X-Git-Url: https://git.sesse.net/?p=stockfish;a=blobdiff_plain;f=src%2Fendgame.cpp;h=311443ec939f82ac7b2af69c836524ba8e8768a4;hp=b26e0a9101637a58e7299ba4c2246011bb46bee5;hb=15e21911110f9d459c4fef2bb17903d97345d0b9;hpb=cca34e234cc98ed4b61e75a25f8cd0d917c2a3fa diff --git a/src/endgame.cpp b/src/endgame.cpp index b26e0a91..311443ec 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 @@ -59,22 +59,42 @@ namespace { const int PushClose[8] = { 0, 0, 100, 80, 60, 40, 20, 10 }; const int PushAway [8] = { 0, 5, 20, 40, 60, 80, 90, 100 }; - // 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. +#ifndef NDEBUG + bool verify_material(const Position& pos, Color c, Value npm, int num_pawns) { + return pos.non_pawn_material(c) == npm && pos.count(c) == num_pawns; + } +#endif + + // 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); assert(code[0] == 'K'); - string sides[] = { code.substr(code.find('K', 1)), // Weaker - code.substr(0, code.find('K', 1)) }; // Stronger + string sides[] = { code.substr(code.find('K', 1)), // Weak + code.substr(0, code.find('K', 1)) }; // Strong 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(); } @@ -97,11 +117,11 @@ Endgames::Endgames() { add("KRKN"); add("KQKP"); add("KQKR"); - add("KBBKN"); add("KNPK"); add("KNPKB"); add("KRPKR"); + add("KRPKB"); add("KBPKB"); add("KBPKN"); add("KBPPKB"); @@ -123,34 +143,34 @@ 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<> Value Endgame::operator()(const Position& pos) const { - assert(pos.non_pawn_material(weakerSide) == VALUE_ZERO); - assert(!pos.count(weakerSide)); + assert(verify_material(pos, weakSide, VALUE_ZERO, 0)); assert(!pos.checkers()); // Eval is never called when in check // Stalemate detection with lone king - if (pos.side_to_move() == weakerSide && !MoveList(pos).size()) + if (pos.side_to_move() == weakSide && !MoveList(pos).size()) return VALUE_DRAW; - Square winnerKSq = pos.king_square(strongerSide); - Square loserKSq = pos.king_square(weakerSide); + Square winnerKSq = pos.king_square(strongSide); + Square loserKSq = pos.king_square(weakSide); - Value result = pos.non_pawn_material(strongerSide) - + pos.count(strongerSide) * PawnValueEg - + PushToEdges[loserKSq] - + PushClose[square_distance(winnerKSq, loserKSq)]; + Value result = pos.non_pawn_material(strongSide) + + pos.count(strongSide) * PawnValueEg + + PushToEdges[loserKSq] + + PushClose[square_distance(winnerKSq, loserKSq)]; - if ( pos.count(strongerSide) - || pos.count(strongerSide) - || pos.bishop_pair(strongerSide)) + if ( pos.count(strongSide) + || pos.count(strongSide) + ||(pos.count(strongSide) && pos.count(strongSide)) + || pos.bishop_pair(strongSide)) result += VALUE_KNOWN_WIN; - return strongerSide == pos.side_to_move() ? result : -result; + return strongSide == pos.side_to_move() ? result : -result; } @@ -159,31 +179,27 @@ Value Endgame::operator()(const Position& pos) const { template<> Value Endgame::operator()(const Position& pos) const { - assert(pos.non_pawn_material(strongerSide) == KnightValueMg + BishopValueMg); - assert(pos.non_pawn_material(weakerSide) == VALUE_ZERO); - assert(pos.count(strongerSide) == 1); - assert(pos.count(strongerSide) == 1); - assert(pos.count< PAWN>(strongerSide) == 0); - assert(pos.count< PAWN>(weakerSide ) == 0); + assert(verify_material(pos, strongSide, KnightValueMg + BishopValueMg, 0)); + assert(verify_material(pos, weakSide, VALUE_ZERO, 0)); - Square winnerKSq = pos.king_square(strongerSide); - Square loserKSq = pos.king_square(weakerSide); - Square bishopSq = pos.list(strongerSide)[0]; + Square winnerKSq = pos.king_square(strongSide); + 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 + PushClose[square_distance(winnerKSq, loserKSq)] + PushToCorners[loserKSq]; - return