2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
4 Copyright (C) 2008-2009 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/>.
30 // Simple macro to wrap a very common while loop, no facny, no flexibility,
31 // hardcoded list name 'mlist' and from square 'from'.
32 #define SERIALIZE_MOVES(b) while (b) (*mlist++).move = make_move(from, pop_1st_bit(&b))
34 // Version used for pawns, where the 'from' square is given as a delta from the 'to' square
35 #define SERIALIZE_MOVES_D(b, d) while (b) { to = pop_1st_bit(&b); (*mlist++).move = make_move(to + (d), to); }
38 //// Local definitions
56 template<CastlingSide Side>
57 MoveStack* generate_castle_moves(const Position&, MoveStack*);
59 template<Color Us, MoveType Type>
60 MoveStack* generate_pawn_moves(const Position&, MoveStack*, Bitboard, Square);
62 // Template generate_piece_moves (captures and non-captures) with specializations and overloads
64 MoveStack* generate_piece_moves(const Position&, MoveStack*, Color, Bitboard);
67 MoveStack* generate_piece_moves<KING>(const Position&, MoveStack*, Color, Bitboard);
69 template<PieceType Piece, MoveType Type>
70 inline MoveStack* generate_piece_moves(const Position& p, MoveStack* m, Color us, Bitboard t) {
72 assert(Piece == PAWN);
73 assert(Type == CAPTURE || Type == NON_CAPTURE || Type == EVASION);
75 return (us == WHITE ? generate_pawn_moves<WHITE, Type>(p, m, t, SQ_NONE)
76 : generate_pawn_moves<BLACK, Type>(p, m, t, SQ_NONE));
79 // Templates for non-capture checks generation
81 template<PieceType Piece>
82 MoveStack* generate_discovered_checks(const Position& pos, MoveStack* mlist, Square from);
85 MoveStack* generate_direct_checks(const Position&, MoveStack*, Color, Bitboard, Square);
88 inline MoveStack* generate_direct_checks<PAWN>(const Position& p, MoveStack* m, Color us, Bitboard dc, Square ksq) {
90 return (us == WHITE ? generate_pawn_moves<WHITE, CHECK>(p, m, dc, ksq)
91 : generate_pawn_moves<BLACK, CHECK>(p, m, dc, ksq));
101 /// generate_captures() generates all pseudo-legal captures and queen
102 /// promotions. Returns a pointer to the end of the move list.
104 MoveStack* generate_captures(const Position& pos, MoveStack* mlist) {
107 assert(!pos.is_check());
109 Color us = pos.side_to_move();
110 Bitboard target = pos.pieces_of_color(opposite_color(us));
112 mlist = generate_piece_moves<QUEEN>(pos, mlist, us, target);
113 mlist = generate_piece_moves<ROOK>(pos, mlist, us, target);
114 mlist = generate_piece_moves<BISHOP>(pos, mlist, us, target);
115 mlist = generate_piece_moves<KNIGHT>(pos, mlist, us, target);
116 mlist = generate_piece_moves<PAWN, CAPTURE>(pos, mlist, us, target);
117 return generate_piece_moves<KING>(pos, mlist, us, target);
121 /// generate_noncaptures() generates all pseudo-legal non-captures and
122 /// underpromotions. Returns a pointer to the end of the move list.
124 MoveStack* generate_noncaptures(const Position& pos, MoveStack* mlist) {
127 assert(!pos.is_check());
129 Color us = pos.side_to_move();
130 Bitboard target = pos.empty_squares();
132 mlist = generate_piece_moves<PAWN, NON_CAPTURE>(pos, mlist, us, target);
133 mlist = generate_piece_moves<KNIGHT>(pos, mlist, us, target);
134 mlist = generate_piece_moves<BISHOP>(pos, mlist, us, target);
135 mlist = generate_piece_moves<ROOK>(pos, mlist, us, target);
136 mlist = generate_piece_moves<QUEEN>(pos, mlist, us, target);
137 mlist = generate_piece_moves<KING>(pos, mlist, us, target);
138 mlist = generate_castle_moves<KING_SIDE>(pos, mlist);
139 return generate_castle_moves<QUEEN_SIDE>(pos, mlist);
143 /// generate_non_capture_checks() generates all pseudo-legal non-captures and knight
144 /// underpromotions that give check. Returns a pointer to the end of the move list.
