2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2023 The Stockfish developers (see AUTHORS file)
5 Stockfish is free software: you can redistribute it and/or modify
6 it under the terms of the GNU General Public License as published by
7 the Free Software Foundation, either version 3 of the License, or
8 (at your option) any later version.
10 Stockfish is distributed in the hope that it will be useful,
11 but WITHOUT ANY WARRANTY; without even the implied warranty of
12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
13 GNU General Public License for more details.
15 You should have received a copy of the GNU General Public License
16 along with this program. If not, see <http://www.gnu.org/licenses/>.
19 #ifndef POSITION_H_INCLUDED
20 #define POSITION_H_INCLUDED
24 #include <memory> // For std::unique_ptr
32 #include "nnue/nnue_accumulator.h"
36 /// StateInfo struct stores information needed to restore a Position object to
37 /// its previous state when we retract a move. Whenever a move is made on the
38 /// board (by calling Position::do_move), a StateInfo object must be passed.
42 // Copied when making a move
45 Value nonPawnMaterial[COLOR_NB];
51 // Not copied when making a move (will be recomputed anyhow)
55 Bitboard blockersForKing[COLOR_NB];
56 Bitboard pinners[COLOR_NB];
57 Bitboard checkSquares[PIECE_TYPE_NB];
62 Eval::NNUE::Accumulator accumulator;
63 DirtyPiece dirtyPiece;
67 /// A list to keep track of the position states along the setup moves (from the
68 /// start position to the position just before the search starts). Needed by
69 /// 'draw by repetition' detection. Use a std::deque because pointers to
70 /// elements are not invalidated upon list resizing.
71 using StateListPtr = std::unique_ptr<std::deque<StateInfo>>;
74 /// Position class stores information regarding the board representation as
75 /// pieces, side to move, hash keys, castling info, etc. Important methods are
76 /// do_move() and undo_move(), used by the search to update node info when
77 /// traversing the search tree.
85 Position(const Position&) = delete;
86 Position& operator=(const Position&) = delete;
88 // FEN string input/output
89 Position& set(const std::string& fenStr, bool isChess960, StateInfo* si, Thread* th);
90 Position& set(const std::string& code, Color c, StateInfo* si);
91 std::string fen() const;
93 // Position representation
94 Bitboard pieces(PieceType pt) const;
95 Bitboard pieces(PieceType pt1, PieceType pt2) const;
96 Bitboard pieces(Color c) const;
97 Bitboard pieces(Color c, PieceType pt) const;
98 Bitboard pieces(Color c, PieceType pt1, PieceType pt2) const;
99 Piece piece_on(Square s) const;
100 Square ep_square() const;
101 bool empty(Square s) const;
102 template<PieceType Pt> int count(Color c) const;
103 template<PieceType Pt> int count() const;
104 template<PieceType Pt> Square square(Color c) const;
105 bool is_on_semiopen_file(Color c, Square s) const;
108 CastlingRights castling_rights(Color c) const;
109 bool can_castle(CastlingRights cr) const;
110 bool castling_impeded(CastlingRights cr) const;
111 Square castling_rook_square(CastlingRights cr) const;
114 Bitboard checkers() const;
115 Bitboard blockers_for_king(Color c) const;
116 Bitboard check_squares(PieceType pt) const;
117 Bitboard pinners(Color c) const;
119 // Attacks to/from a given square
120 Bitboard attackers_to(Square s) const;
121 Bitboard attackers_to(Square s, Bitboard occupied) const;
122 Bitboard slider_blockers(Bitboard sliders, Square s, Bitboard& pinners) const;
123 template<PieceType Pt> Bitboard attacks_by(Color c) const;
125 // Properties of moves
126 bool legal(Move m) const;
127 bool pseudo_legal(const Move m) const;
128 bool capture(Move m) const;
129 bool capture_stage(Move m) const;
130 bool gives_check(Move m) const;
131 Piece moved_piece(Move m) const;
