-
Notifications
You must be signed in to change notification settings - Fork 472
/
movepick.cpp
364 lines (285 loc) · 10.7 KB
/
movepick.cpp
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
/*
Stockfish, a UCI chess playing engine derived from Glaurung 2.1
Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
Copyright (C) 2008-2012 Marco Costalba, Joona Kiiski, Tord Romstad
Stockfish is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.
Stockfish is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
#include <algorithm>
#include <cassert>
#include "movegen.h"
#include "movepick.h"
#include "thread.h"
namespace {
enum Sequencer {
MAIN_SEARCH, CAPTURES_S1, KILLERS_S1, QUIETS_1_S1, QUIETS_2_S1, BAD_CAPTURES_S1,
EVASION, EVASIONS_S2,
QSEARCH_0, CAPTURES_S3, QUIET_CHECKS_S3,
QSEARCH_1, CAPTURES_S4,
PROBCUT, CAPTURES_S5,
RECAPTURE, CAPTURES_S6,
STOP
};
// Unary predicate used by std::partition to split positive scores from remaining
// ones so to sort separately the two sets, and with the second sort delayed.
inline bool has_positive_score(const MoveStack& ms) { return ms.score > 0; }
// Picks and moves to the front the best move in the range [begin, end),
// it is faster than sorting all the moves in advance when moves are few, as
// normally are the possible captures.
inline MoveStack* pick_best(MoveStack* begin, MoveStack* end)
{
std::swap(*begin, *std::max_element(begin, end));
return begin;
}
}
/// Constructors of the MovePicker class. As arguments we pass information
/// to help it to return the presumably good moves first, to decide which
/// moves to return (in the quiescence search, for instance, we only want to
/// search captures, promotions and some checks) and about how important good
/// move ordering is at the current node.
MovePicker::MovePicker(const Position& p, Move ttm, Depth d, const History& h,
Search::Stack* s, Value beta) : pos(p), H(h), depth(d) {
assert(d > DEPTH_ZERO);
captureThreshold = 0;
cur = end = moves;
endBadCaptures = moves + MAX_MOVES - 1;
ss = s;
if (p.in_check())
phase = EVASION;
else
{
phase = MAIN_SEARCH;
killers[0].move = ss->killers[0];
killers[1].move = ss->killers[1];
// Consider sligtly negative captures as good if at low depth and far from beta
if (ss && ss->eval < beta - PawnValueMg && d < 3 * ONE_PLY)
captureThreshold = -PawnValueMg;
// Consider negative captures as good if still enough to reach beta
else if (ss && ss->eval > beta)
captureThreshold = beta - ss->eval;
}
ttMove = (ttm && pos.is_pseudo_legal(ttm) ? ttm : MOVE_NONE);
end += (ttMove != MOVE_NONE);
}
MovePicker::MovePicker(const Position& p, Move ttm, Depth d, const History& h,
Square sq) : pos(p), H(h), cur(moves), end(moves) {
assert(d <= DEPTH_ZERO);
if (p.in_check())
phase = EVASION;
else if (d > DEPTH_QS_NO_CHECKS)
phase = QSEARCH_0;
else if (d > DEPTH_QS_RECAPTURES)
{
phase = QSEARCH_1;
// Skip TT move if is not a capture or a promotion, this avoids qsearch
// tree explosion due to a possible perpetual check or similar rare cases
// when TT table is full.
if (ttm && !pos.is_capture_or_promotion(ttm))
ttm = MOVE_NONE;
}
else
{
phase = RECAPTURE;
recaptureSquare = sq;
ttm = MOVE_NONE;
}
ttMove = (ttm && pos.is_pseudo_legal(ttm) ? ttm : MOVE_NONE);
end += (ttMove != MOVE_NONE);
}
MovePicker::MovePicker(const Position& p, Move ttm, const History& h, PieceType pt)
: pos(p), H(h), cur(moves), end(moves) {
assert(!pos.in_check());
phase = PROBCUT;
// In ProbCut we generate only captures better than parent's captured piece
captureThreshold = PieceValue[Mg][pt];
ttMove = (ttm && pos.is_pseudo_legal(ttm) ? ttm : MOVE_NONE);
if (ttMove && (!pos.is_capture(ttMove) || pos.see(ttMove) <= captureThreshold))
ttMove = MOVE_NONE;
end += (ttMove != MOVE_NONE);
}
/// MovePicker::score_captures(), MovePicker::score_noncaptures() and
/// MovePicker::score_evasions() assign a numerical move ordering score
/// to each move in a move list. The moves with highest scores will be
/// picked first by next_move().
void MovePicker::score_captures() {
// Winning and equal captures in the main search are ordered by MVV/LVA.
// Suprisingly, this appears to perform slightly better than SEE based
// move ordering. The reason is probably that in a position with a winning
// capture, capturing a more valuable (but sufficiently defended) piece
// first usually doesn't hurt. The opponent will have to recapture, and
// the hanging piece will still be hanging (except in the unusual cases
// where it is possible to recapture with the hanging piece). Exchanging
// big pieces before capturing a hanging piece probably helps to reduce
// the subtree size.
