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) 2015-2018 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, KILLER0, KILLER1, COUNTERMOVE, 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 // Helper filter used with select_move()
35 const auto Any = [](){ return true; };
37 // partial_insertion_sort() sorts moves in descending order up to and including
38 // a given limit. The order of moves smaller than the limit is left unspecified.
39 void partial_insertion_sort(ExtMove* begin, ExtMove* end, int limit) {
41 for (ExtMove *sortedEnd = begin, *p = begin + 1; p < end; ++p)
42 if (p->value >= limit)
46 for (q = sortedEnd; q != begin && *(q - 1) < tmp; --q)
55 /// Constructors of the MovePicker class. As arguments we pass information
56 /// to help it to return the (presumably) good moves first, to decide which
57 /// moves to return (in the quiescence search, for instance, we only want to
58 /// search captures, promotions, and some checks) and how important good move
59 /// ordering is at the current node.
61 /// MovePicker constructor for the main search
62 MovePicker::MovePicker(const Position& p, Move ttm, Depth d, const ButterflyHistory* mh,
63 const CapturePieceToHistory* cph, const PieceToHistory** ch, Move cm, Move* killers_p)
64 : pos(p), mainHistory(mh), captureHistory(cph), contHistory(ch),
65 refutations{killers_p[0], killers_p[1], cm}, depth(d){
67 assert(d > DEPTH_ZERO);
69 stage = pos.checkers() ? EVASION_TT : MAIN_TT;
70 ttMove = ttm && pos.pseudo_legal(ttm) ? ttm : MOVE_NONE;
71 stage += (ttMove == MOVE_NONE);
74 /// MovePicker constructor for quiescence search
75 MovePicker::MovePicker(const Position& p, Move ttm, Depth d, const ButterflyHistory* mh,
76 const CapturePieceToHistory* cph, Square rs)
77 : pos(p), mainHistory(mh), captureHistory(cph), recaptureSquare(rs), depth(d) {
79 assert(d <= DEPTH_ZERO);
81 stage = pos.checkers() ? EVASION_TT : QSEARCH_TT;
83 && pos.pseudo_legal(ttm)
84 && (depth > DEPTH_QS_RECAPTURES || to_sq(ttm) == recaptureSquare) ? ttm : MOVE_NONE;
85 stage += (ttMove == MOVE_NONE);
88 /// MovePicker constructor for ProbCut: we generate captures with SEE higher
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), threshold(th) {
93 assert(!pos.checkers());
97 && pos.pseudo_legal(ttm)
99 && pos.see_ge(ttm, threshold) ? ttm : MOVE_NONE;
100 stage += (ttMove == MOVE_NONE);
103 /// MovePicker::score() assigns a numerical value to each move in a list, used
104 /// for sorting. Captures are ordered by Most Valuable Victim (MVV), preferring
105 /// captures with a good history. Quiets moves are ordered using the histories.
106 template<GenType Type>
107 void MovePicker::score() {
109 static_assert(Type == CAPTURES || Type == QUIETS || Type == EVASIONS, "Wrong type");
111 for (auto& m : *this)
112 if (Type == CAPTURES)
113 m.value = PieceValue[MG][pos.piece_on(to_sq(m))]
114 + (*captureHistory)[pos.moved_piece(m)][to_sq(m)][type_of(pos.piece_on(to_sq(m)))];
116 else if (Type == QUIETS)
117 m.value = (*mainHistory)[pos.side_to_move()][from_to(m)]
118 + (*contHistory[0])[pos.moved_piece(m)][to_sq(m)]
119 + (*contHistory[1])[pos.moved_piece(m)][to_sq(m)]
120 + (*contHistory[3])[pos.moved_piece(m)][to_sq(m)];
122 else // Type == EVASIONS
125 m.value = PieceValue[MG][pos.piece_on(to_sq(m))]
126 - Value(type_of(pos.moved_piece(m)));
128 m.value = (*mainHistory)[pos.side_to_move()][from_to(m)] - (1 << 28);
132 /// MovePicker::select_move() returns the next move satisfying a predicate function
133 template<PickType T, typename Pred>
134 Move MovePicker::select_move(Pred filter) {
136 while (cur < endMoves)
139 std::swap(*cur, *std::max_element(cur, endMoves));
143 if (move != ttMove && filter())
146 return move = MOVE_NONE;
149 /// MovePicker::next_move() is the most important method of the MovePicker class. It
150 /// returns a new pseudo legal move every time it is called, until there are no more
151 /// moves left. It picks the move with the highest score from a list of generated moves.
152 Move MovePicker::next_move(bool skipQuiets) {
167 endBadCaptures = cur = moves;
168 endMoves = generate<CAPTURES>(pos, cur);
174 if (select_move<BEST_SCORE>([&](){ return pos.see_ge(move, Value(-55 * (cur-1)->value / 1024)) ?
175 // Move losing capture to endBadCaptures to be tried later
176 true : (*endBadCaptures++ = move, false); }))
179 // If the countermove is the same as a killer, skip it
180 if ( refutations[0] == refutations[2]
181 || refutations[1] == refutations[2])
182 refutations[2] = MOVE_NONE;
189 while (stage <= COUNTERMOVE)
191 move = refutations[ stage++ - KILLER0];
192 if ( move != MOVE_NONE
194 && pos.pseudo_legal(move)
195 && !pos.capture(move))
201 cur = endBadCaptures;
202 endMoves = generate<QUIETS>(pos, cur);
204 partial_insertion_sort(cur, endMoves, -4000 * depth / ONE_PLY);
210 && select_move<NEXT>([&](){return move != refutations[0]
211 && move != refutations[1]
212 && move != refutations[2];}))
215 // Point to beginning and end of bad captures
216 cur = moves, endMoves = endBadCaptures;
221 return select_move<NEXT>(Any);
225 endMoves = generate<EVASIONS>(pos, cur);
231 return select_move<BEST_SCORE>(Any);
234 return select_move<BEST_SCORE>([&](){ return pos.see_ge(move, threshold); });
237 if (select_move<BEST_SCORE>([&](){ return depth > DEPTH_QS_RECAPTURES
238 || to_sq(move) == recaptureSquare; }))
241 // If we did not find any move and we do not try checks, we have finished
242 if (depth != DEPTH_QS_CHECKS)
250 endMoves = generate<QUIET_CHECKS>(pos, cur);
255 return select_move<NEXT>(Any);
259 return MOVE_NONE; // Silence warning