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 Marco Costalba
6 Stockfish is free software: you can redistribute it and/or modify
7 it under the terms of the GNU General Public License as published by
8 the Free Software Foundation, either version 3 of the License, or
9 (at your option) any later version.
11 Stockfish is distributed in the hope that it will be useful,
12 but WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 GNU General Public License for more details.
16 You should have received a copy of the GNU General Public License
17 along with this program. If not, see <http://www.gnu.org/licenses/>.
21 #if !defined(POSITION_H_INCLUDED)
22 #define POSITION_H_INCLUDED
24 // Disable a silly and noisy warning from MSVC compiler
27 // Forcing value to bool 'true' or 'false' (performance warning)
28 #pragma warning(disable: 4800)
38 #include "direction.h"
50 /// FEN string for the initial position:
51 const std::string StartPosition =
52 "rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1";
54 /// Maximum number of plies per game (220 should be enough, because the
55 /// maximum search depth is 100, and during position setup we reset the
56 /// move counter for every non-reversible move):
57 const int MaxGameLength = 220;
64 /// Castle rights, encoded as bit fields:
76 /// The UndoInfo struct stores information we need to restore a Position
77 /// object to its previous state when we retract a move. Whenever a move
78 /// is made on the board (by calling Position::do_move), an UndoInfo object
79 /// must be passed as a parameter. When the move is unmade (by calling
80 /// Position::undo_move), the same UndoInfo object must be passed again.
83 Bitboard pinners[2], pinned[2], dcCandidates[2], checkersBB;
84 Key key, pawnKey, materialKey;
85 int castleRights, rule50;
88 Value mgValue, egValue;
93 /// The position data structure. A position consists of the following data:
95 /// * For each piece type, a bitboard representing the squares occupied
96 /// by pieces of that type.
97 /// * For each color, a bitboard representing the squares occupiecd by
98 /// pieces of that color.
99 /// * A bitboard of all occupied squares.
100 /// * A bitboard of all checking pieces.
101 /// * A 64-entry array of pieces, indexed by the squares of the board.
102 /// * The current side to move.
103 /// * Information about the castling rights for both sides.
104 /// * The initial files of the kings and both pairs of rooks. This is
105 /// used to implement the Chess960 castling rules.
106 /// * The en passant square (which is SQ_NONE if no en passant capture is
108 /// * The squares of the kings for both sides.
109 /// * The last move played.
110 /// * Hash keys for the position itself, the current pawn structure, and
111 /// the current material situation.
112 /// * Hash keys for all previous positions in the game (for detecting
113 /// repetition draws.
114 /// * A counter for detecting 50 move rule draws.
118 friend class MaterialInfo;
119 friend class EndgameFunctions;
124 Position(const Position& pos);
125 Position(const std::string& fen);
128 void from_fen(const std::string& fen);
129 const std::string to_fen() const;
130 void print(Move m = MOVE_NONE) const;
133 void copy(const Position &pos);
134 void flipped_copy(const Position &pos);
136 // The piece on a given square
137 Piece piece_on(Square s) const;
138 PieceType type_of_piece_on(Square s) const;
139 Color color_of_piece_on(Square s) const;
140 bool square_is_empty(Square s) const;
141 bool square_is_occupied(Square s) const;
142 Value midgame_value_of_piece_on(Square s) const;
143 Value endgame_value_of_piece_on(Square s) const;
146 Color side_to_move() const;
148 // Bitboard representation of the position
149 Bitboard empty_squares() const;
150 Bitboard occupied_squares() const;
