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, Bitboard& occupied, Value threshold = VALUE_ZERO) const;
148 bool see_ge(Move m, Value threshold = VALUE_ZERO) const;
150 // Accessing hash keys
152 Key key_after(Move m) const;
153 Key material_key() const;
154 Key pawn_key() const;
156 // Other properties of the position
157 Color side_to_move() const;
158 int game_ply() const;
159 bool is_chess960() const;
160 Thread* this_thread() const;
161 bool is_draw(int ply) const;
162 bool has_game_cycle(int ply) const;
163 bool has_repeated() const;
164 int rule50_count() const;
165 Score psq_score() const;
166 Value psq_eg_stm() const;
167 Value non_pawn_material(Color c) const;
168 Value non_pawn_material() const;
170 // Position consistency check, for debugging
171 bool pos_is_ok() const;
175 StateInfo* state() const;
177 void put_piece(Piece pc, Square s);
178 void remove_piece(Square s);
181 // Initialization helpers (used while setting up a position)
182 void set_castling_right(Color c, Square rfrom);
183 void set_state() const;
184 void set_check_info() const;
187 void move_piece(Square from, Square to);
189 void do_castling(Color us, Square from, Square& to, Square& rfrom, Square& rto);
190 template<bool AfterMove>
191 Key adjust_key50(Key k) const;
194 Piece board[SQUARE_NB];
195 Bitboard byTypeBB[PIECE_TYPE_NB];
196 Bitboard byColorBB[COLOR_NB];
197 int pieceCount[PIECE_NB];
198 int castlingRightsMask[SQUARE_NB];
199 Square castlingRookSquare[CASTLING_RIGHT_NB];
200 Bitboard castlingPath[CASTLING_RIGHT_NB];
209 std::ostream& operator<<(std::ostream& os, const Position& pos);
211 inline Color Position::side_to_move() const {
215 inline Piece Position::piece_on(Square s) const {
220 inline bool Position::empty(Square s) const {
221 return piece_on(s) == NO_PIECE;
224 inline Piece Position::moved_piece(Move m) const {
225 return piece_on(from_sq(m));
228 inline Bitboard Position::pieces(PieceType pt = ALL_PIECES) const {
232 inline Bitboard Position::pieces(PieceType pt1, PieceType pt2) const {
233 return pieces(pt1) | pieces(pt2);
236 inline Bitboard Position::pieces(Color c) const {
240 inline Bitboard Position::pieces(Color c, PieceType pt) const {
241 return pieces(c) & pieces(pt);
244 inline Bitboard Position::pieces(Color c, PieceType pt1, PieceType pt2) const {
245 return pieces(c) & (pieces(pt1) | pieces(pt2));
248 template<PieceType Pt> inline int Position::count(Color c) const {
249 return pieceCount[make_piece(c, Pt)];
252 template<PieceType Pt> inline int Position::count() const {
253 return count<Pt>(WHITE) + count<Pt>(BLACK);
256 template<PieceType Pt> inline Square Position::square(Color c) const {
257 assert(count<Pt>(c) == 1);
258 return lsb(pieces(c, Pt));
261 inline Square Position::ep_square() const {
265 inline bool Position::is_on_semiopen_file(Color c, Square s) const {
266 return !(pieces(c, PAWN) & file_bb(s));
269 inline bool Position::can_castle(CastlingRights cr) const {
270 return st->castlingRights & cr;
273 inline CastlingRights Position::castling_rights(Color c) const {
274 return c & CastlingRights(st->castlingRights);
277 inline bool Position::castling_impeded(CastlingRights cr) const {
278 assert(cr == WHITE_OO || cr == WHITE_OOO || cr == BLACK_OO || cr == BLACK_OOO);
280 return pieces() & castlingPath[cr];
283 inline Square Position::castling_rook_square(CastlingRights cr) const {
284 assert(cr == WHITE_OO || cr == WHITE_OOO || cr == BLACK_OO || cr == BLACK_OOO);
286 return castlingRookSquare[cr];
289 inline Bitboard Position::attackers_to(Square s) const {
290 return attackers_to(s, pieces());
293 template<PieceType Pt>
