2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2021 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/>.
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)
33 *moveList++ = make<PROMOTION>(to - D, to, QUEEN);
34 if (attacks_bb<KNIGHT>(to) & ksq)
35 *moveList++ = make<PROMOTION>(to - D, to, KNIGHT);
38 if (Type == QUIETS || Type == EVASIONS || Type == NON_EVASIONS)
40 *moveList++ = make<PROMOTION>(to - D, to, ROOK);
41 *moveList++ = make<PROMOTION>(to - D, to, BISHOP);
42 if (!(attacks_bb<KNIGHT>(to) & ksq))
43 *moveList++ = make<PROMOTION>(to - D, to, KNIGHT);
50 template<Color Us, GenType Type>
51 ExtMove* generate_pawn_moves(const Position& pos, ExtMove* moveList, Bitboard target) {
53 constexpr Color Them = ~Us;
54 constexpr Bitboard TRank7BB = (Us == WHITE ? Rank7BB : Rank2BB);
55 constexpr Bitboard TRank3BB = (Us == WHITE ? Rank3BB : Rank6BB);
56 constexpr Direction Up = pawn_push(Us);
57 constexpr Direction UpRight = (Us == WHITE ? NORTH_EAST : SOUTH_WEST);
58 constexpr Direction UpLeft = (Us == WHITE ? NORTH_WEST : SOUTH_EAST);
60 const Square ksq = pos.square<KING>(Them);
61 Bitboard emptySquares;
63 Bitboard pawnsOn7 = pos.pieces(Us, PAWN) & TRank7BB;
64 Bitboard pawnsNotOn7 = pos.pieces(Us, PAWN) & ~TRank7BB;
66 Bitboard enemies = (Type == EVASIONS ? pos.pieces(Them) & target:
67 Type == CAPTURES ? target : pos.pieces(Them));
69 // Single and double pawn pushes, no promotions
72 emptySquares = (Type == QUIETS || Type == QUIET_CHECKS ? target : ~pos.pieces());
74 Bitboard b1 = shift<Up>(pawnsNotOn7) & emptySquares;
75 Bitboard b2 = shift<Up>(b1 & TRank3BB) & emptySquares;
77 if (Type == EVASIONS) // Consider only blocking squares
83 if (Type == QUIET_CHECKS)
85 b1 &= pawn_attacks_bb(Them, ksq);
86 b2 &= pawn_attacks_bb(Them, ksq);
88 // Add pawn pushes which give discovered check. This is possible only
89 // if the pawn is not on the same file as the enemy king, because we
90 // don't generate captures. Note that a possible discovered check
91 // promotion has been already generated amongst the captures.
92 Bitboard dcCandidateQuiets = pos.blockers_for_king(Them) & pawnsNotOn7;
93 if (dcCandidateQuiets)
95 Bitboard dc1 = shift<Up>(dcCandidateQuiets) & emptySquares & ~file_bb(ksq);
96 Bitboard dc2 = shift<Up>(dc1 & TRank3BB) & emptySquares;
105 Square to = pop_lsb(&b1);
106 *moveList++ = make_move(to - Up, to);
111 Square to = pop_lsb(&b2);
112 *moveList++ = make_move(to - Up - Up, to);
116 // Promotions and underpromotions
119 if (Type == CAPTURES)
120 emptySquares = ~pos.pieces();
122 if (Type == EVASIONS)
123 emptySquares &= target;
125 Bitboard b1 = shift<UpRight>(pawnsOn7) & enemies;
126 Bitboard b2 = shift<UpLeft >(pawnsOn7) & enemies;
127 Bitboard b3 = shift<Up >(pawnsOn7) & emptySquares;
130 moveList = make_promotions<Type, UpRight>(moveList, pop_lsb(&b1), ksq);
133 moveList = make_promotions<Type, UpLeft >(moveList, pop_lsb(&b2), ksq);
136 moveList = make_promotions<Type, Up >(moveList, pop_lsb(&b3), ksq);
139 // Standard and en passant captures
140 if (Type == CAPTURES || Type == EVASIONS || Type == NON_EVASIONS)
142 Bitboard b1 = shift<UpRight>(pawnsNotOn7) & enemies;
143 Bitboard b2 = shift<UpLeft >(pawnsNotOn7) & enemies;
147 Square to = pop_lsb(&b1);
148 *moveList++ = make_move(to - UpRight, to);
153 Square to = pop_lsb(&b2);
154 *moveList++ = make_move(to - UpLeft, to);
157 if (pos.ep_square() != SQ_NONE)
159 assert(rank_of(pos.ep_square()) == relative_rank(Us, RANK_6));
161 // An en passant capture cannot resolve a discovered check.
