X-Git-Url: https://git.sesse.net/?p=stockfish;a=blobdiff_plain;f=src%2Fendgame.cpp;h=c50bb08ae500e506e04c98cec6abbb65e0f21c15;hp=976b3d6365c46d4316784bb3ea078af54924e0b7;hb=3d8c0f16c237b1fddaec75c5db70545da47e8bcc;hpb=13a73f67c018e58b2fd46f886c45ef2b75188c8e diff --git a/src/endgame.cpp b/src/endgame.cpp index 976b3d63..c50bb08a 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 @@ -80,10 +80,10 @@ namespace { return sq; } - // 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. + // 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. Note that the + // FEN string could correspond to an illegal position. Key key(const string& code, Color c) { assert(code.length() > 0 && code.length() < 8); @@ -118,7 +118,6 @@ Endgames::Endgames() { add("KRKN"); add("KQKP"); add("KQKR"); - add("KBBKN"); add("KNPK"); add("KNPKB"); @@ -187,8 +186,8 @@ 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 flip the kings in order + // 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)) { @@ -286,7 +285,7 @@ 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 { @@ -328,9 +327,8 @@ 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 { @@ -349,35 +347,11 @@ 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. @@ -419,7 +393,7 @@ ScaleFactor Endgame::operator()(const Position& pos) const { Square weakKingSq = pos.king_square(weakSide); Square bishopSq = pos.list(strongSide)[0]; - // There's 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))) @@ -445,8 +419,8 @@ 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 { @@ -469,9 +443,9 @@ 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 isn't very pretty. @@ -556,7 +530,7 @@ 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) { @@ -613,9 +587,8 @@ 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 { @@ -662,8 +635,8 @@ 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) @@ -673,10 +646,10 @@ 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 { @@ -726,8 +699,7 @@ 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 { @@ -796,9 +768,9 @@ 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 { @@ -819,9 +791,8 @@ 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 { @@ -839,8 +810,8 @@ ScaleFactor Endgame::operator()(const Position& pos) const { } -/// 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 { @@ -857,11 +828,11 @@ 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 {