146 MoveStack* generate_non_capture_checks(const Position& pos, MoveStack* mlist) {
149 assert(!pos.is_check());
151 Color us = pos.side_to_move();
152 Square ksq = pos.king_square(opposite_color(us));
153 Bitboard dc = pos.discovered_check_candidates(us);
155 assert(pos.piece_on(ksq) == piece_of_color_and_type(opposite_color(us), KING));
157 // Discovered non-capture checks
161 Square from = pop_1st_bit(&b);
162 switch (pos.type_of_piece_on(from))
164 case PAWN: /* Will be generated togheter with pawns direct checks */ break;
165 case KNIGHT: mlist = generate_discovered_checks<KNIGHT>(pos, mlist, from); break;
166 case BISHOP: mlist = generate_discovered_checks<BISHOP>(pos, mlist, from); break;
167 case ROOK: mlist = generate_discovered_checks<ROOK>(pos, mlist, from); break;
168 case KING: mlist = generate_discovered_checks<KING>(pos, mlist, from); break;
169 default: assert(false); break;
173 // Direct non-capture checks
174 mlist = generate_direct_checks<PAWN>(pos, mlist, us, dc, ksq);
175 mlist = generate_direct_checks<KNIGHT>(pos, mlist, us, dc, ksq);
176 mlist = generate_direct_checks<BISHOP>(pos, mlist, us, dc, ksq);
177 mlist = generate_direct_checks<ROOK>(pos, mlist, us, dc, ksq);
178 return generate_direct_checks<QUEEN>(pos, mlist, us, dc, ksq);
182 /// generate_evasions() generates all pseudo-legal check evasions when
183 /// the side to move is in check. Returns a pointer to the end of the move list.
185 MoveStack* generate_evasions(const Position& pos, MoveStack* mlist) {
188 assert(pos.is_check());
191 Square from, checksq;
193 Color us = pos.side_to_move();
194 Square ksq = pos.king_square(us);
195 Bitboard checkers = pos.checkers();
196 Bitboard sliderAttacks = EmptyBoardBB;
198 assert(pos.piece_on(ksq) == piece_of_color_and_type(us, KING));
201 // Find squares attacked by slider checkers, we will remove
202 // them from the king evasions set so to early skip known
203 // illegal moves and avoid an useless legality check later.
208 checksq = pop_1st_bit(&b);
210 assert(pos.color_of_piece_on(checksq) == opposite_color(us));
212 switch (pos.type_of_piece_on(checksq))
214 case BISHOP: sliderAttacks |= BishopPseudoAttacks[checksq]; break;
215 case ROOK: sliderAttacks |= RookPseudoAttacks[checksq]; break;
217 // In case of a queen remove also squares attacked in the other direction to
218 // avoid possible illegal moves when queen and king are on adjacent squares.
219 if (direction_is_straight(checksq, ksq))
220 sliderAttacks |= RookPseudoAttacks[checksq] | pos.attacks_from<BISHOP>(checksq);
222 sliderAttacks |= BishopPseudoAttacks[checksq] | pos.attacks_from<ROOK>(checksq);
228 // Generate evasions for king, capture and non capture moves
229 b = pos.attacks_from<KING>(ksq) & ~pos.pieces_of_color(us) & ~sliderAttacks;
233 // Generate evasions for other pieces only if not double check
237 // Find squares where a blocking evasion or a capture of the
238 // checker piece is possible.
