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, Bitboard dc) {
149 assert(!pos.is_check());
151 Color us = pos.side_to_move();
152 Square ksq = pos.king_square(opposite_color(us));
154 assert(pos.piece_on(ksq) == piece_of_color_and_type(opposite_color(us), KING));
156 // Discovered non-capture checks
160 Square from = pop_1st_bit(&b);
161 switch (pos.type_of_piece_on(from))
163 case PAWN: /* Will be generated togheter with pawns direct checks */ break;
164 case KNIGHT: mlist = generate_discovered_checks<KNIGHT>(pos, mlist, from); break;
165 case BISHOP: mlist = generate_discovered_checks<BISHOP>(pos, mlist, from); break;
166 case ROOK: mlist = generate_discovered_checks<ROOK>(pos, mlist, from); break;
167 case KING: mlist = generate_discovered_checks<KING>(pos, mlist, from); break;
168 default: assert(false); break;
172 // Direct non-capture checks
173 mlist = generate_direct_checks<PAWN>(pos, mlist, us, dc, ksq);
174 mlist = generate_direct_checks<KNIGHT>(pos, mlist, us, dc, ksq);
175 mlist = generate_direct_checks<BISHOP>(pos, mlist, us, dc, ksq);
176 mlist = generate_direct_checks<ROOK>(pos, mlist, us, dc, ksq);
177 return generate_direct_checks<QUEEN>(pos, mlist, us, dc, ksq);
181 /// generate_evasions() generates all pseudo-legal check evasions when
182 /// the side to move is in check. Returns a pointer to the end of the move list.
184 MoveStack* generate_evasions(const Position& pos, MoveStack* mlist) {
187 assert(pos.is_check());
190 Square from, checksq;
192 Color us = pos.side_to_move();
193 Square ksq = pos.king_square(us);
194 Bitboard checkers = pos.checkers();
195 Bitboard sliderAttacks = EmptyBoardBB;
197 assert(pos.piece_on(ksq) == piece_of_color_and_type(us, KING));
200 // Find squares attacked by slider checkers, we will remove
201 // them from the king evasions set so to early skip known
202 // illegal moves and avoid an useless legality check later.
207 checksq = pop_1st_bit(&b);
209 assert(pos.color_of_piece_on(checksq) == opposite_color(us));
211 switch (pos.type_of_piece_on(checksq))
213 case BISHOP: sliderAttacks |= BishopPseudoAttacks[checksq]; break;
214 case ROOK: sliderAttacks |= RookPseudoAttacks[checksq]; break;
216 // In case of a queen remove also squares attacked in the other direction to
217 // avoid possible illegal moves when queen and king are on adjacent squares.
218 if (direction_is_straight(checksq, ksq))
219 sliderAttacks |= RookPseudoAttacks[checksq] | pos.attacks_from<BISHOP>(checksq);
221 sliderAttacks |= BishopPseudoAttacks[checksq] | pos.attacks_from<ROOK>(checksq);
227 // Generate evasions for king, capture and non capture moves
228 b = pos.attacks_from<KING>(ksq) & ~pos.pieces_of_color(us) & ~sliderAttacks;
232 // Generate evasions for other pieces only if not double check
236 // Find squares where a blocking evasion or a capture of the
237 // checker piece is possible.
238 Bitboard target = squares_between(checksq, ksq) | checkers;
240 mlist = generate_piece_moves<PAWN, EVASION>(pos, mlist, us, target);
241 mlist = generate_piece_moves<KNIGHT>(pos, mlist, us, target);
242 mlist = generate_piece_moves<BISHOP>(pos, mlist, us, target);
243 mlist = generate_piece_moves<ROOK>(pos, mlist, us, target);
244 return generate_piece_moves<QUEEN>(pos, mlist, us, target);
248 /// generate_moves() computes a complete list of legal or pseudo-legal moves in
249 /// the current position. This function is not very fast, and should be used
250 /// only in non time-critical paths.
252 MoveStack* generate_moves(const Position& pos, MoveStack* mlist, bool pseudoLegal) {
257 Bitboard pinned = pos.pinned_pieces(pos.side_to_move());
259 // Generate pseudo-legal moves
261 last = generate_evasions(pos, mlist);
263 last = generate_captures(pos, mlist);
264 last = generate_noncaptures(pos, last);
269 // Remove illegal moves from the list
270 for (MoveStack* cur = mlist; cur != last; cur++)
271 if (!pos.pl_move_is_legal(cur->move, pinned))
273 cur->move = (--last)->move;
280 /// move_is_legal() takes a position and a (not necessarily pseudo-legal)
281 /// move and tests whether the move is legal. This version is not very fast
282 /// and should be used only in non time-critical paths.