151 Bitboard pieces_of_color(Color c) const;
152 Bitboard pieces_of_type(PieceType pt) const;
153 Bitboard pieces_of_color_and_type(Color c, PieceType pt) const;
154 Bitboard pawns() const;
155 Bitboard knights() const;
156 Bitboard bishops() const;
157 Bitboard rooks() const;
158 Bitboard queens() const;
159 Bitboard kings() const;
160 Bitboard rooks_and_queens() const;
161 Bitboard bishops_and_queens() const;
162 Bitboard sliders() const;
163 Bitboard pawns(Color c) const;
164 Bitboard knights(Color c) const;
165 Bitboard bishops(Color c) const;
166 Bitboard rooks(Color c) const;
167 Bitboard queens(Color c) const;
168 Bitboard kings(Color c) const;
169 Bitboard rooks_and_queens(Color c) const;
170 Bitboard bishops_and_queens(Color c) const;
171 Bitboard sliders_of_color(Color c) const;
173 // Number of pieces of each color and type
174 int piece_count(Color c, PieceType pt) const;
176 // The en passant square
177 Square ep_square() const;
179 // Current king position for each color
180 Square king_square(Color c) const;
183 bool can_castle_kingside(Color c) const;
184 bool can_castle_queenside(Color c) const;
185 bool can_castle(Color c) const;
186 Square initial_kr_square(Color c) const;
187 Square initial_qr_square(Color c) const;
190 Bitboard sliding_attacks(Square s, Direction d) const;
191 Bitboard ray_attacks(Square s, SignedDirection d) const;
192 Bitboard pawn_attacks(Color c, Square s) const;
195 Bitboard piece_attacks(Square s) const;
197 // Bitboards for pinned pieces and discovered check candidates
198 Bitboard discovered_check_candidates(Color c) const;
199 Bitboard pinned_pieces(Color c, Bitboard& p) const;
200 Bitboard pinned_pieces(Color c) const;
203 Bitboard checkers() const;
206 Square piece_list(Color c, PieceType pt, int index) const;
208 // Attack information for a given square
209 bool square_is_attacked(Square s, Color c) const;
210 Bitboard attacks_to(Square s) const;
211 Bitboard attacks_to(Square s, Color c) const;
212 bool is_check() const;
213 bool pawn_attacks_square(Color c, Square f, Square t) const;
216 Bitboard piece_attacks_square(Square f, Square t) const; // Dispatch at compile-time
218 bool piece_attacks_square(Piece p, Square f, Square t) const; // Dispatch at run-time
220 // Properties of moves
221 bool pl_move_is_legal(Move m) const;
222 bool move_is_check(Move m) const;
223 bool move_is_capture(Move m) const;
224 bool move_is_deep_pawn_push(Move m) const;
225 bool move_is_pawn_push_to_7th(Move m) const;
226 bool move_is_passed_pawn_push(Move m) const;
227 bool move_was_passed_pawn_push(Move m) const;
228 bool move_attacks_square(Move m, Square s) const;
230 // Information about pawns
231 bool pawn_is_passed(Color c, Square s) const;
232 bool pawn_is_isolated(Color c, Square s) const;
233 bool pawn_is_doubled(Color c, Square s) const;
235 // Open and half-open files
236 bool file_is_open(File f) const;
237 bool file_is_half_open(Color c, File f) const;
240 bool square_is_weak(Square s, Color c) const;
242 // Doing and undoing moves
243 void backup(UndoInfo &u) const;
244 void restore(const UndoInfo &u);
245 void do_move(Move m, UndoInfo &u);
246 void undo_move(Move m, const UndoInfo &u);
247 void do_null_move(UndoInfo &u);
248 void undo_null_move(const UndoInfo &u);
250 // Static exchange evaluation
251 int see(Square from, Square to) const;
252 int see(Move m) const;
253 int see(Square to) const;
255 // Accessing hash keys
257 Key get_pawn_key() const;
258 Key get_material_key() const;
260 // Incremental evaluation
261 Value mg_value() const;
262 Value eg_value() const;
263 Value non_pawn_material(Color c) const;
264 Phase game_phase() const;
265 Value mg_pst_delta(Move m) const;
267 // Game termination checks
268 bool is_mate() const;
269 bool is_draw() const;
