2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
4 Copyright (C) 2008-2010 Marco Costalba, Joona Kiiski, Tord Romstad
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&, MoveStack*, Square);
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());
153 Color us = pos.side_to_move();
154 Square ksq = pos.king_square(opposite_color(us));
156 assert(pos.piece_on(ksq) == piece_of_color_and_type(opposite_color(us), KING));
158 // Discovered non-capture checks
159 b = dc = pos.discovered_check_candidates(us);
163 from = pop_1st_bit(&b);
164 switch (pos.type_of_piece_on(from))
166 case PAWN: /* Will be generated togheter with pawns direct checks */ break;
167 case KNIGHT: mlist = generate_discovered_checks<KNIGHT>(pos, mlist, from); break;
168 case BISHOP: mlist = generate_discovered_checks<BISHOP>(pos, mlist, from); break;
169 case ROOK: mlist = generate_discovered_checks<ROOK>(pos, mlist, from); break;
170 case KING: mlist = generate_discovered_checks<KING>(pos, mlist, from); break;
171 default: assert(false); break;
175 // Direct non-capture checks
176 mlist = generate_direct_checks<PAWN>(pos, mlist, us, dc, ksq);
177 mlist = generate_direct_checks<KNIGHT>(pos, mlist, us, dc, ksq);
178 mlist = generate_direct_checks<BISHOP>(pos, mlist, us, dc, ksq);
179 mlist = generate_direct_checks<ROOK>(pos, mlist, us, dc, ksq);
180 return generate_direct_checks<QUEEN>(pos, mlist, us, dc, ksq);
184 /// generate_evasions() generates all pseudo-legal check evasions when
185 /// the side to move is in check. Returns a pointer to the end of the move list.
187 MoveStack* generate_evasions(const Position& pos, MoveStack* mlist) {
190 assert(pos.is_check());
193 Square from, checksq;
195 Color us = pos.side_to_move();
196 Square ksq = pos.king_square(us);
197 Bitboard checkers = pos.checkers();
198 Bitboard sliderAttacks = EmptyBoardBB;
200 assert(pos.piece_on(ksq) == piece_of_color_and_type(us, KING));
203 // Find squares attacked by slider checkers, we will remove
204 // them from the king evasions set so to early skip known
205 // illegal moves and avoid an useless legality check later.
210 checksq = pop_1st_bit(&b);
212 assert(pos.color_of_piece_on(checksq) == opposite_color(us));
214 switch (pos.type_of_piece_on(checksq))
216 case BISHOP: sliderAttacks |= BishopPseudoAttacks[checksq]; break;
217 case ROOK: sliderAttacks |= RookPseudoAttacks[checksq]; break;
219 // In case of a queen remove also squares attacked in the other direction to
220 // avoid possible illegal moves when queen and king are on adjacent squares.
221 if (direction_is_straight(checksq, ksq))
222 sliderAttacks |= RookPseudoAttacks[checksq] | pos.attacks_from<BISHOP>(checksq);
224 sliderAttacks |= BishopPseudoAttacks[checksq] | pos.attacks_from<ROOK>(checksq);
230 // Generate evasions for king, capture and non capture moves
231 b = pos.attacks_from<KING>(ksq) & ~pos.pieces_of_color(us) & ~sliderAttacks;
235 // Generate evasions for other pieces only if not double check
239 // Find squares where a blocking evasion or a capture of the
240 // checker piece is possible.
241 target = squares_between(checksq, ksq) | checkers;
243 mlist = generate_piece_moves<PAWN, EVASION>(pos, mlist, us, target);
244 mlist = generate_piece_moves<KNIGHT>(pos, mlist, us, target);
245 mlist = generate_piece_moves<BISHOP>(pos, mlist, us, target);
246 mlist = generate_piece_moves<ROOK>(pos, mlist, us, target);
247 return generate_piece_moves<QUEEN>(pos, mlist, us, target);
251 /// generate_moves() computes a complete list of legal or pseudo-legal moves in
252 /// the current position. This function is not very fast, and should be used
253 /// only in non time-critical paths.
255 MoveStack* generate_moves(const Position& pos, MoveStack* mlist, bool pseudoLegal) {
259 MoveStack *last, *cur = mlist;
260 Bitboard pinned = pos.pinned_pieces(pos.side_to_move());
262 // Generate pseudo-legal moves
264 last = generate_evasions(pos, mlist);
266 last = generate_noncaptures(pos, generate_captures(pos, mlist));
271 // Remove illegal moves from the list
273 if (pos.pl_move_is_legal(cur->move, pinned))
276 cur->move = (--last)->move;
282 /// move_is_legal() takes a position and a (not necessarily pseudo-legal)
283 /// move and tests whether the move is legal. This version is not very fast
284 /// and should be used only in non time-critical paths.
