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/>.
34 MAIN_TT, CAPTURE_INIT, GOOD_CAPTURE, REFUTATION, QUIET_INIT, QUIET, BAD_CAPTURE,
35 EVASION_TT, EVASION_INIT, EVASION,
36 PROBCUT_TT, PROBCUT_INIT, PROBCUT,
37 QSEARCH_TT, QCAPTURE_INIT, QCAPTURE, QCHECK_INIT, QCHECK
40 // partial_insertion_sort() sorts moves in descending order up to and including
41 // a given limit. The order of moves smaller than the limit is left unspecified.
42 void partial_insertion_sort(ExtMove* begin, ExtMove* end, int limit) {
44 for (ExtMove *sortedEnd = begin, *p = begin + 1; p < end; ++p)
45 if (p->value >= limit)
49 for (q = sortedEnd; q != begin && *(q - 1) < tmp; --q)
58 /// Constructors of the MovePicker class. As arguments, we pass information
59 /// to help it return the (presumably) good moves first, to decide which
60 /// moves to return (in the quiescence search, for instance, we only want to
61 /// search captures, promotions, and some checks) and how important a good
62 /// move ordering is at the current node.
64 /// MovePicker constructor for the main search
65 MovePicker::MovePicker(const Position& p, Move ttm, Depth d, const ButterflyHistory* mh,
66 const CapturePieceToHistory* cph,
67 const PieceToHistory** ch,
70 : pos(p), mainHistory(mh), captureHistory(cph), continuationHistory(ch),
71 ttMove(ttm), refutations{{killers[0], 0}, {killers[1], 0}, {cm, 0}}, depth(d)
75 stage = (pos.checkers() ? EVASION_TT : MAIN_TT) +
76 !(ttm && pos.pseudo_legal(ttm));
79 /// MovePicker constructor for quiescence search
80 MovePicker::MovePicker(const Position& p, Move ttm, Depth d, const ButterflyHistory* mh,
81 const CapturePieceToHistory* cph,
82 const PieceToHistory** ch,
84 : pos(p), mainHistory(mh), captureHistory(cph), continuationHistory(ch), ttMove(ttm), recaptureSquare(rs), depth(d)
88 stage = (pos.checkers() ? EVASION_TT : QSEARCH_TT) +
90 && pos.pseudo_legal(ttm));
93 /// MovePicker constructor for ProbCut: we generate captures with SEE greater
94 /// than or equal to the given threshold.
95 MovePicker::MovePicker(const Position& p, Move ttm, Value th, const CapturePieceToHistory* cph)
96 : pos(p), captureHistory(cph), ttMove(ttm), threshold(th)
98 assert(!pos.checkers());
100 stage = PROBCUT_TT + !(ttm && pos.capture_stage(ttm)
101 && pos.pseudo_legal(ttm)
102 && pos.see_ge(ttm, threshold));
105 /// MovePicker::score() assigns a numerical value to each move in a list, used
106 /// for sorting. Captures are ordered by Most Valuable Victim (MVV), preferring
107 /// captures with a good history. Quiets moves are ordered using the history tables.
108 template<GenType Type>
109 void MovePicker::score() {
111 static_assert(Type == CAPTURES || Type == QUIETS || Type == EVASIONS, "Wrong type");
113 [[maybe_unused]] Bitboard threatenedByPawn, threatenedByMinor, threatenedByRook, threatenedPieces;
114 if constexpr (Type == QUIETS)
116 Color us = pos.side_to_move();
118 threatenedByPawn = pos.attacks_by<PAWN>(~us);
119 threatenedByMinor = pos.attacks_by<KNIGHT>(~us) | pos.attacks_by<BISHOP>(~us) | threatenedByPawn;
120 threatenedByRook = pos.attacks_by<ROOK>(~us) | threatenedByMinor;
122 // Pieces threatened by pieces of lesser material value
123 threatenedPieces = (pos.pieces(us, QUEEN) & threatenedByRook)
124 | (pos.pieces(us, ROOK) & threatenedByMinor)
125 | (pos.pieces(us, KNIGHT, BISHOP) & threatenedByPawn);
128 for (auto& m : *this)
129 if constexpr (Type == CAPTURES)
130 m.value = (7 * int(PieceValue[pos.piece_on(to_sq(m))])
131 + (*captureHistory)[pos.moved_piece(m)][to_sq(m)][type_of(pos.piece_on(to_sq(m)))]) / 16;
133 else if constexpr (Type == QUIETS)
135 Piece pc = pos.moved_piece(m);
136 PieceType pt = type_of(pos.moved_piece(m));
137 Square from = from_sq(m);
138 Square to = to_sq(m);
141 m.value = 2 * (*mainHistory)[pos.side_to_move()][from_to(m)];
142 m.value += 2 * (*continuationHistory[0])[pc][to];
143 m.value += (*continuationHistory[1])[pc][to];
144 m.value += (*continuationHistory[2])[pc][to] / 4;
145 m.value += (*continuationHistory[3])[pc][to];
146 m.value += (*continuationHistory[5])[pc][to];
149 m.value += bool(pos.check_squares(pt) & to) * 16384;
151 // bonus for escaping from capture
152 m.value += threatenedPieces & from ?