294 inline Bitboard Position::attacks_by(Color c) const {
296 if constexpr (Pt == PAWN)
297 return c == WHITE ? pawn_attacks_bb<WHITE>(pieces(WHITE, PAWN))
298 : pawn_attacks_bb<BLACK>(pieces(BLACK, PAWN));
301 Bitboard threats = 0;
302 Bitboard attackers = pieces(c, Pt);
304 threats |= attacks_bb<Pt>(pop_lsb(attackers), pieces());
309 inline Bitboard Position::checkers() const {
310 return st->checkersBB;
313 inline Bitboard Position::blockers_for_king(Color c) const {
314 return st->blockersForKing[c];
317 inline Bitboard Position::pinners(Color c) const {
318 return st->pinners[c];
321 inline Bitboard Position::check_squares(PieceType pt) const {
322 return st->checkSquares[pt];
325 inline bool Position::pawn_passed(Color c, Square s) const {
326 return !(pieces(~c, PAWN) & passed_pawn_span(c, s));
329 inline int Position::pawns_on_same_color_squares(Color c, Square s) const {
330 return popcount(pieces(c, PAWN) & ((DarkSquares & s) ? DarkSquares : ~DarkSquares));
333 inline Key Position::key() const {
334 return adjust_key50<false>(st->key);
337 template<bool AfterMove>
338 inline Key Position::adjust_key50(Key k) const
340 return st->rule50 < 14 - AfterMove
341 ? k : k ^ make_key((st->rule50 - (14 - AfterMove)) / 8);
344 inline Key Position::pawn_key() const {
348 inline Key Position::material_key() const {
349 return st->materialKey;
352 inline Score Position::psq_score() const {
356 inline Value Position::psq_eg_stm() const {
357 return (sideToMove == WHITE ? 1 : -1) * eg_value(psq);
360 inline Value Position::non_pawn_material(Color c) const {
361 return st->nonPawnMaterial[c];
364 inline Value Position::non_pawn_material() const {
365 return non_pawn_material(WHITE) + non_pawn_material(BLACK);
368 inline int Position::game_ply() const {
372 inline int Position::rule50_count() const {
376 inline bool Position::opposite_bishops() const {
377 return count<BISHOP>(WHITE) == 1
378 && count<BISHOP>(BLACK) == 1
379 && opposite_colors(square<BISHOP>(WHITE), square<BISHOP>(BLACK));
382 inline bool Position::is_chess960() const {
386 inline bool Position::capture(Move m) const {
388 return (!empty(to_sq(m)) && type_of(m) != CASTLING)
389 || type_of(m) == EN_PASSANT;
392 // returns true if a move is generated from the capture stage
393 // having also queen promotions covered, i.e. consistency with the capture stage move generation
394 // is needed to avoid the generation of duplicate moves.
395 inline bool Position::capture_stage(Move m) const {
397 return capture(m) || promotion_type(m) == QUEEN;
400 inline Piece Position::captured_piece() const {
401 return st->capturedPiece;
404 inline Thread* Position::this_thread() const {
408 inline void Position::put_piece(Piece pc, Square s) {
411 byTypeBB[ALL_PIECES] |= byTypeBB[type_of(pc)] |= s;
412 byColorBB[color_of(pc)] |= s;
414 pieceCount[make_piece(color_of(pc), ALL_PIECES)]++;
415 psq += PSQT::psq[pc][s];
418 inline void Position::remove_piece(Square s) {
421 byTypeBB[ALL_PIECES] ^= s;
422 byTypeBB[type_of(pc)] ^= s;
423 byColorBB[color_of(pc)] ^= s;
426 pieceCount[make_piece(color_of(pc), ALL_PIECES)]--;
427 psq -= PSQT::psq[pc][s];
430 inline void Position::move_piece(Square from, Square to) {
432 Piece pc = board[from];
433 Bitboard fromTo = from | to;
434 byTypeBB[ALL_PIECES] ^= fromTo;
435 byTypeBB[type_of(pc)] ^= fromTo;
436 byColorBB[color_of(pc)] ^= fromTo;
437 board[from] = NO_PIECE;
439 psq += PSQT::psq[pc][to] - PSQT::psq[pc][from];
442 inline void Position::do_move(Move m, StateInfo& newSt) {
443 do_move(m, newSt, gives_check(m));
446 inline StateInfo* Position::state() const {
451 } // namespace Stockfish
453 #endif // #ifndef POSITION_H_INCLUDED