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/>.
28 template<GenType Type, Direction D, bool Enemy>
29 ExtMove* make_promotions(ExtMove* moveList, [[maybe_unused]] Square to) {
31 if constexpr (Type == CAPTURES || Type == EVASIONS || Type == NON_EVASIONS)
33 *moveList++ = make<PROMOTION>(to - D, to, QUEEN);
34 if constexpr (Enemy && Type == CAPTURES)
36 *moveList++ = make<PROMOTION>(to - D, to, ROOK);
37 *moveList++ = make<PROMOTION>(to - D, to, BISHOP);
38 *moveList++ = make<PROMOTION>(to - D, to, KNIGHT);
42 if constexpr ((Type == QUIETS && !Enemy) || Type == EVASIONS || Type == NON_EVASIONS)
44 *moveList++ = make<PROMOTION>(to - D, to, ROOK);
45 *moveList++ = make<PROMOTION>(to - D, to, BISHOP);
46 *moveList++ = make<PROMOTION>(to - D, to, KNIGHT);
53 template<Color Us, GenType Type>
54 ExtMove* generate_pawn_moves(const Position& pos, ExtMove* moveList, Bitboard target) {
56 constexpr Color Them = ~Us;
57 constexpr Bitboard TRank7BB = (Us == WHITE ? Rank7BB : Rank2BB);
58 constexpr Bitboard TRank3BB = (Us == WHITE ? Rank3BB : Rank6BB);
59 constexpr Direction Up = pawn_push(Us);
60 constexpr Direction UpRight = (Us == WHITE ? NORTH_EAST : SOUTH_WEST);
61 constexpr Direction UpLeft = (Us == WHITE ? NORTH_WEST : SOUTH_EAST);
63 const Bitboard emptySquares = ~pos.pieces();
64 const Bitboard enemies = Type == EVASIONS ? pos.checkers()
67 Bitboard pawnsOn7 = pos.pieces(Us, PAWN) & TRank7BB;
68 Bitboard pawnsNotOn7 = pos.pieces(Us, PAWN) & ~TRank7BB;
70 // Single and double pawn pushes, no promotions
71 if constexpr (Type != CAPTURES)
73 Bitboard b1 = shift<Up>(pawnsNotOn7) & emptySquares;
74 Bitboard b2 = shift<Up>(b1 & TRank3BB) & emptySquares;
76 if constexpr (Type == EVASIONS) // Consider only blocking squares
82 if constexpr (Type == QUIET_CHECKS)
84 // To make a quiet check, you either make a direct check by pushing a pawn
85 // or push a blocker pawn that is not on the same file as the enemy king.
86 // Discovered check promotion has been already generated amongst the captures.
87 Square ksq = pos.square<KING>(Them);
88 Bitboard dcCandidatePawns = pos.blockers_for_king(Them) & ~file_bb(ksq);
89 b1 &= pawn_attacks_bb(Them, ksq) | shift< Up>(dcCandidatePawns);
90 b2 &= pawn_attacks_bb(Them, ksq) | shift<Up+Up>(dcCandidatePawns);
95 Square to = pop_lsb(b1);
96 *moveList++ = make_move(to - Up, to);
101 Square to = pop_lsb(b2);
102 *moveList++ = make_move(to - Up - Up, to);
106 // Promotions and underpromotions
109 Bitboard b1 = shift<UpRight>(pawnsOn7) & enemies;
110 Bitboard b2 = shift<UpLeft >(pawnsOn7) & enemies;
111 Bitboard b3 = shift<Up >(pawnsOn7) & emptySquares;
113 if constexpr (Type == EVASIONS)
117 moveList = make_promotions<Type, UpRight, true>(moveList, pop_lsb(b1));
120 moveList = make_promotions<Type, UpLeft, true>(moveList, pop_lsb(b2));
123 moveList = make_promotions<Type, Up, false>(moveList, pop_lsb(b3));
126 // Standard and en passant captures
127 if constexpr (Type == CAPTURES || Type == EVASIONS || Type == NON_EVASIONS)
129 Bitboard b1 = shift<UpRight>(pawnsNotOn7) & enemies;
130 Bitboard b2 = shift<UpLeft >(pawnsNotOn7) & enemies;
134 Square to = pop_lsb(b1);
135 *moveList++ = make_move(to - UpRight, to);
140 Square to = pop_lsb(b2);
141 *moveList++ = make_move(to - UpLeft, to);
144 if (pos.ep_square() != SQ_NONE)
146 assert(rank_of(pos.ep_square()) == relative_rank(Us, RANK_6));
148 // An en passant capture cannot resolve a discovered check
149 if (Type == EVASIONS && (target & (pos.ep_square() + Up)))
152 b1 = pawnsNotOn7 & pawn_attacks_bb(Them, pos.ep_square());
157 *moveList++ = make<EN_PASSANT>(pop_lsb(b1), pos.ep_square());
165 template<Color Us, PieceType Pt, bool Checks>
166 ExtMove* generate_moves(const Position& pos, ExtMove* moveList, Bitboard target) {
168 static_assert(Pt != KING && Pt != PAWN, "Unsupported piece type in generate_moves()");
170 Bitboard bb = pos.pieces(Us, Pt);
174 Square from = pop_lsb(bb);
175 Bitboard b = attacks_bb<Pt>(from, pos.pieces()) & target;
177 // To check, you either move freely a blocker or make a direct check.