284 bool move_is_legal(const Position& pos, const Move m) {
286 MoveStack mlist[256];
287 MoveStack* last = generate_moves(pos, mlist, true);
288 for (MoveStack* cur = mlist; cur != last; cur++)
290 return pos.pl_move_is_legal(m, pos.pinned_pieces(pos.side_to_move()));
296 /// Fast version of move_is_legal() that takes a position a move and a
297 /// bitboard of pinned pieces as input, and tests whether the move is legal.
298 /// This version must only be used when the side to move is not in check.
300 bool move_is_legal(const Position& pos, const Move m, Bitboard pinned) {
303 assert(!pos.is_check());
304 assert(move_is_ok(m));
305 assert(pinned == pos.pinned_pieces(pos.side_to_move()));
307 // Use a slower but simpler function for uncommon cases
308 if (move_is_ep(m) || move_is_castle(m))
309 return move_is_legal(pos, m);
311 Color us = pos.side_to_move();
312 Color them = opposite_color(us);
313 Square from = move_from(m);
314 Square to = move_to(m);
315 Piece pc = pos.piece_on(from);
317 // If the from square is not occupied by a piece belonging to the side to
318 // move, the move is obviously not legal.
319 if (color_of_piece(pc) != us)
322 // The destination square cannot be occupied by a friendly piece
323 if (pos.color_of_piece_on(to) == us)
326 // Handle the special case of a pawn move
327 if (type_of_piece(pc) == PAWN)
329 // Move direction must be compatible with pawn color
330 int direction = to - from;
331 if ((us == WHITE) != (direction > 0))
334 // A pawn move is a promotion iff the destination square is
335 // on the 8/1th rank.
336 if (( (square_rank(to) == RANK_8 && us == WHITE)
337 ||(square_rank(to) == RANK_1 && us != WHITE)) != bool(move_is_promotion(m)))
340 // Proceed according to the square delta between the origin and
341 // destination squares.
348 // Capture. The destination square must be occupied by an enemy
349 // piece (en passant captures was handled earlier).
350 if (pos.color_of_piece_on(to) != them)
356 // Pawn push. The destination square must be empty.
357 if (!pos.square_is_empty(to))
362 // Double white pawn push. The destination square must be on the fourth
363 // rank, and both the destination square and the square between the
364 // source and destination squares must be empty.
365 if ( square_rank(to) != RANK_4
366 || !pos.square_is_empty(to)
367 || !pos.square_is_empty(from + DELTA_N))
372 // Double black pawn push. The destination square must be on the fifth
373 // rank, and both the destination square and the square between the
374 // source and destination squares must be empty.
375 if ( square_rank(to) != RANK_5
376 || !pos.square_is_empty(to)
377 || !pos.square_is_empty(from + DELTA_S))
384 // The move is pseudo-legal, check if it is also legal
385 return pos.pl_move_is_legal(m, pinned);
388 // Luckly we can handle all the other pieces in one go
389 return ( bit_is_set(pos.attacks_from(pc, from), to)
390 && pos.pl_move_is_legal(m, pinned)
391 && !move_is_promotion(m));
397 template<PieceType Piece>
398 MoveStack* generate_piece_moves(const Position& pos, MoveStack* mlist, Color us, Bitboard target) {
402 const Square* ptr = pos.piece_list_begin(us, Piece);
404 while ((from = *ptr++) != SQ_NONE)
406 b = pos.attacks_from<Piece>(from) & target;
413 MoveStack* generate_piece_moves<KING>(const Position& pos, MoveStack* mlist, Color us, Bitboard target) {
416 Square from = pos.king_square(us);
418 b = pos.attacks_from<KING>(from) & target;
423 template<Color Us, SquareDelta Direction>
424 inline Bitboard move_pawns(Bitboard p) {
426 if (Direction == DELTA_N)
427 return Us == WHITE ? p << 8 : p >> 8;
428 else if (Direction == DELTA_NE)
429 return Us == WHITE ? p << 9 : p >> 7;
430 else if (Direction == DELTA_NW)
431 return Us == WHITE ? p << 7 : p >> 9;
436 template<Color Us, MoveType Type, SquareDelta Diagonal>
437 inline MoveStack* generate_pawn_captures(MoveStack* mlist, Bitboard pawns, Bitboard enemyPieces, bool possiblePromotion) {
439 // Calculate our parametrized parameters at compile time
440 const Bitboard TRank8BB = (Us == WHITE ? Rank8BB : Rank1BB);
441 const Bitboard TFileABB = (Diagonal == DELTA_NE ? FileABB : FileHBB);
442 const SquareDelta TDELTA_NE = (Us == WHITE ? DELTA_NE : DELTA_SE);
443 const SquareDelta TDELTA_NW = (Us == WHITE ? DELTA_NW : DELTA_SW);
444 const SquareDelta TTDELTA_NE = (Diagonal == DELTA_NE ? TDELTA_NE : TDELTA_NW);
448 // Captures in the a1-h8 (a8-h1 for black) diagonal or in the h1-a8 (h8-a1 for black)
449 Bitboard b1 = move_pawns<Us, Diagonal>(pawns) & ~TFileABB & enemyPieces;
451 // Capturing promotions and under-promotions
452 if (possiblePromotion)
454 Bitboard b2 = b1 & TRank8BB;
458 to = pop_1st_bit(&b2);
460 if (Type == CAPTURE || Type == EVASION)
461 (*mlist++).move = make_promotion_move(to - TTDELTA_NE, to, QUEEN);
463 if (Type == NON_CAPTURE || Type == EVASION)
465 (*mlist++).move = make_promotion_move(to - TTDELTA_NE, to, ROOK);
466 (*mlist++).move = make_promotion_move(to - TTDELTA_NE, to, BISHOP);
467 (*mlist++).move = make_promotion_move(to - TTDELTA_NE, to, KNIGHT);
470 // This is the only possible under promotion that can give a check
471 // not already included in the queen-promotion. It is not sure that
472 // the promoted knight will give check, but it doesn't worth to verify.
