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 const Bitboard emptySquares = Type == QUIETS || Type == QUIET_CHECKS ? target : ~pos.pieces();
62 const Bitboard enemies = Type == EVASIONS ? pos.checkers()
63 : Type == CAPTURES ? target : pos.pieces(Them);
65 Bitboard pawnsOn7 = pos.pieces(Us, PAWN) & TRank7BB;
66 Bitboard pawnsNotOn7 = pos.pieces(Us, PAWN) & ~TRank7BB;
68 // Single and double pawn pushes, no promotions
71 Bitboard b1 = shift<Up>(pawnsNotOn7) & emptySquares;
72 Bitboard b2 = shift<Up>(b1 & TRank3BB) & emptySquares;
74 if (Type == EVASIONS) // Consider only blocking squares
80 if (Type == QUIET_CHECKS)
82 // To make a quiet check, you either make a direct check by pushing a pawn
83 // or push a blocker pawn that is not on the same file as the enemy king.
84 // Discovered check promotion has been already generated amongst the captures.
85 Bitboard dcCandidatePawns = pos.blockers_for_king(Them) & ~file_bb(ksq);
86 b1 &= pawn_attacks_bb(Them, ksq) | shift< Up>(dcCandidatePawns);
87 b2 &= pawn_attacks_bb(Them, ksq) | shift<Up+Up>(dcCandidatePawns);
92 Square to = pop_lsb(b1);
93 *moveList++ = make_move(to - Up, to);
98 Square to = pop_lsb(b2);
99 *moveList++ = make_move(to - Up - Up, to);
103 // Promotions and underpromotions
106 Bitboard b1 = shift<UpRight>(pawnsOn7) & enemies;
107 Bitboard b2 = shift<UpLeft >(pawnsOn7) & enemies;
108 Bitboard b3 = shift<Up >(pawnsOn7) & emptySquares;
110 if (Type == EVASIONS)
114 moveList = make_promotions<Type, UpRight>(moveList, pop_lsb(b1), ksq);
117 moveList = make_promotions<Type, UpLeft >(moveList, pop_lsb(b2), ksq);
120 moveList = make_promotions<Type, Up >(moveList, pop_lsb(b3), ksq);
123 // Standard and en passant captures
124 if (Type == CAPTURES || Type == EVASIONS || Type == NON_EVASIONS)
126 Bitboard b1 = shift<UpRight>(pawnsNotOn7) & enemies;
127 Bitboard b2 = shift<UpLeft >(pawnsNotOn7) & enemies;
131 Square to = pop_lsb(b1);
132 *moveList++ = make_move(to - UpRight, to);
137 Square to = pop_lsb(b2);
138 *moveList++ = make_move(to - UpLeft, to);
141 if (pos.ep_square() != SQ_NONE)
143 assert(rank_of(pos.ep_square()) == relative_rank(Us, RANK_6));
145 // An en passant capture cannot resolve a discovered check
146 if (Type == EVASIONS && (target & (pos.ep_square() + Up)))
149 b1 = pawnsNotOn7 & pawn_attacks_bb(Them, pos.ep_square());
154 *moveList++ = make<EN_PASSANT>(pop_lsb(b1), pos.ep_square());
162 template<Color Us, PieceType Pt, bool Checks>
163 ExtMove* generate_moves(const Position& pos, ExtMove* moveList, Bitboard target) {
165 static_assert(Pt != KING && Pt != PAWN, "Unsupported piece type in generate_moves()");
167 Bitboard bb = pos.pieces(Us, Pt);
171 Square from = pop_lsb(bb);
172 Bitboard b = attacks_bb<Pt>(from, pos.pieces()) & target;
174 // To check, you either move freely a blocker or make a direct check.