286 bool move_is_legal(const Position& pos, const Move m) {
288 MoveStack mlist[256];
289 MoveStack *cur, *last = generate_moves(pos, mlist, true);
291 for (cur = mlist; cur != last; cur++)
293 return pos.pl_move_is_legal(m, pos.pinned_pieces(pos.side_to_move()));
299 /// Fast version of move_is_legal() that takes a position a move and a
300 /// bitboard of pinned pieces as input, and tests whether the move is legal.
302 bool move_is_legal(const Position& pos, const Move m, Bitboard pinned) {
305 assert(move_is_ok(m));
306 assert(pinned == pos.pinned_pieces(pos.side_to_move()));
308 Color us = pos.side_to_move();
309 Color them = opposite_color(us);
310 Square from = move_from(m);
311 Square to = move_to(m);
312 Piece pc = pos.piece_on(from);
314 // Use a slower but simpler function for uncommon cases
315 if (move_is_ep(m) || move_is_castle(m))
316 return move_is_legal(pos, m);
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 // The promotion piece, if any, must be valid
342 if (move_promotion_piece(m) > QUEEN || move_promotion_piece(m) == PAWN)
345 // Proceed according to the square delta between the origin and
346 // destination squares.
353 // Capture. The destination square must be occupied by an enemy
354 // piece (en passant captures was handled earlier).
355 if (pos.color_of_piece_on(to) != them)
361 // Pawn push. The destination square must be empty.
362 if (!pos.square_is_empty(to))
367 // Double white pawn push. The destination square must be on the fourth
368 // rank, and both the destination square and the square between the
369 // source and destination squares must be empty.
370 if ( square_rank(to) != RANK_4
371 || !pos.square_is_empty(to)
372 || !pos.square_is_empty(from + DELTA_N))
377 // Double black pawn push. The destination square must be on the fifth
378 // rank, and both the destination square and the square between the
379 // source and destination squares must be empty.
380 if ( square_rank(to) != RANK_5
381 || !pos.square_is_empty(to)
382 || !pos.square_is_empty(from + DELTA_S))
389 // The move is pseudo-legal, check if it is also legal
390 return pos.is_check() ? pos.pl_move_is_evasion(m, pinned) : pos.pl_move_is_legal(m, pinned);
393 // Luckly we can handle all the other pieces in one go
394 return bit_is_set(pos.attacks_from(pc, from), to)
395 && (pos.is_check() ? pos.pl_move_is_evasion(m, pinned) : pos.pl_move_is_legal(m, pinned))
396 && !move_is_promotion(m);
402 template<PieceType Piece>
403 MoveStack* generate_piece_moves(const Position& pos, MoveStack* mlist, Color us, Bitboard target) {
407 const Square* ptr = pos.piece_list_begin(us, Piece);
409 while ((from = *ptr++) != SQ_NONE)
411 b = pos.attacks_from<Piece>(from) & target;
418 MoveStack* generate_piece_moves<KING>(const Position& pos, MoveStack* mlist, Color us, Bitboard target) {
421 Square from = pos.king_square(us);
423 b = pos.attacks_from<KING>(from) & target;
428 template<Color Us, SquareDelta Direction>
429 inline Bitboard move_pawns(Bitboard p) {
431 if (Direction == DELTA_N)
432 return Us == WHITE ? p << 8 : p >> 8;
433 else if (Direction == DELTA_NE)
434 return Us == WHITE ? p << 9 : p >> 7;
435 else if (Direction == DELTA_NW)
436 return Us == WHITE ? p << 7 : p >> 9;
441 template<Color Us, MoveType Type, SquareDelta Diagonal>
442 inline MoveStack* generate_pawn_captures(MoveStack* mlist, Bitboard pawns, Bitboard enemyPieces) {
444 // Calculate our parametrized parameters at compile time
445 const Bitboard TRank8BB = (Us == WHITE ? Rank8BB : Rank1BB);
446 const Bitboard TFileABB = (Diagonal == DELTA_NE ? FileABB : FileHBB);
447 const SquareDelta TDELTA_NE = (Us == WHITE ? DELTA_NE : DELTA_SE);
448 const SquareDelta TDELTA_NW = (Us == WHITE ? DELTA_NW : DELTA_SW);
449 const SquareDelta TTDELTA_NE = (Diagonal == DELTA_NE ? TDELTA_NE : TDELTA_NW);
454 // Captures in the a1-h8 (a8-h1 for black) diagonal or in the h1-a8 (h8-a1 for black)
455 b1 = move_pawns<Us, Diagonal>(pawns) & ~TFileABB & enemyPieces;
457 // Capturing promotions and under-promotions
464 to = pop_1st_bit(&b2);
466 if (Type == CAPTURE || Type == EVASION)
467 (*mlist++).move = make_promotion_move(to - TTDELTA_NE, to, QUEEN);
469 if (Type == NON_CAPTURE || Type == EVASION)
471 (*mlist++).move = make_promotion_move(to - TTDELTA_NE, to, ROOK);
472 (*mlist++).move = make_promotion_move(to - TTDELTA_NE, to, BISHOP);
473 (*mlist++).move = make_promotion_move(to - TTDELTA_NE, to, KNIGHT);
476 // This is the only possible under promotion that can give a check
477 // not already included in the queen-promotion. It is not sure that
478 // the promoted knight will give check, but it doesn't worth to verify.
