X-Git-Url: https://git.sesse.net/?p=stockfish;a=blobdiff_plain;f=src%2Fendgame.cpp;h=7e005a28277f8d85b639d82af2439e5f5b672670;hp=40f49dce5018d08aaffd60468fd60e6a195a1021;hb=HEAD;hpb=c5b2a92cd17c65a639ec6739dd511767f65e188d diff --git a/src/endgame.cpp b/src/endgame.cpp deleted file mode 100644 index 40f49dce..00000000 --- a/src/endgame.cpp +++ /dev/null @@ -1,745 +0,0 @@ -/* - Stockfish, a UCI chess playing engine derived from Glaurung 2.1 - Copyright (C) 2004-2008 Tord Romstad (Glaurung author) - Copyright (C) 2008-2015 Marco Costalba, Joona Kiiski, Tord Romstad - Copyright (C) 2015-2020 Marco Costalba, Joona Kiiski, Gary Linscott, 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 - the Free Software Foundation, either version 3 of the License, or - (at your option) any later version. - - Stockfish is distributed in the hope that it will be useful, - but WITHOUT ANY WARRANTY; without even the implied warranty of - MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the - GNU General Public License for more details. - - You should have received a copy of the GNU General Public License - along with this program. If not, see . -*/ - -#include - -#include "bitboard.h" -#include "endgame.h" -#include "movegen.h" - -namespace { - - // Used to drive the king towards the edge of the board - // in KX vs K and KQ vs KR endgames. - // Values range from 27 (center squares) to 90 (in the corners) - inline int push_to_edge(Square s) { - int rd = edge_distance(rank_of(s)), fd = edge_distance(file_of(s)); - return 90 - (7 * fd * fd / 2 + 7 * rd * rd / 2); - } - - // Used to drive the king towards A1H8 corners in KBN vs K endgames. - // Values range from 0 on A8H1 diagonal to 7 in A1H8 corners - inline int push_to_corner(Square s) { - return abs(7 - rank_of(s) - file_of(s)); - } - - // Drive a piece close to or away from another piece - inline int push_close(Square s1, Square s2) { return 140 - 20 * distance(s1, s2); } - inline int push_away(Square s1, Square s2) { return 120 - push_close(s1, s2); } - -#ifndef NDEBUG - bool verify_material(const Position& pos, Color c, Value npm, int pawnsCnt) { - return pos.non_pawn_material(c) == npm && pos.count(c) == pawnsCnt; - } -#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.square(strongSide)) >= FILE_E) - sq = flip_file(sq); - - return strongSide == WHITE ? sq : flip_rank(sq); - } - -} // namespace - - -namespace Endgames { - - std::pair, Map> maps; - - void init() { - - add("KPK"); - add("KNNK"); - add("KBNK"); - add("KRKP"); - add("KRKB"); - add("KRKN"); - add("KQKP"); - add("KQKR"); - add("KNNKP"); - - add("KRPKR"); - add("KRPKB"); - add("KBPKB"); - add("KBPKN"); - add("KBPPKB"); - add("KRPPKRP"); - } -} - - -/// 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 -/// 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(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() == weakSide && !MoveList(pos).size()) - return VALUE_DRAW; - - Square strongKing = pos.square(strongSide); - Square weakKing = pos.square(weakSide); - - Value result = pos.non_pawn_material(strongSide) - + pos.count(strongSide) * PawnValueEg - + push_to_edge(weakKing) - + push_close(strongKing, weakKing); - - if ( pos.count(strongSide) - || pos.count(strongSide) - ||(pos.count(strongSide) && pos.count(strongSide)) - || ( (pos.pieces(strongSide, BISHOP) & ~DarkSquares) - && (pos.pieces(strongSide, BISHOP) & DarkSquares))) - result = std::min(result + VALUE_KNOWN_WIN, VALUE_TB_WIN_IN_MAX_PLY - 1); - - return strongSide == pos.side_to_move() ? result : -result; -} - - -/// Mate with KBN vs K. This is similar to KX vs K, but we have to drive the -/// defending king towards a corner square that our bishop attacks. -template<> -Value Endgame::operator()(const Position& pos) const { - - assert(verify_material(pos, strongSide, KnightValueMg + BishopValueMg, 0)); - assert(verify_material(pos, weakSide, VALUE_ZERO, 0)); - - Square strongKing = pos.square(strongSide); - Square strongBishop = pos.square(strongSide); - Square weakKing = pos.square(weakSide); - - // If our bishop does not attack A1/H8, we flip the enemy king square - // to drive to opposite corners (A8/H1). - - Value result = (VALUE_KNOWN_WIN + 3520) - + push_close(strongKing, weakKing) - + 420 * push_to_corner(opposite_colors(strongBishop, SQ_A1) ? flip_file(weakKing) : weakKing); - - assert(abs(result) < VALUE_TB_WIN_IN_MAX_PLY); - return strongSide == pos.side_to_move() ? result : -result; -} - - -/// KP vs K. This endgame is evaluated with the help of a bitbase -template<> -Value Endgame::operator()(const Position& pos) const { - - assert(verify_material(pos, strongSide, VALUE_ZERO, 1)); - assert(verify_material(pos, weakSide, VALUE_ZERO, 0)); - - // Assume strongSide is white and the pawn is on files A-D - Square strongKing = normalize(pos, strongSide, pos.square(strongSide)); - Square strongPawn = normalize(pos, strongSide, pos.square(strongSide)); - Square weakKing = normalize(pos, strongSide, pos.square(weakSide)); - - Color us = strongSide == pos.side_to_move() ? WHITE : BLACK; - - if (!Bitbases::probe(strongKing, strongPawn, weakKing, us)) - return VALUE_DRAW; - - Value result = VALUE_KNOWN_WIN + PawnValueEg + Value(rank_of(strongPawn)); - - return strongSide == pos.side_to_move() ? result : -result; -} - - -/// KR vs KP. This is a somewhat tricky endgame to evaluate precisely without -/// a bitbase. The function below returns drawish scores when the pawn is -/// far advanced with support of the king, while the attacking king is far -/// away. -template<> -Value Endgame::operator()(const Position& pos) const { - - assert(verify_material(pos, strongSide, RookValueMg, 0)); - assert(verify_material(pos, weakSide, VALUE_ZERO, 1)); - - Square strongKing = pos.square(strongSide); - Square weakKing = pos.square(weakSide); - Square strongRook = pos.square(strongSide); - Square weakPawn = pos.square(weakSide); - Square queeningSquare = make_square(file_of(weakPawn), relative_rank(weakSide, RANK_8)); - Value result; - - // If the stronger side's king is in front of the pawn, it's a win - if (forward_file_bb(strongSide, strongKing) & weakPawn) - result = RookValueEg - distance(strongKing, weakPawn); - - // If the weaker side's king is too far from the pawn and the rook, - // it's a win. - else if ( distance(weakKing, weakPawn) >= 3 + (pos.side_to_move() == weakSide) - && distance(weakKing, strongRook) >= 3) - result = RookValueEg - distance(strongKing, weakPawn); - - // If the pawn is far advanced and supported by the defending king, - // the position is drawish - else if ( relative_rank(strongSide, weakKing) <= RANK_3 - && distance(weakKing, weakPawn) == 1 - && relative_rank(strongSide, strongKing) >= RANK_4 - && distance(strongKing, weakPawn) > 2 + (pos.side_to_move() == strongSide)) - result = Value(80) - 8 * distance(strongKing, weakPawn); - - else - result = Value(200) - 8 * ( distance(strongKing, weakPawn + pawn_push(weakSide)) - - distance(weakKing, weakPawn + pawn_push(weakSide)) - - distance(weakPawn, queeningSquare)); - - return strongSide == pos.side_to_move() ? result : -result; -} - - -/// KR vs KB. This is very simple, and always returns drawish scores. The -/// score is slightly bigger when the defending king is close to the edge. -template<> -Value Endgame::operator()(const Position& pos) const { - - assert(verify_material(pos, strongSide, RookValueMg, 0)); - assert(verify_material(pos, weakSide, BishopValueMg, 0)); - - Value result = Value(push_to_edge(pos.square(weakSide))); - return strongSide == pos.side_to_move() ? result : -result; -} - - -/// 