271 // Check if one side threatens a mate in one
272 bool has_mate_threat(Color c);
274 // Number of plies since the last non-reversible move
275 int rule_50_counter() const;
277 // Other properties of the position
278 bool opposite_colored_bishops() const;
279 bool has_pawn_on_7th(Color c) const;
281 // Reset the gamePly variable to 0
282 void reset_game_ply();
284 // Position consistency check, for debugging
285 bool is_ok(int* failedStep = NULL) const;
287 // Static member functions:
288 static void init_zobrist();
289 static void init_piece_square_tables();
292 // Initialization helper functions (used while setting up a position)
294 void put_piece(Piece p, Square s);
295 void allow_oo(Color c);
296 void allow_ooo(Color c);
298 // Helper functions for doing and undoing moves
299 void do_capture_move(Move m, PieceType capture, Color them, Square to);
300 void do_castle_move(Move m);
301 void do_promotion_move(Move m, UndoInfo &u);
302 void do_ep_move(Move m);
303 void undo_castle_move(Move m);
304 void undo_promotion_move(Move m, const UndoInfo &u);
305 void undo_ep_move(Move m);
306 void find_checkers();
308 template<PieceType Piece>
309 void update_checkers(Bitboard* pCheckersBB, Square ksq, Square from, Square to, Bitboard dcCandidates);
311 template<PieceType Piece, bool FindPinned>
312 Bitboard hidden_checks(Color c, Square ksq, Bitboard& pinners) const;
314 // Computing hash keys from scratch (for initialization and debugging)
315 Key compute_key() const;
316 Key compute_pawn_key() const;
317 Key compute_material_key() const;
319 // Computing incremental evaluation scores and material counts
320 Value mg_pst(Color c, PieceType pt, Square s) const;
321 Value eg_pst(Color c, PieceType pt, Square s) const;
322 Value compute_mg_value() const;
323 Value compute_eg_value() const;
324 Value compute_non_pawn_material(Color c) const;
327 Bitboard byColorBB[2], byTypeBB[8];
333 int pieceCount[2][8]; // [color][pieceType]
336 Square pieceList[2][8][16]; // [color][pieceType][index]
340 Square kingSquare[2];
343 Key history[MaxGameLength];
345 File initialKFile, initialKRFile, initialQRFile;
347 // Info backed up in do_move()
348 mutable Bitboard pinners[2], pinned[2], dcCandidates[2];
350 Key key, pawnKey, materialKey;
351 int castleRights, rule50;
354 Value mgValue, egValue;
357 static int castleRightsMask[64];
358 static Key zobrist[2][8][64];
359 static Key zobEp[64];
360 static Key zobCastle[16];
361 static Key zobMaterial[2][8][16];
362 static Key zobSideToMove;
363 static Value MgPieceSquareTable[16][64];
364 static Value EgPieceSquareTable[16][64];
369 //// Inline functions
372 inline Piece Position::piece_on(Square s) const {
376 inline Color Position::color_of_piece_on(Square s) const {
377 return color_of_piece(piece_on(s));
380 inline PieceType Position::type_of_piece_on(Square s) const {
381 return type_of_piece(piece_on(s));
384 inline bool Position::square_is_empty(Square s) const {
385 return piece_on(s) == EMPTY;
388 inline bool Position::square_is_occupied(Square s) const {
389 return !square_is_empty(s);
392 inline Value Position::midgame_value_of_piece_on(Square s) const {
393 return piece_value_midgame(piece_on(s));
396 inline Value Position::endgame_value_of_piece_on(Square s) const {
397 return piece_value_endgame(piece_on(s));
400 inline Color Position::side_to_move() const {
404 inline Bitboard Position::occupied_squares() const {
408 inline Bitboard Position::empty_squares() const {
409 return ~(occupied_squares());
412 inline Bitboard Position::pieces_of_color(Color c) const {
416 inline Bitboard Position::pieces_of_type(PieceType pt) const {
420 inline Bitboard Position::pieces_of_color_and_type(Color c, PieceType pt) const {
421 return pieces_of_color(c) & pieces_of_type(pt);
424 inline Bitboard Position::pawns() const {