175 if (Checks && (Pt == QUEEN || !(pos.blockers_for_king(~Us) & from)))
176 b &= pos.check_squares(Pt);
179 *moveList++ = make_move(from, pop_lsb(b));
186 template<Color Us, GenType Type>
187 ExtMove* generate_all(const Position& pos, ExtMove* moveList) {
189 static_assert(Type != LEGAL, "Unsupported type in generate_all()");
191 constexpr bool Checks = Type == QUIET_CHECKS; // Reduce template instantiations
192 const Square ksq = pos.square<KING>(Us);
195 if (Type == EVASIONS && more_than_one(pos.checkers()))
196 goto kingMoves; // Double check, only a king move can save the day
198 target = Type == EVASIONS ? between_bb(ksq, lsb(pos.checkers()))
199 : Type == NON_EVASIONS ? ~pos.pieces( Us)
200 : Type == CAPTURES ? pos.pieces(~Us)
201 : ~pos.pieces( ); // QUIETS || QUIET_CHECKS
203 moveList = generate_pawn_moves<Us, Type>(pos, moveList, target);
204 moveList = generate_moves<Us, KNIGHT, Checks>(pos, moveList, target);
205 moveList = generate_moves<Us, BISHOP, Checks>(pos, moveList, target);
206 moveList = generate_moves<Us, ROOK, Checks>(pos, moveList, target);
207 moveList = generate_moves<Us, QUEEN, Checks>(pos, moveList, target);
210 if (!Checks || pos.blockers_for_king(~Us) & ksq)
212 Bitboard b = attacks_bb<KING>(ksq) & (Type == EVASIONS ? ~pos.pieces(Us) : target);
214 b &= ~attacks_bb<QUEEN>(pos.square<KING>(~Us));
217 *moveList++ = make_move(ksq, pop_lsb(b));
219 if ((Type == QUIETS || Type == NON_EVASIONS) && pos.can_castle(Us & ANY_CASTLING))
220 for (CastlingRights cr : { Us & KING_SIDE, Us & QUEEN_SIDE } )
221 if (!pos.castling_impeded(cr) && pos.can_castle(cr))
222 *moveList++ = make<CASTLING>(ksq, pos.castling_rook_square(cr));
231 /// <CAPTURES> Generates all pseudo-legal captures plus queen and checking knight promotions
232 /// <QUIETS> Generates all pseudo-legal non-captures and underpromotions (except checking knight)
233 /// <EVASIONS> Generates all pseudo-legal check evasions when the side to move is in check
234 /// <QUIET_CHECKS> Generates all pseudo-legal non-captures giving check, except castling
235 /// <NON_EVASIONS> Generates all pseudo-legal captures and non-captures
237 /// Returns a pointer to the end of the move list.
239 template<GenType Type>
240 ExtMove* generate(const Position& pos, ExtMove* moveList) {
242 static_assert(Type != LEGAL, "Unsupported type in generate()");
243 assert((Type == EVASIONS) == (bool)pos.checkers());
245 Color us = pos.side_to_move();
247 return us == WHITE ? generate_all<WHITE, Type>(pos, moveList)
248 : generate_all<BLACK, Type>(pos, moveList);
251 // Explicit template instantiations
252 template ExtMove* generate<CAPTURES>(const Position&, ExtMove*);
253 template ExtMove* generate<QUIETS>(const Position&, ExtMove*);
254 template ExtMove* generate<EVASIONS>(const Position&, ExtMove*);
255 template ExtMove* generate<QUIET_CHECKS>(const Position&, ExtMove*);
256 template ExtMove* generate<NON_EVASIONS>(const Position&, ExtMove*);
259 /// generate<LEGAL> generates all the legal moves in the given position
262 ExtMove* generate<LEGAL>(const Position& pos, ExtMove* moveList) {
264 Color us = pos.side_to_move();
265 Bitboard pinned = pos.blockers_for_king(us) & pos.pieces(us);
266 Square ksq = pos.square<KING>(us);
267 ExtMove* cur = moveList;
269 moveList = pos.checkers() ? generate<EVASIONS >(pos, moveList)
270 : generate<NON_EVASIONS>(pos, moveList);
271 while (cur != moveList)
272 if ( ((pinned && pinned & from_sq(*cur)) || from_sq(*cur) == ksq || type_of(*cur) == EN_PASSANT)
274 *cur = (--moveList)->move;
281 } // namespace Stockfish