strongerSide == pos.side_to_move() ? result : -result; + return strongSide == pos.side_to_move() ? result : -result; } @@ -191,37 +207,22 @@ Value Endgame::operator()(const Position& pos) const { template<> Value Endgame::operator()(const Position& pos) const { - assert(pos.non_pawn_material(strongerSide) == VALUE_ZERO); - assert(pos.non_pawn_material(weakerSide) == VALUE_ZERO); - assert(pos.count(strongerSide) == 1); - assert(pos.count(weakerSide ) == 0); + assert(verify_material(pos, strongSide, VALUE_ZERO, 1)); + assert(verify_material(pos, weakSide, VALUE_ZERO, 0)); - Square wksq = pos.king_square(strongerSide); - Square bksq = pos.king_square(weakerSide); - Square psq = pos.list(strongerSide)[0]; - Color us = pos.side_to_move(); + // 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 (strongerSide == BLACK) - { - wksq = ~wksq; - bksq = ~bksq; - psq = ~psq; - us = ~us; - } - - 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; Value result = VALUE_KNOWN_WIN + PawnValueEg + Value(rank_of(psq)); - return strongerSide == pos.side_to_move() ? result : -result; + return strongSide == pos.side_to_move() ? result : -result; } @@ -232,52 +233,41 @@ Value Endgame::operator()(const Position& pos) const { template<> Value Endgame::operator()(const Position& pos) const { - assert(pos.non_pawn_material(strongerSide) == RookValueMg); - assert(pos.non_pawn_material(weakerSide) == 0); - assert(pos.count(strongerSide) == 0); - assert(pos.count(weakerSide ) == 1); + assert(verify_material(pos, strongSide, RookValueMg, 0)); + assert(verify_material(pos, weakSide, VALUE_ZERO, 1)); - Square wksq = pos.king_square(strongerSide); - Square bksq = pos.king_square(weakerSide); - Square rsq = pos.list(strongerSide)[0]; - Square psq = pos.list(weakerSide)[0]; + 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]); - if (strongerSide == BLACK) - { - wksq = ~wksq; - bksq = ~bksq; - rsq = ~rsq; - psq = ~psq; - } - - 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 if (wksq < psq && file_of(wksq) == file_of(psq)) - result = RookValueEg - Value(square_distance(wksq, psq)); + result = RookValueEg - square_distance(wksq, psq); // If the weaker side's king is too far from the pawn and the rook, // it's a win. - else if ( square_distance(bksq, psq) >= 3 + (pos.side_to_move() == weakerSide) + else if ( square_distance(bksq, psq) >= 3 + (pos.side_to_move() == weakSide) && square_distance(bksq, rsq) >= 3) - result = RookValueEg - Value(square_distance(wksq, psq)); + result = RookValueEg - square_distance(wksq, psq); // If the pawn is far advanced and supported by the defending king, // the position is drawish else if ( rank_of(bksq) <= RANK_3 && square_distance(bksq, psq) == 1 && rank_of(wksq) >= RANK_4 - && square_distance(wksq, psq) > 2 + (pos.side_to_move() == strongerSide)) - result = Value(80 - square_distance(wksq, psq) * 8); + && square_distance(wksq, psq) > 2 + (pos.side_to_move() == strongSide)) + result = Value(80) - 8 * square_distance(wksq, psq); else - result = Value(200) - - Value(square_distance(wksq, psq + DELTA_S) * 8) - + Value(square_distance(bksq, psq + DELTA_S) * 8) - + Value(square_distance(psq, queeningSq) * 8); + result = Value(200) - 8 * ( square_distance(wksq, psq + DELTA_S) + - square_distance(bksq, psq + DELTA_S) + - square_distance(psq, queeningSq)); - return strongerSide == pos.side_to_move() ? result : -result; + return strongSide == pos.side_to_move() ? result : -result; } @@ -286,253 +276,195 @@ Value Endgame::operator()(const Position& pos) const { template<> Value Endgame::operator()(const Position& pos) const { - assert(pos.non_pawn_material(strongerSide) == RookValueMg); - assert(pos.non_pawn_material(weakerSide ) == BishopValueMg); - assert(pos.count(weakerSide ) == 1); - assert(pos.count< PAWN>(weakerSide ) == 0); - assert(pos.count< PAWN>(strongerSide) == 0); + assert(verify_material(pos, strongSide, RookValueMg, 0)); + assert(verify_material(pos, weakSide, BishopValueMg, 0)); - Value result = Value(PushToEdges[pos.king_square(weakerSide)]); - return strongerSide == pos.side_to_move() ? result : -result; + Value result = Value(PushToEdges[pos.king_square(weakSide)]); + return strongSide == pos.side_to_move() ? result : -result; } -/// 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 { - assert(pos.non_pawn_material(strongerSide) == RookValueMg); - assert(pos.non_pawn_material(weakerSide ) == KnightValueMg); - assert(pos.count(weakerSide ) == 1); - assert(pos.count< PAWN>(weakerSide ) == 0); - assert(pos.count< PAWN>(strongerSide) == 0); + assert(verify_material(pos, strongSide, RookValueMg, 0)); + assert(verify_material(pos, weakSide, KnightValueMg, 0)); - Square bksq = pos.king_square(weakerSide); - Square bnsq = pos.list(weakerSide)[0]; + Square bksq = pos.king_square(weakSide); + Square bnsq = pos.list(weakSide)[0]; Value result = Value(PushToEdges[bksq] + PushAway[square_distance(bksq, bnsq)]); - return strongerSide == pos.side_to_move() ? result : -result; + return strongSide == pos.side_to_move() ? result : -result; } -/// 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 { - assert(pos.non_pawn_material(strongerSide) == QueenValueMg); - assert(pos.non_pawn_material(weakerSide ) == VALUE_ZERO); - assert(pos.count(strongerSide) == 0); - assert(pos.count(weakerSide ) == 1); + assert(verify_material(pos, strongSide, QueenValueMg, 0)); + assert(verify_material(pos, weakSide, VALUE_ZERO, 1)); - Square winnerKSq = pos.king_square(strongerSide); - Square loserKSq = pos.king_square(weakerSide); - Square pawnSq = pos.list(weakerSide)[0]; + Square winnerKSq = pos.king_square(strongSide); + Square loserKSq = pos.king_square(weakSide); + Square pawnSq = pos.list(weakSide)[0]; Value result = Value(PushClose[square_distance(winnerKSq, loserKSq)]); - if ( relative_rank(weakerSide, pawnSq) != RANK_7 + if ( relative_rank(weakSide, pawnSq) != RANK_7 || square_distance(loserKSq, pawnSq) != 1 || !((FileABB | FileCBB | FileFBB | FileHBB) & pawnSq)) result += QueenValueEg - PawnValueEg; - return strongerSide == pos.side_to_move() ? result : -result; + return strongSide == pos.side_to_move() ? result : -result; } /// 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 { - assert(pos.non_pawn_material(strongerSide) == QueenValueMg); - assert(pos.non_pawn_material(weakerSide ) == RookValueMg); - assert(pos.count(strongerSide) == 0); - assert(pos.count(weakerSide ) == 0); + assert(verify_material(pos, strongSide, QueenValueMg, 0)); + assert(verify_material(pos, weakSide, RookValueMg, 0)); - Square winnerKSq = pos.king_square(strongerSide); - Square loserKSq = pos.king_square(weakerSide); + Square winnerKSq = pos.king_square(strongSide); + Square loserKSq = pos.king_square(weakSide); Value result = QueenValueEg - RookValueEg + PushToEdges[loserKSq] + PushClose[square_distance(winnerKSq, loserKSq)]; - return strongerSide == pos.side_to_move() ? result : -result; -} - - -/// 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(pos.non_pawn_material(strongerSide) == 2 * BishopValueMg); - assert(pos.non_pawn_material(weakerSide ) == KnightValueMg); - assert(pos.count(strongerSide) == 2); - assert(pos.count(weakerSide ) == 1); - assert(!pos.pieces(PAWN)); - - Square winnerKSq = pos.king_square(strongerSide); - Square loserKSq = pos.king_square(weakerSide); - Square knightSq = pos.list(weakerSide)[0]; - - Value result = VALUE_KNOWN_WIN - + PushToCorners[loserKSq] - + PushClose[square_distance(winnerKSq, loserKSq)] - + PushAway[square_distance(loserKSq, knightSq)]; - - return