474 (*mlist++).move = make_promotion_move(to - TTDELTA_NE, to, KNIGHT);
478 // Serialize standard captures
479 if (Type == CAPTURE || Type == EVASION)
480 SERIALIZE_MOVES_D(b1, -TTDELTA_NE);
485 template<Color Us, MoveType Type>
486 MoveStack* generate_pawn_moves(const Position& pos, MoveStack* mlist, Bitboard target, Square ksq) {
488 // Calculate our parametrized parameters at compile time
489 const Color Them = (Us == WHITE ? BLACK : WHITE);
490 const Bitboard TRank8BB = (Us == WHITE ? Rank8BB : Rank1BB);
491 const Bitboard TRank7BB = (Us == WHITE ? Rank7BB : Rank2BB);
492 const Bitboard TRank3BB = (Us == WHITE ? Rank3BB : Rank6BB);
493 const SquareDelta TDELTA_N = (Us == WHITE ? DELTA_N : DELTA_S);
496 Bitboard b1, b2, enemyPieces, emptySquares;
497 Bitboard pawns = pos.pieces(PAWN, Us);
498 bool possiblePromotion = pawns & TRank7BB;
500 // Standard captures and capturing promotions and underpromotions
501 if (Type == CAPTURE || Type == EVASION || possiblePromotion)
503 enemyPieces = (Type == CAPTURE ? target : pos.pieces_of_color(opposite_color(Us)));
506 enemyPieces &= target; // Capture only the checker piece
508 mlist = generate_pawn_captures<Us, Type, DELTA_NE>(mlist, pawns, enemyPieces, possiblePromotion);
509 mlist = generate_pawn_captures<Us, Type, DELTA_NW>(mlist, pawns, enemyPieces, possiblePromotion);
512 // Non-capturing promotions and underpromotions
513 if (possiblePromotion)
515 b1 = move_pawns<Us, DELTA_N>(pawns) & TRank8BB & pos.empty_squares();
518 b1 &= target; // Only blocking promotion pushes
522 to = pop_1st_bit(&b1);
524 if (Type == CAPTURE || Type == EVASION)
525 (*mlist++).move = make_promotion_move(to - TDELTA_N, to, QUEEN);
527 if (Type == NON_CAPTURE || Type == EVASION)
529 (*mlist++).move = make_promotion_move(to - TDELTA_N, to, ROOK);
530 (*mlist++).move = make_promotion_move(to - TDELTA_N, to, BISHOP);
531 (*mlist++).move = make_promotion_move(to - TDELTA_N, to, KNIGHT);
534 // This is the only possible under promotion that can give a check
535 // not already included in the queen-promotion.
536 if (Type == CHECK && bit_is_set(pos.attacks_from<KNIGHT>(to), pos.king_square(Them)))
537 (*mlist++).move = make_promotion_move(to - TDELTA_N, to, KNIGHT);
541 // Standard pawn pushes and double pushes
544 emptySquares = (Type == NON_CAPTURE ? target : pos.empty_squares());
546 // Single and double pawn pushes
547 b1 = move_pawns<Us, DELTA_N>(pawns) & emptySquares & ~TRank8BB;
548 b2 = move_pawns<Us, DELTA_N>(b1 & TRank3BB) & emptySquares;
550 // Filter out unwanted pushes according to the move type
556 else if (Type == CHECK)
558 // Pawn moves which give direct cheks
559 b1 &= pos.attacks_from<PAWN>(ksq, Them);
560 b2 &= pos.attacks_from<PAWN>(ksq, Them);
562 // Pawn moves which gives discovered check. This is possible only if
563 // the pawn is not on the same file as the enemy king, because we
564 // don't generate captures.
