X-Git-Url: https://git.sesse.net/?p=stockfish;a=blobdiff_plain;f=src%2Fendgame.cpp;h=d28772277f2f65af11451e2c6b3c203ee8774fa4;hp=c2e892eef0b9d8e712151b2d148786cbfae4bb09;hb=c2d42ea8339b49e52a116e488214a14fda09d413;hpb=c2c185423b13b0227c86009c6006e48e8d258896 diff --git a/src/endgame.cpp b/src/endgame.cpp index c2e892ee..d2877227 100644 --- a/src/endgame.cpp +++ b/src/endgame.cpp @@ -18,6 +18,7 @@ */ #include +#include #include "bitcount.h" #include "endgame.h" @@ -59,10 +60,6 @@ namespace { // the two kings in basic endgames. const int DistanceBonus[8] = { 0, 0, 100, 80, 60, 40, 20, 10 }; - // Penalty for big distance between king and knight for the defending king - // and knight in KR vs KN endgames. - const int KRKNKingKnightDistancePenalty[8] = { 0, 0, 4, 10, 20, 32, 48, 70 }; - // Build corresponding key code for the opposite color: "KBPKN" -> "KNKBP" const string swap_colors(const string& keyCode) { @@ -90,7 +87,7 @@ namespace { fen += string(1, '0' + int(8 - keyCode.length())) + "/8/8/8/8/8/8/8 w - - 0 10"; // Build a Position out of the fen string and get its material key - return Position(fen, false, 0).get_material_key(); + return Position(fen, false, 0).material_key(); } } // namespace @@ -145,7 +142,7 @@ void Endgames::add(const string& keyCode) { /// 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::apply(const Position& pos) const { +Value Endgame::operator()(const Position& pos) const { assert(pos.non_pawn_material(weakerSide) == VALUE_ZERO); assert(pos.piece_count(weakerSide, PAWN) == VALUE_ZERO); @@ -171,7 +168,7 @@ Value Endgame::apply(const Position& pos) const { /// Mate with KBN vs K. This is similar to KX vs K, but we have to drive the /// defending king towards a corner square of the right color. template<> -Value Endgame::apply(const Position& pos) const { +Value Endgame::operator()(const Position& pos) const { assert(pos.non_pawn_material(weakerSide) == VALUE_ZERO); assert(pos.piece_count(weakerSide, PAWN) == VALUE_ZERO); @@ -187,7 +184,7 @@ Value Endgame::apply(const Position& pos) const { // 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. - if (opposite_color_squares(bishopSquare, SQ_A1)) + if (opposite_colors(bishopSquare, SQ_A1)) { winnerKSq = mirror(winnerKSq); loserKSq = mirror(loserKSq); @@ -203,7 +200,7 @@ Value Endgame::apply(const Position& pos) const { /// KP vs K. This endgame is evaluated with the help of a bitbase. template<> -Value Endgame::apply(const Position& pos) const { +Value Endgame::operator()(const Position& pos) const { assert(pos.non_pawn_material(strongerSide) == VALUE_ZERO); assert(pos.non_pawn_material(weakerSide) == VALUE_ZERO); @@ -251,7 +248,7 @@ Value Endgame::apply(const Position& pos) const { /// far advanced with support of the king, while the attacking king is far /// away. template<> -Value Endgame::apply(const Position& pos) const { +Value Endgame::operator()(const Position& pos) const { assert(pos.non_pawn_material(strongerSide) == RookValueMidgame); assert(pos.piece_count(strongerSide, PAWN) == 0); @@ -308,7 +305,7 @@ Value Endgame::apply(const Position& pos) const { /// 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::apply(const Position& pos) const { +Value Endgame::operator()(const Position& pos) const { assert(pos.non_pawn_material(strongerSide) == RookValueMidgame); assert(pos.piece_count(strongerSide, PAWN) == 0); @@ -324,7 +321,7 @@ Value Endgame::apply(const Position& pos) const { /// 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::apply(const Position& pos) const { +Value Endgame::operator()(const Position& pos) const { assert(pos.non_pawn_material(strongerSide) == RookValueMidgame); assert(pos.piece_count(strongerSide, PAWN) == 0); @@ -332,14 +329,11 @@ Value Endgame::apply(const Position& pos) const { assert(pos.piece_count(weakerSide, PAWN) == 0); assert(pos.piece_count(weakerSide, KNIGHT) == 1); - Square defendingKSq = pos.king_square(weakerSide); - Square nSq = pos.piece_list(weakerSide, KNIGHT)[0]; - - int d = square_distance(defendingKSq, nSq); - Value result = Value(10) - + MateTable[defendingKSq] - + KRKNKingKnightDistancePenalty[d]; + const int penalty[8] = { 0, 10, 14, 20, 30, 42, 58, 80 }; + Square bksq = pos.king_square(weakerSide); + Square bnsq = pos.piece_list(weakerSide, KNIGHT)[0]; + Value result = Value(MateTable[bksq] + penalty[square_distance(bksq, bnsq)]); return strongerSide == pos.side_to_move() ? result : -result; } @@ -350,7 +344,7 @@ Value Endgame::apply(const Position& pos) const { /// for the defending side in the search, this is usually sufficient to be /// able to win KQ vs KR. template<> -Value Endgame::apply(const Position& pos) const { +Value Endgame::operator()(const Position& pos) const { assert(pos.non_pawn_material(strongerSide) == QueenValueMidgame); assert(pos.piece_count(strongerSide, PAWN) == 0); @@ -369,13 +363,13 @@ Value Endgame::apply(const Position& pos) const { } template<> -Value Endgame::apply(const Position& pos) const { +Value Endgame::operator()(const Position& pos) const { assert(pos.piece_count(strongerSide, BISHOP) == 2); assert(pos.non_pawn_material(strongerSide) == 2*BishopValueMidgame); assert(pos.piece_count(weakerSide, KNIGHT) == 1); assert(pos.non_pawn_material(weakerSide) == KnightValueMidgame); - assert(pos.pieces(PAWN) == EmptyBoardBB); + assert(!pos.pieces(PAWN)); Value result = BishopValueEndgame; Square wksq = pos.king_square(strongerSide); @@ -398,22 +392,21 @@ Value Endgame::apply(const Position& pos) const { /// K and two minors vs K and one or two minors or K and two knights against /// king alone are always draw. template<> -Value Endgame::apply(const Position&) const { +Value Endgame::operator()(const Position&) const { return VALUE_DRAW; } template<> -Value Endgame::apply(const Position&) const { +Value Endgame::operator()(const Position&) const { return VALUE_DRAW; } -/// KBPKScalingFunction scales endgames where the stronger side has king, -/// bishop and one or more pawns. It checks for draws with rook pawns and a -/// bishop of the wrong color. If such a draw is detected, SCALE_FACTOR_ZERO is -/// returned. If not, the return value is SCALE_FACTOR_NONE, i.e. no scaling +/// K, bishop 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::apply(const Position& pos) const { +ScaleFactor Endgame::operator()(const Position& pos) const { assert(pos.non_pawn_material(strongerSide) == BishopValueMidgame); assert(pos.piece_count(strongerSide, BISHOP) == 1); @@ -427,13 +420,13 @@ ScaleFactor Endgame::apply(const Position& pos) const { // All pawns are on a single rook file ? if ( (pawnFile == FILE_A || pawnFile == FILE_H) - && (pawns & ~file_bb(pawnFile)) == EmptyBoardBB) + && !(pawns & ~file_bb(pawnFile))) { Square bishopSq = pos.piece_list(strongerSide, BISHOP)[0]; Square queeningSq = relative_square(strongerSide, make_square(pawnFile, RANK_8)); Square kingSq = pos.king_square(weakerSide); - if ( opposite_color_squares(queeningSq, bishopSq) + if ( opposite_colors(queeningSq, bishopSq) && abs(file_of(kingSq) - pawnFile) <= 1) { // The bishop has the wrong color, and the defending king is on the @@ -442,12 +435,12 @@ ScaleFactor Endgame::apply(const Position& pos) const { Rank rank; if (strongerSide == WHITE) { - for (rank = RANK_7; (rank_bb(rank) & pawns) == EmptyBoardBB; rank--) {} + for (rank = RANK_7; !(rank_bb(rank) & pawns); rank--) {} assert(rank >= RANK_2 && rank <= RANK_7); } else { - for (rank = RANK_2; (rank_bb(rank) & pawns) == EmptyBoardBB; rank++) {} + for (rank = RANK_2; !