153 (pt == QUEEN && !(to & threatenedByRook) ? 50000
154 : pt == ROOK && !(to & threatenedByMinor) ? 25000
155 : !(to & threatenedByPawn) ? 15000
159 // malus for putting piece en prise
160 m.value -= !(threatenedPieces & from) ?
161 (pt == QUEEN ? bool(to & threatenedByRook) * 50000
162 + bool(to & threatenedByMinor) * 10000
163 + bool(to & threatenedByPawn) * 20000
164 : pt == ROOK ? bool(to & threatenedByMinor) * 25000
165 + bool(to & threatenedByPawn) * 10000
166 : pt != PAWN ? bool(to & threatenedByPawn) * 15000
171 else // Type == EVASIONS
173 if (pos.capture_stage(m))
174 m.value = PieceValue[pos.piece_on(to_sq(m))]
175 - Value(type_of(pos.moved_piece(m)))
178 m.value = (*mainHistory)[pos.side_to_move()][from_to(m)]
179 + (*continuationHistory[0])[pos.moved_piece(m)][to_sq(m)];
183 /// MovePicker::select() returns the next move satisfying a predicate function.
184 /// It never returns the TT move.
185 template<MovePicker::PickType T, typename Pred>
186 Move MovePicker::select(Pred filter) {
188 while (cur < endMoves)
190 if constexpr (T == Best)
191 std::swap(*cur, *std::max_element(cur, endMoves));
193 if (*cur != ttMove && filter())
201 /// MovePicker::next_move() is the most important method of the MovePicker class. It
202 /// returns a new pseudo-legal move every time it is called until there are no more
203 /// moves left, picking the move with the highest score from a list of generated moves.
204 Move MovePicker::next_move(bool skipQuiets) {
219 cur = endBadCaptures = moves;
220 endMoves = generate<CAPTURES>(pos, cur);
223 partial_insertion_sort(cur, endMoves, std::numeric_limits<int>::min());
228 if (select<Next>([&](){
229 return pos.see_ge(*cur, Value(-cur->value)) ?
230 // Move losing capture to endBadCaptures to be tried later
231 true : (*endBadCaptures++ = *cur, false); }))
234 // Prepare the pointers to loop over the refutations array
235 cur = std::begin(refutations);
236 endMoves = std::end(refutations);
238 // If the countermove is the same as a killer, skip it
239 if ( refutations[0].move == refutations[2].move
240 || refutations[1].move == refutations[2].move)
247 if (select<Next>([&](){ return *cur != MOVE_NONE
248 && !pos.capture_stage(*cur)
249 && pos.pseudo_legal(*cur); }))
257 cur = endBadCaptures;
258 endMoves = generate<QUIETS>(pos, cur);
261 partial_insertion_sort(cur, endMoves, -3000 * depth);
269 && select<Next>([&](){return *cur != refutations[0].move
270 && *cur != refutations[1].move
271 && *cur != refutations[2].move;}))
274 // Prepare the pointers to loop over the bad captures
276 endMoves = endBadCaptures;
282 return select<Next>([](){ return true; });
286 endMoves = generate<EVASIONS>(pos, cur);
293 return select<Best>([](){ return true; });
296 return select<Next>([&](){ return pos.see_ge(*cur, threshold); });
299 if (select<Next>([&](){ return depth > DEPTH_QS_RECAPTURES
300 || to_sq(*cur) == recaptureSquare; }))
303 // If we did not find any move and we do not try checks, we have finished
304 if (depth != DEPTH_QS_CHECKS)
312 endMoves = generate<QUIET_CHECKS>(pos, cur);
318 return select<Next>([](){ return true; });
322 return MOVE_NONE; // Silence warning
325 } // namespace Stockfish