1/*
2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
4 Copyright (C) 2008-2015 Marco Costalba, Joona Kiiski, Tord Romstad
5 Copyright (C) 2015-2019 Marco Costalba, Joona Kiiski, Gary Linscott, Tord Romstad
6
7 Stockfish is free software: you can redistribute it and/or modify
8 it under the terms of the GNU General Public License as published by
9 the Free Software Foundation, either version 3 of the License, or
10 (at your option) any later version.
11
12 Stockfish is distributed in the hope that it will be useful,
13 but WITHOUT ANY WARRANTY; without even the implied warranty of
14 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
15 GNU General Public License for more details.
16
17 You should have received a copy of the GNU General Public License
18 along with this program. If not, see <http://www.gnu.org/licenses/>.
19*/
20
21#include <cassert>
22
23#include "movegen.h"
24#include "position.h"
25
26namespace {
27
28 template<GenType Type, Direction D>
29 ExtMove* make_promotions(ExtMove* moveList, Square to, Square ksq) {
30
31 if (Type == CAPTURES || Type == EVASIONS || Type == NON_EVASIONS)
32 *moveList++ = make<PROMOTION>(to - D, to, QUEEN);
33
34 if (Type == QUIETS || Type == EVASIONS || Type == NON_EVASIONS)
35 {
36 *moveList++ = make<PROMOTION>(to - D, to, ROOK);
37 *moveList++ = make<PROMOTION>(to - D, to, BISHOP);
38 *moveList++ = make<PROMOTION>(to - D, to, KNIGHT);
39 }
40
41 // Knight promotion is the only promotion that can give a direct check
42 // that's not already included in the queen promotion.
43 if (Type == QUIET_CHECKS && (PseudoAttacks[KNIGHT][to] & ksq))
44 *moveList++ = make<PROMOTION>(to - D, to, KNIGHT);
45 else
46 (void)ksq; // Silence a warning under MSVC
47
48 return moveList;
49 }
50
51
52 template<Color Us, GenType Type>
53 ExtMove* generate_pawn_moves(const Position& pos, ExtMove* moveList, Bitboard target) {
54
55 // Compute some compile time parameters relative to the white side
56 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
57 constexpr Bitboard TRank7BB = (Us == WHITE ? Rank7BB : Rank2BB);
58 constexpr Bitboard TRank3BB = (Us == WHITE ? Rank3BB : Rank6BB);
59 constexpr Direction Up = (Us == WHITE ? NORTH : SOUTH);
60 constexpr Direction UpRight = (Us == WHITE ? NORTH_EAST : SOUTH_WEST);
61 constexpr Direction UpLeft = (Us == WHITE ? NORTH_WEST : SOUTH_EAST);
62
63 Bitboard emptySquares;
64
65 Bitboard pawnsOn7 = pos.pieces(Us, PAWN) & TRank7BB;
66 Bitboard pawnsNotOn7 = pos.pieces(Us, PAWN) & ~TRank7BB;
67
68 Bitboard enemies = (Type == EVASIONS ? pos.pieces(Them) & target:
69 Type == CAPTURES ? target : pos.pieces(Them));
70
71 // Single and double pawn pushes, no promotions
72 if (Type != CAPTURES)
73 {
74 emptySquares = (Type == QUIETS || Type == QUIET_CHECKS ? target : ~pos.pieces());
75
76 Bitboard b1 = shift<Up>(pawnsNotOn7) & emptySquares;
77 Bitboard b2 = shift<Up>(b1 & TRank3BB) & emptySquares;
78
79 if (Type == EVASIONS) // Consider only blocking squares
80 {
81 b1 &= target;
82 b2 &= target;
83 }
84
85 if (Type == QUIET_CHECKS)
86 {
87 Square ksq = pos.square<KING>(Them);
88
89 b1 &= pos.attacks_from<PAWN>(ksq, Them);
90 b2 &= pos.attacks_from<PAWN>(ksq, Them);
91
92 // Add pawn pushes which give discovered check. This is possible only
93 // if the pawn is not on the same file as the enemy king, because we
94 // don't generate captures. Note that a possible discovery check
95 // promotion has been already generated amongst the captures.
