1/*
2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
4 Copyright (C) 2008-2015 Marco Costalba, Joona Kiiski, Tord Romstad
5 Copyright (C) 2015-2019 Marco Costalba, Joona Kiiski, Gary Linscott, Tord Romstad
6
7 Stockfish is free software: you can redistribute it and/or modify
8 it under the terms of the GNU General Public License as published by
9 the Free Software Foundation, either version 3 of the License, or
10 (at your option) any later version.
11
12 Stockfish is distributed in the hope that it will be useful,
13 but WITHOUT ANY WARRANTY; without even the implied warranty of
14 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
15 GNU General Public License for more details.
16
17 You should have received a copy of the GNU General Public License
18 along with this program. If not, see <http://www.gnu.org/licenses/>.
19*/
20
21#ifndef POSITION_H_INCLUDED
22#define POSITION_H_INCLUDED
23
24#include <cassert>
25#include <deque>
26#include <memory> // For std::unique_ptr
27#include <string>
28
29#include "bitboard.h"
30#include "types.h"
31
32
33/// StateInfo struct stores information needed to restore a Position object to
34/// its previous state when we retract a move. Whenever a move is made on the
35/// board (by calling Position::do_move), a StateInfo object must be passed.
36
37struct StateInfo {
38
39 // Copied when making a move
40 Key pawnKey;
41 Key materialKey;
42 Value nonPawnMaterial[COLOR_NB];
43 int castlingRights;
44 int rule50;
45 int pliesFromNull;
46 Square epSquare;
47
48 // Not copied when making a move (will be recomputed anyhow)
49 int repetition;
50 Key key;
51 Bitboard checkersBB;
52 Piece capturedPiece;
53 StateInfo* previous;
54 Bitboard blockersForKing[COLOR_NB];
55 Bitboard pinners[COLOR_NB];
56 Bitboard checkSquares[PIECE_TYPE_NB];
57};
58
59/// A list to keep track of the position states along the setup moves (from the
60/// start position to the position just before the search starts). Needed by
61/// 'draw by repetition' detection. Use a std::deque because pointers to
62/// elements are not invalidated upon list resizing.
63typedef std::unique_ptr<std::deque<StateInfo>> StateListPtr;
64
65
66/// Position class stores information regarding the board representation as
67/// pieces, side to move, hash keys, castling info, etc. Important methods are
68/// do_move() and undo_move(), used by the search to update node info when
69/// traversing the search tree.
70class Thread;
71
72class Position {
73public:
74 static void init();
75
76 Position() = default;
77 Position(const Position&) = delete;
78 Position& operator=(const Position&) = delete;
79
80 // FEN string input/output
81 Position& set(const std::string& fenStr, bool isChess960, StateInfo* si, Thread* th);
82 Position& set(const std::string& code, Color c, StateInfo* si);
83 const std::string fen() const;
84
85 // Position representation
86 Bitboard pieces() const;
87 Bitboard pieces(PieceType pt) const;
88 Bitboard pieces(PieceType pt1, PieceType pt2) const;
89 Bitboard pieces(Color c) const;
90 Bitboard pieces(Color c, PieceType pt) const;
91 Bitboard pieces(Color c, PieceType pt1, PieceType pt2) const;
92 Piece piece_on(Square s) const;
93 Square ep_square() const;
94 bool empty(Square s) const;
95 template<PieceType Pt> int count(Color c) const;
96 template<PieceType Pt> int count() const;
97 template<PieceType Pt> const Square* squares(Color c) const;
98 template<PieceType Pt> Square square(Color c) const;
99 bool is_on_semiopen_file(Color c, Square s) const;
100
101 // Castling
