2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2023 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/>.
22 #include <initializer_list>
31 template<GenType Type, Direction D, bool Enemy>
32 ExtMove* make_promotions(ExtMove* moveList, [[maybe_unused]] Square to) {
34 constexpr bool all = Type == EVASIONS || Type == NON_EVASIONS;
36 if constexpr (Type == CAPTURES || all)
37 *moveList++ = make<PROMOTION>(to - D, to, QUEEN);
39 if constexpr ((Type == CAPTURES && Enemy) || (Type == QUIETS && !Enemy) || all)
41 *moveList++ = make<PROMOTION>(to - D, to, ROOK);
42 *moveList++ = make<PROMOTION>(to - D, to, BISHOP);
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 Bitboard emptySquares = ~pos.pieces();
61 const Bitboard enemies = Type == EVASIONS ? pos.checkers() : pos.pieces(Them);
63 Bitboard pawnsOn7 = pos.pieces(Us, PAWN) & TRank7BB;
64 Bitboard pawnsNotOn7 = pos.pieces(Us, PAWN) & ~TRank7BB;
66 // Single and double pawn pushes, no promotions
67 if constexpr (Type != CAPTURES)
69 Bitboard b1 = shift<Up>(pawnsNotOn7) & emptySquares;
70 Bitboard b2 = shift<Up>(b1 & TRank3BB) & emptySquares;
72 if constexpr (Type == EVASIONS) // Consider only blocking squares
78 if constexpr (Type == QUIET_CHECKS)
80 // To make a quiet check, you either make a direct check by pushing a pawn
81 // or push a blocker pawn that is not on the same file as the enemy king.
82 // Discovered check promotion has been already generated amongst the captures.
83 Square ksq = pos.square<KING>(Them);
84 Bitboard dcCandidatePawns = pos.blockers_for_king(Them) & ~file_bb(ksq);
85 b1 &= pawn_attacks_bb(Them, ksq) | shift<Up>(dcCandidatePawns);
86 b2 &= pawn_attacks_bb(Them, ksq) | shift<Up + Up>(dcCandidatePawns);
91 Square to = pop_lsb(b1);
92 *moveList++ = make_move(to - Up, to);
97 Square to = pop_lsb(b2);
98 *moveList++ = make_move(to - Up - Up, to);
102 // Promotions and underpromotions
105 Bitboard b1 = shift<UpRight>(pawnsOn7) & enemies;
106 Bitboard b2 = shift<UpLeft>(pawnsOn7) & enemies;
107 Bitboard b3 = shift<Up>(pawnsOn7) & emptySquares;
109 if constexpr (Type == EVASIONS)
113 moveList = make_promotions<Type, UpRight, true>(moveList, pop_lsb(b1));
116 moveList = make_promotions<Type, UpLeft, true>(moveList, pop_lsb(b2));
119 moveList = make_promotions<Type, Up, false>(moveList, pop_lsb(b3));
122 // Standard and en passant captures
123 if constexpr (Type == CAPTURES || Type == EVASIONS || Type == NON_EVASIONS)
125 Bitboard b1 = shift<UpRight>(pawnsNotOn7) & enemies;
126 Bitboard b2 = shift<UpLeft>(pawnsNotOn7) & enemies;
130 Square to = pop_lsb(b1);
131 *moveList++ = make_move(to - UpRight, to);
136 Square to = pop_lsb(b2);
137 *moveList++ = make_move(to - UpLeft, to);
140 if (pos.ep_square() != SQ_NONE)
142 assert(rank_of(pos.ep_square()) == relative_rank(Us, RANK_6));
144 // An en passant capture cannot resolve a discovered check
145 if (Type == EVASIONS && (target & (pos.ep_square() + Up)))
148 b1 = pawnsNotOn7 & pawn_attacks_bb(Them, pos.ep_square());
153 *moveList++ = make<EN_PASSANT>(pop_lsb(b1), pos.ep_square());
161 template<Color Us, PieceType Pt, bool Checks>
162 ExtMove* generate_moves(const Position& pos, ExtMove* moveList, Bitboard target) {
164 static_assert(Pt != KING && Pt != PAWN, "Unsupported piece type in generate_moves()");
166 Bitboard bb = pos.pieces(Us, Pt);
170 Square from = pop_lsb(bb);
171 Bitboard b = attacks_bb<Pt>(from, pos.pieces()) & target;
173 // To check, you either move freely a blocker or make a direct check.
