1/*
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) 2015-2019 Marco Costalba, Joona Kiiski, Gary Linscott, Tord Romstad
6
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.
11
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.
16
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/>.
19*/
20
21#include <cassert>
22
23#include "movepick.h"
24
25namespace {
26
27 enum Stages {
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
32 };
33
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) {
37
38 for (ExtMove *sortedEnd = begin, *p = begin + 1; p < end; ++p)
39 if (p->value >= limit)
40 {
41 ExtMove tmp = *p, *q;
42 *p = *++sortedEnd;
43 for (q = sortedEnd; q != begin && *(q - 1) < tmp; --q)
44 *q = *(q - 1);
45 *q = tmp;
46 }
47 }
48
49} // namespace
50
51
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.
57
58/// MovePicker constructor for the main search
59MovePicker::MovePicker(const Position& p, Move ttm, Depth d, const ButterflyHistory* mh,
60 const CapturePieceToHistory* cph, const PieceToHistory** ch, Move cm, Move* killers)
61 : pos(p), mainHistory(mh), captureHistory(cph), continuationHistory(ch),
62 refutations{{killers[0], 0}, {killers[1], 0}, {cm, 0}}, depth(d) {
63
64 assert(d > DEPTH_ZERO);
65
66 stage = pos.checkers() ? EVASION_TT : MAIN_TT;
67 ttMove = ttm && pos.pseudo_legal(ttm) ? ttm : MOVE_NONE;
68 stage += (ttMove == MOVE_NONE);
69}
70
71/// MovePicker constructor for quiescence search
72MovePicker::MovePicker(const Position& p, Move ttm, Depth d, const ButterflyHistory* mh,
73 const CapturePieceToHistory* cph, const PieceToHistory** ch, Square rs)
74 : pos(p), mainHistory(mh), captureHistory(cph), continuationHistory(ch), recaptureSquare(rs), depth(d) {
75
76 assert(d <= DEPTH_ZERO);
77
78 stage = pos.checkers() ? EVASION_TT : QSEARCH_TT;
79 ttMove = ttm
80 && (depth > DEPTH_QS_RECAPTURES || to_sq(ttm) == recaptureSquare)
81 && pos.pseudo_legal(ttm) ? ttm : MOVE_NONE;
82 stage += (ttMove == MOVE_NONE);
83}
84
85/// MovePicker constructor for ProbCut: we generate captures with SEE greater
86/// than or equal to the given threshold.
87MovePicker::MovePicker(const Position& p, Move ttm, Value th, const CapturePieceToHistory* cph)
88 : pos(p), captureHistory(cph), threshold(th) {
89
90 assert(!pos.checkers());
91
92 stage = PROBCUT_TT;
93 ttMove = ttm
94 && pos.capture(ttm)
95 && pos.pseudo_legal(ttm)
96 && pos.see_ge(ttm, threshold) ? ttm : MOVE_NONE;
97 stage += (ttMove == MOVE_NONE);
98}
99
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 histories.
103template<GenType Type>
104void MovePicker::score() {
105
106 static_assert(Type == CAPTURES || Type == QUIETS || Type == EVASIONS, "Wrong type");
107
108 for (auto& m : *this)
109 if (Type == CAPTURES)
110 m.value = int(PieceValue[MG][pos.piece_on(to_sq(m))]) * 6
111 + (*captureHistory)[pos.moved_piece(m)][to_sq(m)][type_of(pos.piece_on(to_sq(m)))];
112
113 else if (Type == QUIETS)
114 m.value = (*mainHistory)[pos.side_to_move()][from_to(m)]
115 + (*continuationHistory[0])[pos.moved_piece(m)][to_sq(m)]
116 + (*continuationHistory[1])[pos.moved_piece(m)][to_sq(m)]
117 + (*continuationHistory[3])[pos.moved_piece(m)][to_sq(m)]
118 + (*continuationHistory[5])[pos.moved_piece(m)][to_sq(m)] / 2;
119
120 else // Type == EVASIONS
121 {
122 if (pos.capture(m))
123 m.value = PieceValue[MG][pos.piece_on(to_sq(m))]
124 - Value(type_of(pos.moved_piece(m)));
125 else
126 m.value = (*mainHistory)[pos.side_to_move()][from_to(m)]
127 + (*continuationHistory[0])[pos.moved_piece(m)][to_sq(m)]
128 - (1 << 28);
129 }
130}
131
132/// MovePicker::select() returns the next move satisfying a predicate function.