(rank_bb(rank) & pawns); rank++) {} rank = Rank(rank ^ 7); // HACK to get the relative rank assert(rank >= RANK_2 && rank <= RANK_7); } @@ -455,19 +448,17 @@ ScaleFactor Endgame::apply(const Position& pos) const { // is placed somewhere in front of the pawn, it's a draw. if ( square_distance(kingSq, queeningSq) <= 1 || relative_rank(strongerSide, kingSq) >= rank) - return SCALE_FACTOR_ZERO; + return SCALE_FACTOR_DRAW; } } return SCALE_FACTOR_NONE; } -/// KQKRPScalingFunction scales endgames where the stronger side has only -/// king and queen, while the weaker side has at least a rook and a pawn. -/// It tests for fortress draws with a rook on the third rank defended by -/// a pawn. +/// 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. template<> -ScaleFactor Endgame::apply(const Position& pos) const { +ScaleFactor Endgame::operator()(const Position& pos) const { assert(pos.non_pawn_material(strongerSide) == QueenValueMidgame); assert(pos.piece_count(strongerSide, QUEEN) == 1); @@ -484,21 +475,20 @@ ScaleFactor Endgame::apply(const Position& pos) const { { Square rsq = pos.piece_list(weakerSide, ROOK)[0]; if (pos.attacks_from(rsq, strongerSide) & pos.pieces(PAWN, weakerSide)) - return SCALE_FACTOR_ZERO; + return SCALE_FACTOR_DRAW; } return SCALE_FACTOR_NONE; } -/// KRPKRScalingFunction scales KRP vs KR endgames. 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. +/// 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. /// /// 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. template<> -ScaleFactor Endgame::apply(const Position& pos) const { +ScaleFactor Endgame::operator()(const Position& pos) const { assert(pos.non_pawn_material(strongerSide) == RookValueMidgame); assert(pos.piece_count(strongerSide, PAWN) == 1); @@ -541,7 +531,7 @@ ScaleFactor Endgame::apply(const Position& pos) const { && square_distance(bksq, queeningSq) <= 1 && wksq <= SQ_H5 && (rank_of(brsq) == RANK_6 || (r <= RANK_3 && rank_of(wrsq) != RANK_6))) - return SCALE_FACTOR_ZERO; + 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. @@ -549,13 +539,13 @@ ScaleFactor Endgame::apply(const Position& pos) const { && square_distance(bksq, queeningSq) <= 1 && rank_of(wksq) + tempo <= RANK_6 && (rank_of(brsq) == RANK_1 || (!tempo && abs(file_of(brsq) - f) >= 3))) - return SCALE_FACTOR_ZERO; + return SCALE_FACTOR_DRAW; if ( r >= RANK_6 && bksq == queeningSq && rank_of(brsq) == RANK_1 && (!tempo || square_distance(wksq, wpsq) >= 2)) - return SCALE_FACTOR_ZERO; + 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. @@ -564,7 +554,7 @@ ScaleFactor Endgame::apply(const Position& pos) const { && (bksq == SQ_H7 || bksq == SQ_G7) && file_of(brsq) == FILE_A && (rank_of(brsq) <= RANK_3 || file_of(wksq) >= FILE_D || rank_of(wksq) <= RANK_5)) - return SCALE_FACTOR_ZERO; + return SCALE_FACTOR_DRAW; // If the defending king blocks the pawn and the attacking king is too far // away, it's a draw. @@ -572,7 +562,7 @@ ScaleFactor Endgame::apply(const Position& pos) const { && bksq == wpsq + DELTA_N && square_distance(wksq, wpsq) - tempo >= 2 && square_distance(wksq, brsq) - tempo >= 2) - return SCALE_FACTOR_ZERO; + 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, @@ -612,11 +602,11 @@ ScaleFactor Endgame::apply(const Position& pos) const { } -/// KRPPKRPScalingFunction scales KRPP vs KRP endgames. There is only a -/// single pattern: If the stronger side has no pawns and the defending king +/// 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. template<> -ScaleFactor Endgame::apply(const Position& pos) const { +ScaleFactor Endgame::operator()(const Position& pos) const { assert(pos.non_pawn_material(strongerSide) == RookValueMidgame); assert(pos.piece_count(strongerSide, PAWN) == 2); @@ -632,7 +622,7 @@ ScaleFactor Endgame::apply(const Position& pos) const { || pos.pawn_is_passed(strongerSide, wpsq2)) return SCALE_FACTOR_NONE; - Rank r = Max(relative_rank(strongerSide, wpsq1), relative_rank(strongerSide, wpsq2)); + Rank r = std::max(relative_rank(strongerSide, wpsq1), relative_rank(strongerSide, wpsq2)); if ( file_distance(bksq, wpsq1) <= 1 && file_distance(bksq, wpsq2) <= 1 @@ -651,11 +641,10 @@ ScaleFactor Endgame::apply(const Position& pos) const { } -/// KPsKScalingFunction scales endgames with king and two or more pawns -/// against king. 