425 return pieces_of_type(PAWN);
428 inline Bitboard Position::knights() const {
429 return pieces_of_type(KNIGHT);
432 inline Bitboard Position::bishops() const {
433 return pieces_of_type(BISHOP);
436 inline Bitboard Position::rooks() const {
437 return pieces_of_type(ROOK);
440 inline Bitboard Position::queens() const {
441 return pieces_of_type(QUEEN);
444 inline Bitboard Position::kings() const {
445 return pieces_of_type(KING);
448 inline Bitboard Position::rooks_and_queens() const {
449 return rooks() | queens();
452 inline Bitboard Position::bishops_and_queens() const {
453 return bishops() | queens();
456 inline Bitboard Position::sliders() const {
457 return bishops() | queens() | rooks();
460 inline Bitboard Position::pawns(Color c) const {
461 return pieces_of_color_and_type(c, PAWN);
464 inline Bitboard Position::knights(Color c) const {
465 return pieces_of_color_and_type(c, KNIGHT);
468 inline Bitboard Position::bishops(Color c) const {
469 return pieces_of_color_and_type(c, BISHOP);
472 inline Bitboard Position::rooks(Color c) const {
473 return pieces_of_color_and_type(c, ROOK);
476 inline Bitboard Position::queens(Color c) const {
477 return pieces_of_color_and_type(c, QUEEN);
480 inline Bitboard Position::kings(Color c) const {
481 return pieces_of_color_and_type(c, KING);
484 inline Bitboard Position::rooks_and_queens(Color c) const {
485 return rooks_and_queens() & pieces_of_color(c);
488 inline Bitboard Position::bishops_and_queens(Color c) const {
489 return bishops_and_queens() & pieces_of_color(c);
492 inline Bitboard Position::sliders_of_color(Color c) const {
493 return sliders() & pieces_of_color(c);
496 inline int Position::piece_count(Color c, PieceType pt) const {
497 return pieceCount[c][pt];
500 inline Square Position::piece_list(Color c, PieceType pt, int index) const {
501 return pieceList[c][pt][index];
504 inline Square Position::ep_square() const {
508 inline Square Position::king_square(Color c) const {
509 return kingSquare[c];
512 inline bool Position::can_castle_kingside(Color side) const {
513 return castleRights & (1+int(side));
516 inline bool Position::can_castle_queenside(Color side) const {
517 return castleRights & (4+4*int(side));
520 inline bool Position::can_castle(Color side) const {
521 return can_castle_kingside(side) || can_castle_queenside(side);
524 inline Square Position::initial_kr_square(Color c) const {
525 return relative_square(c, make_square(initialKRFile, RANK_1));
528 inline Square Position::initial_qr_square(Color c) const {
529 return relative_square(c, make_square(initialQRFile, RANK_1));
532 inline Bitboard Position::pawn_attacks(Color c, Square s) const {
533 return StepAttackBB[piece_of_color_and_type(c, PAWN)][s];
537 inline Bitboard Position::piece_attacks<PAWN>(Square s) const {
538 return StepAttackBB[piece_of_color_and_type(opposite_color(sideToMove), PAWN)][s];
542 inline Bitboard Position::piece_attacks<KNIGHT>(Square s) const {
543 return StepAttackBB[KNIGHT][s];
547 inline Bitboard Position::piece_attacks<BISHOP>(Square s) const {
548 return bishop_attacks_bb(s, occupied_squares());
552 inline Bitboard Position::piece_attacks<ROOK>(Square s) const {
553 return rook_attacks_bb(s, occupied_squares());
557 inline Bitboard Position::piece_attacks<QUEEN>(Square s) const {
558 return piece_attacks<ROOK>(s) | piece_attacks<BISHOP>(s);
562 inline Bitboard Position::piece_attacks<KING>(Square s) const {
563 return StepAttackBB[KING][s];
566 inline Bitboard Position::checkers() const {
570 inline bool Position::is_check() const {
571 return checkersBB != EmptyBoardBB;
574 inline bool Position::pawn_attacks_square(Color c, Square f, Square t) const {
575 return bit_is_set(pawn_attacks(c, f), t);
578 template<PieceType Piece>
579 Bitboard Position::piece_attacks_square(Square f, Square t) const {