178 if (Checks && (Pt == QUEEN || !(pos.blockers_for_king(~Us) & from)))
179 b &= pos.check_squares(Pt);
182 *moveList++ = make_move(from, pop_lsb(b));
189 template<Color Us, GenType Type>
190 ExtMove* generate_all(const Position& pos, ExtMove* moveList) {
192 static_assert(Type != LEGAL, "Unsupported type in generate_all()");
194 constexpr bool Checks = Type == QUIET_CHECKS; // Reduce template instantiations
195 const Square ksq = pos.square<KING>(Us);
198 // Skip generating non-king moves when in double check
199 if (Type != EVASIONS || !more_than_one(pos.checkers()))
201 target = Type == EVASIONS ? between_bb(ksq, lsb(pos.checkers()))
202 : Type == NON_EVASIONS ? ~pos.pieces( Us)
203 : Type == CAPTURES ? pos.pieces(~Us)
204 : ~pos.pieces( ); // QUIETS || QUIET_CHECKS
206 moveList = generate_pawn_moves<Us, Type>(pos, moveList, target);
207 moveList = generate_moves<Us, KNIGHT, Checks>(pos, moveList, target);
208 moveList = generate_moves<Us, BISHOP, Checks>(pos, moveList, target);
209 moveList = generate_moves<Us, ROOK, Checks>(pos, moveList, target);
210 moveList = generate_moves<Us, QUEEN, Checks>(pos, moveList, target);
213 if (!Checks || pos.blockers_for_king(~Us) & ksq)
215 Bitboard b = attacks_bb<KING>(ksq) & (Type == EVASIONS ? ~pos.pieces(Us) : target);
217 b &= ~attacks_bb<QUEEN>(pos.square<KING>(~Us));
220 *moveList++ = make_move(ksq, pop_lsb(b));
222 if ((Type == QUIETS || Type == NON_EVASIONS) && pos.can_castle(Us & ANY_CASTLING))
223 for (CastlingRights cr : { Us & KING_SIDE, Us & QUEEN_SIDE } )
224 if (!pos.castling_impeded(cr) && pos.can_castle(cr))
225 *moveList++ = make<CASTLING>(ksq, pos.castling_rook_square(cr));
234 /// <CAPTURES> Generates all pseudo-legal captures plus queen promotions
235 /// <QUIETS> Generates all pseudo-legal non-captures and underpromotions
236 /// <EVASIONS> Generates all pseudo-legal check evasions when the side to move is in check
237 /// <QUIET_CHECKS> Generates all pseudo-legal non-captures giving check, except castling and promotions
238 /// <NON_EVASIONS> Generates all pseudo-legal captures and non-captures
240 /// Returns a pointer to the end of the move list.
242 template<GenType Type>
243 ExtMove* generate(const Position& pos, ExtMove* moveList) {
245 static_assert(Type != LEGAL, "Unsupported type in generate()");
246 assert((Type == EVASIONS) == (bool)pos.checkers());
248 Color us = pos.side_to_move();
250 return us == WHITE ? generate_all<WHITE, Type>(pos, moveList)
251 : generate_all<BLACK, Type>(pos, moveList);
254 // Explicit template instantiations
255 template ExtMove* generate<CAPTURES>(const Position&, ExtMove*);
256 template ExtMove* generate<QUIETS>(const Position&, ExtMove*);
257 template ExtMove* generate<EVASIONS>(const Position&, ExtMove*);
258 template ExtMove* generate<QUIET_CHECKS>(const Position&, ExtMove*);
259 template ExtMove* generate<NON_EVASIONS>(const Position&, ExtMove*);
262 /// generate<LEGAL> generates all the legal moves in the given position
265 ExtMove* generate<LEGAL>(const Position& pos, ExtMove* moveList) {
267 Color us = pos.side_to_move();
268 Bitboard pinned = pos.blockers_for_king(us) & pos.pieces(us);
269 Square ksq = pos.square<KING>(us);
270 ExtMove* cur = moveList;
272 moveList = pos.checkers() ? generate<EVASIONS >(pos, moveList)
273 : generate<NON_EVASIONS>(pos, moveList);
274 while (cur != moveList)
275 if ( ((pinned & from_sq(*cur)) || from_sq(*cur) == ksq || type_of(*cur) == EN_PASSANT)
277 *cur = (--moveList)->move;
284 } // namespace Stockfish