96 Bitboard dcCandidateQuiets = pos.blockers_for_king(Them) & pawnsNotOn7;
97 if (dcCandidateQuiets)
98 {
99 Bitboard dc1 = shift<Up>(dcCandidateQuiets) & emptySquares & ~file_bb(ksq);
100 Bitboard dc2 = shift<Up>(dc1 & TRank3BB) & emptySquares;
101
102 b1 |= dc1;
103 b2 |= dc2;
104 }
105 }
106
107 while (b1)
108 {
109 Square to = pop_lsb(&b1);
110 *moveList++ = make_move(to - Up, to);
111 }
112
113 while (b2)
114 {
115 Square to = pop_lsb(&b2);
116 *moveList++ = make_move(to - Up - Up, to);
117 }
118 }
119
120 // Promotions and underpromotions
121 if (pawnsOn7)
122 {
123 if (Type == CAPTURES)
124 emptySquares = ~pos.pieces();
125
126 if (Type == EVASIONS)
127 emptySquares &= target;
128
129 Bitboard b1 = shift<UpRight>(pawnsOn7) & enemies;
130 Bitboard b2 = shift<UpLeft >(pawnsOn7) & enemies;
131 Bitboard b3 = shift<Up >(pawnsOn7) & emptySquares;
132
133 Square ksq = pos.square<KING>(Them);
134
135 while (b1)
136 moveList = make_promotions<Type, UpRight>(moveList, pop_lsb(&b1), ksq);
137
138 while (b2)
139 moveList = make_promotions<Type, UpLeft >(moveList, pop_lsb(&b2), ksq);
140
141 while (b3)
142 moveList = make_promotions<Type, Up >(moveList, pop_lsb(&b3), ksq);
143 }
144
145 // Standard and en-passant captures
146 if (Type == CAPTURES || Type == EVASIONS || Type == NON_EVASIONS)
147 {
148 Bitboard b1 = shift<UpRight>(pawnsNotOn7) & enemies;
149 Bitboard b2 = shift<UpLeft >(pawnsNotOn7) & enemies;
150
151 while (b1)
152 {
153 Square to = pop_lsb(&b1);
154 *moveList++ = make_move(to - UpRight, to);
155 }
156
157 while (b2)
158 {
159 Square to = pop_lsb(&b2);
160 *moveList++ = make_move(to - UpLeft, to);
161 }
162
163 if (pos.ep_square() != SQ_NONE)
164 {
165 assert(rank_of(pos.ep_square()) == relative_rank(Us, RANK_6));
166
167 // An en passant capture can be an evasion only if the checking piece
168 // is the double pushed pawn and so is in the target. Otherwise this
169 // is a discovery check and we are forced to do otherwise.
170 if (Type == EVASIONS && !(target & (pos.ep_square() - Up)))
171 return moveList;
172
173 b1 = pawnsNotOn7 & pos.attacks_from<PAWN>(pos.ep_square(), Them);
174
175 assert(b1);
176
177 while (b1)
178 *moveList++ = make<ENPASSANT>(pop_lsb(&b1), pos.ep_square());
179 }
180 }
181
182 return moveList;
183 }
184
185
186 template<PieceType Pt, bool Checks>
187 ExtMove* generate_moves(const Position& pos, ExtMove* moveList, Color us,
188 Bitboard target) {
189
190 assert(Pt != KING && Pt != PAWN);
191
192 const Square* pl = pos.squares<Pt>(us);
193
194 for (Square from = *pl; from != SQ_NONE; from = *++pl)
195 {
196 if (Checks)
197 {
198 if ( (Pt == BISHOP || Pt == ROOK || Pt == QUEEN)
199 && !(PseudoAttacks[Pt][from] & target & pos.check_squares(Pt)))
200 continue;
201
202 if (pos.blockers_for_king(~us) & from)
203 continue;
204 }
205
206 Bitboard b = pos.attacks_from<Pt>(from) & target;
207
208 if (Checks)
209 b &= pos.check_squares(Pt);
210
211 while (b)
212 *moveList++ = make_move(from, pop_lsb(&b));
213 }
214
215 return moveList;
216 }
217
218
219 template<Color Us, GenType Type>
220 ExtMove* generate_all(const Position& pos, ExtMove* moveList, Bitboard target) {
221
222 constexpr CastlingRight OO = Us | KING_SIDE;
223 constexpr CastlingRight OOO = Us | QUEEN_SIDE;
224 constexpr bool Checks = Type == QUIET_CHECKS; // Reduce template instantations
225
226 moveList = generate_pawn_moves<Us, Type>(pos, moveList, target);
227 moveList = generate_moves<KNIGHT, Checks>(pos, moveList, Us, target);
228 moveList = generate_moves<BISHOP, Checks>(pos, moveList, Us, target);
229 moveList = generate_moves< ROOK, Checks>(pos, moveList, Us, target);
230 moveList = generate_moves< QUEEN, Checks>(pos, moveList, Us, target);
231
232 if (Type != QUIET_CHECKS && Type != EVASIONS)
233 {
234 Square ksq = pos.square<KING>(Us);
235 Bitboard b = pos.attacks_from<KING>(ksq) & target;
236 while (b)
237 *moveList++ = make_move(ksq, pop_lsb(&b));
238
239 if (Type != CAPTURES && pos.can_castle(CastlingRight(OO | OOO)))
240 {
241 if (!pos.castling_impeded(OO) && pos.can_castle(OO))
242 *moveList++ = make<CASTLING>(ksq, pos.castling_rook_square(OO));
243
244 if (!pos.castling_impeded(OOO) && pos.can_castle(OOO))
245 *moveList++ = make<CASTLING>(ksq, pos.castling_rook_square(OOO));
246 }
247 }
248
249 return moveList;
250 }
251
252} // namespace
253
254
255/// <CAPTURES> Generates all pseudo-legal captures and queen promotions
256/// <QUIETS> Generates all pseudo-legal non-captures and underpromotions
257/// <NON_EVASIONS> Generates all pseudo-legal captures and non-captures
258///
259/// Returns a pointer to the end of the move list.
