+++ /dev/null
-/*
- Stockfish, a UCI chess playing engine derived from Glaurung 2.1
- Copyright (C) 2004-2020 The Stockfish developers (see AUTHORS file)
-
- 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 <cassert>
-
-#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<PAWN>(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<PAWN>(strongSide) == 1);
-
- if (file_of(pos.square<PAWN>(strongSide)) >= FILE_E)
- sq = flip_file(sq);
-
- return strongSide == WHITE ? sq : flip_rank(sq);
- }
-
-} // namespace
-
-
-namespace Endgames {
-
- std::pair<Map<Value>, Map<ScaleFactor>> maps;
-
- void init() {
-
- 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<KNNKP>("KNNKP");
-
- add<KRPKR>("KRPKR");
- add<KRPKB>("KRPKB");
- add<KBPKB>("KBPKB");
- add<KBPKN>("KBPKN");
- add<KBPPKB>("KBPPKB");
- add<KRPPKRP>("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<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 strongKing = pos.square<KING>(strongSide);
- Square weakKing = pos.square<KING>(weakSide);
-
- Value result = pos.non_pawn_material(strongSide)
- + pos.count<PAWN>(strongSide) * PawnValueEg
- + push_to_edge(weakKing)
- + push_close(strongKing, weakKing);
-
- if ( pos.count<QUEEN>(strongSide)
- || pos.count<ROOK>(strongSide)
- ||(pos.count<BISHOP>(strongSide) && pos.count<KNIGHT>(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<KBNK>::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<KING>(strongSide);
- Square strongBishop = pos.square<BISHOP>(strongSide);
- Square weakKing = pos.square<KING>(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<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 strongKing = normalize(pos, strongSide, pos.square<KING>(strongSide));
- Square strongPawn = normalize(pos, strongSide, pos.square<PAWN>(strongSide));
- Square weakKing = normalize(pos, strongSide, pos.square<KING>(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<KRKP>::operator()(const Position& pos) const {
-
- assert(verify_material(pos, strongSide, RookValueMg, 0));
- assert(verify_material(pos, weakSide, VALUE_ZERO, 1));
-
- Square strongKing = pos.square<KING>(strongSide);
- Square weakKing = pos.square<KING>(weakSide);
- Square strongRook = pos.square<ROOK>(strongSide);
- Square weakPawn = pos.square<PAWN>(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<KRKB>::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<KING>(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 weakKing = pos.square<KING>(weakSide);
- Square weakKnight = pos.square<KNIGHT>(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<KQKP>::operator()(const Position& pos) const {
-
- assert(verify_material(pos, strongSide, QueenValueMg, 0));
- assert(verify_material(pos, weakSide, VALUE_ZERO, 1));
-
- Square strongKing = pos.square<KING>(strongSide);
- Square weakKing = pos.square<KING>(weakSide);
- Square weakPawn = pos.square<PAWN>(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<KQKR>::operator()(const Position& pos) const {
-
- assert(verify_material(pos, strongSide, QueenValueMg, 0));
- assert(verify_material(pos, weakSide, RookValueMg, 0));
-
- Square strongKing = pos.square<KING>(strongSide);
- Square weakKing = pos.square<KING>(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<KNNKP>::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<KING>(weakSide);
- Square weakPawn = pos.square<PAWN>(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<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 strongPawns = pos.pieces(strongSide, PAWN);
- Bitboard allPawns = pos.pieces(PAWN);
-
- Square strongBishop = pos.square<BISHOP>(strongSide);
- Square weakKing = pos.square<KING>(weakSide);
- Square strongKing = pos.square<KING>(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<PAWN>(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<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 strongKing = pos.square<KING>(strongSide);
- Square weakKing = pos.square<KING>(weakSide);
- Square weakRook = pos.square<ROOK>(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<KING>(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<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 strongKing = normalize(pos, strongSide, pos.square<KING>(strongSide));
- Square strongRook = normalize(pos, strongSide, pos.square<ROOK>(strongSide));
- Square strongPawn = normalize(pos, strongSide, pos.square<PAWN>(strongSide));
- Square weakKing = normalize(pos, strongSide, pos.square<KING>(weakSide));
- Square weakRook = normalize(pos, strongSide, pos.square<ROOK>(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<File>(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<File>(weakKing, strongPawn) == 1
- && distance(strongKing, weakKing) > 2)
- return ScaleFactor(24 - 2 * distance(strongKing, weakKing));
- }
- 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 weakKing = pos.square<KING>(weakSide);
- Square weakBishop = pos.square<BISHOP>(weakSide);
- Square strongKing = pos.square<KING>(strongSide);
- Square strongPawn = pos.square<PAWN>(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<BISHOP>(weakBishop) & (strongPawn + push))
- && distance<File>(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<KRPPKRP>::operator()(const Position& pos) const {
-
- assert(verify_material(pos, strongSide, RookValueMg, 2));
- assert(verify_material(pos, weakSide, RookValueMg, 1));
-
- Square strongPawn1 = pos.squares<PAWN>(strongSide)[0];
- Square strongPawn2 = pos.squares<PAWN>(strongSide)[1];
- Square weakKing = pos.square<KING>(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<File>(weakKing, strongPawn1) <= 1
- && distance<File>(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<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 weakKing = pos.square<KING>(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 | 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<KBPKB>::operator()(const Position& pos) const {
-
- assert(verify_material(pos, strongSide, BishopValueMg, 1));
- assert(verify_material(pos, weakSide, BishopValueMg, 0));
-
- Square strongPawn = pos.square<PAWN>(strongSide);
- Square strongBishop = pos.square<BISHOP>(strongSide);
- Square weakBishop = pos.square<BISHOP>(weakSide);
- Square weakKing = pos.square<KING>(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<KBPPKB>::operator()(const Position& pos) const {
-
- assert(verify_material(pos, strongSide, BishopValueMg, 2));
- assert(verify_material(pos, weakSide, BishopValueMg, 0));
-
- Square strongBishop = pos.square<BISHOP>(strongSide);
- Square weakBishop = pos.square<BISHOP>(weakSide);
-
- if (!opposite_colors(strongBishop, weakBishop))
- return SCALE_FACTOR_NONE;
-
- Square weakKing = pos.square<KING>(weakSide);
- Square strongPawn1 = pos.squares<PAWN>(strongSide)[0];
- Square strongPawn2 = pos.squares<PAWN>(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<File>(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<BISHOP>(blockSq2, pos.pieces()) & pos.pieces(weakSide, BISHOP))
- || distance<Rank>(strongPawn1, strongPawn2) >= 2))
- return SCALE_FACTOR_DRAW;
-
- else if ( weakKing == blockSq2
- && opposite_colors(weakKing, strongBishop)
- && ( weakBishop == blockSq1
- || (attacks_bb<BISHOP>(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<KBPKN>::operator()(const Position& pos) const {
-
- assert(verify_material(pos, strongSide, BishopValueMg, 1));
- assert(verify_material(pos, weakSide, KnightValueMg, 0));
-
- Square strongPawn = pos.square<PAWN>(strongSide);
- Square strongBishop = pos.square<BISHOP>(strongSide);
- Square weakKing = pos.square<KING>(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<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 strongKing = normalize(pos, strongSide, pos.square<KING>(strongSide));
- Square weakKing = normalize(pos, strongSide, pos.square<KING>(weakSide));
- Square strongPawn = normalize(pos, strongSide, pos.square<PAWN>(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;
-}
projects / stockfish / blobdiff