2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2020 The Stockfish developers (see AUTHORS file)
5 Stockfish is free software: you can redistribute it and/or modify
6 it under the terms of the GNU General Public License as published by
7 the Free Software Foundation, either version 3 of the License, or
8 (at your option) any later version.
10 Stockfish is distributed in the hope that it will be useful,
11 but WITHOUT ANY WARRANTY; without even the implied warranty of
12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
13 GNU General Public License for more details.
15 You should have received a copy of the GNU General Public License
16 along with this program. If not, see <http://www.gnu.org/licenses/>.
26 template<GenType Type, Direction D>
27 ExtMove* make_promotions(ExtMove* moveList, Square to, Square ksq) {
29 if (Type == CAPTURES || Type == EVASIONS || Type == NON_EVASIONS)
31 *moveList++ = make<PROMOTION>(to - D, to, QUEEN);
32 if (attacks_bb<KNIGHT>(to) & ksq)
33 *moveList++ = make<PROMOTION>(to - D, to, KNIGHT);
36 if (Type == QUIETS || Type == EVASIONS || Type == NON_EVASIONS)
38 *moveList++ = make<PROMOTION>(to - D, to, ROOK);
39 *moveList++ = make<PROMOTION>(to - D, to, BISHOP);
40 if (!(attacks_bb<KNIGHT>(to) & ksq))
41 *moveList++ = make<PROMOTION>(to - D, to, KNIGHT);
48 template<Color Us, GenType Type>
49 ExtMove* generate_pawn_moves(const Position& pos, ExtMove* moveList, Bitboard target) {
51 constexpr Color Them = ~Us;
52 constexpr Bitboard TRank7BB = (Us == WHITE ? Rank7BB : Rank2BB);
53 constexpr Bitboard TRank3BB = (Us == WHITE ? Rank3BB : Rank6BB);
54 constexpr Direction Up = pawn_push(Us);
55 constexpr Direction UpRight = (Us == WHITE ? NORTH_EAST : SOUTH_WEST);
56 constexpr Direction UpLeft = (Us == WHITE ? NORTH_WEST : SOUTH_EAST);
58 const Square ksq = pos.square<KING>(Them);
59 Bitboard emptySquares;
61 Bitboard pawnsOn7 = pos.pieces(Us, PAWN) & TRank7BB;
62 Bitboard pawnsNotOn7 = pos.pieces(Us, PAWN) & ~TRank7BB;
64 Bitboard enemies = (Type == EVASIONS ? pos.pieces(Them) & target:
65 Type == CAPTURES ? target : pos.pieces(Them));
67 // Single and double pawn pushes, no promotions
70 emptySquares = (Type == QUIETS || Type == QUIET_CHECKS ? target : ~pos.pieces());
72 Bitboard b1 = shift<Up>(pawnsNotOn7) & emptySquares;
73 Bitboard b2 = shift<Up>(b1 & TRank3BB) & emptySquares;
75 if (Type == EVASIONS) // Consider only blocking squares
81 if (Type == QUIET_CHECKS)
83 b1 &= pawn_attacks_bb(Them, ksq);
84 b2 &= pawn_attacks_bb(Them, ksq);
86 // Add pawn pushes which give discovered check. This is possible only
87 // if the pawn is not on the same file as the enemy king, because we
88 // don't generate captures. Note that a possible discovery check
89 // promotion has been already generated amongst the captures.