strongerSide == pos.side_to_move() ? result : -result; + 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. template<> ScaleFactor Endgame::operator()(const Position& pos) const { - assert(pos.non_pawn_material(strongerSide) == BishopValueMg); - assert(pos.count(strongerSide) == 1); - assert(pos.count< PAWN>(strongerSide) >= 1); + assert(pos.non_pawn_material(strongSide) == BishopValueMg); + assert(pos.count(strongSide) >= 1); - // No assertions about the material of weakerSide, because we want draws to + // No assertions about the material of weakSide, because we want draws to // be detected even when the weaker side has some pawns. - Bitboard pawns = pos.pieces(strongerSide, PAWN); - File pawnFile = file_of(pos.list(strongerSide)[0]); + Bitboard pawns = pos.pieces(strongSide, PAWN); + File pawnFile = file_of(pos.list(strongSide)[0]); // All pawns are on a single rook file ? if ( (pawnFile == FILE_A || pawnFile == FILE_H) && !(pawns & ~file_bb(pawnFile))) { - Square bishopSq = pos.list(strongerSide)[0]; - Square queeningSq = relative_square(strongerSide, pawnFile | RANK_8); - Square kingSq = pos.king_square(weakerSide); + Square bishopSq = pos.list(strongSide)[0]; + Square queeningSq = relative_square(strongSide, make_square(pawnFile, RANK_8)); + Square kingSq = pos.king_square(weakSide); if ( opposite_colors(queeningSq, bishopSq) - && abs(file_of(kingSq) - pawnFile) <= 1) - { - // The bishop has the wrong color, and the defending king is on the - // file of the pawn(s) or the adjacent file. Find the rank of the - // frontmost pawn. - Square pawnSq = frontmost_sq(strongerSide, pawns); - - // If the defending king has distance 1 to the promotion square or - // is placed somewhere in front of the pawn, it's a draw. - if ( square_distance(kingSq, queeningSq) <= 1 - || relative_rank(weakerSide, kingSq) <= relative_rank(weakerSide, pawnSq)) - return SCALE_FACTOR_DRAW; - } + && square_distance(queeningSq, kingSq) <= 1) + 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(weakerSide) == 0 - && pos.count(weakerSide) >= 1) + && pos.non_pawn_material(weakSide) == 0 + && pos.count(weakSide) >= 1) { - // Get weakerSide pawn that is closest to home rank - Square weakerPawnSq = backmost_sq(weakerSide, pos.pieces(weakerSide, PAWN)); - - Square strongerKingSq = pos.king_square(strongerSide); - Square weakerKingSq = pos.king_square(weakerSide); - Square bishopSq = pos.list(strongerSide)[0]; - - // Draw if weaker pawn is on rank 7, bishop can't attack the pawn, and - // weaker king can stop opposing opponent's king from penetrating. - if ( relative_rank(strongerSide, weakerPawnSq) == RANK_7 - && opposite_colors(bishopSq, weakerPawnSq) - && square_distance(weakerPawnSq, weakerKingSq) <= square_distance(weakerPawnSq, strongerKingSq)) - return SCALE_FACTOR_DRAW; + // 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]; + + // 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))) + && (opposite_colors(bishopSq, weakPawnSq) || pos.count(strongSide) == 1)) + { + int strongKingDist = square_distance(weakPawnSq, strongKingSq); + int weakKingDist = square_distance(weakPawnSq, weakKingSq); + + // 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 + // and positions where qsearch will immediately correct the + // problem such as 8/4k1p1/6P1/1K6/3B4/8/8/8 w) + if ( relative_rank(strongSide, weakKingSq) >= RANK_7 + && weakKingDist <= 2 + && weakKingDist <= strongKingDist) + return SCALE_FACTOR_DRAW; + } } return SCALE_FACTOR_NONE; } -/// 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 { - assert(pos.non_pawn_material(strongerSide) == QueenValueMg); - assert(pos.count(strongerSide) == 