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) 2015-2017 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, KILLERS, COUNTERMOVE, QUIET_INIT, QUIET, BAD_CAPTURES,
29 EVASION, EVASIONS_INIT, ALL_EVASIONS,
30 PROBCUT, PROBCUT_INIT, PROBCUT_CAPTURES,
31 QSEARCH_WITH_CHECKS, QCAPTURES_1_INIT, QCAPTURES_1, QCHECKS,
32 QSEARCH_NO_CHECKS, QCAPTURES_2_INIT, QCAPTURES_2,
33 QSEARCH_RECAPTURES, QRECAPTURES
36 // partial_insertion_sort() sorts moves in descending order up to and including
37 // a given limit. The order of moves smaller than the limit is left unspecified.
38 void partial_insertion_sort(ExtMove* begin, ExtMove* end, int limit) {
40 for (ExtMove *sortedEnd = begin, *p = begin + 1; p < end; ++p)
41 if (p->value >= limit)
45 for (q = sortedEnd; q != begin && *(q - 1) < tmp; --q)
51 // pick_best() finds the best move in the range (begin, end) and moves it to
52 // the front. It's faster than sorting all the moves in advance when there
53 // are few moves, e.g., the possible captures.
54 Move pick_best(ExtMove* begin, ExtMove* end) {
56 std::swap(*begin, *std::max_element(begin, end));
63 /// Constructors of the MovePicker class. As arguments we pass information
64 /// to help it to return the (presumably) good moves first, to decide which
65 /// moves to return (in the quiescence search, for instance, we only want to
66 /// search captures, promotions, and some checks) and how important good move
67 /// ordering is at the current node.
69 /// MovePicker constructor for the main search
70 MovePicker::MovePicker(const Position& p, Move ttm, Depth d, const ButterflyHistory* mh,
71 const CapturePieceToHistory* cph, const PieceToHistory** ch, Move cm, Move* killers_p)
72 : pos(p), mainHistory(mh), captureHistory(cph), contHistory(ch), countermove(cm),
73 killers{killers_p[0], killers_p[1]}, depth(d){
75 assert(d > DEPTH_ZERO);
77 stage = pos.checkers() ? EVASION : MAIN_SEARCH;
78 ttMove = ttm && pos.pseudo_legal(ttm) ? ttm : MOVE_NONE;
79 stage += (ttMove == MOVE_NONE);
82 /// MovePicker constructor for quiescence search
83 MovePicker::MovePicker(const Position& p, Move ttm, Depth d, const ButterflyHistory* mh, const CapturePieceToHistory* cph, Square s)
84 : pos(p), mainHistory(mh), captureHistory(cph) {
86 assert(d <= DEPTH_ZERO);
91 else if (d > DEPTH_QS_NO_CHECKS)
92 stage = QSEARCH_WITH_CHECKS;
94 else if (d > DEPTH_QS_RECAPTURES)
95 stage = QSEARCH_NO_CHECKS;
99 stage = QSEARCH_RECAPTURES;
104 ttMove = ttm && pos.pseudo_legal(ttm) ? ttm : MOVE_NONE;
105 stage += (ttMove == MOVE_NONE);
108 /// MovePicker constructor for ProbCut: we generate captures with SEE higher
109 /// than or equal to the given threshold.
110 MovePicker::MovePicker(const Position& p, Move ttm, Value th, const CapturePieceToHistory* cph)
111 : pos(p), captureHistory(cph), threshold(th) {
113 assert(!pos.checkers());
117 && pos.pseudo_legal(ttm)
119 && pos.see_ge(ttm, threshold) ? ttm : MOVE_NONE;
121 stage += (ttMove == MOVE_NONE);
124 /// score() assigns a numerical value to each move in a list, used for sorting.
125 /// Captures are ordered by Most Valuable Victim (MVV), preferring captures
126 /// near our home rank. Quiets are ordered using the histories.