260
261template<GenType Type>
262ExtMove* generate(const Position& pos, ExtMove* moveList) {
263
264 assert(Type == CAPTURES || Type == QUIETS || Type == NON_EVASIONS);
265 assert(!pos.checkers());
266
267 Color us = pos.side_to_move();
268
269 Bitboard target = Type == CAPTURES ? pos.pieces(~us)
270 : Type == QUIETS ? ~pos.pieces()
271 : Type == NON_EVASIONS ? ~pos.pieces(us) : 0;
272
273 return us == WHITE ? generate_all<WHITE, Type>(pos, moveList, target)
274 : generate_all<BLACK, Type>(pos, moveList, target);
275}
276
277// Explicit template instantiations
278template ExtMove* generate<CAPTURES>(const Position&, ExtMove*);
279template ExtMove* generate<QUIETS>(const Position&, ExtMove*);
280template ExtMove* generate<NON_EVASIONS>(const Position&, ExtMove*);
281
282
283/// generate<QUIET_CHECKS> generates all pseudo-legal non-captures and knight
284/// underpromotions that give check. Returns a pointer to the end of the move list.
285template<>
286ExtMove* generate<QUIET_CHECKS>(const Position& pos, ExtMove* moveList) {
287
288 assert(!pos.checkers());
289
290 Color us = pos.side_to_move();
291 Bitboard dc = pos.blockers_for_king(~us) & pos.pieces(us);
292
293 while (dc)
294 {
295 Square from = pop_lsb(&dc);
296 PieceType pt = type_of(pos.piece_on(from));
297
298 if (pt == PAWN)
299 continue; // Will be generated together with direct checks
300
301 Bitboard b = pos.attacks_from(pt, from) & ~pos.pieces();
302
303 if (pt == KING)
304 b &= ~PseudoAttacks[QUEEN][pos.square<KING>(~us)];
305
306 while (b)
307 *moveList++ = make_move(from, pop_lsb(&b));
308 }
309
310 return us == WHITE ? generate_all<WHITE, QUIET_CHECKS>(pos, moveList, ~pos.pieces())
311 : generate_all<BLACK, QUIET_CHECKS>(pos, moveList, ~pos.pieces());
312}
313
314
315/// generate<EVASIONS> generates all pseudo-legal check evasions when the side
316/// to move is in check. Returns a pointer to the end of the move list.
317template<>
318ExtMove* generate<EVASIONS>(const Position& pos, ExtMove* moveList) {
319
320 assert(pos.checkers());
321
322 Color us = pos.side_to_move();
323 Square ksq = pos.square<KING>(us);
324 Bitboard sliderAttacks = 0;
325 Bitboard sliders = pos.checkers() & ~pos.pieces(KNIGHT, PAWN);
326
327 // Find all the squares attacked by slider checkers. We will remove them from
328 // the king evasions in order to skip known illegal moves, which avoids any
329 // useless legality checks later on.
330 while (sliders)
331 {
332 Square checksq = pop_lsb(&sliders);
333 sliderAttacks |= LineBB[checksq][ksq] ^ checksq;
334 }
335
336 // Generate evasions for king, capture and non capture moves
337 Bitboard b = pos.attacks_from<KING>(ksq) & ~pos.pieces(us) & ~sliderAttacks;
338 while (b)
339 *moveList++ = make_move(ksq, pop_lsb(&b));
340
341 if (more_than_one(pos.checkers()))
342 return moveList; // Double check, only a king move can save the day
343
344 // Generate blocking evasions or captures of the checking piece
345 Square checksq = lsb(pos.checkers());
346 Bitboard target = between_bb(checksq, ksq) | checksq;
347
348 return us == WHITE ? generate_all<WHITE, EVASIONS>(pos, moveList, target)
349 : generate_all<BLACK, EVASIONS>(pos, moveList, target);
350}
351
352
353/// generate<LEGAL> generates all the legal moves in the given position
354
355template<>
356ExtMove* generate<LEGAL>(const Position& pos, ExtMove* moveList) {
357
358 Color us = pos.side_to_move();
359 Bitboard pinned = pos.blockers_for_king(us) & pos.pieces(us);
360 Square ksq = pos.square<KING>(us);
361 ExtMove* cur = moveList;
362
363 moveList = pos.checkers() ? generate<EVASIONS >(pos, moveList)
364 : generate<NON_EVASIONS>(pos, moveList);
365 while (cur != moveList)
366 if ( (pinned || from_sq(*cur) == ksq || type_of(*cur) == ENPASSANT)
367 && !pos.legal(*cur))
368 *cur = (--moveList)->move;
369 else
370 ++cur;
371
372 return moveList;
373}
374