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
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.
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.
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/>.
28 template<GenType Type, Direction D>
29 ExtMove* make_promotions(ExtMove* moveList, Square to, Square ksq) {
31 if (Type == CAPTURES || Type == EVASIONS || Type == NON_EVASIONS)
32 *moveList++ = make<PROMOTION>(to - D, to, QUEEN);
34 if (Type == QUIETS || Type == EVASIONS || Type == NON_EVASIONS)
36 *moveList++ = make<PROMOTION>(to - D, to, ROOK);
37 *moveList++ = make<PROMOTION>(to - D, to, BISHOP);
38 *moveList++ = make<PROMOTION>(to - D, to, KNIGHT);
41 // Knight promotion is the only promotion that can give a direct check
42 // that's not already included in the queen promotion.
43 if (Type == QUIET_CHECKS && (PseudoAttacks[KNIGHT][to] & ksq))
44 *moveList++ = make<PROMOTION>(to - D, to, KNIGHT);
46 (void)ksq; // Silence a warning under MSVC
52 template<Color Us, GenType Type>
53 ExtMove* generate_pawn_moves(const Position& pos, ExtMove* moveList, Bitboard target) {
55 // Compute some compile time parameters relative to the white side
56 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
57 constexpr Bitboard TRank7BB = (Us == WHITE ? Rank7BB : Rank2BB);
58 constexpr Bitboard TRank3BB = (Us == WHITE ? Rank3BB : Rank6BB);
59 constexpr Direction Up = (Us == WHITE ? NORTH : SOUTH);
60 constexpr Direction UpRight = (Us == WHITE ? NORTH_EAST : SOUTH_WEST);
61 constexpr Direction UpLeft = (Us == WHITE ? NORTH_WEST : SOUTH_EAST);
63 const Square ksq = pos.square<KING>(Them);
64 Bitboard emptySquares;
66 Bitboard pawnsOn7 = pos.pieces(Us, PAWN) & TRank7BB;
67 Bitboard pawnsNotOn7 = pos.pieces(Us, PAWN) & ~TRank7BB;
69 Bitboard enemies = (Type == EVASIONS ? pos.pieces(Them) & target:
70 Type == CAPTURES ? target : pos.pieces(Them));
72 // Single and double pawn pushes, no promotions
75 emptySquares = (Type == QUIETS || Type == QUIET_CHECKS ? target : ~pos.pieces());
77 Bitboard b1 = shift<Up>(pawnsNotOn7) & emptySquares;
78 Bitboard b2 = shift<Up>(b1 & TRank3BB) & emptySquares;
80 if (Type == EVASIONS) // Consider only blocking squares
86 if (Type == QUIET_CHECKS)
88 b1 &= pos.attacks_from<PAWN>(ksq, Them);
89 b2 &= pos.attacks_from<PAWN>(ksq, Them);
91 // Add pawn pushes which give discovered check. This is possible only
92 // if the pawn is not on the same file as the enemy king, because we
93 // don't generate captures. Note that a possible discovery check
94 // promotion has been already generated amongst the captures.