565 if (pawns & target) // For CHECK type target is dc bitboard
567 Bitboard dc1 = move_pawns<Us, DELTA_N>(pawns & target & ~file_bb(ksq)) & emptySquares & ~TRank8BB;
568 Bitboard dc2 = move_pawns<Us, DELTA_N>(dc1 & TRank3BB) & emptySquares;
574 SERIALIZE_MOVES_D(b1, -TDELTA_N);
575 SERIALIZE_MOVES_D(b2, -TDELTA_N -TDELTA_N);
578 // En passant captures
579 if ((Type == CAPTURE || Type == EVASION) && pos.ep_square() != SQ_NONE)
581 assert(Us != WHITE || square_rank(pos.ep_square()) == RANK_6);
582 assert(Us != BLACK || square_rank(pos.ep_square()) == RANK_3);
584 // An en passant capture can be an evasion only if the checking piece
585 // is the double pushed pawn and so is in the target. Otherwise this
586 // is a discovery check and we are forced to do otherwise.
587 if (Type == EVASION && !bit_is_set(target, pos.ep_square() - TDELTA_N))
590 b1 = pawns & pos.attacks_from<PAWN>(pos.ep_square(), Them);
592 assert(b1 != EmptyBoardBB);
596 to = pop_1st_bit(&b1);
597 (*mlist++).move = make_ep_move(to, pos.ep_square());
603 template<PieceType Piece>
604 MoveStack* generate_discovered_checks(const Position& pos, MoveStack* mlist, Square from) {
606 assert(Piece != QUEEN);
608 Bitboard b = pos.attacks_from<Piece>(from) & pos.empty_squares();
611 Square ksq = pos.king_square(opposite_color(pos.side_to_move()));
612 b &= ~QueenPseudoAttacks[ksq];
618 template<PieceType Piece>
619 MoveStack* generate_direct_checks(const Position& pos, MoveStack* mlist, Color us,
620 Bitboard dc, Square ksq) {
621 assert(Piece != KING);
625 const Square* ptr = pos.piece_list_begin(us, Piece);
627 if ((from = *ptr++) == SQ_NONE)
630 checkSqs = pos.attacks_from<Piece>(ksq) & pos.empty_squares();
634 if ( (Piece == QUEEN && !(QueenPseudoAttacks[from] & checkSqs))
635 || (Piece == ROOK && !(RookPseudoAttacks[from] & checkSqs))
636 || (Piece == BISHOP && !(BishopPseudoAttacks[from] & checkSqs)))
639 if (dc && bit_is_set(dc, from))
642 Bitboard bb = pos.attacks_from<Piece>(from) & checkSqs;
645 } while ((from = *ptr++) != SQ_NONE);
650 template<CastlingSide Side>
651 MoveStack* generate_castle_moves(const Position& pos, MoveStack* mlist) {
653 Color us = pos.side_to_move();
655 if ( (Side == KING_SIDE && pos.can_castle_kingside(us))
656 ||(Side == QUEEN_SIDE && pos.can_castle_queenside(us)))
658 Color them = opposite_color(us);
659 Square ksq = pos.king_square(us);
661 assert(pos.piece_on(ksq) == piece_of_color_and_type(us, KING));
663 Square rsq = (Side == KING_SIDE ? pos.initial_kr_square(us) : pos.initial_qr_square(us));
664 Square s1 = relative_square(us, Side == KING_SIDE ? SQ_G1 : SQ_C1);
665 Square s2 = relative_square(us, Side == KING_SIDE ? SQ_F1 : SQ_D1);
667 bool illegal = false;
669 assert(pos.piece_on(rsq) == piece_of_color_and_type(us, ROOK));
671 // It is a bit complicated to correctly handle Chess960
672 for (s = Min(ksq, s1); s <= Max(ksq, s1); s++)
673 if ( (s != ksq && s != rsq && pos.square_is_occupied(s))
674 ||(pos.attackers_to(s) & pos.pieces_of_color(them)))
677 for (s = Min(rsq, s2); s <= Max(rsq, s2); s++)
678 if (s != ksq && s != rsq && pos.square_is_occupied(s))
681 if ( Side == QUEEN_SIDE
682 && square_file(rsq) == FILE_B
683 && ( pos.piece_on(relative_square(us, SQ_A1)) == piece_of_color_and_type(them, ROOK)
684 || pos.piece_on(relative_square(us, SQ_A1)) == piece_of_color_and_type(them, QUEEN)))
688 (*mlist++).move = make_castle_move(ksq, rsq);