSq == relative_square(strongSide, SQ_H7) - && square_distance(weakKingSq, relative_square(strongSide, SQ_H8)) <= 1) + if (pawnSq == SQ_A7 && square_distance(SQ_A8, weakKingSq) <= 1) return SCALE_FACTOR_DRAW; return SCALE_FACTOR_NONE; } -/// K, knight and a pawn vs K and bishop. If knight can block bishop from taking -/// pawn, it's a win. Otherwise, drawn. +/// KNP vs KB. If knight can block bishop from taking pawn, it's a win. +/// Otherwise the position is drawn. template<> ScaleFactor Endgame::operator()(const Position& pos) const { @@ -885,36 +827,23 @@ ScaleFactor Endgame::operator()(const Position& pos) const { } -/// K and a pawn vs K and a pawn. This is done by removing the weakest side's -/// pawn and probing the KP vs K bitbase: If the weakest side has a draw without -/// the pawn, she probably has at least a draw with the pawn as well. The exception -/// is when the stronger side's pawn is far advanced and not on a rook file; in -/// this case it is often possible to win (e.g. 8/4k3/3p4/3P4/6K1/8/8/8 w - - 0 1). +/// KP vs KP. This is done by removing the weakest side's pawn and probing the +/// KP vs K bitbase: If the weakest side has a draw without the pawn, it probably +/// has at least a draw with the pawn as well. The exception is when the stronger +/// side's pawn is far advanced and not on a rook file; in this case it is often +/// possible to win (e.g. 8/4k3/3p4/3P4/6K1/8/8/8 w - - 0 1). template<> ScaleFactor Endgame::operator()(const Position& pos) const { assert(verify_material(pos, strongSide, VALUE_ZERO, 1)); assert(verify_material(pos, weakSide, VALUE_ZERO, 1)); - Square wksq = pos.king_square(strongSide); - Square bksq = pos.king_square(weakSide); - Square psq = pos.list(strongSide)[0]; - Color us = pos.side_to_move(); - - if (strongSide == BLACK) - { - wksq = ~wksq; - bksq = ~bksq; - psq = ~psq; - us = ~us; - } + // Assume strongSide is white and the pawn is on files A-D + Square wksq = normalize(pos, strongSide, pos.king_square(strongSide)); + Square bksq = normalize(pos, strongSide, pos.king_square(weakSide)); + Square psq = normalize(pos, strongSide, pos.list(strongSide)[0]); - if (file_of(psq) >= FILE_E) - { - wksq = mirror(wksq); - bksq = mirror(bksq); - psq = mirror(psq); - } + Color us = strongSide == pos.side_to_move() ? WHITE : BLACK; // If the pawn has advanced to the fifth rank or further, and is not a // rook pawn, it's too dangerous to assume that it's at least a draw.