480 (*mlist++).move = make_promotion_move(to - TTDELTA_NE, to, KNIGHT);
484 // Serialize standard captures
485 if (Type == CAPTURE || Type == EVASION)
486 SERIALIZE_MOVES_D(b1, -TTDELTA_NE);
491 template<Color Us, MoveType Type>
492 MoveStack* generate_pawn_moves(const Position& pos, MoveStack* mlist, Bitboard target, Square ksq) {
494 // Calculate our parametrized parameters at compile time
495 const Color Them = (Us == WHITE ? BLACK : WHITE);
496 const Bitboard TRank8BB = (Us == WHITE ? Rank8BB : Rank1BB);
497 const Bitboard TRank7BB = (Us == WHITE ? Rank7BB : Rank2BB);
498 const Bitboard TRank3BB = (Us == WHITE ? Rank3BB : Rank6BB);
499 const SquareDelta TDELTA_N = (Us == WHITE ? DELTA_N : DELTA_S);
502 Bitboard b1, b2, enemyPieces, emptySquares;
503 Bitboard pawns = pos.pieces(PAWN, Us);
505 // Standard captures and capturing promotions and underpromotions
506 if (Type == CAPTURE || Type == EVASION || (pawns & TRank7BB))
508 enemyPieces = (Type == CAPTURE ? target : pos.pieces_of_color(opposite_color(Us)));
511 enemyPieces &= target; // Capture only the checker piece
513 mlist = generate_pawn_captures<Us, Type, DELTA_NE>(mlist, pawns, enemyPieces);
514 mlist = generate_pawn_captures<Us, Type, DELTA_NW>(mlist, pawns, enemyPieces);
517 // Non-capturing promotions and underpromotions
518 if (pawns & TRank7BB)
520 b1 = move_pawns<Us, DELTA_N>(pawns) & TRank8BB & pos.empty_squares();
523 b1 &= target; // Only blocking promotion pushes
527 to = pop_1st_bit(&b1);
529 if (Type == CAPTURE || Type == EVASION)
530 (*mlist++).move = make_promotion_move(to - TDELTA_N, to, QUEEN);
532 if (Type == NON_CAPTURE || Type == EVASION)
534 (*mlist++).move = make_promotion_move(to - TDELTA_N, to, ROOK);
535 (*mlist++).move = make_promotion_move(to - TDELTA_N, to, BISHOP);
536 (*mlist++).move = make_promotion_move(to - TDELTA_N, to, KNIGHT);
539 // This is the only possible under promotion that can give a check
540 // not already included in the queen-promotion.
541 if (Type == CHECK && bit_is_set(pos.attacks_from<KNIGHT>(to), pos.king_square(Them)))
542 (*mlist++).move = make_promotion_move(to - TDELTA_N, to, KNIGHT);
546 // Standard pawn pushes and double pushes
549 emptySquares = (Type == NON_CAPTURE ? target : pos.empty_squares());
551 // Single and double pawn pushes
552 b1 = move_pawns<Us, DELTA_N>(pawns) & emptySquares & ~TRank8BB;
553 b2 = move_pawns<Us, DELTA_N>(b1 & TRank3BB) & emptySquares;
555 // Filter out unwanted pushes according to the move type
561 else if (Type == CHECK)
563 // Pawn moves which give direct cheks
564 b1 &= pos.attacks_from<PAWN>(ksq, Them);
565 b2 &= pos.attacks_from<PAWN>(ksq, Them);
567 // Pawn moves which gives discovered check. This is possible only if
568 // the pawn is not on the same file as the enemy king, because we
569 // don't generate captures.
