1 /*
2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2021 The Stockfish developers (see AUTHORS file)
4
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.
9
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.
14
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/>.
17 */
18
19 #ifndef POSITION_H_INCLUDED
20 #define POSITION_H_INCLUDED
21
22 #include <cassert>
23 #include <deque>
24 #include <memory> // For std::unique_ptr
25 #include <string>
26
27 #include "bitboard.h"
28 #include "evaluate.h"
29 #include "psqt.h"
30 #include "types.h"
31
32 #include "nnue/nnue_accumulator.h"
33
34 namespace Stockfish {
35
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.
39
40 struct StateInfo {
41
42 // Copied when making a move
43 Key pawnKey;
44 Key materialKey;
45 Value nonPawnMaterial[COLOR_NB];
46 int castlingRights;
47 int rule50;
48 int pliesFromNull;
49 Square epSquare;
50
51 // Not copied when making a move (will be recomputed anyhow)
52 Key key;
53 Bitboard checkersBB;
54 StateInfo* previous;
55 Bitboard blockersForKing[COLOR_NB];
56 Bitboard pinners[COLOR_NB];
57 Bitboard checkSquares[PIECE_TYPE_NB];
58 Piece capturedPiece;
59 int repetition;
60
61 // Used by NNUE
62 Eval::NNUE::Accumulator accumulator;
63 DirtyPiece dirtyPiece;
64 };
65
66
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 typedef std::unique_ptr<std::deque<StateInfo>> StateListPtr;
72
73
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.
78 class Thread;
79
80 class Position {
81 public:
82 static void init();
83
84 Position() = default;
85 Position(const Position&) = delete;
86 Position& operator=(const Position&) = delete;
87
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;
92
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;
106
107 // Castling
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;
112
113 // Checking
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;
118
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
124 // Properties of moves
125 bool legal(Move m) const;
126 bool pseudo_legal(const Move m) const;
127 bool capture(Move m) const;
128 bool capture_or_promotion(Move m) const;
129 bool gives_check(Move m) const;
130 Piece moved_piece(Move m) const;
131 Piece captured_piece() const;
132
133 // Piece specific
134 bool pawn_passed(Color c, Square s) const;
135 bool opposite_bishops() const;
136 int pawns_on_same_color_squares(Color c, Square s) const;
137
138 // Doing and undoing moves
139 void do_move(Move m, StateInfo& newSt);
140 void do_move(Move m, StateInfo& newSt, bool givesCheck);
141 void undo_move(Move m);
142 void do_null_move(StateInfo& newSt);
143 void undo_null_move();
144
145 // Static Exchange Evaluation
146 bool see_ge(Move m, Value threshold = VALUE_ZERO) const;
147
148 // Accessing hash keys
149 Key key() const;
150 Key key_after(Move m) const;
151 Key material_key() const;
152 Key pawn_key() const;
153
154 // Other properties of the position
155 Color side_to_move() const;
156 int game_ply() const;
157 bool is_chess960() const;
158 Thread* this_thread() const;
159 bool is_draw(int ply) const;
160 bool has_game_cycle(int ply) const;
161 bool has_repeated() const;
162 int rule50_count() const;
163 Score psq_score() const;
164 Value non_pawn_material(Color c) const;
165 Value non_pawn_material() const;
166
167 // Position consistency check, for debugging
168 bool pos_is_ok() const;
169 void flip();
170
171 // Used by NNUE
172 StateInfo* state() const;
173
174 void put_piece(Piece pc, Square s);
175 void remove_piece(Square s);
176
177 private:
178 // Initialization helpers (used while setting up a position)
179 void set_castling_right(Color c, Square rfrom);
180 void set_state(StateInfo* si) const;
181 void set_check_info(StateInfo* si) const;
