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_SEARCH, CAPTURES_INIT, GOOD_CAPTURES, KILLER0, KILLER1, COUNTERMOVE, QUIET_INIT, QUIET, BAD_CAPTURES,
29 EVASION, EVASIONS_INIT, ALL_EVASIONS,
30 PROBCUT, PROBCUT_CAPTURES_INIT, PROBCUT_CAPTURES,
31 QSEARCH, QCAPTURES_INIT, QCAPTURES, QCHECKS
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)
49 // pick_best() finds the best move in the range (begin, end) and moves it to
50 // the front. It's faster than sorting all the moves in advance when there
51 // are few moves, e.g., the possible captures.
52 Move pick_best(ExtMove* begin, ExtMove* end) {
54 std::swap(*begin, *std::max_element(begin, end));
61 /// Constructors of the MovePicker class. As arguments we pass information
62 /// to help it to return the (presumably) good moves first, to decide which
63 /// moves to return (in the quiescence search, for instance, we only want to
64 /// search captures, promotions, and some checks) and how important good move
65 /// ordering is at the current node.
67 /// MovePicker constructor for the main search
68 MovePicker::MovePicker(const Position& p, Move ttm, Depth d, const ButterflyHistory* mh,
69 const CapturePieceToHistory* cph, const PieceToHistory** ch, Move cm, Move* killers_p)
70 : pos(p), mainHistory(mh), captureHistory(cph), contHistory(ch), countermove(cm),
71 killers{killers_p[0], killers_p[1]}, depth(d){
73 assert(d > DEPTH_ZERO);
75 stage = pos.checkers() ? EVASION : MAIN_SEARCH;
76 ttMove = ttm && pos.pseudo_legal(ttm) ? ttm : MOVE_NONE;
77 stage += (ttMove == MOVE_NONE);
80 /// MovePicker constructor for quiescence search
81 MovePicker::MovePicker(const Position& p, Move ttm, Depth d, const ButterflyHistory* mh, const CapturePieceToHistory* cph, Square s)
82 : pos(p), mainHistory(mh), captureHistory(cph), recaptureSquare(s), depth(d) {
84 assert(d <= DEPTH_ZERO);
86 stage = pos.checkers() ? EVASION : QSEARCH;
88 && pos.pseudo_legal(ttm)
89 && (depth > DEPTH_QS_RECAPTURES || to_sq(ttm) == recaptureSquare) ? ttm : MOVE_NONE;
90 stage += (ttMove == MOVE_NONE);
93 /// MovePicker constructor for ProbCut: we generate captures with SEE higher
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), threshold(th) {
98 assert(!pos.checkers());
102 && pos.pseudo_legal(ttm)
104 && pos.see_ge(ttm, threshold) ? ttm : MOVE_NONE;
105 stage += (ttMove == MOVE_NONE);
108 /// score() assigns a numerical value to each move in a list, used for sorting.
109 /// Captures are ordered by Most Valuable Victim (MVV), preferring captures
110 /// with a good history. Quiets are ordered using the histories.
111 template<GenType Type>
112 void MovePicker::score() {
114 static_assert(Type == CAPTURES || Type == QUIETS || Type == EVASIONS, "Wrong type");
116 for (auto& m : *this)
117 if (Type == CAPTURES)
118 m.value = PieceValue[MG][pos.piece_on(to_sq(m))]
119 + (*captureHistory)[pos.moved_piece(m)][to_sq(m)][type_of(pos.piece_on(to_sq(m)))];
121 else if (Type == QUIETS)
122 m.value = (*mainHistory)[pos.side_to_move()][from_to(m)]
123 + (*contHistory[0])[pos.moved_piece(m)][to_sq(m)]
124 + (*contHistory[1])[pos.moved_piece(m)][to_sq(m)]
125 + (*contHistory[3])[pos.moved_piece(m)][to_sq(m)];
127 else // Type == EVASIONS
130 m.value = PieceValue[MG][pos.piece_on(to_sq(m))]
131 - Value(type_of(pos.moved_piece(m)));
133 m.value = (*mainHistory)[pos.side_to_move()][from_to(m)] - (1 << 28);
137 /// next_move() is the most important method of the MovePicker class. It returns
138 /// a new pseudo legal move every time it is called, until there are no more moves
139 /// left. It picks the move with the biggest value from a list of generated moves
140 /// taking care not to return the ttMove if it has already been searched.
142 Move MovePicker::next_move(bool skipQuiets) {
148 case MAIN_SEARCH: case EVASION: case QSEARCH: case PROBCUT:
153 case PROBCUT_CAPTURES_INIT:
155 endBadCaptures = cur = moves;
156 endMoves = generate<CAPTURES>(pos, cur);
160 // Rebranch at the top of the switch via a recursive call
161 return next_move(skipQuiets);
164 while (cur < endMoves)
166 move = pick_best(cur++, endMoves);
169 if (pos.see_ge(move, Value(-55 * (cur-1)->value / 1024)))
172 // Losing capture, move it to the beginning of the array
173 *endBadCaptures++ = move;
183 move = killers[++stage - KILLER1];
184 if ( move != MOVE_NONE
186 && pos.pseudo_legal(move)
187 && !pos.capture(move))
189 } while (stage <= KILLER1);
195 if ( move != MOVE_NONE
197 && move != killers[0]
198 && move != killers[1]
199 && pos.pseudo_legal(move)
200 && !pos.capture(move))
205 cur = endBadCaptures;
206 endMoves = generate<QUIETS>(pos, cur);
208 partial_insertion_sort(cur, endMoves, -4000 * depth / ONE_PLY);
214 while (cur < endMoves)
218 && move != killers[0]
219 && move != killers[1]
220 && move != countermove)
224 cur = moves; // Point to beginning of bad captures
228 if (cur < endBadCaptures)
234 endMoves = generate<EVASIONS>(pos, cur);
240 while (cur < endMoves)
242 move = pick_best(cur++, endMoves);
248 case PROBCUT_CAPTURES:
249 while (cur < endMoves)
251 move = pick_best(cur++, endMoves);
253 && pos.see_ge(move, threshold))
259 while (cur < endMoves)
261 move = pick_best(cur++, endMoves);
263 && (depth > DEPTH_QS_RECAPTURES || to_sq(move) == recaptureSquare))
266 if (depth <= DEPTH_QS_NO_CHECKS)
269 endMoves = generate<QUIET_CHECKS>(pos, cur);
274 while (cur < endMoves)