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. +/// 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::apply(const Position& pos) const { +ScaleFactor Endgame::operator()(const Position& pos) const { assert(pos.non_pawn_material(strongerSide) == VALUE_ZERO); assert(pos.piece_count(strongerSide, PAWN) >= 2); @@ -666,34 +655,33 @@ ScaleFactor Endgame::apply(const Position& pos) const { Bitboard pawns = pos.pieces(PAWN, strongerSide); // Are all pawns on the 'a' file? - if ((pawns & ~FileABB) == EmptyBoardBB) + 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, ksq) & pawns) == EmptyBoardBB)) - return SCALE_FACTOR_ZERO; + && !in_front_bb(strongerSide, ksq) & pawns)) + return SCALE_FACTOR_DRAW; } // Are all pawns on the 'h' file? - else if ((pawns & ~FileHBB) == EmptyBoardBB) + 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, ksq) & pawns) == EmptyBoardBB)) - return SCALE_FACTOR_ZERO; + && !in_front_bb(strongerSide, ksq) & pawns)) + return SCALE_FACTOR_DRAW; } return SCALE_FACTOR_NONE; } -/// KBPKBScalingFunction scales KBP vs KB endgames. 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. +/// 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. template<> -ScaleFactor Endgame::apply(const Position& pos) const { +ScaleFactor Endgame::operator()(const Position& pos) const { assert(pos.non_pawn_material(strongerSide) == BishopValueMidgame); assert(pos.piece_count(strongerSide, BISHOP) == 1); @@ -710,12 +698,12 @@ ScaleFactor Endgame::apply(const Position& pos) const { // 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_color_squares(weakerKingSq, strongerBishopSq) + && ( opposite_colors(weakerKingSq, strongerBishopSq) || relative_rank(strongerSide, weakerKingSq) <= RANK_6)) - return SCALE_FACTOR_ZERO; + return SCALE_FACTOR_DRAW; // Case 2: Opposite colored bishops - if (opposite_color_squares(strongerBishopSq, weakerBishopSq)) + if (opposite_colors(strongerBishopSq, weakerBishopSq)) { // We assume that the position is drawn in the following three situations: // @@ -728,27 +716,27 @@ ScaleFactor Endgame::apply(const Position& pos) const { // reasonably well. if (relative_rank(strongerSide, pawnSq) <= RANK_5) - return SCALE_FACTOR_ZERO; + return SCALE_FACTOR_DRAW; else { Bitboard path = squares_in_front_of(strongerSide, pawnSq); if (path & pos.pieces(KING, weakerSide)) - return SCALE_FACTOR_ZERO; + return SCALE_FACTOR_DRAW; if ( (pos.attacks_from(weakerBishopSq) & path) && square_distance(weakerBishopSq, pawnSq) >= 3) - return SCALE_FACTOR_ZERO; + return SCALE_FACTOR_DRAW; } } return SCALE_FACTOR_NONE; } -/// KBPPKBScalingFunction scales KBPP vs KB endgames. It detects a few basic -/// draws with opposite-colored bishops. +/// K, bishop and two pawns vs K and bishop. It detects a few basic draws with +/// opposite-colored bishops. template<> -ScaleFactor Endgame::apply(const Position& pos) const { +ScaleFactor Endgame::operator()(const Position& pos) const { assert(pos.non_pawn_material(strongerSide) == BishopValueMidgame); assert(pos.piece_count(strongerSide, BISHOP) == 1); @@ -760,7 +748,7 @@ ScaleFactor Endgame::apply(const Position& pos) const { Square wbsq = pos.piece_list(strongerSide, BISHOP)[0]; Square bbsq = pos.piece_list(weakerSide, BISHOP)[0]; - if (!opposite_color_squares(wbsq, bbsq)) + if (!opposite_colors(wbsq, bbsq)) return SCALE_FACTOR_NONE; Square ksq = pos.king_square(weakerSide); @@ -788,8 +776,8 @@ ScaleFactor Endgame::apply(const Position& pos) const { // some square in the frontmost pawn's path. if ( file_of(ksq) == file_of(blockSq1) && relative_rank(strongerSide, ksq) >= relative_rank(strongerSide, blockSq1) - && opposite_color_squares(ksq, wbsq)) - return SCALE_FACTOR_ZERO; + && opposite_colors(ksq, wbsq)) + return SCALE_FACTOR_DRAW; else return SCALE_FACTOR_NONE; @@ -798,17 +786,17 @@ ScaleFactor Endgame::apply(const Position& pos) const { // 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_color_squares(ksq, wbsq) + && opposite_colors(ksq, wbsq) && ( bbsq == blockSq2 || (pos.attacks_from(blockSq2) & pos.pieces(BISHOP, weakerSide)) || abs(r1 - r2) >= 2)) - return SCALE_FACTOR_ZERO; + return SCALE_FACTOR_DRAW; else if ( ksq == blockSq2 - && opposite_color_squares(ksq, wbsq) + && opposite_colors(ksq, wbsq) && ( bbsq == blockSq1 || (pos.attacks_from(blockSq1) & pos.pieces(BISHOP, weakerSide)))) - return SCALE_FACTOR_ZERO; + return SCALE_FACTOR_DRAW; else return SCALE_FACTOR_NONE; @@ -819,12 +807,11 @@ ScaleFactor Endgame::apply(const Position& pos) const { } -/// KBPKNScalingFunction scales KBP vs KN endgames. 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. +/// 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. template<> -ScaleFactor Endgame::apply(const Position& pos) const { +ScaleFactor Endgame::operator()(const Position& pos) const { assert(pos.non_pawn_material(strongerSide) == BishopValueMidgame); assert(pos.piece_count(strongerSide, BISHOP) == 1); @@ -839,19 +826,19 @@ ScaleFactor Endgame::apply(const Position& pos) const { if ( file_of(weakerKingSq) == file_of(pawnSq) && relative_rank(strongerSide, pawnSq) < relative_rank(strongerSide, weakerKingSq) - && ( opposite_color_squares(weakerKingSq, strongerBishopSq) + && ( opposite_colors(weakerKingSq, strongerBishopSq) || relative_rank(strongerSide, weakerKingSq) <= RANK_6)) - return SCALE_FACTOR_ZERO; + return SCALE_FACTOR_DRAW; return SCALE_FACTOR_NONE; } -/// KNPKScalingFunction scales KNP vs K endgames. 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. +/// 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. template<> -ScaleFactor Endgame::apply(const Position& pos) const { +ScaleFactor Endgame::operator()(const Position& pos) const { assert(pos.non_pawn_material(strongerSide) == KnightValueMidgame); assert(pos.piece_count(strongerSide, KNIGHT) == 1); @@ -864,46 +851,40 @@ ScaleFactor Endgame::apply(const Position& pos) const { if ( pawnSq == relative_square(strongerSide, SQ_A7) && square_distance(weakerKingSq, relative_square(strongerSide, SQ_A8)) <= 1) - return SCALE_FACTOR_ZERO; + return SCALE_FACTOR_DRAW; if ( pawnSq == relative_square(strongerSide, SQ_H7) && square_distance(weakerKingSq, relative_square(strongerSide, SQ_H8)) <= 1) - return SCALE_FACTOR_ZERO; + return SCALE_FACTOR_DRAW; return SCALE_FACTOR_NONE; } -/// KPKPScalingFunction scales KP vs KP endgames. 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). +/// 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). template<> -ScaleFactor Endgame::apply(const Position& pos) const { +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.piece_count(WHITE, PAWN) == 1); assert(pos.piece_count(BLACK, PAWN) == 1); - Square wksq, bksq, wpsq; - Color stm; + Square wksq = pos.king_square(strongerSide); + Square bksq = pos.king_square(weakerSide); + Square wpsq = pos.piece_list(strongerSide, PAWN)[0]; + Color stm = pos.side_to_move(); - if (strongerSide == WHITE) - { - wksq = pos.king_square(WHITE); - bksq = pos.king_square(BLACK); - wpsq = pos.piece_list(WHITE, PAWN)[0]; - stm = pos.side_to_move(); - } - else + if (strongerSide == BLACK) { - wksq = flip(pos.king_square(BLACK)); - bksq = flip(pos.king_square(WHITE)); - wpsq = flip(pos.piece_list(BLACK, PAWN)[0]); - stm = flip(pos.side_to_move()); + wksq = flip(wksq); + bksq = flip(bksq); + wpsq = flip(wpsq); + stm = flip(stm); } if (file_of(wpsq) >= FILE_E) @@ -919,7 +900,7 @@ ScaleFactor Endgame::apply(const Position& pos) const { && file_of(wpsq) != 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 probe_kpk_bitbase(wksq, wpsq, bksq, stm) ? SCALE_FACTOR_NONE : SCALE_FACTOR_ZERO; + // 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 probe_kpk_bitbase(wksq, wpsq, bksq, stm) ? SCALE_FACTOR_NONE : SCALE_FACTOR_DRAW; }