1); - assert(pos.count< PAWN>(strongerSide) == 0); - assert(pos.count< ROOK>(weakerSide ) == 1); - assert(pos.count< PAWN>(weakerSide ) >= 1); - - Square kingSq = pos.king_square(weakerSide); - Square rsq = pos.list(weakerSide)[0]; - - if ( relative_rank(weakerSide, kingSq) <= RANK_2 - && relative_rank(weakerSide, pos.king_square(strongerSide)) >= RANK_4 - && (pos.pieces(weakerSide, ROOK) & rank_bb(relative_rank(weakerSide, RANK_3))) - && (pos.pieces(weakerSide, PAWN) & rank_bb(relative_rank(weakerSide, RANK_2))) - && (pos.attacks_from(kingSq) & pos.pieces(weakerSide, PAWN)) - && (pos.attacks_from(rsq, strongerSide) & pos.pieces(weakerSide, PAWN))) + assert(verify_material(pos, strongSide, QueenValueMg, 0)); + assert(pos.count(weakSide) == 1); + assert(pos.count(weakSide) >= 1); + + Square kingSq = pos.king_square(weakSide); + Square rsq = pos.list(weakSide)[0]; + + if ( relative_rank(weakSide, kingSq) <= RANK_2 + && relative_rank(weakSide, pos.king_square(strongSide)) >= RANK_4 + && relative_rank(weakSide, rsq) == RANK_3 + && ( pos.pieces(weakSide, PAWN) + & pos.attacks_from(kingSq) + & pos.attacks_from(rsq, strongSide))) return SCALE_FACTOR_DRAW; return SCALE_FACTOR_NONE; } -/// 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(pos.non_pawn_material(strongerSide) == RookValueMg); - assert(pos.non_pawn_material(weakerSide) == RookValueMg); - assert(pos.count(strongerSide) == 1); - assert(pos.count(weakerSide ) == 0); - - Square wksq = pos.king_square(strongerSide); - Square bksq = pos.king_square(weakerSide); - Square wrsq = pos.list(strongerSide)[0]; - Square wpsq = pos.list(strongerSide)[0]; - Square brsq = pos.list(weakerSide)[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 (strongerSide == BLACK) - { - wksq = ~wksq; - wrsq = ~wrsq; - wpsq = ~wpsq; - bksq = ~bksq; - brsq = ~brsq; - } + assert(verify_material(pos, strongSide, RookValueMg, 1)); + assert(verify_material(pos, weakSide, RookValueMg, 0)); - 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; - int tempo = (pos.side_to_move() == strongerSide); + 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 // queening square, use the third-rank defence. @@ -597,7 +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) { @@ -610,31 +542,71 @@ ScaleFactor Endgame::operator()(const Position& pos) const { return SCALE_FACTOR_NONE; } +template<> +ScaleFactor Endgame::operator()(const Position& pos) const { + + assert(verify_material(pos, strongSide, RookValueMg, 1)); + assert(verify_material(pos, weakSide, BishopValueMg, 0)); -/// 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. + // Test for a rook pawn + if (pos.pieces(PAWN) & (FileABB | FileHBB)) + { + Square ksq = pos.king_square(weakSide); + Square bsq = pos.list(weakSide)[0]; + Square psq = pos.list(strongSide)[0]; + Rank rk = relative_rank(strongSide, psq); + Square push = pawn_push(strongSide); + + // If the pawn is on the 5th rank and the pawn (currently) is on + // the same color square as the bishop then there is a chance of + // a fortress. Depending on the king position give a moderate + // reduction or a stronger one if the defending king is near the + // corner but not trapped there. + if (rk == RANK_5 && !opposite_colors(bsq, psq)) + { + int d = square_distance(psq + 3 * push, ksq); + + if (d <= 2 && !