570 if (pawns & target) // For CHECK type target is dc bitboard
572 Bitboard dc1 = move_pawns<Us, DELTA_N>(pawns & target & ~file_bb(ksq)) & emptySquares & ~TRank8BB;
573 Bitboard dc2 = move_pawns<Us, DELTA_N>(dc1 & TRank3BB) & emptySquares;
579 SERIALIZE_MOVES_D(b1, -TDELTA_N);
580 SERIALIZE_MOVES_D(b2, -TDELTA_N -TDELTA_N);
583 // En passant captures
584 if ((Type == CAPTURE || Type == EVASION) && pos.ep_square() != SQ_NONE)
586 assert(Us != WHITE || square_rank(pos.ep_square()) == RANK_6);
587 assert(Us != BLACK || square_rank(pos.ep_square()) == RANK_3);
589 // An en passant capture can be an evasion only if the checking piece
590 // is the double pushed pawn and so is in the target. Otherwise this
591 // is a discovery check and we are forced to do otherwise.
592 if (Type == EVASION && !bit_is_set(target, pos.ep_square() - TDELTA_N))
595 b1 = pawns & pos.attacks_from<PAWN>(pos.ep_square(), Them);
597 assert(b1 != EmptyBoardBB);
601 to = pop_1st_bit(&b1);
602 (*mlist++).move = make_ep_move(to, pos.ep_square());
608 template<PieceType Piece>
609 MoveStack* generate_discovered_checks(const Position& pos, MoveStack* mlist, Square from) {
611 assert(Piece != QUEEN);
613 Bitboard b = pos.attacks_from<Piece>(from) & pos.empty_squares();
616 Square ksq = pos.king_square(opposite_color(pos.side_to_move()));
617 b &= ~QueenPseudoAttacks[ksq];
623 template<PieceType Piece>
624 MoveStack* generate_direct_checks(const Position& pos, MoveStack* mlist, Color us,
625 Bitboard dc, Square ksq) {
626 assert(Piece != KING);
628 Bitboard checkSqs, b;
630 const Square* ptr = pos.piece_list_begin(us, Piece);
632 if ((from = *ptr++) == SQ_NONE)
635 checkSqs = pos.attacks_from<Piece>(ksq) & pos.empty_squares();
639 if ( (Piece == QUEEN && !(QueenPseudoAttacks[from] & checkSqs))
640 || (Piece == ROOK && !(RookPseudoAttacks[from] & checkSqs))
641 || (Piece == BISHOP && !(BishopPseudoAttacks[from] & checkSqs)))
644 if (dc && bit_is_set(dc, from))
647 b = pos.attacks_from<Piece>(from) & checkSqs;
650 } while ((from = *ptr++) != SQ_NONE);
655 template<CastlingSide Side>
656 MoveStack* generate_castle_moves(const Position& pos, MoveStack* mlist) {
658 Color us = pos.side_to_move();
660 if ( (Side == KING_SIDE && pos.can_castle_kingside(us))
661 ||(Side == QUEEN_SIDE && pos.can_castle_queenside(us)))
663 Color them = opposite_color(us);
664 Square ksq = pos.king_square(us);
666 assert(pos.piece_on(ksq) == piece_of_color_and_type(us, KING));
668 Square rsq = (Side == KING_SIDE ? pos.initial_kr_square(us) : pos.initial_qr_square(us));
669 Square s1 = relative_square(us, Side == KING_SIDE ? SQ_G1 : SQ_C1);
670 Square s2 = relative_square(us, Side == KING_SIDE ? SQ_F1 : SQ_D1);
672 bool illegal = false;
674 assert(pos.piece_on(rsq) == piece_of_color_and_type(us, ROOK));
676 // It is a bit complicated to correctly handle Chess960
677 for (s = Min(ksq, s1); s <= Max(ksq, s1); s++)
678 if ( (s != ksq && s != rsq && pos.square_is_occupied(s))
679 ||(pos.attackers_to(s) & pos.pieces_of_color(them)))
682 for (s = Min(rsq, s2); s <= Max(rsq, s2); s++)
683 if (s != ksq && s != rsq && pos.square_is_occupied(s))
686 if ( Side == QUEEN_SIDE
687 && square_file(rsq) == FILE_B
688 && ( pos.piece_on(relative_square(us, SQ_A1)) == piece_of_color_and_type(them, ROOK)
689 || pos.piece_on(relative_square(us, SQ_A1)) == piece_of_color_and_type(them, QUEEN)))
693 (*mlist++).move = make_castle_move(ksq, rsq);