102 int castling_rights(Color c) const;
103 bool can_castle(CastlingRight cr) const;
104 bool castling_impeded(CastlingRight cr) const;
105 Square castling_rook_square(CastlingRight cr) const;
106
107 // Checking
108 Bitboard checkers() const;
109 Bitboard blockers_for_king(Color c) const;
110 Bitboard check_squares(PieceType pt) const;
111 bool is_discovery_check_on_king(Color c, Move m) const;
112
113 // Attacks to/from a given square
114 Bitboard attackers_to(Square s) const;
115 Bitboard attackers_to(Square s, Bitboard occupied) const;
116 Bitboard attacks_from(PieceType pt, Square s) const;
117 template<PieceType> Bitboard attacks_from(Square s) const;
118 template<PieceType> Bitboard attacks_from(Square s, Color c) const;
119 Bitboard slider_blockers(Bitboard sliders, Square s, Bitboard& pinners) const;
120
121 // Properties of moves
122 bool legal(Move m) const;
123 bool pseudo_legal(const Move m) const;
124 bool capture(Move m) const;
125 bool capture_or_promotion(Move m) const;
126 bool gives_check(Move m) const;
127 bool advanced_pawn_push(Move m) const;
128 Piece moved_piece(Move m) const;
129 Piece captured_piece() const;
130
131 // Piece specific
132 bool pawn_passed(Color c, Square s) const;
133 bool opposite_bishops() const;
134 int pawns_on_same_color_squares(Color c, Square s) const;
135
136 // Doing and undoing moves
137 void do_move(Move m, StateInfo& newSt);
138 void do_move(Move m, StateInfo& newSt, bool givesCheck);
139 void undo_move(Move m);
140 void do_null_move(StateInfo& newSt);
141 void undo_null_move();
142
143 // Static Exchange Evaluation
144 bool see_ge(Move m, Value threshold = VALUE_ZERO) const;
145
146 // Accessing hash keys
147 Key key() const;
148 Key key_after(Move m) const;
149 Key material_key() const;
150 Key pawn_key() const;
151
152 // Other properties of the position
153 Color side_to_move() const;
154 int game_ply() const;
155 bool is_chess960() const;
156 Thread* this_thread() const;
157 bool is_draw(int ply) const;
158 bool has_game_cycle(int ply) const;
159 bool has_repeated() const;
160 int rule50_count() const;
161 Score psq_score() const;
162 Value non_pawn_material(Color c) const;
163 Value non_pawn_material() const;
164
165 // Position consistency check, for debugging
166 bool pos_is_ok() const;
167 void flip();
168
169private:
170 // Initialization helpers (used while setting up a position)
171 void set_castling_right(Color c, Square rfrom);
172 void set_state(StateInfo* si) const;
173 void set_check_info(StateInfo* si) const;
174
175 // Other helpers
176 void put_piece(Piece pc, Square s);
177 void remove_piece(Piece pc, Square s);
178 void move_piece(Piece pc, Square from, Square to);
179 template<bool Do>
180 void do_castling(Color us, Square from, Square& to, Square& rfrom, Square& rto);
181
182 // Data members
183 Piece board[SQUARE_NB];
184 Bitboard byTypeBB[PIECE_TYPE_NB];
185 Bitboard byColorBB[COLOR_NB];
186 int pieceCount[PIECE_NB];
187 Square pieceList[PIECE_NB][16];
188 int index[SQUARE_NB];
189 int castlingRightsMask[SQUARE_NB];
190 Square castlingRookSquare[CASTLING_RIGHT_NB];
191 Bitboard castlingPath[CASTLING_RIGHT_NB];
192 int gamePly;
193 Color sideToMove;
194 Score psq;
195 Thread* thisThread;
196 StateInfo* st;
197 bool chess960;
198};
199
200namespace PSQT {
201 extern Score psq[PIECE_NB][SQUARE_NB];
202}
203
204extern std::ostream& operator<<(std::ostream& os, const Position& pos);
205
206inline Color Position::side_to_move() const {
207 return sideToMove;
208}
209
210inline bool Position::empty(Square s) const {