90 Bitboard dcCandidateQuiets = pos.blockers_for_king(Them) & pawnsNotOn7;
91 if (dcCandidateQuiets)
93 Bitboard dc1 = shift<Up>(dcCandidateQuiets) & emptySquares & ~file_bb(ksq);
94 Bitboard dc2 = shift<Up>(dc1 & TRank3BB) & emptySquares;
103 Square to = pop_lsb(&b1);
104 *moveList++ = make_move(to - Up, to);
109 Square to = pop_lsb(&b2);
110 *moveList++ = make_move(to - Up - Up, to);
114 // Promotions and underpromotions
117 if (Type == CAPTURES)
118 emptySquares = ~pos.pieces();
120 if (Type == EVASIONS)
121 emptySquares &= target;
123 Bitboard b1 = shift<UpRight>(pawnsOn7) & enemies;
124 Bitboard b2 = shift<UpLeft >(pawnsOn7) & enemies;
125 Bitboard b3 = shift<Up >(pawnsOn7) & emptySquares;
128 moveList = make_promotions<Type, UpRight>(moveList, pop_lsb(&b1), ksq);
131 moveList = make_promotions<Type, UpLeft >(moveList, pop_lsb(&b2), ksq);
134 moveList = make_promotions<Type, Up >(moveList, pop_lsb(&b3), ksq);
137 // Standard and en-passant captures
138 if (Type == CAPTURES || Type == EVASIONS || Type == NON_EVASIONS)
140 Bitboard b1 = shift<UpRight>(pawnsNotOn7) & enemies;
141 Bitboard b2 = shift<UpLeft >(pawnsNotOn7) & enemies;
145 Square to = pop_lsb(&b1);
146 *moveList++ = make_move(to - UpRight, to);
151 Square to = pop_lsb(&b2);
152 *moveList++ = make_move(to - UpLeft, to);
155 if (pos.ep_square() != SQ_NONE)
157 assert(rank_of(pos.ep_square()) == relative_rank(Us, RANK_6));
159 // An en passant capture can be an evasion only if the checking piece
160 // is the double pushed pawn and so is in the target. Otherwise this
161 // is a discovery check and we are forced to do otherwise.
162 if (Type == EVASIONS && !(target & (pos.ep_square() - Up)))
165 b1 = pawnsNotOn7 & pawn_attacks_bb(Them, pos.ep_square());
170 *moveList++ = make<ENPASSANT>(pop_lsb(&b1), pos.ep_square());
178 template<Color Us, PieceType Pt, bool Checks>
179 ExtMove* generate_moves(const Position& pos, ExtMove* moveList, Bitboard target) {
181 static_assert(Pt != KING && Pt != PAWN, "Unsupported piece type in generate_moves()");
183 const Square* pl = pos.squares<Pt>(Us);
185 for (Square from = *pl; from != SQ_NONE; from = *++pl)
189 if ( (Pt == BISHOP || Pt == ROOK || Pt == QUEEN)
190 && !(attacks_bb<Pt>(from) & target & pos.check_squares(Pt)))
193 if (pos.blockers_for_king(~Us) & from)
197 Bitboard b = attacks_bb<Pt>(from, pos.pieces()) & target;
200 b &= pos.check_squares(Pt);
203 *moveList++ = make_move(from, pop_lsb(&b));
210 template<Color Us, GenType Type>
211 ExtMove* generate_all(const Position& pos, ExtMove* moveList) {
212 constexpr bool Checks = Type == QUIET_CHECKS; // Reduce template instantations
218 target = pos.pieces(~Us);
222 target = ~pos.pieces();
226 Square checksq = lsb(pos.checkers());
227 target = between_bb(pos.square<KING>(Us), checksq) | checksq;
231 target = ~pos.pieces(Us);
234 static_assert(true, "Unsupported type in generate_all()");
237 moveList = generate_pawn_moves<Us, Type>(pos, moveList, target);
238 moveList = generate_moves<Us, KNIGHT, Checks>(pos, moveList, target);
239 moveList = generate_moves<Us, BISHOP, Checks>(pos, moveList, target);
240 moveList = generate_moves<Us, ROOK, Checks>(pos, moveList, target);
241 moveList = generate_moves<Us, QUEEN, Checks>(pos, moveList, target);
243 if (Type != QUIET_CHECKS && Type != EVASIONS)
245 Square ksq = pos.square<KING>(Us);
246 Bitboard b = attacks_bb<KING>(ksq) & target;
248 *moveList++ = make_move(ksq, pop_lsb(&b));
250 if ((Type != CAPTURES) && pos.can_castle(Us & ANY_CASTLING))
251 for (CastlingRights cr : { Us & KING_SIDE, Us & QUEEN_SIDE } )
252 if (!pos.castling_impeded(cr) && pos.can_castle(cr))
253 *moveList++ = make<CASTLING>(ksq, pos.castling_rook_square(cr));
262 /// <CAPTURES> Generates all pseudo-legal captures plus queen and checking knight promotions
263 /// <QUIETS> Generates all pseudo-legal non-captures and underpromotions(except checking knight)
264 /// <NON_EVASIONS> Generates all pseudo-legal captures and non-captures
266 /// Returns a pointer to the end of the move list.