133/// It never returns the TT move.
134template<MovePicker::PickType T, typename Pred>
135Move MovePicker::select(Pred filter) {
136
137 while (cur < endMoves)
138 {
139 if (T == Best)
140 std::swap(*cur, *std::max_element(cur, endMoves));
141
142 if (*cur != ttMove && filter())
143 return *cur++;
144
145 cur++;
146 }
147 return MOVE_NONE;
148}
149
150/// MovePicker::next_move() is the most important method of the MovePicker class. It
151/// returns a new pseudo legal move every time it is called until there are no more
152/// moves left, picking the move with the highest score from a list of generated moves.
153Move MovePicker::next_move(bool skipQuiets) {
154
155top:
156 switch (stage) {
157
158 case MAIN_TT:
159 case EVASION_TT:
160 case QSEARCH_TT:
161 case PROBCUT_TT:
162 ++stage;
163 return ttMove;
164
165 case CAPTURE_INIT:
166 case PROBCUT_INIT:
167 case QCAPTURE_INIT:
168 cur = endBadCaptures = moves;
169 endMoves = generate<CAPTURES>(pos, cur);
170
171 score<CAPTURES>();
172 ++stage;
173 goto top;
174
175 case GOOD_CAPTURE:
176 if (select<Best>([&](){
177 return pos.see_ge(*cur, Value(-55 * cur->value / 1024)) ?
178 // Move losing capture to endBadCaptures to be tried later
179 true : (*endBadCaptures++ = *cur, false); }))
180 return *(cur - 1);
181
182 // Prepare the pointers to loop over the refutations array
183 cur = std::begin(refutations);
184 endMoves = std::end(refutations);
185
186 // If the countermove is the same as a killer, skip it
187 if ( refutations[0].move == refutations[2].move
188 || refutations[1].move == refutations[2].move)
189 --endMoves;
190
191 ++stage;
192 /* fallthrough */
193
194 case REFUTATION:
195 if (select<Next>([&](){ return *cur != MOVE_NONE
196 && !pos.capture(*cur)
197 && pos.pseudo_legal(*cur); }))
198 return *(cur - 1);
199 ++stage;
200 /* fallthrough */
201
202 case QUIET_INIT:
203 if (!skipQuiets)
204 {
205 cur = endBadCaptures;
206 endMoves = generate<QUIETS>(pos, cur);
207
208 score<QUIETS>();
209 partial_insertion_sort(cur, endMoves, -4000 * depth / ONE_PLY);
210 }
211
212 ++stage;
213 /* fallthrough */
214
215 case QUIET:
216 if ( !skipQuiets
217 && select<Next>([&](){return *cur != refutations[0].move
218 && *cur != refutations[1].move
219 && *cur != refutations[2].move;}))
220 return *(cur - 1);
221
222 // Prepare the pointers to loop over the bad captures
223 cur = moves;
224 endMoves = endBadCaptures;
225
226 ++stage;
227 /* fallthrough */
228
229 case BAD_CAPTURE:
230 return select<Next>([](){ return true; });
231
232 case EVASION_INIT:
233 cur = moves;
234 endMoves = generate<EVASIONS>(pos, cur);
235
236 score<EVASIONS>();
237 ++stage;
238 /* fallthrough */
239
240 case EVASION:
241 return select<Best>([](){ return true; });
242
243 case PROBCUT:
244 return select<Best>([&](){ return pos.see_ge(*cur, threshold); });
245
246 case QCAPTURE:
247 if (select<Best>([&](){ return depth > DEPTH_QS_RECAPTURES
248 || to_sq(*cur) == recaptureSquare; }))
249 return *(cur - 1);
250
251 // If we did not find any move and we do not try checks, we have finished
252 if (depth != DEPTH_QS_CHECKS)
253 return MOVE_NONE;
254
255 ++stage;
256 /* fallthrough */
257
258 case QCHECK_INIT:
259 cur = moves;
260 endMoves = generate<QUIET_CHECKS>(pos, cur);
261
262 ++stage;
263 /* fallthrough */
264
265 case QCHECK:
266 return select<Next>([](){ return true; });
267 }
268
269 assert(false);
270 return MOVE_NONE; // Silence warning
271}
272