580 return bit_is_set(piece_attacks<Piece>(f), t);
583 inline Bitboard Position::attacks_to(Square s, Color c) const {
585 return attacks_to(s) & pieces_of_color(c);
588 inline bool Position::square_is_attacked(Square s, Color c) const {
590 return attacks_to(s, c) != EmptyBoardBB;
593 inline bool Position::pawn_is_passed(Color c, Square s) const {
594 return !(pawns(opposite_color(c)) & passed_pawn_mask(c, s));
597 inline bool Position::pawn_is_isolated(Color c, Square s) const {
598 return !(pawns(c) & neighboring_files_bb(s));
601 inline bool Position::pawn_is_doubled(Color c, Square s) const {
602 return pawns(c) & squares_behind(c, s);
605 inline bool Position::file_is_open(File f) const {
606 return !(pawns() & file_bb(f));
609 inline bool Position::file_is_half_open(Color c, File f) const {
610 return !(pawns(c) & file_bb(f));
613 inline bool Position::square_is_weak(Square s, Color c) const {
614 return !(pawns(c) & outpost_mask(opposite_color(c), s));
617 inline Key Position::get_key() const {
621 inline Key Position::get_pawn_key() const {
625 inline Key Position::get_material_key() const {
629 inline Value Position::mg_pst(Color c, PieceType pt, Square s) const {
630 return MgPieceSquareTable[piece_of_color_and_type(c, pt)][s];
633 inline Value Position::mg_pst_delta(Move m) const {
634 return MgPieceSquareTable[piece_on(move_from(m))][move_to(m)]
635 -MgPieceSquareTable[piece_on(move_from(m))][move_from(m)];
638 inline Value Position::eg_pst(Color c, PieceType pt, Square s) const {
639 return EgPieceSquareTable[piece_of_color_and_type(c, pt)][s];
642 inline Value Position::mg_value() const {
646 inline Value Position::eg_value() const {
650 inline Value Position::non_pawn_material(Color c) const {
651 return npMaterial[c];
654 inline Phase Position::game_phase() const {
656 // The purpose of the Value(325) terms below is to make sure the difference
657 // between MidgameLimit and EndgameLimit is a power of 2, which should make
658 // the division at the end of the function a bit faster.
659 static const Value MidgameLimit = 2 * QueenValueMidgame
660 + 2 * RookValueMidgame
661 + 6 * BishopValueMidgame
664 static const Value EndgameLimit = 4 * RookValueMidgame - Value(325);
666 Value npm = non_pawn_material(WHITE) + non_pawn_material(BLACK);
668 if (npm >= MidgameLimit)
669 return PHASE_MIDGAME;
670 else if(npm <= EndgameLimit)
671 return PHASE_ENDGAME;
673 return Phase(((npm - EndgameLimit) * 128) / (MidgameLimit - EndgameLimit));
676 inline bool Position::move_is_deep_pawn_push(Move m) const {
678 Color c = side_to_move();
679 return piece_on(move_from(m)) == piece_of_color_and_type(c, PAWN)
680 && relative_rank(c, move_to(m)) > RANK_4;
683 inline bool Position::move_is_pawn_push_to_7th(Move m) const {
685 Color c = side_to_move();
686 return piece_on(move_from(m)) == piece_of_color_and_type(c, PAWN)
687 && relative_rank(c, move_to(m)) == RANK_7;
690 inline bool Position::move_is_passed_pawn_push(Move m) const {
692 Color c = side_to_move();
693 return piece_on(move_from(m)) == piece_of_color_and_type(c, PAWN)
694 && pawn_is_passed(c, move_to(m));
697 inline bool Position::move_was_passed_pawn_push(Move m) const {
699 Color c = opposite_color(side_to_move());
700 return piece_on(move_to(m)) == piece_of_color_and_type(c, PAWN)
701 && pawn_is_passed(c, move_to(m));
704 inline int Position::rule_50_counter() const {
709 inline bool Position::opposite_colored_bishops() const {
711 return piece_count(WHITE, BISHOP) == 1
712 && piece_count(BLACK, BISHOP) == 1
713 && square_color(piece_list(WHITE, BISHOP, 0)) != square_color(piece_list(BLACK, BISHOP, 0));
716 inline bool Position::has_pawn_on_7th(Color c) const {
718 return pawns(c) & relative_rank_bb(c, RANK_7);
722 #endif // !defined(POSITION_H_INCLUDED)