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(verify_material(pos, strongSide, RookValueMg, 0)); - assert(verify_material(pos, weakSide, KnightValueMg, 0)); - - Square weakKing = pos.square(weakSide); - Square weakKnight = pos.square(weakSide); - Value result = Value(push_to_edge(weakKing) + push_away(weakKing, weakKnight)); - return strongSide == pos.side_to_move() ? result : -result; -} - - -/// 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(verify_material(pos, strongSide, QueenValueMg, 0)); - assert(verify_material(pos, weakSide, VALUE_ZERO, 1)); - - Square strongKing = pos.square(strongSide); - Square weakKing = pos.square(weakSide); - Square weakPawn = pos.square(weakSide); - - Value result = Value(push_close(strongKing, weakKing)); - - if ( relative_rank(weakSide, weakPawn) != RANK_7 - || distance(weakKing, weakPawn) != 1 - || ((FileBBB | FileDBB | FileEBB | FileGBB) & weakPawn)) - result += QueenValueEg - PawnValueEg; - - 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 win KQ vs KR. -template<> -Value Endgame::operator()(const Position& pos) const { - - assert(verify_material(pos, strongSide, QueenValueMg, 0)); - assert(verify_material(pos, weakSide, RookValueMg, 0)); - - Square strongKing = pos.square(strongSide); - Square weakKing = pos.square(weakSide); - - Value result = QueenValueEg - - RookValueEg - + push_to_edge(weakKing) - + push_close(strongKing, weakKing); - - return strongSide == pos.side_to_move() ? result : -result; -} - - -/// KNN vs KP. Very drawish, but there are some mate opportunities if we can -/// press the weakSide King to a corner before the pawn advances too much. -template<> -Value Endgame::operator()(const Position& pos) const { - - assert(verify_material(pos, strongSide, 2 * KnightValueMg, 0)); - assert(verify_material(pos, weakSide, VALUE_ZERO, 1)); - - Square weakKing = pos.square(weakSide); - Square weakPawn = pos.square(weakSide); - - Value result = PawnValueEg - + 2 * push_to_edge(weakKing) - - 10 * relative_rank(weakSide, weakPawn); - - return strongSide == pos.side_to_move() ? result : -result; -} - - -/// Some cases of trivial draws -template<> Value Endgame::operator()(const Position&) const { return VALUE_DRAW; } - - -/// 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(strongSide) == BishopValueMg); - assert(pos.count(strongSide) >= 1); - - // No assertions about the material of weakSide, because we want draws to - // be detected even when the weaker side has some pawns. - - Bitboard strongPawns = pos.pieces(strongSide, PAWN); - Bitboard allPawns = pos.pieces(PAWN); - - Square strongBishop = pos.square(strongSide); - Square weakKing = pos.square(weakSide); - Square strongKing = pos.square(strongSide); - - // All strongSide pawns are on a single rook file? - if (!(strongPawns & ~FileABB) || !(strongPawns & ~FileHBB)) - { - Square queeningSquare = relative_square(strongSide, make_square(file_of(lsb(strongPawns)), RANK_8)); - - if ( opposite_colors(queeningSquare, strongBishop) - && distance(queeningSquare, weakKing) <= 1) - return SCALE_FACTOR_DRAW; - } - - // If all the pawns are on the same B or G file, then it's potentially a draw - if ((!(allPawns & ~FileBBB) || !(allPawns & ~FileGBB)) - && pos.non_pawn_material(weakSide) == 0 - && pos.count(weakSide) >= 1) - { - // Get the least advanced weakSide pawn - Square weakPawn = frontmost_sq(strongSide, pos.pieces(weakSide, PAWN)); - - // 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, weakPawn) == RANK_7 - && (strongPawns & (weakPawn + pawn_push(weakSide))) - && (opposite_colors(strongBishop, weakPawn) || !more_than_one(strongPawns))) - { - int strongKingDist = distance(weakPawn, strongKing); - int weakKingDist = distance(weakPawn, weakKing); - - // 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, weakKing) >= RANK_7 - && weakKingDist <= 2 - && weakKingDist <= strongKingDist) - return SCALE_FACTOR_DRAW; - } - } - - return SCALE_FACTOR_NONE; -} - - -/// 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(verify_material(pos, strongSide, QueenValueMg, 0)); - assert(pos.count(weakSide) == 1); - assert(pos.count(weakSide) >= 1); - - Square strongKing = pos.square(strongSide); - Square weakKing = pos.square(weakSide); - Square weakRook = pos.square(weakSide); - - if ( relative_rank(weakSide, weakKing) <= RANK_2 - && relative_rank(weakSide, strongKing) >= RANK_4 - && relative_rank(weakSide, weakRook) == RANK_3 - && ( pos.pieces(weakSide, PAWN) - & attacks_bb(weakKing) - & pawn_attacks_bb(strongSide, weakRook))) - return SCALE_FACTOR_DRAW; - - return SCALE_FACTOR_NONE; -} - - -/// 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. -template<> -ScaleFactor Endgame::operator()(const Position& pos) const { - - assert(verify_material(pos, strongSide, RookValueMg, 1)); - assert(verify_material(pos, weakSide, RookValueMg, 0)); - - // Assume strongSide is white and the pawn is on files A-D - Square strongKing = normalize(pos, strongSide, pos.square(strongSide)); - Square strongRook = normalize(pos, strongSide, pos.square(strongSide)); - Square strongPawn = normalize(pos, strongSide, pos.square(strongSide)); - Square weakKing = normalize(pos, strongSide, pos.square(weakSide)); - Square weakRook = normalize(pos, strongSide, pos.square(weakSide)); - - File pawnFile = file_of(strongPawn); - Rank pawnRank = rank_of(strongPawn); - Square queeningSquare = make_square(pawnFile, 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. - if ( pawnRank <= RANK_5 - && distance(weakKing, queeningSquare) <= 1 - && strongKing <= SQ_H5 - && (rank_of(weakRook) == RANK_6 || (pawnRank <= RANK_3 && rank_of(strongRook) != RANK_6))) - return SCALE_FACTOR_DRAW; - - // The defending side saves a draw by checking from behind in case the pawn - // has advanced to the 6th rank with the king behind. - if ( pawnRank == RANK_6 - && distance(weakKing, queeningSquare) <= 1 - && rank_of(strongKing) + tempo <= RANK_6 - && (rank_of(weakRook) == RANK_1 || (!tempo && distance(weakRook, strongPawn) >= 3))) - return SCALE_FACTOR_DRAW; - - if ( pawnRank >= RANK_6 - && weakKing == queeningSquare - && rank_of(weakRook) == RANK_1 - && (!tempo || distance(strongKing, strongPawn) >= 2)) - return SCALE_FACTOR_DRAW; - - // White pawn on a7 and rook on a8 is a draw if black's king is on g7 or h7 - // and the black rook is behind the pawn. - if ( strongPawn == SQ_A7 - && strongRook == SQ_A8 - && (weakKing == SQ_H7 || weakKing == SQ_G7) - && file_of(weakRook) == FILE_A - && (rank_of(weakRook) <= RANK_3 || file_of(strongKing) >= FILE_D || rank_of(strongKing) <= RANK_5)) - return SCALE_FACTOR_DRAW; - - // If the defending king blocks the pawn and the attacking king is too far - // away, it's a draw. - if ( pawnRank <= RANK_5 - && weakKing == strongPawn + NORTH - && distance(strongKing, strongPawn) - tempo >= 2 - && distance(strongKing, weakRook) - tempo >= 2) - return SCALE_FACTOR_DRAW; - - // Pawn on the 7th rank supported by the rook from behind usually wins if the - // attacking king is closer to the queening square than the defending king, - // and the defending king cannot gain tempi by threatening the attacking rook. - if ( pawnRank == RANK_7 - && pawnFile != FILE_A - && file_of(strongRook) == pawnFile - && strongRook != queeningSquare - && (distance(strongKing, queeningSquare) < distance(weakKing, queeningSquare) - 2 + tempo) - && (distance(strongKing, queeningSquare) < distance(weakKing, strongRook) + tempo)) - return ScaleFactor(SCALE_FACTOR_MAX - 2 * distance(strongKing, queeningSquare)); - - // Similar to the above, but with the pawn further back - if ( pawnFile != FILE_A - && file_of(strongRook) == pawnFile - && strongRook < strongPawn - && (distance(strongKing, queeningSquare) < distance(weakKing, queeningSquare) - 2 + tempo) - && (distance(strongKing, strongPawn + NORTH) < distance(weakKing, strongPawn + NORTH) - 2 + tempo) - && ( distance(weakKing, strongRook) + tempo >= 3 - || ( distance(strongKing, queeningSquare) < distance(weakKing, strongRook) + tempo - && (distance(strongKing, strongPawn + NORTH) < distance(weakKing, strongPawn) + tempo)))) - return ScaleFactor( SCALE_FACTOR_MAX - - 8 * distance(strongPawn, queeningSquare) - - 2 * distance(strongKing, queeningSquare)); - - // If the pawn is not far advanced and the defending king is somewhere in - // the pawn's path, it's probably a draw. - if (pawnRank <= RANK_4 && weakKing > strongPawn) - { - if (file_of(weakKing) == file_of(strongPawn)) - return ScaleFactor(10); - if ( distance(weakKing, strongPawn) == 1 - && distance(strongKing, weakKing) > 2) - return ScaleFactor(24 - 2 * distance(strongKing, weakKing)); - } - 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)); - - // Test for a rook pawn - if (pos.pieces(PAWN) & (FileABB | FileHBB)) - { - Square weakKing = pos.square(weakSide); - Square weakBishop = pos.square(weakSide); - Square strongKing = pos.square(strongSide); - Square strongPawn = pos.square(strongSide); - Rank pawnRank = relative_rank(strongSide, strongPawn); - Direction 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 (pawnRank == RANK_5 && !opposite_colors(weakBishop, strongPawn)) - { - int d = distance(strongPawn + 3 * push, weakKing); - - if (d <= 2 && !(d == 0 && weakKing == strongKing + 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 ( pawnRank == RANK_6 - && distance(strongPawn + 2 * push, weakKing) <= 1 - && (attacks_bb(weakBishop) & (strongPawn + push)) - && distance(weakBishop, strongPawn) >= 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(verify_material(pos, strongSide, RookValueMg, 2)); - assert(verify_material(pos, weakSide, RookValueMg, 1)); - - Square strongPawn1 = pos.squares(strongSide)[0]; - Square strongPawn2 = pos.squares(strongSide)[1]; - Square weakKing = pos.square(weakSide); - - // Does the stronger side have a passed pawn? - if (pos.pawn_passed(strongSide, strongPawn1) || pos.pawn_passed(strongSide, strongPawn2)) - return SCALE_FACTOR_NONE; - - Rank pawnRank = std::max(relative_rank(strongSide, strongPawn1), relative_rank(strongSide, strongPawn2)); - - if ( distance(weakKing, strongPawn1) <= 1 - && distance(weakKing, strongPawn2) <= 1 - && relative_rank(strongSide, weakKing) > pawnRank) - { - assert(pawnRank > RANK_1 && pawnRank < RANK_7); - return ScaleFactor(7 * pawnRank); - } - return SCALE_FACTOR_NONE; -} - - -/// K and two or more pawns vs K. There is just a single rule here: if all pawns -/// are on the same rook file and are blocked by the defending king, it's a draw. -template<> -ScaleFactor Endgame::operator()(const Position& pos) const { - - assert(pos.non_pawn_material(strongSide) == VALUE_ZERO); - assert(pos.count(strongSide) >= 2); - assert(verify_material(pos, weakSide, VALUE_ZERO, 0)); - - Square weakKing = pos.square(weakSide); - Bitboard strongPawns = pos.pieces(strongSide, PAWN); - - // If all pawns are ahead of the king on a single rook file, it's a draw. - if (!((strongPawns & ~FileABB) || (strongPawns & ~FileHBB)) && - !