239 Bitboard target = squares_between(checksq, ksq) | checkers;
241 mlist = generate_piece_moves<PAWN, EVASION>(pos, mlist, us, target);
242 mlist = generate_piece_moves<KNIGHT>(pos, mlist, us, target);
243 mlist = generate_piece_moves<BISHOP>(pos, mlist, us, target);
244 mlist = generate_piece_moves<ROOK>(pos, mlist, us, target);
245 return generate_piece_moves<QUEEN>(pos, mlist, us, target);
249 /// generate_moves() computes a complete list of legal or pseudo-legal moves in
250 /// the current position. This function is not very fast, and should be used
251 /// only in non time-critical paths.
253 MoveStack* generate_moves(const Position& pos, MoveStack* mlist, bool pseudoLegal) {
258 Bitboard pinned = pos.pinned_pieces(pos.side_to_move());
260 // Generate pseudo-legal moves
262 last = generate_evasions(pos, mlist);
264 last = generate_captures(pos, mlist);
265 last = generate_noncaptures(pos, last);
270 // Remove illegal moves from the list
271 for (MoveStack* cur = mlist; cur != last; cur++)
272 if (!pos.pl_move_is_legal(cur->move, pinned))
274 cur->move = (--last)->move;
281 /// move_is_legal() takes a position and a (not necessarily pseudo-legal)
282 /// move and tests whether the move is legal. This version is not very fast
283 /// and should be used only in non time-critical paths.
285 bool move_is_legal(const Position& pos, const Move m) {
287 MoveStack mlist[256];
288 MoveStack* last = generate_moves(pos, mlist, true);
289 for (MoveStack* cur = mlist; cur != last; cur++)
291 return pos.pl_move_is_legal(m, pos.pinned_pieces(pos.side_to_move()));
297 /// Fast version of move_is_legal() that takes a position a move and a
298 /// bitboard of pinned pieces as input, and tests whether the move is legal.
299 /// This version must only be used when the side to move is not in check.
301 bool move_is_legal(const Position& pos, const Move m, Bitboard pinned) {
304 assert(!pos.is_check());
305 assert(move_is_ok(m));
306 assert(pinned == pos.pinned_pieces(pos.side_to_move()));
308 // Use a slower but simpler function for uncommon cases
309 if (move_is_ep(m) || move_is_castle(m))
310 return move_is_legal(pos, m);
312 Color us = pos.side_to_move();
313 Color them = opposite_color(us);
314 Square from = move_from(m);
315 Square to = move_to(m);
316 Piece pc = pos.piece_on(from);
318 // If the from square is not occupied by a piece belonging to the side to
319 // move, the move is obviously not legal.
320 if (color_of_piece(pc) != us)
323 // The destination square cannot be occupied by a friendly piece
324 if (pos.color_of_piece_on(to) == us)
327 // Handle the special case of a pawn move
328 if (type_of_piece(pc) == PAWN)
330 // Move direction must be compatible with pawn color
331 int direction = to - from;
332 if ((us == WHITE) != (direction > 0))
335 // A pawn move is a promotion iff the destination square is
336 // on the 8/1th rank.
337 if (( (square_rank(to) == RANK_8 && us == WHITE)
338 ||(square_rank(to) == RANK_1 && us != WHITE)) != bool(move_is_promotion(m)))
341 // Proceed according to the square delta between the origin and
342 // destination squares.
349 // Capture. The destination square must be occupied by an enemy
350 // piece (en passant captures was handled earlier).
351 if (pos.color_of_piece_on(to) != them)
357 // Pawn push. The destination square must be empty.
358 if (!pos.square_is_empty(to))
363 // Double white pawn push. The destination square must be on the fourth
364 // rank, and both the destination square and the square between the
365 // source and destination squares must be empty.
366 if ( square_rank(to) != RANK_4
367 || !pos.square_is_empty(to)
368 || !pos.square_is_empty(from + DELTA_N))
373 // Double black pawn push. The destination square must be on the fifth
374 // rank, and both the destination square and the square between the
375 // source and destination squares must be empty.