95 Bitboard dcCandidateQuiets = pos.blockers_for_king(Them) & pawnsNotOn7;
96 if (dcCandidateQuiets)
98 Bitboard dc1 = shift<Up>(dcCandidateQuiets) & emptySquares & ~file_bb(ksq);
99 Bitboard dc2 = shift<Up>(dc1 & TRank3BB) & emptySquares;
108 Square to = pop_lsb(&b1);
109 *moveList++ = make_move(to - Up, to);
114 Square to = pop_lsb(&b2);
115 *moveList++ = make_move(to - Up - Up, to);
119 // Promotions and underpromotions
122 if (Type == CAPTURES)
123 emptySquares = ~pos.pieces();
125 if (Type == EVASIONS)
126 emptySquares &= target;
128 Bitboard b1 = shift<UpRight>(pawnsOn7) & enemies;
129 Bitboard b2 = shift<UpLeft >(pawnsOn7) & enemies;
130 Bitboard b3 = shift<Up >(pawnsOn7) & emptySquares;
133 moveList = make_promotions<Type, UpRight>(moveList, pop_lsb(&b1), ksq);
136 moveList = make_promotions<Type, UpLeft >(moveList, pop_lsb(&b2), ksq);
139 moveList = make_promotions<Type, Up >(moveList, pop_lsb(&b3), ksq);
142 // Standard and en-passant captures
143 if (Type == CAPTURES || Type == EVASIONS || Type == NON_EVASIONS)
145 Bitboard b1 = shift<UpRight>(pawnsNotOn7) & enemies;
146 Bitboard b2 = shift<UpLeft >(pawnsNotOn7) & enemies;
150 Square to = pop_lsb(&b1);
151 *moveList++ = make_move(to - UpRight, to);
156 Square to = pop_lsb(&b2);
157 *moveList++ = make_move(to - UpLeft, to);
160 if (pos.ep_square() != SQ_NONE)
162 assert(rank_of(pos.ep_square()) == relative_rank(Us, RANK_6));
164 // An en passant capture can be an evasion only if the checking piece
165 // is the double pushed pawn and so is in the target. Otherwise this
166 // is a discovery check and we are forced to do otherwise.
167 if (Type == EVASIONS && !(target & (pos.ep_square() - Up)))
170 b1 = pawnsNotOn7 & pos.attacks_from<PAWN>(pos.ep_square(), Them);
175 *moveList++ = make<ENPASSANT>(pop_lsb(&b1), pos.ep_square());
183 template<PieceType Pt, bool Checks>
184 ExtMove* generate_moves(const Position& pos, ExtMove* moveList, Color us,
187 static_assert(Pt != KING && Pt != PAWN, "Unsupported piece type in generate_moves()");
189 const Square* pl = pos.squares<Pt>(us);
191 for (Square from = *pl; from != SQ_NONE; from = *++pl)
195 if ( (Pt == BISHOP || Pt == ROOK || Pt == QUEEN)
196 && !(PseudoAttacks[Pt][from] & target & pos.check_squares(Pt)))
199 if (pos.blockers_for_king(~us) & from)
203 Bitboard b = pos.attacks_from<Pt>(from) & target;
206 b &= pos.check_squares(Pt);
209 *moveList++ = make_move(from, pop_lsb(&b));
216 template<Color Us, GenType Type>
217 ExtMove* generate_all(const Position& pos, ExtMove* moveList, Bitboard target) {
219 constexpr CastlingRights OO = Us & KING_SIDE;
220 constexpr CastlingRights OOO = Us & QUEEN_SIDE;
221 constexpr bool Checks = Type == QUIET_CHECKS; // Reduce template instantations
223 moveList = generate_pawn_moves<Us, Type>(pos, moveList, target);
224 moveList = generate_moves<KNIGHT, Checks>(pos, moveList, Us, target);
225 moveList = generate_moves<BISHOP, Checks>(pos, moveList, Us, target);
226 moveList = generate_moves< ROOK, Checks>(pos, moveList, Us, target);
227 moveList = generate_moves< QUEEN, Checks>(pos, moveList, Us, target);
229 if (Type != QUIET_CHECKS && Type != EVASIONS)
231 Square ksq = pos.square<KING>(Us);
232 Bitboard b = pos.attacks_from<KING>(ksq) & target;
234 *moveList++ = make_move(ksq, pop_lsb(&b));
236 if (Type != CAPTURES && pos.can_castle(CastlingRights(OO | OOO)))
238 if (!pos.castling_impeded(OO) && pos.can_castle(OO))
239 *moveList++ = make<CASTLING>(ksq, pos.castling_rook_square(OO));
241 if (!pos.castling_impeded(OOO) && pos.can_castle(OOO))
242 *moveList++ = make<CASTLING>(ksq, pos.castling_rook_square(OOO));
252 /// <CAPTURES> Generates all pseudo-legal captures and queen promotions
253 /// <QUIETS> Generates all pseudo-legal non-captures and underpromotions
254 /// <NON_EVASIONS> Generates all pseudo-legal captures and non-captures
256 /// Returns a pointer to the end of the move list.