268 template<GenType Type>
269 ExtMove* generate(const Position& pos, ExtMove* moveList) {
271 static_assert(Type == CAPTURES || Type == QUIETS || Type == NON_EVASIONS, "Unsupported type in generate()");
272 assert(!pos.checkers());
274 Color us = pos.side_to_move();
276 return us == WHITE ? generate_all<WHITE, Type>(pos, moveList)
277 : generate_all<BLACK, Type>(pos, moveList);
280 // Explicit template instantiations
281 template ExtMove* generate<CAPTURES>(const Position&, ExtMove*);
282 template ExtMove* generate<QUIETS>(const Position&, ExtMove*);
283 template ExtMove* generate<NON_EVASIONS>(const Position&, ExtMove*);
286 /// generate<QUIET_CHECKS> generates all pseudo-legal non-captures.
287 /// Returns a pointer to the end of the move list.
289 ExtMove* generate<QUIET_CHECKS>(const Position& pos, ExtMove* moveList) {
291 assert(!pos.checkers());
293 Color us = pos.side_to_move();
294 Bitboard dc = pos.blockers_for_king(~us) & pos.pieces(us) & ~pos.pieces(PAWN);
298 Square from = pop_lsb(&dc);
299 PieceType pt = type_of(pos.piece_on(from));
301 Bitboard b = attacks_bb(pt, from, pos.pieces()) & ~pos.pieces();
304 b &= ~attacks_bb<QUEEN>(pos.square<KING>(~us));
307 *moveList++ = make_move(from, pop_lsb(&b));
310 return us == WHITE ? generate_all<WHITE, QUIET_CHECKS>(pos, moveList)
311 : generate_all<BLACK, QUIET_CHECKS>(pos, moveList);
315 /// generate<EVASIONS> generates all pseudo-legal check evasions when the side
316 /// to move is in check. Returns a pointer to the end of the move list.
318 ExtMove* generate<EVASIONS>(const Position& pos, ExtMove* moveList) {
320 assert(pos.checkers());
322 Color us = pos.side_to_move();
323 Square ksq = pos.square<KING>(us);
324 Bitboard sliderAttacks = 0;
325 Bitboard sliders = pos.checkers() & ~pos.pieces(KNIGHT, PAWN);
327 // Find all the squares attacked by slider checkers. We will remove them from
328 // the king evasions in order to skip known illegal moves, which avoids any
329 // useless legality checks later on.
331 sliderAttacks |= line_bb(ksq, pop_lsb(&sliders)) & ~pos.checkers();
333 // Generate evasions for king, capture and non capture moves
334 Bitboard b = attacks_bb<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 return us == WHITE ? generate_all<WHITE, EVASIONS>(pos, moveList)
343 : generate_all<BLACK, EVASIONS>(pos, moveList);
347 /// generate<LEGAL> generates all the legal moves in the given position
350 ExtMove* generate<LEGAL>(const Position& pos, ExtMove* moveList) {
352 Color us = pos.side_to_move();
353 Bitboard pinned = pos.blockers_for_king(us) & pos.pieces(us);
354 Square ksq = pos.square<KING>(us);
355 ExtMove* cur = moveList;
357 moveList = pos.checkers() ? generate<EVASIONS >(pos, moveList)
358 : generate<NON_EVASIONS>(pos, moveList);
359 while (cur != moveList)
360 if ( (pinned || from_sq(*cur) == ksq || type_of(*cur) == ENPASSANT)
362 *cur = (--moveList)->move;