376 if ( square_rank(to) != RANK_5
377 || !pos.square_is_empty(to)
378 || !pos.square_is_empty(from + DELTA_S))
385 // The move is pseudo-legal, check if it is also legal
386 return pos.pl_move_is_legal(m, pinned);
389 // Luckly we can handle all the other pieces in one go
390 return ( bit_is_set(pos.attacks_from(pc, from), to)
391 && pos.pl_move_is_legal(m, pinned)
392 && !move_is_promotion(m));
398 template<PieceType Piece>
399 MoveStack* generate_piece_moves(const Position& pos, MoveStack* mlist, Color us, Bitboard target) {
403 const Square* ptr = pos.piece_list_begin(us, Piece);
405 while ((from = *ptr++) != SQ_NONE)
407 b = pos.attacks_from<Piece>(from) & target;
414 MoveStack* generate_piece_moves<KING>(const Position& pos, MoveStack* mlist, Color us, Bitboard target) {
417 Square from = pos.king_square(us);
419 b = pos.attacks_from<KING>(from) & target;
424 template<Color Us, SquareDelta Direction>
425 inline Bitboard move_pawns(Bitboard p) {
427 if (Direction == DELTA_N)
428 return Us == WHITE ? p << 8 : p >> 8;
429 else if (Direction == DELTA_NE)
430 return Us == WHITE ? p << 9 : p >> 7;
431 else if (Direction == DELTA_NW)
432 return Us == WHITE ? p << 7 : p >> 9;
437 template<Color Us, MoveType Type, SquareDelta Diagonal>
438 inline MoveStack* generate_pawn_captures(MoveStack* mlist, Bitboard pawns, Bitboard enemyPieces, bool possiblePromotion) {
440 // Calculate our parametrized parameters at compile time
441 const Bitboard TRank8BB = (Us == WHITE ? Rank8BB : Rank1BB);
442 const Bitboard TFileABB = (Diagonal == DELTA_NE ? FileABB : FileHBB);
443 const SquareDelta TDELTA_NE = (Us == WHITE ? DELTA_NE : DELTA_SE);
444 const SquareDelta TDELTA_NW = (Us == WHITE ? DELTA_NW : DELTA_SW);
445 const SquareDelta TTDELTA_NE = (Diagonal == DELTA_NE ? TDELTA_NE : TDELTA_NW);
449 // Captures in the a1-h8 (a8-h1 for black) diagonal or in the h1-a8 (h8-a1 for black)
450 Bitboard b1 = move_pawns<Us, Diagonal>(pawns) & ~TFileABB & enemyPieces;
452 // Capturing promotions and under-promotions
453 if (possiblePromotion)
455 Bitboard b2 = b1 & TRank8BB;
459 to = pop_1st_bit(&b2);
461 if (Type == CAPTURE || Type == EVASION)
462 (*mlist++).move = make_promotion_move(to - TTDELTA_NE, to, QUEEN);
464 if (Type == NON_CAPTURE || Type == EVASION)
466 (*mlist++).move = make_promotion_move(to - TTDELTA_NE, to, ROOK);
467 (*mlist++).move = make_promotion_move(to - TTDELTA_NE, to, BISHOP);
468 (*mlist++).move = make_promotion_move(to - TTDELTA_NE, to, KNIGHT);
471 // This is the only possible under promotion that can give a check
472 // not already included in the queen-promotion. It is not sure that
473 // the promoted knight will give check, but it doesn't worth to verify.