132 Piece captured_piece() const;
135 bool pawn_passed(Color c, Square s) const;
136 bool opposite_bishops() const;
137 int pawns_on_same_color_squares(Color c, Square s) const;
139 // Doing and undoing moves
140 void do_move(Move m, StateInfo& newSt);
141 void do_move(Move m, StateInfo& newSt, bool givesCheck);
142 void undo_move(Move m);
143 void do_null_move(StateInfo& newSt);
144 void undo_null_move();
146 // Static Exchange Evaluation
147 bool see_ge(Move m, Value threshold = VALUE_ZERO) const;
149 // Accessing hash keys
151 Key key_after(Move m) const;
152 Key material_key() const;
153 Key pawn_key() const;
155 // Other properties of the position
156 Color side_to_move() const;
157 int game_ply() const;
158 bool is_chess960() const;
159 Thread* this_thread() const;
160 bool is_draw(int ply) const;
161 bool has_game_cycle(int ply) const;
162 bool has_repeated() const;
163 int rule50_count() const;
164 Score psq_score() const;
165 Value psq_eg_stm() const;
166 Value non_pawn_material(Color c) const;
167 Value non_pawn_material() const;
169 // Position consistency check, for debugging
170 bool pos_is_ok() const;
174 StateInfo* state() const;
176 void put_piece(Piece pc, Square s);
177 void remove_piece(Square s);
180 // Initialization helpers (used while setting up a position)
181 void set_castling_right(Color c, Square rfrom);
182 void set_state(StateInfo* si) const;
183 void set_check_info(StateInfo* si) const;
186 void move_piece(Square from, Square to);
188 void do_castling(Color us, Square from, Square& to, Square& rfrom, Square& rto);
189 template<bool AfterMove>
190 Key adjust_key50(Key k) const;
193 Piece board[SQUARE_NB];
194 Bitboard byTypeBB[PIECE_TYPE_NB];
195 Bitboard byColorBB[COLOR_NB];
196 int pieceCount[PIECE_NB];
197 int castlingRightsMask[SQUARE_NB];
198 Square castlingRookSquare[CASTLING_RIGHT_NB];
199 Bitboard castlingPath[CASTLING_RIGHT_NB];
208 std::ostream& operator<<(std::ostream& os, const Position& pos);
210 inline Color Position::side_to_move() const {
214 inline Piece Position::piece_on(Square s) const {
219 inline bool Position::empty(Square s) const {
220 return piece_on(s) == NO_PIECE;
223 inline Piece Position::moved_piece(Move m) const {
224 return piece_on(from_sq(m));
227 inline Bitboard Position::pieces(PieceType pt = ALL_PIECES) const {
231 inline Bitboard Position::pieces(PieceType pt1, PieceType pt2) const {
232 return pieces(pt1) | pieces(pt2);
235 inline Bitboard Position::pieces(Color c) const {
239 inline Bitboard Position::pieces(Color c, PieceType pt) const {
240 return pieces(c) & pieces(pt);
243 inline Bitboard Position::pieces(Color c, PieceType pt1, PieceType pt2) const {
244 return pieces(c) & (pieces(pt1) | pieces(pt2));
247 template<PieceType Pt> inline int Position::count(Color c) const {
248 return pieceCount[make_piece(c, Pt)];
251 template<PieceType Pt> inline int Position::count() const {
252 return count<Pt>(WHITE) + count<Pt>(BLACK);
255 template<PieceType Pt> inline Square Position::square(Color c) const {
256 assert(count<Pt>(c) == 1);
257 return lsb(pieces(c, Pt));
260 inline Square Position::ep_square() const {
264 inline bool Position::is_on_semiopen_file(Color c, Square s) const {
265 return !(pieces(c, PAWN) & file_bb(s));
268 inline bool Position::can_castle(CastlingRights cr) const {
269 return st->castlingRights & cr;
272 inline CastlingRights Position::castling_rights(Color c) const {
273 return c & CastlingRights(st->castlingRights);
276 inline bool Position::castling_impeded(CastlingRights cr) const {
277 assert(cr == WHITE_OO || cr == WHITE_OOO || cr == BLACK_OO || cr == BLACK_OOO);
279 return pieces() & castlingPath[cr];
282 inline Square Position::castling_rook_square(CastlingRights cr) const {
283 assert(cr == WHITE_OO || cr == WHITE_OOO || cr == BLACK_OO || cr == BLACK_OOO);
