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) 2015-2020 Marco Costalba, Joona Kiiski, Gary Linscott, Tord Romstad
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.
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.
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/>.
28 MAIN_TT, CAPTURE_INIT, GOOD_CAPTURE, REFUTATION, QUIET_INIT, QUIET, BAD_CAPTURE,
29 EVASION_TT, EVASION_INIT, EVASION,
30 PROBCUT_TT, PROBCUT_INIT, PROBCUT,
31 QSEARCH_TT, QCAPTURE_INIT, QCAPTURE, QCHECK_INIT, QCHECK
34 // partial_insertion_sort() sorts moves in descending order up to and including
35 // a given limit. The order of moves smaller than the limit is left unspecified.
36 void partial_insertion_sort(ExtMove* begin, ExtMove* end, int limit) {
38 for (ExtMove *sortedEnd = begin, *p = begin + 1; p < end; ++p)
39 if (p->value >= limit)
43 for (q = sortedEnd; q != begin && *(q - 1) < tmp; --q)
52 /// Constructors of the MovePicker class. As arguments we pass information
53 /// to help it to return the (presumably) good moves first, to decide which
54 /// moves to return (in the quiescence search, for instance, we only want to
55 /// search captures, promotions, and some checks) and how important good move
56 /// ordering is at the current node.
58 /// MovePicker constructor for the main search
59 MovePicker::MovePicker(const Position& p, Move ttm, Depth d, const ButterflyHistory* mh, const LowPlyHistory* lp,
60 const CapturePieceToHistory* cph, const PieceToHistory** ch, Move cm, Move* killers, int pl)
61 : pos(p), mainHistory(mh), lowPlyHistory(lp), captureHistory(cph), continuationHistory(ch),
62 ttMove(ttm), refutations{{killers[0], 0}, {killers[1], 0}, {cm, 0}}, depth(d), ply(pl) {
66 stage = (pos.checkers() ? EVASION_TT : MAIN_TT) +
67 !(ttm && pos.pseudo_legal(ttm));
70 /// MovePicker constructor for quiescence search
71 MovePicker::MovePicker(const Position& p, Move ttm, Depth d, const ButterflyHistory* mh,
72 const CapturePieceToHistory* cph, const PieceToHistory** ch, Square rs)
73 : pos(p), mainHistory(mh), captureHistory(cph), continuationHistory(ch), ttMove(ttm), recaptureSquare(rs), depth(d) {
77 stage = (pos.checkers() ? EVASION_TT : QSEARCH_TT) +
78 !(ttm && (depth > DEPTH_QS_RECAPTURES || to_sq(ttm) == recaptureSquare)
79 && pos.pseudo_legal(ttm));
82 /// MovePicker constructor for ProbCut: we generate captures with SEE greater
83 /// than or equal to the given threshold.
84 MovePicker::MovePicker(const Position& p, Move ttm, Value th, const CapturePieceToHistory* cph)
85 : pos(p), captureHistory(cph), ttMove(ttm), threshold(th) {
87 assert(!pos.checkers());
89 stage = PROBCUT_TT + !(ttm && pos.capture(ttm)
90 && pos.pseudo_legal(ttm)
91 && pos.see_ge(ttm, threshold));
94 /// MovePicker::score() assigns a numerical value to each move in a list, used
95 /// for sorting. Captures are ordered by Most Valuable Victim (MVV), preferring
96 /// captures with a good history. Quiets moves are ordered using the histories.
97 template<GenType Type>
98 void MovePicker::score() {
100 static_assert(Type == CAPTURES || Type == QUIETS || Type == EVASIONS, "Wrong type");
102 for (auto& m : *this)
103 if (Type == CAPTURES)
104 m.value = int(PieceValue[MG][pos.piece_on(to_sq(m))]) * 6
105 + (*captureHistory)[pos.moved_piece(m)][to_sq(m)][type_of(pos.piece_on(to_sq(m)))];
107 else if (Type == QUIETS)
108 m.value = (*mainHistory)[pos.side_to_move()][from_to(m)]
109 + 2 * (*continuationHistory[0])[pos.moved_piece(m)][to_sq(m)]
110 + 2 * (*continuationHistory[1])[pos.moved_piece(m)][to_sq(m)]
111 + 2 * (*continuationHistory[3])[pos.moved_piece(m)][to_sq(m)]
112 + (*continuationHistory[5])[pos.moved_piece(m)][to_sq(m)]
113 + (ply < MAX_LPH ? 4 * (*lowPlyHistory)[ply][from_to(m)] : 0);
115 else // Type == EVASIONS
118 m.value = PieceValue[MG][pos.piece_on(to_sq(m))]
119 - Value(type_of(pos.moved_piece(m)));
121 m.value = (*mainHistory)[pos.side_to_move()][from_to(m)]
122 + (*continuationHistory[0])[pos.moved_piece(m)][to_sq(m)]
127 /// MovePicker::select() returns the next move satisfying a predicate function.
128 /// It never returns the TT move.
129 template<MovePicker::PickType T, typename Pred>
130 Move MovePicker::select(Pred filter) {
132 while (cur < endMoves)
135 std::swap(*cur, *std::max_element(cur, endMoves));
137 if (*cur != ttMove && filter())
145 /// MovePicker::next_move() is the most important method of the MovePicker class. It
146 /// returns a new pseudo legal move every time it is called until there are no more
147 /// moves left, picking the move with the highest score from a list of generated moves.
148 Move MovePicker::next_move(bool skipQuiets) {
163 cur = endBadCaptures = moves;
164 endMoves = generate<CAPTURES>(pos, cur);
171 if (select<Best>([&](){
172 return pos.see_ge(*cur, Value(-69 * cur->value / 1024)) ?
173 // Move losing capture to endBadCaptures to be tried later
174 true : (*endBadCaptures++ = *cur, false); }))
177 // Prepare the pointers to loop over the refutations array
178 cur = std::begin(refutations);
179 endMoves = std::end(refutations);
181 // If the countermove is the same as a killer, skip it
182 if ( refutations[0].move == refutations[2].move
183 || refutations[1].move == refutations[2].move)
190 if (select<Next>([&](){ return *cur != MOVE_NONE
191 && !pos.capture(*cur)
192 && pos.pseudo_legal(*cur); }))
200 cur = endBadCaptures;
201 endMoves = generate<QUIETS>(pos, cur);
204 partial_insertion_sort(cur, endMoves, -3000 * depth);
212 && select<Next>([&](){return *cur != refutations[0].move
213 && *cur != refutations[1].move
214 && *cur != refutations[2].move;}))
217 // Prepare the pointers to loop over the bad captures
219 endMoves = endBadCaptures;
225 return select<Next>([](){ return true; });
229 endMoves = generate<EVASIONS>(pos, cur);
236 return select<Best>([](){ return true; });
239 return select<Best>([&](){ return pos.see_ge(*cur, threshold); });
242 if (select<Best>([&](){ return depth > DEPTH_QS_RECAPTURES
243 || to_sq(*cur) == recaptureSquare; }))
246 // If we did not find any move and we do not try checks, we have finished
247 if (depth != DEPTH_QS_CHECKS)
255 endMoves = generate<QUIET_CHECKS>(pos, cur);
261 return select<Next>([](){ return true; });
265 return MOVE_NONE; // Silence warning