(strongPawns & ~passed_pawn_span(weakSide, weakKing))) - return SCALE_FACTOR_DRAW; - - return SCALE_FACTOR_NONE; -} - - -/// 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(verify_material(pos, strongSide, BishopValueMg, 1)); - assert(verify_material(pos, weakSide, BishopValueMg, 0)); - - Square strongPawn = pos.square(strongSide); - Square strongBishop = pos.square(strongSide); - Square weakBishop = pos.square(weakSide); - Square weakKing = pos.square(weakSide); - - // Case 1: Defending king blocks the pawn, and cannot be driven away - if ( (forward_file_bb(strongSide, strongPawn) & weakKing) - && ( opposite_colors(weakKing, strongBishop) - || relative_rank(strongSide, weakKing) <= RANK_6)) - return SCALE_FACTOR_DRAW; - - // Case 2: Opposite colored bishops - if (opposite_colors(strongBishop, weakBishop)) - return SCALE_FACTOR_DRAW; - - return SCALE_FACTOR_NONE; -} - - -/// KBPP vs KB. It detects a few basic draws with opposite-colored bishops -template<> -ScaleFactor Endgame::operator()(const Position& pos) const { - - assert(verify_material(pos, strongSide, BishopValueMg, 2)); - assert(verify_material(pos, weakSide, BishopValueMg, 0)); - - Square strongBishop = pos.square(strongSide); - Square weakBishop = pos.square(weakSide); - - if (!opposite_colors(strongBishop, weakBishop)) - return SCALE_FACTOR_NONE; - - Square weakKing = pos.square(weakSide); - Square strongPawn1 = pos.squares(strongSide)[0]; - Square strongPawn2 = pos.squares(strongSide)[1]; - Square blockSq1, blockSq2; - - if (relative_rank(strongSide, strongPawn1) > relative_rank(strongSide, strongPawn2)) - { - blockSq1 = strongPawn1 + pawn_push(strongSide); - blockSq2 = make_square(file_of(strongPawn2), rank_of(strongPawn1)); - } - else - { - blockSq1 = strongPawn2 + pawn_push(strongSide); - blockSq2 = make_square(file_of(strongPawn1), rank_of(strongPawn2)); - } - - switch (distance(strongPawn1, strongPawn2)) - { - case 0: - // 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(weakKing) == file_of(blockSq1) - && relative_rank(strongSide, weakKing) >= relative_rank(strongSide, blockSq1) - && opposite_colors(weakKing, strongBishop)) - return SCALE_FACTOR_DRAW; - else - return SCALE_FACTOR_NONE; - - case 1: - // 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 ( weakKing == blockSq1 - && opposite_colors(weakKing, strongBishop) - && ( weakBishop == blockSq2 - || (attacks_bb(blockSq2, pos.pieces()) & pos.pieces(weakSide, BISHOP)) - || distance(strongPawn1, strongPawn2) >= 2)) - return SCALE_FACTOR_DRAW; - - else if ( weakKing == blockSq2 - && opposite_colors(weakKing, strongBishop) - && ( weakBishop == blockSq1 - || (attacks_bb(blockSq1, pos.pieces()) & pos.pieces(weakSide, BISHOP)))) - return SCALE_FACTOR_DRAW; - else - return SCALE_FACTOR_NONE; - - default: - // The pawns are not on the same file or adjacent files. No scaling. - return SCALE_FACTOR_NONE; - } -} - - -/// 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(verify_material(pos, strongSide, BishopValueMg, 1)); - assert(verify_material(pos, weakSide, KnightValueMg, 0)); - - Square strongPawn = pos.square(strongSide); - Square strongBishop = pos.square(strongSide); - Square weakKing = pos.square(weakSide); - - if ( file_of(weakKing) == file_of(strongPawn) - && relative_rank(strongSide, strongPawn) < relative_rank(strongSide, weakKing) - && ( opposite_colors(weakKing, strongBishop) - || relative_rank(strongSide, weakKing) <= RANK_6)) - return SCALE_FACTOR_DRAW; - - return SCALE_FACTOR_NONE; -} - - -/// 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)); - - // Assume strongSide is white and the pawn is on files A-D - Square strongKing = normalize(pos, strongSide, pos.square(strongSide)); - Square weakKing = normalize(pos, strongSide, pos.square(weakSide)); - Square strongPawn = normalize(pos, strongSide, pos.square(strongSide)); - - 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. - if (rank_of(strongPawn) >= RANK_5 && file_of(strongPawn) != FILE_A) - return SCALE_FACTOR_NONE; - - // Probe the KPK bitbase with the weakest side's pawn removed. If it's a draw, - // it's probably at least a draw even with the pawn. - return Bitbases::probe(strongKing, strongPawn, weakKing, us) ? SCALE_FACTOR_NONE : SCALE_FACTOR_DRAW; -}