285 return castlingRookSquare[cr];
288 inline Bitboard Position::attackers_to(Square s) const {
289 return attackers_to(s, pieces());
292 template<PieceType Pt>
293 inline Bitboard Position::attacks_by(Color c) const {
295 if constexpr (Pt == PAWN)
296 return c == WHITE ? pawn_attacks_bb<WHITE>(pieces(WHITE, PAWN))
297 : pawn_attacks_bb<BLACK>(pieces(BLACK, PAWN));
300 Bitboard threats = 0;
301 Bitboard attackers = pieces(c, Pt);
303 threats |= attacks_bb<Pt>(pop_lsb(attackers), pieces());
308 inline Bitboard Position::checkers() const {
309 return st->checkersBB;
312 inline Bitboard Position::blockers_for_king(Color c) const {
313 return st->blockersForKing[c];
316 inline Bitboard Position::pinners(Color c) const {
317 return st->pinners[c];
320 inline Bitboard Position::check_squares(PieceType pt) const {
321 return st->checkSquares[pt];
324 inline bool Position::pawn_passed(Color c, Square s) const {
325 return !(pieces(~c, PAWN) & passed_pawn_span(c, s));
328 inline int Position::pawns_on_same_color_squares(Color c, Square s) const {
329 return popcount(pieces(c, PAWN) & ((DarkSquares & s) ? DarkSquares : ~DarkSquares));
332 inline Key Position::key() const {
333 return adjust_key50<false>(st->key);
336 template<bool AfterMove>
337 inline Key Position::adjust_key50(Key k) const
339 return st->rule50 < 14 - AfterMove
340 ? k : k ^ make_key((st->rule50 - (14 - AfterMove)) / 8);
343 inline Key Position::pawn_key() const {
347 inline Key Position::material_key() const {
348 return st->materialKey;
351 inline Score Position::psq_score() const {
355 inline Value Position::psq_eg_stm() const {
356 return (sideToMove == WHITE ? 1 : -1) * eg_value(psq);
359 inline Value Position::non_pawn_material(Color c) const {
360 return st->nonPawnMaterial[c];
363 inline Value Position::non_pawn_material() const {
364 return non_pawn_material(WHITE) + non_pawn_material(BLACK);
367 inline int Position::game_ply() const {
371 inline int Position::rule50_count() const {
375 inline bool Position::opposite_bishops() const {
376 return count<BISHOP>(WHITE) == 1
377 && count<BISHOP>(BLACK) == 1
378 && opposite_colors(square<BISHOP>(WHITE), square<BISHOP>(BLACK));
381 inline bool Position::is_chess960() const {
385 inline bool Position::capture(Move m) const {
387 return (!empty(to_sq(m)) && type_of(m) != CASTLING)
388 || type_of(m) == EN_PASSANT;
391 // returns true if a move is generated from the capture stage
392 // having also queen promotions covered, i.e. consistency with the capture stage move generation
393 // is needed to avoid the generation of duplicate moves.
394 inline bool Position::capture_stage(Move m) const {
396 return capture(m) || promotion_type(m) == QUEEN;
399 inline Piece Position::captured_piece() const {
400 return st->capturedPiece;
403 inline Thread* Position::this_thread() const {
407 inline void Position::put_piece(Piece pc, Square s) {
410 byTypeBB[ALL_PIECES] |= byTypeBB[type_of(pc)] |= s;
411 byColorBB[color_of(pc)] |= s;
413 pieceCount[make_piece(color_of(pc), ALL_PIECES)]++;
414 psq += PSQT::psq[pc][s];
417 inline void Position::remove_piece(Square s) {
420 byTypeBB[ALL_PIECES] ^= s;
421 byTypeBB[type_of(pc)] ^= s;
422 byColorBB[color_of(pc)] ^= s;
425 pieceCount[make_piece(color_of(pc), ALL_PIECES)]--;
426 psq -= PSQT::psq[pc][s];
429 inline void Position::move_piece(Square from, Square to) {
431 Piece pc = board[from];
432 Bitboard fromTo = from | to;
433 byTypeBB[ALL_PIECES] ^= fromTo;
434 byTypeBB[type_of(pc)] ^= fromTo;
435 byColorBB[color_of(pc)] ^= fromTo;
436 board[from] = NO_PIECE;
438 psq += PSQT::psq[pc][to] - PSQT::psq[pc][from];
441 inline void Position::do_move(Move m, StateInfo& newSt) {
442 do_move(m, newSt, gives_check(m));
445 inline StateInfo* Position::state() const {
450 } // namespace Stockfish
452 #endif // #ifndef POSITION_H_INCLUDED