475 (*mlist++).move = make_promotion_move(to - TTDELTA_NE, to, KNIGHT);
479 // Serialize standard captures
480 if (Type == CAPTURE || Type == EVASION)
481 SERIALIZE_MOVES_D(b1, -TTDELTA_NE);
486 template<Color Us, MoveType Type>
487 MoveStack* generate_pawn_moves(const Position& pos, MoveStack* mlist, Bitboard target, Square ksq) {
489 // Calculate our parametrized parameters at compile time
490 const Color Them = (Us == WHITE ? BLACK : WHITE);
491 const Bitboard TRank8BB = (Us == WHITE ? Rank8BB : Rank1BB);
492 const Bitboard TRank7BB = (Us == WHITE ? Rank7BB : Rank2BB);
493 const Bitboard TRank3BB = (Us == WHITE ? Rank3BB : Rank6BB);
494 const SquareDelta TDELTA_N = (Us == WHITE ? DELTA_N : DELTA_S);
497 Bitboard b1, b2, enemyPieces, emptySquares;
498 Bitboard pawns = pos.pieces(PAWN, Us);
499 bool possiblePromotion = pawns & TRank7BB;
501 // Standard captures and capturing promotions and underpromotions
502 if (Type == CAPTURE || Type == EVASION || possiblePromotion)
504 enemyPieces = (Type == CAPTURE ? target : pos.pieces_of_color(opposite_color(Us)));
507 enemyPieces &= target; // Capture only the checker piece
509 mlist = generate_pawn_captures<Us, Type, DELTA_NE>(mlist, pawns, enemyPieces, possiblePromotion);
510 mlist = generate_pawn_captures<Us, Type, DELTA_NW>(mlist, pawns, enemyPieces, possiblePromotion);
513 // Non-capturing promotions and underpromotions
514 if (possiblePromotion)
516 b1 = move_pawns<Us, DELTA_N>(pawns) & TRank8BB & pos.empty_squares();
519 b1 &= target; // Only blocking promotion pushes
523 to = pop_1st_bit(&b1);
525 if (Type == CAPTURE || Type == EVASION)
526 (*mlist++).move = make_promotion_move(to - TDELTA_N, to, QUEEN);
528 if (Type == NON_CAPTURE || Type == EVASION)
530 (*mlist++).move = make_promotion_move(to - TDELTA_N, to, ROOK);
531 (*mlist++).move = make_promotion_move(to - TDELTA_N, to, BISHOP);
532 (*mlist++).move = make_promotion_move(to - TDELTA_N, to, KNIGHT);
535 // This is the only possible under promotion that can give a check
536 // not already included in the queen-promotion.
537 if (Type == CHECK && bit_is_set(pos.attacks_from<KNIGHT>(to), pos.king_square(Them)))
538 (*mlist++).move = make_promotion_move(to - TDELTA_N, to, KNIGHT);
542 // Standard pawn pushes and double pushes
545 emptySquares = (Type == NON_CAPTURE ? target : pos.empty_squares());
547 // Single and double pawn pushes
548 b1 = move_pawns<Us, DELTA_N>(pawns) & emptySquares & ~TRank8BB;
549 b2 = move_pawns<Us, DELTA_N>(b1 & TRank3BB) & emptySquares;
551 // Filter out unwanted pushes according to the move type
557 else if (Type == CHECK)
559 // Pawn moves which give direct cheks
560 b1 &= pos.attacks_from<PAWN>(ksq, Them);
561 b2 &= pos.attacks_from<PAWN>(ksq, Them);
563 // Pawn moves which gives discovered check. This is possible only if
564 // the pawn is not on the same file as the enemy king, because we
565 // don't generate captures.
566 if (pawns & target) // For CHECK type target is dc bitboard
568 Bitboard dc1 = move_pawns<Us, DELTA_N>(pawns & target & ~file_bb(ksq)) & emptySquares & ~TRank8BB;
569 Bitboard dc2 = move_pawns<Us, DELTA_N>(dc1 & TRank3BB) & emptySquares;
575 SERIALIZE_MOVES_D(b1, -TDELTA_N);
576 SERIALIZE_MOVES_D(b2, -TDELTA_N -TDELTA_N);
579 // En passant captures
580 if ((Type == CAPTURE || Type == EVASION) && pos.ep_square() != SQ_NONE)
582 assert(Us != WHITE || square_rank(pos.ep_square()) == RANK_6);
583 assert(Us != BLACK || square_rank(pos.ep_square()) == RANK_3);
585 // An en passant capture can be an evasion only if the checking piece
586 // is the double pushed pawn and so is in the target. Otherwise this
587 // is a discovery check and we are forced to do otherwise.
