+++ /dev/null
-/*
- Stockfish, a UCI chess playing engine derived from Glaurung 2.1
- Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
- 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
- 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 <http://www.gnu.org/licenses/>.
-*/
-
-#include <algorithm>
-#include <cassert>
-
-#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 num_pawns) {
- return pos.non_pawn_material(c) == npm && pos.count<PAWN>(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<PAWN>(strongSide) == 1);
-
- if (file_of(pos.list<PAWN>(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, NULL).material_key();
- }
-
- template<typename M>
- void delete_endgame(const typename M::value_type& p) { delete p.second; }
-
-} // namespace
-
-
-/// Endgames members definitions
-
-Endgames::Endgames() {
-
- add<KPK>("KPK");
- add<KNNK>("KNNK");
- add<KBNK>("KBNK");
- add<KRKP>("KRKP");
- add<KRKB>("KRKB");
- add<KRKN>("KRKN");
- add<KQKP>("KQKP");
- add<KQKR>("KQKR");
-
- add<KNPK>("KNPK");
- add<KNPKB>("KNPKB");
- add<KRPKR>("KRPKR");
- add<KRPKB>("KRPKB");
- add<KBPKB>("KBPKB");
- add<KBPKN>("KBPKN");
- add<KBPPKB>("KBPPKB");
- add<KRPPKRP>("KRPPKRP");
-}
-
-Endgames::~Endgames() {
-
- for_each(m1.begin(), m1.end(), delete_endgame<M1>);
- for_each(m2.begin(), m2.end(), delete_endgame<M2>);
-}
-
-template<EndgameType E>
-void Endgames::add(const string& code) {
-
- map((Endgame<E>*)0)[key(code, WHITE)] = new Endgame<E>(WHITE);
- map((Endgame<E>*)0)[key(code, BLACK)] = new Endgame<E>(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<KXK>::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<LEGAL>(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<PAWN>(strongSide) * PawnValueEg
- + PushToEdges[loserKSq]
- + PushClose[square_distance(winnerKSq, loserKSq)];
-
- if ( pos.count<QUEEN>(strongSide)
- || pos.count<ROOK>(strongSide)
- ||(pos.count<BISHOP>(strongSide) && pos.count<KNIGHT>(strongSide))
- || pos.bishop_pair(strongSide))
- 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<KBNK>::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<BISHOP>(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[square_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<KPK>::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<PAWN>(strongSide)[0]);
-
- 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 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<KRKP>::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<ROOK>(strongSide)[0]);
- Square psq = relative_square(strongSide, pos.list<PAWN>(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 - 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() == weakSide)
- && square_distance(bksq, rsq) >= 3)
- 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() == strongSide))
- result = Value(80) - 8 * square_distance(wksq, psq);
-
- else
- result = Value(200) - 8 * ( square_distance(wksq, psq + DELTA_S)
- - square_distance(bksq, psq + DELTA_S)
- - square_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<KRKB>::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<KRKN>::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<KNIGHT>(weakSide)[0];
- Value result = Value(PushToEdges[bksq] + PushAway[square_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<KQKP>::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<PAWN>(weakSide)[0];
-
- Value result = Value(PushClose[square_distance(winnerKSq, loserKSq)]);
-
- if ( relative_rank(weakSide, pawnSq) != RANK_7
- || square_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<KQKR>::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[square_distance(winnerKSq, loserKSq)];
-
- return strongSide == pos.side_to_move() ? result : -result;
-}
-
-
-/// Some cases of trivial draws
-template<> Value Endgame<KNNK>::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<KBPsK>::operator()(const Position& pos) const {
-
- assert(pos.non_pawn_material(strongSide) == BishopValueMg);
- assert(pos.count<PAWN>(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 pawnsFile = file_of(lsb(pawns));
-
- // All pawns are on a single rook file ?
- if ( (pawnsFile == FILE_A || pawnsFile == FILE_H)
- && !(pawns & ~file_bb(pawnsFile)))
- {
- Square bishopSq = pos.list<BISHOP>(strongSide)[0];
- Square queeningSq = relative_square(strongSide, make_square(pawnsFile, RANK_8));
- Square kingSq = pos.king_square(weakSide);
-
- // If the bishop has the wrong color, and the defending king is on the file
- // of the pawn(s) or the neighboring file, then it's potentially a draw.
- if ( opposite_colors(queeningSq, bishopSq)
- && file_distance(kingSq, lsb(pawns)) <= 1)
- {
- // If the defending king has distance <= 1 to the promotion square or
- // is placed somewhere in front of the frontmost pawn, it's a draw.
