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>
29 ExtMove* make_promotions(ExtMove* moveList, [[maybe_unused]] Square to) {
31 if constexpr (Type == CAPTURES || Type == EVASIONS || Type == NON_EVASIONS)
32 *moveList++ = make<PROMOTION>(to - D, to, QUEEN);
34 if constexpr (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);
45 template<Color Us, GenType Type>
46 ExtMove* generate_pawn_moves(const Position& pos, ExtMove* moveList, Bitboard target) {
48 constexpr Color Them = ~Us;
49 constexpr Bitboard TRank7BB = (Us == WHITE ? Rank7BB : Rank2BB);
50 constexpr Bitboard TRank3BB = (Us == WHITE ? Rank3BB : Rank6BB);
51 constexpr Direction Up = pawn_push(Us);
52 constexpr Direction UpRight = (Us == WHITE ? NORTH_EAST : SOUTH_WEST);
53 constexpr Direction UpLeft = (Us == WHITE ? NORTH_WEST : SOUTH_EAST);
55 const Bitboard emptySquares = ~pos.pieces();
56 const Bitboard enemies = Type == EVASIONS ? pos.checkers()
59 Bitboard pawnsOn7 = pos.pieces(Us, PAWN) & TRank7BB;
60 Bitboard pawnsNotOn7 = pos.pieces(Us, PAWN) & ~TRank7BB;
62 // Single and double pawn pushes, no promotions
63 if constexpr (Type != CAPTURES)
65 Bitboard b1 = shift<Up>(pawnsNotOn7) & emptySquares;
66 Bitboard b2 = shift<Up>(b1 & TRank3BB) & emptySquares;
68 if constexpr (Type == EVASIONS) // Consider only blocking squares
74 if constexpr (Type == QUIET_CHECKS)
76 // To make a quiet check, you either make a direct check by pushing a pawn
77 // or push a blocker pawn that is not on the same file as the enemy king.
78 // Discovered check promotion has been already generated amongst the captures.
79 Square ksq = pos.square<KING>(Them);
80 Bitboard dcCandidatePawns = pos.blockers_for_king(Them) & ~file_bb(ksq);
81 b1 &= pawn_attacks_bb(Them, ksq) | shift< Up>(dcCandidatePawns);
82 b2 &= pawn_attacks_bb(Them, ksq) | shift<Up+Up>(dcCandidatePawns);
87 Square to = pop_lsb(b1);
88 *moveList++ = make_move(to - Up, to);
93 Square to = pop_lsb(b2);
94 *moveList++ = make_move(to - Up - Up, to);
98 // Promotions and underpromotions
101 Bitboard b1 = shift<UpRight>(pawnsOn7) & enemies;
102 Bitboard b2 = shift<UpLeft >(pawnsOn7) & enemies;
103 Bitboard b3 = shift<Up >(pawnsOn7) & emptySquares;
105 if constexpr (Type == EVASIONS)
109 moveList = make_promotions<Type, UpRight>(moveList, pop_lsb(b1));
112 moveList = make_promotions<Type, UpLeft >(moveList, pop_lsb(b2));
115 moveList = make_promotions<Type, Up >(moveList, pop_lsb(b3));
118 // Standard and en passant captures
119 if constexpr (Type == CAPTURES || Type == EVASIONS || Type == NON_EVASIONS)
121 Bitboard b1 = shift<UpRight>(pawnsNotOn7) & enemies;
122 Bitboard b2 = shift<UpLeft >(pawnsNotOn7) & enemies;
126 Square to = pop_lsb(b1);
127 *moveList++ = make_move(to - UpRight, to);
132 Square to = pop_lsb(b2);
133 *moveList++ = make_move(to - UpLeft, to);
136 if (pos.ep_square() != SQ_NONE)
138 assert(rank_of(pos.ep_square()) == relative_rank(Us, RANK_6));
140 // An en passant capture cannot resolve a discovered check
141 if (Type == EVASIONS && (target & (pos.ep_square() + Up)))
144 b1 = pawnsNotOn7 & pawn_attacks_bb(Them, pos.ep_square());
149 *moveList++ = make<EN_PASSANT>(pop_lsb(b1), pos.ep_square());
157 template<Color Us, PieceType Pt, bool Checks>
158 ExtMove* generate_moves(const Position& pos, ExtMove* moveList, Bitboard target) {
160 static_assert(Pt != KING && Pt != PAWN, "Unsupported piece type in generate_moves()");
162 Bitboard bb = pos.pieces(Us, Pt);
166 Square from = pop_lsb(bb);
167 Bitboard b = attacks_bb<Pt>(from, pos.pieces()) & target;
169 // To check, you either move freely a blocker or make a direct check.