588 if (Type == EVASION && !bit_is_set(target, pos.ep_square() - TDELTA_N))
591 b1 = pawns & pos.attacks_from<PAWN>(pos.ep_square(), Them);
593 assert(b1 != EmptyBoardBB);
597 to = pop_1st_bit(&b1);
598 (*mlist++).move = make_ep_move(to, pos.ep_square());
604 template<PieceType Piece>
605 MoveStack* generate_discovered_checks(const Position& pos, MoveStack* mlist, Square from) {
607 assert(Piece != QUEEN);
609 Bitboard b = pos.attacks_from<Piece>(from) & pos.empty_squares();
612 Square ksq = pos.king_square(opposite_color(pos.side_to_move()));
613 b &= ~QueenPseudoAttacks[ksq];
619 template<PieceType Piece>
620 MoveStack* generate_direct_checks(const Position& pos, MoveStack* mlist, Color us,
621 Bitboard dc, Square ksq) {
622 assert(Piece != KING);
626 const Square* ptr = pos.piece_list_begin(us, Piece);
628 if ((from = *ptr++) == SQ_NONE)
631 checkSqs = pos.attacks_from<Piece>(ksq) & pos.empty_squares();
635 if ( (Piece == QUEEN && !(QueenPseudoAttacks[from] & checkSqs))
636 || (Piece == ROOK && !(RookPseudoAttacks[from] & checkSqs))
637 || (Piece == BISHOP && !(BishopPseudoAttacks[from] & checkSqs)))
640 if (dc && bit_is_set(dc, from))
643 Bitboard bb = pos.attacks_from<Piece>(from) & checkSqs;
646 } while ((from = *ptr++) != SQ_NONE);
651 template<CastlingSide Side>
652 MoveStack* generate_castle_moves(const Position& pos, MoveStack* mlist) {
654 Color us = pos.side_to_move();
656 if ( (Side == KING_SIDE && pos.can_castle_kingside(us))
657 ||(Side == QUEEN_SIDE && pos.can_castle_queenside(us)))
659 Color them = opposite_color(us);
660 Square ksq = pos.king_square(us);
662 assert(pos.piece_on(ksq) == piece_of_color_and_type(us, KING));
664 Square rsq = (Side == KING_SIDE ? pos.initial_kr_square(us) : pos.initial_qr_square(us));
665 Square s1 = relative_square(us, Side == KING_SIDE ? SQ_G1 : SQ_C1);
666 Square s2 = relative_square(us, Side == KING_SIDE ? SQ_F1 : SQ_D1);
668 bool illegal = false;
670 assert(pos.piece_on(rsq) == piece_of_color_and_type(us, ROOK));
672 // It is a bit complicated to correctly handle Chess960
673 for (s = Min(ksq, s1); s <= Max(ksq, s1); s++)
674 if ( (s != ksq && s != rsq && pos.square_is_occupied(s))
675 ||(pos.attackers_to(s) & pos.pieces_of_color(them)))
678 for (s = Min(rsq, s2); s <= Max(rsq, s2); s++)
679 if (s != ksq && s != rsq && pos.square_is_occupied(s))
682 if ( Side == QUEEN_SIDE
683 && square_file(rsq) == FILE_B
684 && ( pos.piece_on(relative_square(us, SQ_A1)) == piece_of_color_and_type(them, ROOK)
685 || pos.piece_on(relative_square(us, SQ_A1)) == piece_of_color_and_type(them, QUEEN)))
689 (*mlist++).move = make_castle_move(ksq, rsq);