182
183 // Other helpers
184 void move_piece(Square from, Square to);
185 template<bool Do>
186 void do_castling(Color us, Square from, Square& to, Square& rfrom, Square& rto);
187
188 // Data members
189 Piece board[SQUARE_NB];
190 Bitboard byTypeBB[PIECE_TYPE_NB];
191 Bitboard byColorBB[COLOR_NB];
192 int pieceCount[PIECE_NB];
193 int castlingRightsMask[SQUARE_NB];
194 Square castlingRookSquare[CASTLING_RIGHT_NB];
195 Bitboard castlingPath[CASTLING_RIGHT_NB];
196 Thread* thisThread;
197 StateInfo* st;
198 int gamePly;
199 Color sideToMove;
200 Score psq;
201 bool chess960;
202 };
203
204 extern std::ostream& operator<<(std::ostream& os, const Position& pos);
205
side_to_move()206 inline Color Position::side_to_move() const {
207 return sideToMove;
208 }
209
piece_on(Square s)210 inline Piece Position::piece_on(Square s) const {
211 assert(is_ok(s));
212 return board[s];
213 }
214
empty(Square s)215 inline bool Position::empty(Square s) const {
216 return piece_on(s) == NO_PIECE;
217 }
218
moved_piece(Move m)219 inline Piece Position::moved_piece(Move m) const {
220 return piece_on(from_sq(m));
221 }
222
223 inline Bitboard Position::pieces(PieceType pt = ALL_PIECES) const {
224 return byTypeBB[pt];
225 }
226
pieces(PieceType pt1,PieceType pt2)227 inline Bitboard Position::pieces(PieceType pt1, PieceType pt2) const {
228 return pieces(pt1) | pieces(pt2);
229 }
230
pieces(Color c)231 inline Bitboard Position::pieces(Color c) const {
232 return byColorBB[c];
233 }
234
pieces(Color c,PieceType pt)235 inline Bitboard Position::pieces(Color c, PieceType pt) const {
236 return pieces(c) & pieces(pt);
237 }
238
pieces(Color c,PieceType pt1,PieceType pt2)239 inline Bitboard Position::pieces(Color c, PieceType pt1, PieceType pt2) const {
240 return pieces(c) & (pieces(pt1) | pieces(pt2));
241 }
242
count(Color c)243 template<PieceType Pt> inline int Position::count(Color c) const {
244 return pieceCount[make_piece(c, Pt)];
245 }
246
count()247 template<PieceType Pt> inline int Position::count() const {
248 return count<Pt>(WHITE) + count<Pt>(BLACK);
249 }
250
square(Color c)251 template<PieceType Pt> inline Square Position::square(Color c) const {
252 assert(count<Pt>(c) == 1);
253 return lsb(pieces(c, Pt));
254 }
255
ep_square()256 inline Square Position::ep_square() const {
257 return st->epSquare;
258 }
259
is_on_semiopen_file(Color c,Square s)260 inline bool Position::is_on_semiopen_file(Color c, Square s) const {
261 return !(pieces(c, PAWN) & file_bb(s));
262 }
263
can_castle(CastlingRights cr)264 inline bool Position::can_castle(CastlingRights cr) const {
265 return st->castlingRights & cr;
266 }
267
castling_rights(Color c)268 inline CastlingRights Position::castling_rights(Color c) const {
269 return c & CastlingRights(st->castlingRights);
270 }
271
castling_impeded(CastlingRights cr)272 inline bool Position::castling_impeded(CastlingRights cr) const {
273 assert(cr == WHITE_OO || cr == WHITE_OOO || cr == BLACK_OO || cr == BLACK_OOO);
274
275 return pieces() & castlingPath[cr];
276 }
277
castling_rook_square(CastlingRights cr)278 inline Square Position::castling_rook_square(CastlingRights cr) const {
279 assert(cr == WHITE_OO || cr == WHITE_OOO || cr == BLACK_OO || cr == BLACK_OOO);
280
281 return castlingRookSquare[cr];
282 }
283
attackers_to(Square s)284 inline Bitboard Position::attackers_to(Square s) const {
285 return attackers_to(s, pieces());
286 }
287
checkers()288 inline Bitboard Position::checkers() const {
289 return st->checkersBB;
290 }
291
blockers_for_king(Color c)292 inline Bitboard Position::blockers_for_king(Color c) const {
293 return st->blockersForKing[c];
294 }
295
pinners(Color c)296 inline Bitboard Position::pinners(Color c) const {