211 return board[s] == NO_PIECE;
212}
213
214inline Piece Position::piece_on(Square s) const {
215 return board[s];
216}
217
218inline Piece Position::moved_piece(Move m) const {
219 return board[from_sq(m)];
220}
221
222inline Bitboard Position::pieces() const {
223 return byTypeBB[ALL_PIECES];
224}
225
226inline Bitboard Position::pieces(PieceType pt) const {
227 return byTypeBB[pt];
228}
229
230inline Bitboard Position::pieces(PieceType pt1, PieceType pt2) const {
231 return byTypeBB[pt1] | byTypeBB[pt2];
232}
233
234inline Bitboard Position::pieces(Color c) const {
235 return byColorBB[c];
236}
237
238inline Bitboard Position::pieces(Color c, PieceType pt) const {
239 return byColorBB[c] & byTypeBB[pt];
240}
241
242inline Bitboard Position::pieces(Color c, PieceType pt1, PieceType pt2) const {
243 return byColorBB[c] & (byTypeBB[pt1] | byTypeBB[pt2]);
244}
245
246template<PieceType Pt> inline int Position::count(Color c) const {
247 return pieceCount[make_piece(c, Pt)];
248}
249
250template<PieceType Pt> inline int Position::count() const {
251 return pieceCount[make_piece(WHITE, Pt)] + pieceCount[make_piece(BLACK, Pt)];
252}
253
254template<PieceType Pt> inline const Square* Position::squares(Color c) const {
255 return pieceList[make_piece(c, Pt)];
256}
257
258template<PieceType Pt> inline Square Position::square(Color c) const {
259 assert(pieceCount[make_piece(c, Pt)] == 1);
260 return pieceList[make_piece(c, Pt)][0];
261}
262
263inline Square Position::ep_square() const {
264 return st->epSquare;
265}
266
267inline bool Position::is_on_semiopen_file(Color c, Square s) const {
268 return !(pieces(c, PAWN) & file_bb(s));
269}
270
271inline bool Position::can_castle(CastlingRight cr) const {
272 return st->castlingRights & cr;
273}
274
275inline int Position::castling_rights(Color c) const {
276 return st->castlingRights & (c == WHITE ? WHITE_CASTLING : BLACK_CASTLING);
277}
278
279inline bool Position::castling_impeded(CastlingRight cr) const {
280 return byTypeBB[ALL_PIECES] & castlingPath[cr];
281}
282
283inline Square Position::castling_rook_square(CastlingRight cr) const {
284 return castlingRookSquare[cr];
285}
286
287template<PieceType Pt>
288inline Bitboard Position::attacks_from(Square s) const {
289 assert(Pt != PAWN);
290 return Pt == BISHOP || Pt == ROOK ? attacks_bb<Pt>(s, byTypeBB[ALL_PIECES])
291 : Pt == QUEEN ? attacks_from<ROOK>(s) | attacks_from<BISHOP>(s)
292 : PseudoAttacks[Pt][s];
293}
294
295template<>
296inline Bitboard Position::attacks_from<PAWN>(Square s, Color c) const {
297 return PawnAttacks[c][s];
298}
299
300inline Bitboard Position::attacks_from(PieceType pt, Square s) const {
301 return attacks_bb(pt, s, byTypeBB[ALL_PIECES]);
302}
303
304inline Bitboard Position::attackers_to(Square s) const {
305 return attackers_to(s, byTypeBB[ALL_PIECES]);
306}
307
308inline Bitboard Position::checkers() const {
309 return st->checkersBB;
310}
311
312inline Bitboard Position::blockers_for_king(Color c) const {
313 return st->blockersForKing[c];
314}
315
316inline Bitboard Position::check_squares(PieceType pt) const {
317 return st->checkSquares[pt];
318}
319
320inline bool Position::is_discovery_check_on_king(Color c, Move m) const {
321 return st->blockersForKing[c] & from_sq(m);
322}
323
324inline bool Position::pawn_passed(Color c, Square s) const {
325 return !(pieces(~c, PAWN) & passed_pawn_span(c, s));
326}
327
328inline bool Position::advanced_pawn_push(Move m) const {
329 return type_of(moved_piece(m)) == PAWN
330 && relative_rank(sideToMove, to_sq(m)) > RANK_5;
331}
332