162 if (Type == EVASIONS && (target & (pos.ep_square() + Up)))
165 b1 = pawnsNotOn7 & pawn_attacks_bb(Them, pos.ep_square());
170 *moveList++ = make<EN_PASSANT>(pop_lsb(&b1), pos.ep_square());
178 template<PieceType Pt, bool Checks>
179 ExtMove* generate_moves(const Position& pos, ExtMove* moveList, Bitboard piecesToMove, Bitboard target) {
181 static_assert(Pt != KING && Pt != PAWN, "Unsupported piece type in generate_moves()");
183 Bitboard bb = piecesToMove & pos.pieces(Pt);
188 [[maybe_unused]] const Bitboard checkSquares = pos.check_squares(Pt);
191 Square from = pop_lsb(&bb);
193 Bitboard b = attacks_bb<Pt>(from, pos.pieces()) & target;
194 if constexpr (Checks)
198 *moveList++ = make_move(from, pop_lsb(&b));
205 template<Color Us, GenType Type>
206 ExtMove* generate_all(const Position& pos, ExtMove* moveList) {
208 static_assert(Type != LEGAL, "Unsupported type in generate_all()");
210 constexpr bool Checks = Type == QUIET_CHECKS; // Reduce template instantiations
211 Bitboard target, piecesToMove = pos.pieces(Us);
213 if(Type == QUIET_CHECKS)
214 piecesToMove &= ~pos.blockers_for_king(~Us);
219 target = pos.pieces(~Us);
223 target = ~pos.pieces();
227 Square checksq = lsb(pos.checkers());
228 target = between_bb(pos.square<KING>(Us), checksq) | checksq;
232 target = ~pos.pieces(Us);
236 moveList = generate_pawn_moves<Us, Type>(pos, moveList, target);
237 moveList = generate_moves<KNIGHT, Checks>(pos, moveList, piecesToMove, target);
238 moveList = generate_moves<BISHOP, Checks>(pos, moveList, piecesToMove, target);
239 moveList = generate_moves< ROOK, Checks>(pos, moveList, piecesToMove, target);
240 moveList = generate_moves< QUEEN, Checks>(pos, moveList, piecesToMove, target);
242 if (Type != QUIET_CHECKS && Type != EVASIONS)
244 Square ksq = pos.square<KING>(Us);
245 Bitboard b = attacks_bb<KING>(ksq) & target;
247 *moveList++ = make_move(ksq, pop_lsb(&b));
249 if ((Type != CAPTURES) && pos.can_castle(Us & ANY_CASTLING))
250 for (CastlingRights cr : { Us & KING_SIDE, Us & QUEEN_SIDE } )
251 if (!pos.castling_impeded(cr) && pos.can_castle(cr))
252 *moveList++ = make<CASTLING>(ksq, pos.castling_rook_square(cr));
261 /// <CAPTURES> Generates all pseudo-legal captures plus queen and checking knight promotions
262 /// <QUIETS> Generates all pseudo-legal non-captures and underpromotions (except checking knight)
263 /// <NON_EVASIONS> Generates all pseudo-legal captures and non-captures
265 /// Returns a pointer to the end of the move list.