174 if (Checks && (Pt == QUEEN || !(pos.blockers_for_king(~Us) & from)))
175 b &= pos.check_squares(Pt);
178 *moveList++ = make_move(from, pop_lsb(b));
185 template<Color Us, GenType Type>
186 ExtMove* generate_all(const Position& pos, ExtMove* moveList) {
188 static_assert(Type != LEGAL, "Unsupported type in generate_all()");
190 constexpr bool Checks = Type == QUIET_CHECKS; // Reduce template instantiations
191 const Square ksq = pos.square<KING>(Us);
194 // Skip generating non-king moves when in double check
195 if (Type != EVASIONS || !more_than_one(pos.checkers()))
197 target = Type == EVASIONS ? between_bb(ksq, lsb(pos.checkers()))
198 : Type == NON_EVASIONS ? ~pos.pieces(Us)
199 : Type == CAPTURES ? pos.pieces(~Us)
200 : ~pos.pieces(); // QUIETS || QUIET_CHECKS
202 moveList = generate_pawn_moves<Us, Type>(pos, moveList, target);
203 moveList = generate_moves<Us, KNIGHT, Checks>(pos, moveList, target);
204 moveList = generate_moves<Us, BISHOP, Checks>(pos, moveList, target);
205 moveList = generate_moves<Us, ROOK, Checks>(pos, moveList, target);
206 moveList = generate_moves<Us, QUEEN, Checks>(pos, moveList, target);
209 if (!Checks || pos.blockers_for_king(~Us) & ksq)
211 Bitboard b = attacks_bb<KING>(ksq) & (Type == EVASIONS ? ~pos.pieces(Us) : target);
213 b &= ~attacks_bb<QUEEN>(pos.square<KING>(~Us));
216 *moveList++ = make_move(ksq, pop_lsb(b));
218 if ((Type == QUIETS || Type == NON_EVASIONS) && pos.can_castle(Us & ANY_CASTLING))
219 for (CastlingRights cr : {Us & KING_SIDE, Us & QUEEN_SIDE})
220 if (!pos.castling_impeded(cr) && pos.can_castle(cr))
221 *moveList++ = make<CASTLING>(ksq, pos.castling_rook_square(cr));
230 // <CAPTURES> Generates all pseudo-legal captures plus queen promotions
231 // <QUIETS> Generates all pseudo-legal non-captures and underpromotions
232 // <EVASIONS> Generates all pseudo-legal check evasions
233 // <NON_EVASIONS> Generates all pseudo-legal captures and non-captures
234 // <QUIET_CHECKS> Generates all pseudo-legal non-captures giving check,
235 // except castling and promotions
237 // Returns a pointer to the end of the move list.
238 template<GenType Type>
239 ExtMove* generate(const Position& pos, ExtMove* moveList) {
241 static_assert(Type != LEGAL, "Unsupported type in generate()");
242 assert((Type == EVASIONS) == bool(pos.checkers()));
244 Color us = pos.side_to_move();
246 return us == WHITE ? generate_all<WHITE, Type>(pos, moveList)
247 : generate_all<BLACK, Type>(pos, moveList);
250 // Explicit template instantiations
251 template ExtMove* generate<CAPTURES>(const Position&, ExtMove*);
252 template ExtMove* generate<QUIETS>(const Position&, ExtMove*);
253 template ExtMove* generate<EVASIONS>(const Position&, ExtMove*);
254 template ExtMove* generate<QUIET_CHECKS>(const Position&, ExtMove*);
255 template ExtMove* generate<NON_EVASIONS>(const Position&, ExtMove*);
258 // generate<LEGAL> generates all the legal moves in the given position
261 ExtMove* generate<LEGAL>(const Position& pos, ExtMove* moveList) {
263 Color us = pos.side_to_move();
264 Bitboard pinned = pos.blockers_for_king(us) & pos.pieces(us);
265 Square ksq = pos.square<KING>(us);
266 ExtMove* cur = moveList;
269 pos.checkers() ? generate<EVASIONS>(pos, moveList) : generate<NON_EVASIONS>(pos, moveList);
270 while (cur != moveList)
271 if (((pinned & from_sq(*cur)) || from_sq(*cur) == ksq || type_of(*cur) == EN_PASSANT)
273 *cur = (--moveList)->move;
280 } // namespace Stockfish