(d == 0 && ksq == pos.king_square(strongSide) + 2 * push)) + return ScaleFactor(24); + else + return ScaleFactor(48); + } + + // When the pawn has moved to the 6th rank we can be fairly sure + // it's drawn if the bishop attacks the square in front of the + // pawn from a reasonable distance and the defending king is near + // the corner + if ( rk == RANK_6 + && square_distance(psq + 2 * push, ksq) <= 1 + && (PseudoAttacks[BISHOP][bsq] & (psq + push)) + && file_distance(bsq, psq) >= 2) + return ScaleFactor(8); + } + + return SCALE_FACTOR_NONE; +} + +/// 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 { - assert(pos.non_pawn_material(strongerSide) == RookValueMg); - assert(pos.non_pawn_material(weakerSide) == RookValueMg); - assert(pos.count(strongerSide) == 2); - assert(pos.count(weakerSide ) == 1); + assert(verify_material(pos, strongSide, RookValueMg, 2)); + assert(verify_material(pos, weakSide, RookValueMg, 1)); - Square wpsq1 = pos.list(strongerSide)[0]; - Square wpsq2 = pos.list(strongerSide)[1]; - Square bksq = pos.king_square(weakerSide); + Square wpsq1 = pos.list(strongSide)[0]; + Square wpsq2 = pos.list(strongSide)[1]; + Square bksq = pos.king_square(weakSide); // Does the stronger side have a passed pawn? - if (pos.pawn_passed(strongerSide, wpsq1) || pos.pawn_passed(strongerSide, wpsq2)) + if (pos.pawn_passed(strongSide, wpsq1) || pos.pawn_passed(strongSide, wpsq2)) return SCALE_FACTOR_NONE; - Rank r = std::max(relative_rank(strongerSide, wpsq1), relative_rank(strongerSide, wpsq2)); + Rank r = std::max(relative_rank(strongSide, wpsq1), relative_rank(strongSide, wpsq2)); if ( file_distance(bksq, wpsq1) <= 1 && file_distance(bksq, wpsq2) <= 1 - && relative_rank(strongerSide, bksq) > r) + && relative_rank(strongSide, bksq) > r) { switch (r) { case RANK_2: return ScaleFactor(10); @@ -654,64 +626,49 @@ ScaleFactor Endgame::operator()(const Position& pos) const { template<> ScaleFactor Endgame::operator()(const Position& pos) const { - assert(pos.non_pawn_material(strongerSide) == VALUE_ZERO); - assert(pos.non_pawn_material(weakerSide) == VALUE_ZERO); - assert(pos.count(strongerSide) >= 2); - assert(pos.count(weakerSide ) == 0); + assert(pos.non_pawn_material(strongSide) == VALUE_ZERO); + assert(pos.count(strongSide) >= 2); + assert(verify_material(pos, weakSide, VALUE_ZERO, 0)); - Square ksq = pos.king_square(weakerSide); - Bitboard pawns = pos.pieces(strongerSide, PAWN); + Square ksq = pos.king_square(weakSide); + Bitboard pawns = pos.pieces(strongSide, PAWN); + Square psq = pos.list(strongSide)[0]; + + // 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) + return SCALE_FACTOR_DRAW; - // Are all pawns on the 'a' file? - if (!(pawns & ~FileABB)) - { - // Does the defending king block the pawns? - if ( square_distance(ksq, relative_square(strongerSide, SQ_A8)) <= 1 - || ( file_of(ksq) == FILE_A - && !(in_front_bb(strongerSide, rank_of(ksq)) & pawns))) - return SCALE_FACTOR_DRAW; - } - // Are all pawns on the 'h' file? - else if (!(pawns & ~FileHBB)) - { - // Does the defending king block the pawns? - if ( square_distance(ksq, relative_square(strongerSide, SQ_H8)) <= 1 - || ( file_of(ksq) == FILE_H - && !(in_front_bb(strongerSide, rank_of(ksq)) & pawns))) - return SCALE_FACTOR_DRAW; - } return SCALE_FACTOR_NONE; } -/// 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 { - assert(pos.non_pawn_material(strongerSide) == BishopValueMg); - assert(pos.non_pawn_material(weakerSide ) == BishopValueMg); - assert(pos.count(strongerSide) == 1); - assert(pos.count(weakerSide ) == 1); - assert(pos.count< PAWN>(strongerSide) == 1); - assert(pos.count< PAWN>(weakerSide ) == 0); + assert(verify_material(pos, strongSide, BishopValueMg, 1)); + assert(verify_material(pos, weakSide, BishopValueMg, 0)); - Square pawnSq = pos.list(strongerSide)[0]; - Square strongerBishopSq = pos.list(strongerSide)[0]; - Square weakerBishopSq = pos.list(weakerSide)[0]; - Square weakerKingSq = pos.king_square(weakerSide); + Square pawnSq = pos.list(strongSide)[0]; + Square strongBishopSq = pos.list(strongSide)[0]; + Square weakBishopSq = pos.list(weakSide)[0]; + Square weakKingSq = pos.king_square(weakSide); // Case 1: Defending