267 template<GenType Type>
268 ExtMove* generate(const Position& pos, ExtMove* moveList) {
270 static_assert(Type == CAPTURES || Type == QUIETS || Type == NON_EVASIONS, "Unsupported type in generate()");
271 assert(!pos.checkers());
273 Color us = pos.side_to_move();
275 return us == WHITE ? generate_all<WHITE, Type>(pos, moveList)
276 : generate_all<BLACK, Type>(pos, moveList);
279 // Explicit template instantiations
280 template ExtMove* generate<CAPTURES>(const Position&, ExtMove*);
281 template ExtMove* generate<QUIETS>(const Position&, ExtMove*);
282 template ExtMove* generate<NON_EVASIONS>(const Position&, ExtMove*);
285 /// generate<QUIET_CHECKS> generates all pseudo-legal non-captures giving check,
286 /// except castling. Returns a pointer to the end of the move list.
288 ExtMove* generate<QUIET_CHECKS>(const Position& pos, ExtMove* moveList) {
290 assert(!pos.checkers());
292 Color us = pos.side_to_move();
293 Bitboard dc = pos.blockers_for_king(~us) & pos.pieces(us) & ~pos.pieces(PAWN);
297 Square from = pop_lsb(&dc);
298 PieceType pt = type_of(pos.piece_on(from));
300 Bitboard b = attacks_bb(pt, from, pos.pieces()) & ~pos.pieces();
303 b &= ~attacks_bb<QUEEN>(pos.square<KING>(~us));
306 *moveList++ = make_move(from, pop_lsb(&b));
309 return us == WHITE ? generate_all<WHITE, QUIET_CHECKS>(pos, moveList)
310 : generate_all<BLACK, QUIET_CHECKS>(pos, moveList);
314 /// generate<EVASIONS> generates all pseudo-legal check evasions when the side
315 /// to move is in check. Returns a pointer to the end of the move list.
317 ExtMove* generate<EVASIONS>(const Position& pos, ExtMove* moveList) {
319 assert(pos.checkers());
321 Color us = pos.side_to_move();
322 Square ksq = pos.square<KING>(us);
323 Bitboard sliderAttacks = 0;
324 Bitboard sliders = pos.checkers() & ~pos.pieces(KNIGHT, PAWN);
326 // Find all the squares attacked by slider checkers. We will remove them from
327 // the king evasions in order to skip known illegal moves, which avoids any
328 // useless legality checks later on.
330 sliderAttacks |= line_bb(ksq, pop_lsb(&sliders)) & ~pos.checkers();
332 // Generate evasions for king, capture and non capture moves
333 Bitboard b = attacks_bb<KING>(ksq) & ~pos.pieces(us) & ~sliderAttacks;
335 *moveList++ = make_move(ksq, pop_lsb(&b));
337 if (more_than_one(pos.checkers()))
338 return moveList; // Double check, only a king move can save the day
340 // Generate blocking evasions or captures of the checking piece
341 return us == WHITE ? generate_all<WHITE, EVASIONS>(pos, moveList)
342 : generate_all<BLACK, EVASIONS>(pos, moveList);
346 /// generate<LEGAL> generates all the legal moves in the given position
349 ExtMove* generate<LEGAL>(const Position& pos, ExtMove* moveList) {
351 Color us = pos.side_to_move();
352 Bitboard pinned = pos.blockers_for_king(us) & pos.pieces(us);
353 Square ksq = pos.square<KING>(us);
354 ExtMove* cur = moveList;
356 moveList = pos.checkers() ? generate<EVASIONS >(pos, moveList)
357 : generate<NON_EVASIONS>(pos, moveList);
358 while (cur != moveList)
359 if ( ((pinned && pinned & from_sq(*cur)) || from_sq(*cur) == ksq || type_of(*cur) == EN_PASSANT)
361 *cur = (--moveList)->move;
368 } // namespace Stockfish