333inline int Position::pawns_on_same_color_squares(Color c, Square s) const {
334 return popcount(pieces(c, PAWN) & ((DarkSquares & s) ? DarkSquares : ~DarkSquares));
335}
336
337inline Key Position::key() const {
338 return st->key;
339}
340
341inline Key Position::pawn_key() const {
342 return st->pawnKey;
343}
344
345inline Key Position::material_key() const {
346 return st->materialKey;
347}
348
349inline Score Position::psq_score() const {
350 return psq;
351}
352
353inline Value Position::non_pawn_material(Color c) const {
354 return st->nonPawnMaterial[c];
355}
356
357inline Value Position::non_pawn_material() const {
358 return st->nonPawnMaterial[WHITE] + st->nonPawnMaterial[BLACK];
359}
360
361inline int Position::game_ply() const {
362 return gamePly;
363}
364
365inline int Position::rule50_count() const {
366 return st->rule50;
367}
368
369inline bool Position::opposite_bishops() const {
370 return pieceCount[W_BISHOP] == 1
371 && pieceCount[B_BISHOP] == 1
372 && opposite_colors(square<BISHOP>(WHITE), square<BISHOP>(BLACK));
373}
374
375inline bool Position::is_chess960() const {
376 return chess960;
377}
378
379inline bool Position::capture_or_promotion(Move m) const {
380 assert(is_ok(m));
381 return type_of(m) != NORMAL ? type_of(m) != CASTLING : !empty(to_sq(m));
382}
383
384inline bool Position::capture(Move m) const {
385 assert(is_ok(m));
386 // Castling is encoded as "king captures rook"
387 return (!empty(to_sq(m)) && type_of(m) != CASTLING) || type_of(m) == ENPASSANT;
388}
389
390inline Piece Position::captured_piece() const {
391 return st->capturedPiece;
392}
393
394inline Thread* Position::this_thread() const {
395 return thisThread;
396}
397
398inline void Position::put_piece(Piece pc, Square s) {
399
400 board[s] = pc;
401 byTypeBB[ALL_PIECES] |= s;
402 byTypeBB[type_of(pc)] |= s;
403 byColorBB[color_of(pc)] |= s;
404 index[s] = pieceCount[pc]++;
405 pieceList[pc][index[s]] = s;
406 pieceCount[make_piece(color_of(pc), ALL_PIECES)]++;
407 psq += PSQT::psq[pc][s];
408}
409
410inline void Position::remove_piece(Piece pc, Square s) {
411
412 // WARNING: This is not a reversible operation. If we remove a piece in
413 // do_move() and then replace it in undo_move() we will put it at the end of
414 // the list and not in its original place, it means index[] and pieceList[]
415 // are not invariant to a do_move() + undo_move() sequence.
416 byTypeBB[ALL_PIECES] ^= s;
417 byTypeBB[type_of(pc)] ^= s;
418 byColorBB[color_of(pc)] ^= s;
419 /* board[s] = NO_PIECE; Not needed, overwritten by the capturing one */
420 Square lastSquare = pieceList[pc][--pieceCount[pc]];
421 index[lastSquare] = index[s];
422 pieceList[pc][index[lastSquare]] = lastSquare;
423 pieceList[pc][pieceCount[pc]] = SQ_NONE;
424 pieceCount[make_piece(color_of(pc), ALL_PIECES)]--;
425 psq -= PSQT::psq[pc][s];
426}
427
428inline void Position::move_piece(Piece pc, Square from, Square to) {
429
430 // index[from] is not updated and becomes stale. This works as long as index[]
431 // is accessed just by known occupied squares.
432 Bitboard fromTo = square_bb(from) | square_bb(to);
433 byTypeBB[ALL_PIECES] ^= fromTo;
434 byTypeBB[type_of(pc)] ^= fromTo;
435 byColorBB[color_of(pc)] ^= fromTo;
436 board[from] = NO_PIECE;
437 board[to] = pc;
438 index[to] = index[from];
439 pieceList[pc][index[to]] = to;
440 psq += PSQT::psq[pc][to] - PSQT::psq[pc][from];
441}
442
443inline void Position::do_move(Move m, StateInfo& newSt) {
444 do_move(m, newSt, gives_check(m));
445}
446
447#endif // #ifndef POSITION_H_INCLUDED
448