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/>.
29 MAIN_TT, CAPTURE_INIT, GOOD_CAPTURE, REFUTATION, QUIET_INIT, QUIET, BAD_CAPTURE,
30 EVASION_TT, EVASION_INIT, EVASION,
31 PROBCUT_TT, PROBCUT_INIT, PROBCUT,
32 QSEARCH_TT, QCAPTURE_INIT, QCAPTURE, QCHECK_INIT, QCHECK
35 // partial_insertion_sort() sorts moves in descending order up to and including
36 // a given limit. The order of moves smaller than the limit is left unspecified.
37 void partial_insertion_sort(ExtMove* begin, ExtMove* end, int limit) {
39 for (ExtMove *sortedEnd = begin, *p = begin + 1; p < end; ++p)
40 if (p->value >= limit)
44 for (q = sortedEnd; q != begin && *(q - 1) < tmp; --q)
53 /// Constructors of the MovePicker class. As arguments we pass information
54 /// to help it to return the (presumably) good moves first, to decide which
55 /// moves to return (in the quiescence search, for instance, we only want to
56 /// search captures, promotions, and some checks) and how important good move
57 /// ordering is at the current node.
59 /// MovePicker constructor for the main search
60 MovePicker::MovePicker(const Position& p, Move ttm, Depth d, const ButterflyHistory* mh,
61 const CapturePieceToHistory* cph,
62 const PieceToHistory** ch,
65 : pos(p), mainHistory(mh), captureHistory(cph), continuationHistory(ch),
66 ttMove(ttm), refutations{{killers[0], 0}, {killers[1], 0}, {cm, 0}}, depth(d)
70 stage = (pos.checkers() ? EVASION_TT : MAIN_TT) +
71 !(ttm && pos.pseudo_legal(ttm));
74 /// MovePicker constructor for quiescence search
75 MovePicker::MovePicker(const Position& p, Move ttm, Depth d, const ButterflyHistory* mh,
76 const CapturePieceToHistory* cph,
77 const PieceToHistory** ch,
79 : pos(p), mainHistory(mh), captureHistory(cph), continuationHistory(ch), ttMove(ttm), recaptureSquare(rs), depth(d)
83 stage = (pos.checkers() ? EVASION_TT : QSEARCH_TT) +
85 && pos.pseudo_legal(ttm));
88 /// MovePicker constructor for ProbCut: we generate captures with SEE greater
89 /// than or equal to the given threshold.
90 MovePicker::MovePicker(const Position& p, Move ttm, Value th, const CapturePieceToHistory* cph)
91 : pos(p), captureHistory(cph), ttMove(ttm), threshold(th)
93 assert(!pos.checkers());
95 stage = PROBCUT_TT + !(ttm && pos.capture_stage(ttm)
96 && pos.pseudo_legal(ttm)
97 && pos.see_ge(ttm, threshold));
100 /// MovePicker::score() assigns a numerical value to each move in a list, used
101 /// for sorting. Captures are ordered by Most Valuable Victim (MVV), preferring
102 /// captures with a good history. Quiets moves are ordered using the history tables.
103 template<GenType Type>
104 void MovePicker::score() {
106 static_assert(Type == CAPTURES || Type == QUIETS || Type == EVASIONS, "Wrong type");
108 [[maybe_unused]] Bitboard threatenedByPawn, threatenedByMinor, threatenedByRook, threatenedPieces;
109 if constexpr (Type == QUIETS)
111 Color us = pos.side_to_move();
113 threatenedByPawn = pos.attacks_by<PAWN>(~us);
114 threatenedByMinor = pos.attacks_by<KNIGHT>(~us) | pos.attacks_by<BISHOP>(~us) | threatenedByPawn;
115 threatenedByRook = pos.attacks_by<ROOK>(~us) | threatenedByMinor;
117 // Pieces threatened by pieces of lesser material value
118 threatenedPieces = (pos.pieces(us, QUEEN) & threatenedByRook)
119 | (pos.pieces(us, ROOK) & threatenedByMinor)
120 | (pos.pieces(us, KNIGHT, BISHOP) & threatenedByPawn);
123 for (auto& m : *this)
124 if constexpr (Type == CAPTURES)
125 m.value = (7 * int(PieceValue[pos.piece_on(to_sq(m))])
126 + (*captureHistory)[pos.moved_piece(m)][to_sq(m)][type_of(pos.piece_on(to_sq(m)))]) / 16;
128 else if constexpr (Type == QUIETS)
130 Piece pc = pos.moved_piece(m);
131 PieceType pt = type_of(pos.moved_piece(m));
132 Square from = from_sq(m);
133 Square to = to_sq(m);
136 m.value = 2 * (*mainHistory)[pos.side_to_move()][from_to(m)];
137 m.value += 2 * (*continuationHistory[0])[pc][to];
138 m.value += (*continuationHistory[1])[pc][to];
139 m.value += (*continuationHistory[3])[pc][to];
140 m.value += (*continuationHistory[5])[pc][to];
143 m.value += bool(pos.check_squares(pt) & to) * 16384;
145 // bonus for escaping from capture
146 m.value += threatenedPieces & from ?