127 template<GenType Type>
128 void MovePicker::score() {
130 static_assert(Type == CAPTURES || Type == QUIETS || Type == EVASIONS, "Wrong type");
132 for (auto& m : *this)
133 if (Type == CAPTURES)
134 m.value = PieceValue[MG][pos.piece_on(to_sq(m))]
135 + Value((*captureHistory)[pos.moved_piece(m)][to_sq(m)][type_of(pos.piece_on(to_sq(m)))]);
137 else if (Type == QUIETS)
138 m.value = (*mainHistory)[pos.side_to_move()][from_to(m)]
139 + (*contHistory[0])[pos.moved_piece(m)][to_sq(m)]
140 + (*contHistory[1])[pos.moved_piece(m)][to_sq(m)]
141 + (*contHistory[3])[pos.moved_piece(m)][to_sq(m)];
143 else // Type == EVASIONS
146 m.value = PieceValue[MG][pos.piece_on(to_sq(m))]
147 - Value(type_of(pos.moved_piece(m)));
149 m.value = (*mainHistory)[pos.side_to_move()][from_to(m)] - (1 << 28);
153 /// next_move() is the most important method of the MovePicker class. It returns
154 /// a new pseudo legal move every time it is called, until there are no more moves
155 /// left. It picks the move with the biggest value from a list of generated moves
156 /// taking care not to return the ttMove if it has already been searched.
158 Move MovePicker::next_move(bool skipQuiets) {
164 case MAIN_SEARCH: case EVASION: case QSEARCH_WITH_CHECKS:
165 case QSEARCH_NO_CHECKS: case PROBCUT:
170 endBadCaptures = cur = moves;
171 endMoves = generate<CAPTURES>(pos, cur);
177 while (cur < endMoves)
179 move = pick_best(cur++, endMoves);
182 if (pos.see_ge(move))
185 if ( type_of(pos.piece_on(to_sq(move))) == KNIGHT
186 && type_of(pos.moved_piece(move)) == BISHOP
187 && (cur-1)->value > 1090)
190 // Losing capture, move it to the beginning of the array
191 *endBadCaptures++ = move;
196 move = killers[0]; // First killer move
197 if ( move != MOVE_NONE
199 && pos.pseudo_legal(move)
200 && !pos.capture(move))
206 move = killers[1]; // Second killer move
207 if ( move != MOVE_NONE
209 && pos.pseudo_legal(move)
210 && !pos.capture(move))
217 if ( move != MOVE_NONE
219 && move != killers[0]
220 && move != killers[1]
221 && pos.pseudo_legal(move)
222 && !pos.capture(move))
227 cur = endBadCaptures;
228 endMoves = generate<QUIETS>(pos, cur);
230 partial_insertion_sort(cur, endMoves, -4000 * depth / ONE_PLY);
235 while ( cur < endMoves
236 && (!skipQuiets || cur->value >= VALUE_ZERO))
241 && move != killers[0]
242 && move != killers[1]
243 && move != countermove)
247 cur = moves; // Point to beginning of bad captures
251 if (cur < endBadCaptures)
257 endMoves = generate<EVASIONS>(pos, cur);
263 while (cur < endMoves)
265 move = pick_best(cur++, endMoves);
273 endMoves = generate<CAPTURES>(pos, cur);
278 case PROBCUT_CAPTURES:
279 while (cur < endMoves)
281 move = pick_best(cur++, endMoves);
283 && pos.see_ge(move, threshold))
288 case QCAPTURES_1_INIT: case QCAPTURES_2_INIT:
290 endMoves = generate<CAPTURES>(pos, cur);
295 case QCAPTURES_1: case QCAPTURES_2:
296 while (cur < endMoves)
298 move = pick_best(cur++, endMoves);
302 if (stage == QCAPTURES_2)
305 endMoves = generate<QUIET_CHECKS>(pos, cur);
310 while (cur < endMoves)
318 case QSEARCH_RECAPTURES:
320 endMoves = generate<CAPTURES>(pos, cur);
326 while (cur < endMoves)
328 move = pick_best(cur++, endMoves);
329 if (to_sq(move) == recaptureSquare)