297 return st->pinners[c];
298 }
299
check_squares(PieceType pt)300 inline Bitboard Position::check_squares(PieceType pt) const {
301 return st->checkSquares[pt];
302 }
303
pawn_passed(Color c,Square s)304 inline bool Position::pawn_passed(Color c, Square s) const {
305 return !(pieces(~c, PAWN) & passed_pawn_span(c, s));
306 }
307
pawns_on_same_color_squares(Color c,Square s)308 inline int Position::pawns_on_same_color_squares(Color c, Square s) const {
309 return popcount(pieces(c, PAWN) & ((DarkSquares & s) ? DarkSquares : ~DarkSquares));
310 }
311
key()312 inline Key Position::key() const {
313 return st->rule50 < 14 ? st->key
314 : st->key ^ make_key((st->rule50 - 14) / 8);
315 }
316
pawn_key()317 inline Key Position::pawn_key() const {
318 return st->pawnKey;
319 }
320
material_key()321 inline Key Position::material_key() const {
322 return st->materialKey;
323 }
324
psq_score()325 inline Score Position::psq_score() const {
326 return psq;
327 }
328
non_pawn_material(Color c)329 inline Value Position::non_pawn_material(Color c) const {
330 return st->nonPawnMaterial[c];
331 }
332
non_pawn_material()333 inline Value Position::non_pawn_material() const {
334 return non_pawn_material(WHITE) + non_pawn_material(BLACK);
335 }
336
game_ply()337 inline int Position::game_ply() const {
338 return gamePly;
339 }
340
rule50_count()341 inline int Position::rule50_count() const {
342 return st->rule50;
343 }
344
opposite_bishops()345 inline bool Position::opposite_bishops() const {
346 return count<BISHOP>(WHITE) == 1
347 && count<BISHOP>(BLACK) == 1
348 && opposite_colors(square<BISHOP>(WHITE), square<BISHOP>(BLACK));
349 }
350
is_chess960()351 inline bool Position::is_chess960() const {
352 return chess960;
353 }
354
capture_or_promotion(Move m)355 inline bool Position::capture_or_promotion(Move m) const {
356 assert(is_ok(m));
357 return type_of(m) != NORMAL ? type_of(m) != CASTLING : !empty(to_sq(m));
358 }
359
capture(Move m)360 inline bool Position::capture(Move m) const {
361 assert(is_ok(m));
362 // Castling is encoded as "king captures rook"
363 return (!empty(to_sq(m)) && type_of(m) != CASTLING) || type_of(m) == EN_PASSANT;
364 }
365
captured_piece()366 inline Piece Position::captured_piece() const {
367 return st->capturedPiece;
368 }
369
this_thread()370 inline Thread* Position::this_thread() const {
371 return thisThread;
372 }
373
put_piece(Piece pc,Square s)374 inline void Position::put_piece(Piece pc, Square s) {
375
376 board[s] = pc;
377 byTypeBB[ALL_PIECES] |= byTypeBB[type_of(pc)] |= s;
378 byColorBB[color_of(pc)] |= s;
379 pieceCount[pc]++;
380 pieceCount[make_piece(color_of(pc), ALL_PIECES)]++;
381 psq += PSQT::psq[pc][s];
382 }
383
remove_piece(Square s)384 inline void Position::remove_piece(Square s) {
385
386 Piece pc = board[s];
387 byTypeBB[ALL_PIECES] ^= s;
388 byTypeBB[type_of(pc)] ^= s;
389 byColorBB[color_of(pc)] ^= s;
390 board[s] = NO_PIECE;
391 pieceCount[pc]--;
392 pieceCount[make_piece(color_of(pc), ALL_PIECES)]--;
393 psq -= PSQT::psq[pc][s];
394 }
395
move_piece(Square from,Square to)396 inline void Position::move_piece(Square from, Square to) {
397
398 Piece pc = board[from];
399 Bitboard fromTo = from | to;
400 byTypeBB[ALL_PIECES] ^= fromTo;
401 byTypeBB[type_of(pc)] ^= fromTo;
402 byColorBB[color_of(pc)] ^= fromTo;
403 board[from] = NO_PIECE;
404 board[to] = pc;
405 psq += PSQT::psq[pc][to] - PSQT::psq[pc][from];
406 }
407
do_move(Move m,StateInfo & newSt)408 inline void Position::do_move(Move m, StateInfo& newSt) {
409 do_move(m, newSt, gives_check(m));
410 }
411
state()412 inline StateInfo* Position::state() const {
413
414 return st;
415 }
416
417 } // namespace Stockfish
418
419 #endif // #ifndef POSITION_H_INCLUDED
420