170 if (Checks && (Pt == QUEEN || !(pos.blockers_for_king(~Us) & from)))
171 b &= pos.check_squares(Pt);
174 *moveList++ = make_move(from, pop_lsb(b));
181 template<Color Us, GenType Type>
182 ExtMove* generate_all(const Position& pos, ExtMove* moveList) {
184 static_assert(Type != LEGAL, "Unsupported type in generate_all()");
186 constexpr bool Checks = Type == QUIET_CHECKS; // Reduce template instantiations
187 const Square ksq = pos.square<KING>(Us);
190 // Skip generating non-king moves when in double check
191 if (Type != EVASIONS || !more_than_one(pos.checkers()))
193 target = Type == EVASIONS ? between_bb(ksq, lsb(pos.checkers()))
194 : Type == NON_EVASIONS ? ~pos.pieces( Us)
195 : Type == CAPTURES ? pos.pieces(~Us)
196 : ~pos.pieces( ); // QUIETS || QUIET_CHECKS
198 moveList = generate_pawn_moves<Us, Type>(pos, moveList, target);
199 moveList = generate_moves<Us, KNIGHT, Checks>(pos, moveList, target);
200 moveList = generate_moves<Us, BISHOP, Checks>(pos, moveList, target);
201 moveList = generate_moves<Us, ROOK, Checks>(pos, moveList, target);
202 moveList = generate_moves<Us, QUEEN, Checks>(pos, moveList, target);
205 if (!Checks || pos.blockers_for_king(~Us) & ksq)
207 Bitboard b = attacks_bb<KING>(ksq) & (Type == EVASIONS ? ~pos.pieces(Us) : target);
209 b &= ~attacks_bb<QUEEN>(pos.square<KING>(~Us));
212 *moveList++ = make_move(ksq, pop_lsb(b));
214 if ((Type == QUIETS || Type == NON_EVASIONS) && pos.can_castle(Us & ANY_CASTLING))
215 for (CastlingRights cr : { Us & KING_SIDE, Us & QUEEN_SIDE } )
216 if (!pos.castling_impeded(cr) && pos.can_castle(cr))
217 *moveList++ = make<CASTLING>(ksq, pos.castling_rook_square(cr));
226 /// <CAPTURES> Generates all pseudo-legal captures plus queen promotions
227 /// <QUIETS> Generates all pseudo-legal non-captures and underpromotions
228 /// <EVASIONS> Generates all pseudo-legal check evasions when the side to move is in check
229 /// <QUIET_CHECKS> Generates all pseudo-legal non-captures giving check, except castling and promotions
230 /// <NON_EVASIONS> Generates all pseudo-legal captures and non-captures
232 /// Returns a pointer to the end of the move list.
234 template<GenType Type>
235 ExtMove* generate(const Position& pos, ExtMove* moveList) {
237 static_assert(Type != LEGAL, "Unsupported type in generate()");
238 assert((Type == EVASIONS) == (bool)pos.checkers());
240 Color us = pos.side_to_move();
242 return us == WHITE ? generate_all<WHITE, Type>(pos, moveList)
243 : generate_all<BLACK, Type>(pos, moveList);
246 // Explicit template instantiations
247 template ExtMove* generate<CAPTURES>(const Position&, ExtMove*);
248 template ExtMove* generate<QUIETS>(const Position&, ExtMove*);
249 template ExtMove* generate<EVASIONS>(const Position&, ExtMove*);
250 template ExtMove* generate<QUIET_CHECKS>(const Position&, ExtMove*);
251 template ExtMove* generate<NON_EVASIONS>(const Position&, ExtMove*);
254 /// generate<LEGAL> generates all the legal moves in the given position
257 ExtMove* generate<LEGAL>(const Position& pos, ExtMove* moveList) {
259 Color us = pos.side_to_move();
260 Bitboard pinned = pos.blockers_for_king(us) & pos.pieces(us);
261 Square ksq = pos.square<KING>(us);
262 ExtMove* cur = moveList;
264 moveList = pos.checkers() ? generate<EVASIONS >(pos, moveList)
265 : generate<NON_EVASIONS>(pos, moveList);
266 while (cur != moveList)
267 if ( ((pinned & from_sq(*cur)) || from_sq(*cur) == ksq || type_of(*cur) == EN_PASSANT)
269 *cur = (--moveList)->move;
276 } // namespace Stockfish