king blocks the pawn, and cannot be driven away - if ( file_of(weakerKingSq) == file_of(pawnSq) - && relative_rank(strongerSide, pawnSq) < relative_rank(strongerSide, weakerKingSq) - && ( opposite_colors(weakerKingSq, strongerBishopSq) - || relative_rank(strongerSide, weakerKingSq) <= RANK_6)) + if ( file_of(weakKingSq) == file_of(pawnSq) + && relative_rank(strongSide, pawnSq) < relative_rank(strongSide, weakKingSq) + && ( opposite_colors(weakKingSq, strongBishopSq) + || relative_rank(strongSide, weakKingSq) <= RANK_6)) return SCALE_FACTOR_DRAW; // Case 2: Opposite colored bishops - if (opposite_colors(strongerBishopSq, weakerBishopSq)) + if (opposite_colors(strongBishopSq, weakBishopSq)) { // We assume that the position is drawn in the following three situations: // @@ -723,17 +680,17 @@ ScaleFactor Endgame::operator()(const Position& pos) const { // These rules are probably not perfect, but in practice they work // reasonably well. - if (relative_rank(strongerSide, pawnSq) <= RANK_5) + if (relative_rank(strongSide, pawnSq) <= RANK_5) return SCALE_FACTOR_DRAW; else { - Bitboard path = forward_bb(strongerSide, pawnSq); + Bitboard path = forward_bb(strongSide, pawnSq); - if (path & pos.pieces(weakerSide, KING)) + if (path & pos.pieces(weakSide, KING)) return SCALE_FACTOR_DRAW; - if ( (pos.attacks_from(weakerBishopSq) & path) - && square_distance(weakerBishopSq, pawnSq) >= 3) + if ( (pos.attacks_from(weakBishopSq) & path) + && square_distance(weakBishopSq, pawnSq) >= 3) return SCALE_FACTOR_DRAW; } } @@ -741,69 +698,64 @@ 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 { - assert(pos.non_pawn_material(strongerSide) == BishopValueMg); - assert(pos.non_pawn_material(weakerSide ) == BishopValueMg); - assert(pos.count(strongerSide) == 1); - assert(pos.count(weakerSide ) == 1); - assert(pos.count< PAWN>(strongerSide) == 2); - assert(pos.count< PAWN>(weakerSide ) == 0); + assert(verify_material(pos, strongSide, BishopValueMg, 2)); + assert(verify_material(pos, weakSide, BishopValueMg, 0)); - Square wbsq = pos.list(strongerSide)[0]; - Square bbsq = pos.list(weakerSide)[0]; + Square wbsq = pos.list(strongSide)[0]; + Square bbsq = pos.list(weakSide)[0]; if (!opposite_colors(wbsq, bbsq)) return SCALE_FACTOR_NONE; - Square ksq = pos.king_square(weakerSide); - Square psq1 = pos.list(strongerSide)[0]; - Square psq2 = pos.list(strongerSide)[1]; + Square ksq = pos.king_square(weakSide); + Square psq1 = pos.list(strongSide)[0]; + Square psq2 = pos.list(strongSide)[1]; Rank r1 = rank_of(psq1); Rank r2 = rank_of(psq2); Square blockSq1, blockSq2; - if (relative_rank(strongerSide, psq1) > relative_rank(strongerSide, psq2)) + if (relative_rank(strongSide, psq1) > relative_rank(strongSide, psq2)) { - blockSq1 = psq1 + pawn_push(strongerSide); - blockSq2 = file_of(psq2) | rank_of(psq1); + blockSq1 = psq1 + pawn_push(strongSide); + blockSq2 = make_square(file_of(psq2), rank_of(psq1)); } else { - blockSq1 = psq2 + pawn_push(strongerSide); - blockSq2 = file_of(psq1) | rank_of(psq2); + blockSq1 = psq2 + pawn_push(strongSide); + 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(strongerSide, ksq) >= relative_rank(strongerSide, blockSq1) + && relative_rank(strongSide, ksq) >= relative_rank(strongSide, blockSq1) && opposite_colors(ksq, wbsq)) return SCALE_FACTOR_DRAW; else 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 - || (pos.attacks_from(blockSq2) & pos.pieces(weakerSide, BISHOP)) + || (pos.attacks_from(blockSq2) & pos.pieces(weakSide, BISHOP)) || abs(r1 - r2) >= 2)) return SCALE_FACTOR_DRAW; else if ( ksq == blockSq2 && opposite_colors(ksq, wbsq) && ( bbsq == blockSq1 - || (pos.attacks_from(blockSq1) & pos.pieces(weakerSide, BISHOP)))) + || (pos.attacks_from(blockSq1) & pos.pieces(weakSide, BISHOP)))) return