X-Git-Url: https://git.sesse.net/?p=stockfish;a=blobdiff_plain;f=src%2Fendgame.cpp;h=9021f242313279a16bcbc9ddc1f0f20c2eb47a2d;hp=836621d2a5428f02e220bd8c643005e6a21e4cc9;hb=HEAD;hpb=be509525336b65419e708678abe4e16efb5f6f4d diff --git a/src/endgame.cpp b/src/endgame.cpp deleted file mode 100644 index 836621d2..00000000 --- a/src/endgame.cpp +++ /dev/null @@ -1,848 +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 - - 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 - -#include "bitboard.h" -#include "bitcount.h" -#include "endgame.h" -#include "movegen.h" - -using std::string; - -namespace { - - // Table used to drive the king towards the edge of the board - // in KX vs K and KQ vs KR endgames. - const int PushToEdges[SQUARE_NB] = { - 100, 90, 80, 70, 70, 80, 90, 100, - 90, 70, 60, 50, 50, 60, 70, 90, - 80, 60, 40, 30, 30, 40, 60, 80, - 70, 50, 30, 20, 20, 30, 50, 70, - 70, 50, 30, 20, 20, 30, 50, 70, - 80, 60, 40, 30, 30, 40, 60, 80, - 90, 70, 60, 50, 50, 60, 70, 90, - 100, 90, 80, 70, 70, 80, 90, 100, - }; - - // Table used to drive the king towards a corner square of the - // right color in KBN vs K endgames. - const int PushToCorners[SQUARE_NB] = { - 200, 190, 180, 170, 160, 150, 140, 130, - 190, 180, 170, 160, 150, 140, 130, 140, - 180, 170, 155, 140, 140, 125, 140, 150, - 170, 160, 140, 120, 110, 140, 150, 160, - 160, 150, 140, 110, 120, 140, 160, 170, - 150, 140, 125, 140, 140, 155, 170, 180, - 140, 130, 140, 150, 160, 170, 180, 190, - 130, 140, 150, 160, 170, 180, 190, 200 - }; - - // Tables used to drive a piece towards or away from another piece - const int PushClose[8] = { 0, 0, 100, 80, 60, 40, 20, 10 }; - const int PushAway [8] = { 0, 5, 20, 40, 60, 80, 90, 100 }; - -#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.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)), // 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(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, nullptr).material_key(); - } - -} // namespace - - -/// Endgames members definitions - -Endgames::Endgames() { - - add("KPK"); - add("KNNK"); - add("KBNK"); - add("KRKP"); - add("KRKB"); - add("KRKN"); - add("KQKP"); - add("KQKR"); - - add("KNPK"); - add("KNPKB"); - add("KRPKR"); - add("KRPKB"); - add("KBPKB"); - add("KBPKN"); - add("KBPPKB"); - add("KRPPKRP"); -} - - -template -void Endgames::add(const string& code) { - map()[key(code, WHITE)] = std::unique_ptr>(new Endgame(WHITE)); - map()[key(code, BLACK)] = std::unique_ptr>(new Endgame(BLACK)); -} - - -/// 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 winnerKSq = pos.king_square(strongSide); - Square loserKSq = pos.king_square(weakSide); - - Value result = pos.non_pawn_material(strongSide) - + pos.count(strongSide) * PawnValueEg - + PushToEdges[loserKSq] - + PushClose[distance(winnerKSq, loserKSq)]; - - if ( pos.count(strongSide) - || pos.count(strongSide) - ||(pos.count(strongSide) && pos.count(strongSide)) - ||(pos.count(strongSide) > 1 && opposite_colors(pos.list(strongSide)[0], - pos.list(strongSide)[1]))) - result += VALUE_KNOWN_WIN; - - 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 of the right color. -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 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 flip the kings in order - // to drive the enemy toward corners A8 or H1. - if (opposite_colors(bishopSq, SQ_A1)) - { - winnerKSq = ~winnerKSq; - loserKSq = ~loserKSq; - } - - Value result = VALUE_KNOWN_WIN - + PushClose[distance(winnerKSq, loserKSq)] - + PushToCorners[loserKSq]; - - 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 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]); - - Color us = strongSide == pos.side_to_move() ? WHITE : BLACK; - - if (!Bitbases::probe(wksq, psq, bksq, us)) - return VALUE_DRAW; - - Value result = VALUE_KNOWN_WIN + PawnValueEg + Value(rank_of(psq)); - - 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 wksq = relative_square(strongSide, pos.king_square(strongSide)); - Square bksq = relative_square(strongSide, pos.king_square(weakSide)); - Square rsq = relative_square(strongSide, pos.list(strongSide)[0]); - Square psq = relative_square(strongSide, pos.list(weakSide)[0]); - - Square queeningSq = 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 - distance(wksq, psq); - - // If the weaker side's king is too far from the pawn and the rook, - // it's a win. - else if ( distance(bksq, psq) >= 3 + (pos.side_to_move() == weakSide) - && distance(bksq, rsq) >= 3) - result = RookValueEg - 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 - && distance(bksq, psq) == 1 - && rank_of(wksq) >= RANK_4 - && distance(wksq, psq) > 2 + (pos.side_to_move() == strongSide)) - result = Value(80) - 8 * distance(wksq, psq); - - else - result = Value(200) - 8 * ( distance(wksq, psq + DELTA_S) - - distance(bksq, psq + DELTA_S) - - distance(psq, queeningSq)); - - 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(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 -/// 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 bksq = pos.king_square(weakSide); - Square bnsq = pos.list(weakSide)[0]; - Value result = Value(PushToEdges[bksq] + PushAway[distance(bksq, bnsq)]); - 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 winnerKSq = pos.king_square(strongSide); - Square loserKSq = pos.king_square(weakSide); - Square pawnSq = pos.list(weakSide)[0]; - - Value result = Value(PushClose[distance(winnerKSq, loserKSq)]); - - if ( relative_rank(weakSide, pawnSq) != RANK_7 - || distance(loserKSq, pawnSq) != 1 - || !((FileABB | FileCBB | FileFBB | FileHBB) & pawnSq)) - 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 winnerKSq = pos.king_square(strongSide); - Square loserKSq = pos.king_square(weakSide); - - Value result = QueenValueEg - - RookValueEg - + PushToEdges[loserKSq] - + PushClose[distance(winnerKSq, loserKSq)]; - - 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 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(strongSide)[0]; - Square queeningSq = relative_square(strongSide, make_square(pawnFile, RANK_8)); - Square kingSq = pos.king_square(weakSide); - - if ( opposite_colors(queeningSq, bishopSq) - && distance(queeningSq, kingSq) <= 1) - return SCALE_FACTOR_DRAW; - } - - // If all the pawns are on the same B or G file, then it's potentially a draw - if ( (pawnFile == FILE_B || pawnFile == FILE_G) - && !(pos.pieces(PAWN) & ~file_bb(pawnFile)) - && pos.non_pawn_material(weakSide) == 0 - && pos.count(weakSide) >= 1) - { - // Get weakSide pawn that is closest to 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 = distance(weakPawnSq, strongKingSq); - int weakKingDist = 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; -} - - -/// 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 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; -} - - -/// 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 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 = 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. - if ( r <= RANK_5 - && distance(bksq, queeningSq) <= 1 - && wksq <= SQ_H5 - && (rank_of(brsq) == RANK_6 || (r <= RANK_3 && rank_of(wrsq) != 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 ( r == RANK_6 - && distance(bksq, queeningSq) <= 1 - && rank_of(wksq) + tempo <= RANK_6 - && (rank_of(brsq) == RANK_1 || (!tempo && distance(file_of(brsq), f) >= 3))) - return SCALE_FACTOR_DRAW; - - if ( r >= RANK_6 - && bksq == queeningSq - && rank_of(brsq) == RANK_1 - && (!tempo || distance(wksq, wpsq) >= 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 ( wpsq == SQ_A7 - && wrsq == SQ_A8 - && (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_DRAW; - - // If the defending king blocks the pawn and the attacking king is too far - // away, it's a draw. - if ( r <= RANK_5 - && bksq == wpsq + DELTA_N - && distance(wksq, wpsq) - tempo >= 2 - && distance(wksq, brsq) - 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 ( r == RANK_7 - && f != FILE_A - && file_of(wrsq) == f - && wrsq != queeningSq - && (distance(wksq, queeningSq) < distance(bksq, queeningSq) - 2 + tempo) - && (distance(wksq, queeningSq) < distance(bksq, wrsq) + tempo)) - return ScaleFactor(SCALE_FACTOR_MAX - 2 * distance(wksq, queeningSq)); - - // Similar to the above, but with the pawn further back - if ( f != FILE_A - && file_of(wrsq) == f - && wrsq < wpsq - && (distance(wksq, queeningSq) < distance(bksq, queeningSq) - 2 + tempo) - && (distance(wksq, wpsq + DELTA_N) < distance(bksq, wpsq + DELTA_N) - 2 + tempo) - && ( distance(bksq, wrsq) + tempo >= 3 - || ( distance(wksq, queeningSq) < distance(bksq, wrsq) + tempo - && (distance(wksq, wpsq + DELTA_N) < distance(bksq, wrsq) + tempo)))) - return ScaleFactor( SCALE_FACTOR_MAX - - 8 * distance(wpsq, queeningSq) - - 2 * distance(wksq, queeningSq)); - - // 