147 (pt == QUEEN && !(to & threatenedByRook) ? 50000
148 : pt == ROOK && !(to & threatenedByMinor) ? 25000
149 : !(to & threatenedByPawn) ? 15000
153 // malus for putting piece en prise
154 m.value -= !(threatenedPieces & from) ?
155 (pt == QUEEN ? bool(to & threatenedByRook) * 50000
156 + bool(to & threatenedByMinor) * 10000
157 + bool(to & threatenedByPawn) * 20000
158 : pt == ROOK ? bool(to & threatenedByMinor) * 25000
159 + bool(to & threatenedByPawn) * 10000
160 : pt != PAWN ? bool(to & threatenedByPawn) * 15000
165 else // Type == EVASIONS
167 if (pos.capture_stage(m))
168 m.value = PieceValue[pos.piece_on(to_sq(m))]
169 - Value(type_of(pos.moved_piece(m)))
172 m.value = (*mainHistory)[pos.side_to_move()][from_to(m)]
173 + (*continuationHistory[0])[pos.moved_piece(m)][to_sq(m)];
177 /// MovePicker::select() returns the next move satisfying a predicate function.
178 /// It never returns the TT move.
179 template<MovePicker::PickType T, typename Pred>
180 Move MovePicker::select(Pred filter) {
182 while (cur < endMoves)
184 if constexpr (T == Best)
185 std::swap(*cur, *std::max_element(cur, endMoves));
187 if (*cur != ttMove && filter())
195 /// MovePicker::next_move() is the most important method of the MovePicker class. It
196 /// returns a new pseudo-legal move every time it is called until there are no more
197 /// moves left, picking the move with the highest score from a list of generated moves.
198 Move MovePicker::next_move(bool skipQuiets) {
213 cur = endBadCaptures = moves;
214 endMoves = generate<CAPTURES>(pos, cur);
217 partial_insertion_sort(cur, endMoves, std::numeric_limits<int>::min());
222 if (select<Next>([&](){
223 return pos.see_ge(*cur, Value(-cur->value)) ?
224 // Move losing capture to endBadCaptures to be tried later
225 true : (*endBadCaptures++ = *cur, false); }))
228 // Prepare the pointers to loop over the refutations array
229 cur = std::begin(refutations);
230 endMoves = std::end(refutations);
232 // If the countermove is the same as a killer, skip it
233 if ( refutations[0].move == refutations[2].move
234 || refutations[1].move == refutations[2].move)
241 if (select<Next>([&](){ return *cur != MOVE_NONE
242 && !pos.capture_stage(*cur)
243 && pos.pseudo_legal(*cur); }))
251 cur = endBadCaptures;
252 endMoves = generate<QUIETS>(pos, cur);
255 partial_insertion_sort(cur, endMoves, -3000 * depth);
263 && select<Next>([&](){return *cur != refutations[0].move
264 && *cur != refutations[1].move
265 && *cur != refutations[2].move;}))
268 // Prepare the pointers to loop over the bad captures
270 endMoves = endBadCaptures;
276 return select<Next>([](){ return true; });
280 endMoves = generate<EVASIONS>(pos, cur);
287 return select<Best>([](){ return true; });
290 return select<Next>([&](){ return pos.see_ge(*cur, threshold); });
293 if (select<Next>([&](){ return depth > DEPTH_QS_RECAPTURES
294 || to_sq(*cur) == recaptureSquare; }))
297 // If we did not find any move and we do not try checks, we have finished
298 if (depth != DEPTH_QS_CHECKS)
306 endMoves = generate<QUIET_CHECKS>(pos, cur);
312 return select<Next>([](){ return true; });
316 return MOVE_NONE; // Silence warning
319 } // namespace Stockfish