SCALE_FACTOR_DRAW; else return SCALE_FACTOR_NONE; @@ -815,110 +767,83 @@ 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 { - assert(pos.non_pawn_material(strongerSide) == BishopValueMg); - assert(pos.non_pawn_material(weakerSide ) == KnightValueMg); - assert(pos.count(strongerSide) == 1); - assert(pos.count(weakerSide ) == 1); - assert(pos.count< PAWN>(strongerSide) == 1); - assert(pos.count< PAWN>(weakerSide ) == 0); - - Square pawnSq = pos.list(strongerSide)[0]; - Square strongerBishopSq = pos.list(strongerSide)[0]; - Square weakerKingSq = pos.king_square(weakerSide); - - if ( file_of(weakerKingSq) == file_of(pawnSq) - && relative_rank(strongerSide, pawnSq) < relative_rank(strongerSide, weakerKingSq) - && ( opposite_colors(weakerKingSq, strongerBishopSq) - || relative_rank(strongerSide, weakerKingSq) <= RANK_6)) + assert(verify_material(pos, strongSide, BishopValueMg, 1)); + assert(verify_material(pos, weakSide, KnightValueMg, 0)); + + Square pawnSq = pos.list(strongSide)[0]; + Square strongBishopSq = pos.list(strongSide)[0]; + Square weakKingSq = pos.king_square(weakSide); + + if ( file_of(weakKingSq) == file_of(pawnSq) + && relative_rank(strongSide, pawnSq) < relative_rank(strongSide, weakKingSq) + && ( opposite_colors(weakKingSq, strongBishopSq) + || relative_rank(strongSide, weakKingSq) <= RANK_6)) return SCALE_FACTOR_DRAW; return SCALE_FACTOR_NONE; } -/// 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(pos.non_pawn_material(strongerSide) == KnightValueMg); - assert(pos.non_pawn_material(weakerSide ) == VALUE_ZERO); - assert(pos.count(strongerSide) == 1); - assert(pos.count< PAWN>(strongerSide) == 1); - assert(pos.count< PAWN>(weakerSide ) == 0); + assert(verify_material(pos, strongSide, KnightValueMg, 1)); + assert(verify_material(pos, weakSide, VALUE_ZERO, 0)); - Square pawnSq = pos.list(strongerSide)[0]; - Square weakerKingSq = pos.king_square(weakerSide); + // 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(strongerSide, SQ_A7) - && square_distance(weakerKingSq, relative_square(strongerSide, SQ_A8)) <= 1) - return SCALE_FACTOR_DRAW; - - if ( pawnSq == relative_square(strongerSide, SQ_H7) - && square_distance(weakerKingSq, relative_square(strongerSide, 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 { - Square pawnSq = pos.list(strongerSide)[0]; - Square bishopSq = pos.list(weakerSide)[0]; - Square weakerKingSq = pos.king_square(weakerSide); + Square pawnSq = pos.list(strongSide)[0]; + Square bishopSq = pos.list(weakSide)[0]; + Square weakKingSq = pos.king_square(weakSide); // King needs to get close to promoting pawn to prevent knight from blocking. // Rules for this are very tricky, so just approximate. - if (forward_bb(strongerSide, pawnSq) & pos.attacks_from(bishopSq)) - return ScaleFactor(square_distance(weakerKingSq, pawnSq)); + if (forward_bb(strongSide, pawnSq) & pos.attacks_from(bishopSq)) + return ScaleFactor(square_distance(weakKingSq, pawnSq)); return SCALE_FACTOR_NONE; } -/// 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(pos.non_pawn_material(strongerSide) == VALUE_ZERO); - assert(pos.non_pawn_material(weakerSide ) == VALUE_ZERO); - assert(pos.count(WHITE) == 1); - assert(pos.count(BLACK) == 1); + assert(verify_material(pos, strongSide, VALUE_ZERO, 1)); + assert(verify_material(pos, weakSide, VALUE_ZERO, 1)); - Square wksq = pos.king_square(strongerSide); - Square bksq = pos.king_square(weakerSide); - Square psq = pos.list(strongerSide)[0]; - Color us = pos.side_to_move(); + // 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 (strongerSide == BLACK) - { - wksq = ~wksq; - bksq = ~bksq; - psq = ~psq; - us = ~us; - } - - 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.