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) - { - if (file_of(bksq) == file_of(wpsq)) - return ScaleFactor(10); - if ( distance(bksq, wpsq) == 1 - && distance(wksq, bksq) > 2) - return ScaleFactor(24 - 2 * distance(wksq, bksq)); - } - 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 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 = 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 - && distance(psq + 2 * push, ksq) <= 1 - && (PseudoAttacks[BISHOP][bsq] & (psq + push)) - && 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(verify_material(pos, strongSide, RookValueMg, 2)); - assert(verify_material(pos, weakSide, RookValueMg, 1)); - - 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(strongSide, wpsq1) || pos.pawn_passed(strongSide, wpsq2)) - return SCALE_FACTOR_NONE; - - Rank r = std::max(relative_rank(strongSide, wpsq1), relative_rank(strongSide, wpsq2)); - - if ( distance(bksq, wpsq1) <= 1 - && distance(bksq, wpsq2) <= 1 - && relative_rank(strongSide, bksq) > r) - { - switch (r) { - case RANK_2: return ScaleFactor(10); - case RANK_3: return ScaleFactor(10); - case RANK_4: return ScaleFactor(15); - case RANK_5: return ScaleFactor(20); - case RANK_6: return ScaleFactor(40); - default: assert(false); - } - } - 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 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)) - && distance(ksq, psq) <= 1) - 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 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(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(strongBishopSq, weakBishopSq)) - { - // We assume that the position is drawn in the following three situations: - // - // a. The pawn is on rank 5 or further back. - // b. The defending king is somewhere in the pawn's path. - // c. The defending bishop attacks some square along the pawn's path, - // and is at least three squares away from the pawn. - // - // These rules are probably not perfect, but in practice they work - // reasonably well. - - if (relative_rank(strongSide, pawnSq) <= RANK_5) - return SCALE_FACTOR_DRAW; - else - { - Bitboard path = forward_bb(strongSide, pawnSq); - - if (path & pos.pieces(weakSide, KING)) - return SCALE_FACTOR_DRAW; - - if ( (pos.attacks_from(weakBishopSq) & path) - && distance(weakBishopSq, pawnSq) >= 3) - 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 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(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(strongSide, psq1) > relative_rank(strongSide, psq2)) - { - blockSq1 = psq1 + pawn_push(strongSide); - blockSq2 = make_square(file_of(psq2), rank_of(psq1)); - } - else - { - blockSq1 = psq2 + pawn_push(strongSide); - blockSq2 = make_square(file_of(psq1), rank_of(psq2)); - } - - switch (distance(psq1, psq2)) - { - 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(ksq) == file_of(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. 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(weakSide, BISHOP)) - || distance(r1, r2) >= 2)) - return SCALE_FACTOR_DRAW; - - else if ( ksq == blockSq2 - && opposite_colors(ksq, wbsq) - && ( bbsq == blockSq1 - || (pos.attacks_from(blockSq1) & 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 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; -} - - -/// KNP vs K. There is a single rule: if the pawn is a rook pawn on the 7th rank -/// and the defending king prevents the pawn from advancing, the position is drawn. -template<> -ScaleFactor Endgame::operator()(const Position& pos) const { - - assert(verify_material(pos, strongSide, KnightValueMg, 1)); - assert(verify_material(pos, weakSide, VALUE_ZERO, 0)); - - // 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 == SQ_A7 && distance(SQ_A8, weakKingSq) <= 1) - return SCALE_FACTOR_DRAW; - - return SCALE_FACTOR_NONE; -} - - -/// 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(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(strongSide, pawnSq) & pos.attacks_from(bishopSq)) - return ScaleFactor(distance(weakKingSq, pawnSq)); - - 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 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]); - - 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(psq) >= RANK_5 && file_of(psq) != 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(wksq, psq, bksq, us) ? SCALE_FACTOR_NONE : SCALE_FACTOR_DRAW; -}