258 template<GenType Type>
259 ExtMove* generate(const Position& pos, ExtMove* moveList) {
261 static_assert(Type == CAPTURES || Type == QUIETS || Type == NON_EVASIONS, "Unsupported type in generate()");
262 assert(!pos.checkers());
264 Color us = pos.side_to_move();
266 Bitboard target = Type == CAPTURES ? pos.pieces(~us)
267 : Type == QUIETS ? ~pos.pieces()
268 : Type == NON_EVASIONS ? ~pos.pieces(us) : 0;
270 return us == WHITE ? generate_all<WHITE, Type>(pos, moveList, target)
271 : generate_all<BLACK, Type>(pos, moveList, target);
274 // Explicit template instantiations
275 template ExtMove* generate<CAPTURES>(const Position&, ExtMove*);
276 template ExtMove* generate<QUIETS>(const Position&, ExtMove*);
277 template ExtMove* generate<NON_EVASIONS>(const Position&, ExtMove*);
280 /// generate<QUIET_CHECKS> generates all pseudo-legal non-captures and knight
281 /// underpromotions that give check. Returns a pointer to the end of the move list.
283 ExtMove* generate<QUIET_CHECKS>(const Position& pos, ExtMove* moveList) {
285 assert(!pos.checkers());
287 Color us = pos.side_to_move();
288 Bitboard dc = pos.blockers_for_king(~us) & pos.pieces(us);
292 Square from = pop_lsb(&dc);
293 PieceType pt = type_of(pos.piece_on(from));
296 continue; // Will be generated together with direct checks
298 Bitboard b = pos.attacks_from(pt, from) & ~pos.pieces();
301 b &= ~PseudoAttacks[QUEEN][pos.square<KING>(~us)];
304 *moveList++ = make_move(from, pop_lsb(&b));
307 return us == WHITE ? generate_all<WHITE, QUIET_CHECKS>(pos, moveList, ~pos.pieces())
308 : generate_all<BLACK, QUIET_CHECKS>(pos, moveList, ~pos.pieces());
312 /// generate<EVASIONS> generates all pseudo-legal check evasions when the side
313 /// to move is in check. Returns a pointer to the end of the move list.
315 ExtMove* generate<EVASIONS>(const Position& pos, ExtMove* moveList) {
317 assert(pos.checkers());
319 Color us = pos.side_to_move();
320 Square ksq = pos.square<KING>(us);
321 Bitboard sliderAttacks = 0;
322 Bitboard sliders = pos.checkers() & ~pos.pieces(KNIGHT, PAWN);
324 // Find all the squares attacked by slider checkers. We will remove them from
325 // the king evasions in order to skip known illegal moves, which avoids any
326 // useless legality checks later on.
329 Square checksq = pop_lsb(&sliders);
330 sliderAttacks |= LineBB[checksq][ksq] ^ checksq;
333 // Generate evasions for king, capture and non capture moves
334 Bitboard b = pos.attacks_from<KING>(ksq) & ~pos.pieces(us) & ~sliderAttacks;
336 *moveList++ = make_move(ksq, pop_lsb(&b));
338 if (more_than_one(pos.checkers()))
339 return moveList; // Double check, only a king move can save the day
341 // Generate blocking evasions or captures of the checking piece
342 Square checksq = lsb(pos.checkers());
343 Bitboard target = between_bb(checksq, ksq) | checksq;
345 return us == WHITE ? generate_all<WHITE, EVASIONS>(pos, moveList, target)
346 : generate_all<BLACK, EVASIONS>(pos, moveList, target);
350 /// generate<LEGAL> generates all the legal moves in the given position
353 ExtMove* generate<LEGAL>(const Position& pos, ExtMove* moveList) {
355 Color us = pos.side_to_move();
356 Bitboard pinned = pos.blockers_for_king(us) & pos.pieces(us);
357 Square ksq = pos.square<KING>(us);
358 ExtMove* cur = moveList;
360 moveList = pos.checkers() ? generate<EVASIONS >(pos, moveList)
361 : generate<NON_EVASIONS>(pos, moveList);
362 while (cur != moveList)
363 if ( (pinned || from_sq(*cur) == ksq || type_of(*cur) == ENPASSANT)
365 *cur = (--moveList)->move;