- Rank rank = relative_rank(strongSide, (frontmost_sq(strongSide, pawns)));
-
- if ( square_distance(kingSq, queeningSq) <= 1
- || relative_rank(strongSide, kingSq) >= rank)
- 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<KQKRPs>::operator()(const Position& pos) const {
-
- assert(verify_material(pos, strongSide, QueenValueMg, 0));
- assert(pos.count<ROOK>(weakSide) == 1);
- assert(pos.count<PAWN>(weakSide) >= 1);
-
- Square kingSq = pos.king_square(weakSide);
- Square rsq = pos.list<ROOK>(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<KING>(kingSq)
- & pos.attacks_from<PAWN>(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<KRPKR>::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<ROOK>(strongSide)[0]);
- Square wpsq = normalize(pos, strongSide, pos.list<PAWN>(strongSide)[0]);
- Square brsq = normalize(pos, strongSide, pos.list<ROOK>(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
- && square_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
- && 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_DRAW;
-
- if ( r >= RANK_6
- && bksq == queeningSq
- && rank_of(brsq) == RANK_1
- && (!tempo || square_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
- && square_distance(wksq, wpsq) - tempo >= 2
- && square_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
- && (square_distance(wksq, queeningSq) < square_distance(bksq, queeningSq) - 2 + tempo)
- && (square_distance(wksq, queeningSq) < square_distance(bksq, wrsq) + tempo))
- return ScaleFactor(SCALE_FACTOR_MAX - 2 * square_distance(wksq, queeningSq));
-
- // Similar to the above, but with the pawn further back
- if ( f != FILE_A
- && file_of(wrsq) == f
- && wrsq < wpsq
- && (square_distance(wksq, queeningSq) < square_distance(bksq, queeningSq) - 2 + tempo)
- && (square_distance(wksq, wpsq + DELTA_N) < square_distance(bksq, wpsq + DELTA_N) - 2 + tempo)
- && ( square_distance(bksq, wrsq) + tempo >= 3
- || ( square_distance(wksq, queeningSq) < square_distance(bksq, wrsq) + tempo
- && (square_distance(wksq, wpsq + DELTA_N) < square_distance(bksq, wrsq) + tempo))))
- return ScaleFactor( SCALE_FACTOR_MAX
- - 8 * square_distance(wpsq, queeningSq)
- - 2 * square_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 ( abs(file_of(bksq) - file_of(wpsq)) == 1
- && square_distance(wksq, bksq) > 2)
- return ScaleFactor(24 - 2 * square_distance(wksq, bksq));
- }
- return SCALE_FACTOR_NONE;
-}
-
-template<>
-ScaleFactor Endgame<KRPKB>::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<BISHOP>(weakSide)[0];
- Square psq = pos.list<PAWN>(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<KRPPKRP>::operator()(const Position& pos) const {
-
- assert(verify_material(pos, strongSide, RookValueMg, 2));
- assert(verify_material(pos, weakSide, RookValueMg, 1));
-
- Square wpsq1 = pos.list<PAWN>(strongSide)[0];
- Square wpsq2 = pos.list<PAWN>(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 ( file_distance(bksq, wpsq1) <= 1
- && file_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<KPsK>::operator()(const Position& pos) const {
-
- assert(pos.non_pawn_material(strongSide) == VALUE_ZERO);
- assert(pos.count<PAWN>(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<PAWN>(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;
-
- 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<KBPKB>::operator()(const Position& pos) const {
-
- assert(verify_material(pos, strongSide, BishopValueMg, 1));
- assert(verify_material(pos, weakSide, BishopValueMg, 0));
-
- Square pawnSq = pos.list<PAWN>(strongSide)[0];
- Square strongBishopSq = pos.list<BISHOP>(strongSide)[0];
- Square weakBishopSq = pos.list<BISHOP>(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<BISHOP>(weakBishopSq) & path)
- && square_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<KBPPKB>::operator()(const Position& pos) const {
-
- assert(verify_material(pos, strongSide, BishopValueMg, 2));
- assert(verify_material(pos, weakSide, BishopValueMg, 0));
-
- Square wbsq = pos.list<BISHOP>(strongSide)[0];
- Square bbsq = pos.list<BISHOP>(weakSide)[0];
-
- if (!opposite_colors(wbsq, bbsq))
- return SCALE_FACTOR_NONE;
-
- Square ksq = pos.king_square(weakSide);
- Square psq1 = pos.list<PAWN>(strongSide)[0];
- Square psq2 = pos.list<PAWN>(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 (file_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<BISHOP>(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<BISHOP>(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<KBPKN>::operator()(const Position& pos) const {
-
- assert(verify_material(pos, strongSide, BishopValueMg, 1));
- assert(verify_material(pos, weakSide, KnightValueMg, 0));
-
- Square pawnSq = pos.list<PAWN>(strongSide)[0];
- Square strongBishopSq = pos.list<BISHOP>(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<KNPK>::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<PAWN>(strongSide)[0]);
- Square weakKingSq = normalize(pos, strongSide, pos.king_square(weakSide));
-
- if (pawnSq == SQ_A7 && square_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<KNPKB>::operator()(const Position& pos) const {
-
- Square pawnSq = pos.list<PAWN>(strongSide)[0];
- Square bishopSq = pos.list<BISHOP>(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<BISHOP>(bishopSq))
- return ScaleFactor(square_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<KPKP>::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<PAWN>(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_kpk(wksq, psq, bksq, us) ? SCALE_FACTOR_NONE : SCALE_FACTOR_DRAW;
-}
projects / stockfish / blobdiff