// In main search we want to push captures with negative SEE values to
// badCaptures[] array, but instead of doing it now we delay till when
// the move has been picked up in pick_move_from_list(), this way we save
// some SEE calls in case we get a cutoff (idea from Pablo Vazquez).
Move m;
for (MoveStack* it = moves; it != end; ++it)
{
m = it->move;
it->score = PieceValue[Mg][pos.piece_on(to_sq(m))]
- type_of(pos.piece_moved(m));
if (type_of(m) == PROMOTION)
it->score += PieceValue[Mg][promotion_type(m)];
}
}
void MovePicker::score_noncaptures() {
Move m;
for (MoveStack* it = moves; it != end; ++it)
{
m = it->move;
it->score = H.value(pos.piece_moved(m), to_sq(m));
}
}
void MovePicker::score_evasions() {
// Try good captures ordered by MVV/LVA, then non-captures if destination square
// is not under attack, ordered by history value, then bad-captures and quiet
// moves with a negative SEE. This last group is ordered by the SEE score.
Move m;
int seeScore;
if (end < moves + 2)
return;
for (MoveStack* it = moves; it != end; ++it)
{
m = it->move;
if ((seeScore = pos.see_sign(m)) < 0)
it->score = seeScore - History::MaxValue; // Be sure we are at the bottom
else if (pos.is_capture(m))
it->score = PieceValue[Mg][pos.piece_on(to_sq(m))]
- type_of(pos.piece_moved(m)) + History::MaxValue;
else
it->score = H.value(pos.piece_moved(m), to_sq(m));
}
}
/// MovePicker::generate_next() generates, scores and sorts the next bunch of moves,
/// when there are no more moves to try for the current phase.
void MovePicker::generate_next() {
cur = moves;
switch (++phase) {
case CAPTURES_S1: case CAPTURES_S3: case CAPTURES_S4: case CAPTURES_S5: case CAPTURES_S6:
end = generate<CAPTURES>(pos, moves);
score_captures();
return;
case KILLERS_S1:
cur = killers;
end = cur + 2;
return;
case QUIETS_1_S1:
endQuiets = end = generate<QUIETS>(pos, moves);
score_noncaptures();
end = std::partition(cur, end, has_positive_score);
sort<MoveStack>(cur, end);
return;
case QUIETS_2_S1:
cur = end;
end = endQuiets;
if (depth >= 3 * ONE_PLY)
sort<MoveStack>(cur, end);
return;
case BAD_CAPTURES_S1:
// Just pick them in reverse order to get MVV/LVA ordering
cur = moves + MAX_MOVES - 1;
end = endBadCaptures;
return;
case EVASIONS_S2:
end = generate<EVASIONS>(pos, moves);
score_evasions();
return;
case QUIET_CHECKS_S3:
end = generate<QUIET_CHECKS>(pos, moves);
return;
case EVASION: case QSEARCH_0: case QSEARCH_1: case PROBCUT: case RECAPTURE:
phase = STOP;
case STOP:
end = cur + 1; // Avoid another next_phase() call
return;
default:
assert(false);
}
}
/// MovePicker::next_move() is the most important method of the MovePicker class.
/// It returns a new pseudo legal move every time it is called, until there
/// are no more moves left. It picks the move with the biggest score from a list
/// of generated moves taking care not to return the tt move if has already been
/// searched previously.
template<>
Move MovePicker::next_move<false>() {
Move move;
while (true)
{
while (cur == end)
generate_next();
switch (phase) {
case MAIN_SEARCH: case EVASION: case QSEARCH_0: case QSEARCH_1: case PROBCUT:
cur++;
return ttMove;
case CAPTURES_S1:
move = pick_best(cur++, end)->move;
if (move != ttMove)
{
assert(captureThreshold <= 0); // Otherwise we cannot use see_sign()
if (pos.see_sign(move) >= captureThreshold)
return move;
// Losing capture, move it to the tail of the array
(endBadCaptures--)->move = move;
}
break;
case KILLERS_S1:
move = (cur++)->move;
if ( move != MOVE_NONE
&& pos.is_pseudo_legal(move)
&& move != ttMove
&& !pos.is_capture(move))
return move;
break;
case QUIETS_1_S1: case QUIETS_2_S1:
move = (cur++)->move;
if ( move != ttMove
&& move != killers[0].move
&& move != killers[1].move)
return move;
break;
case BAD_CAPTURES_S1:
return (cur--)->move;
case EVASIONS_S2: case CAPTURES_S3: case CAPTURES_S4:
move = pick_best(cur++, end)->move;
if (move != ttMove)
return move;
break;
case CAPTURES_S5:
move = pick_best(cur++, end)->move;
if (move != ttMove && pos.see(move) > captureThreshold)
return move;
break;
case CAPTURES_S6:
move = pick_best(cur++, end)->move;
if (to_sq(move) == recaptureSquare)
return move;
break;
case QUIET_CHECKS_S3:
move = (cur++)->move;
if (move != ttMove)
return move;
break;
case STOP:
return MOVE_NONE;
default:
assert(false);
}
}
}
/// Version of next_move() to use at split point nodes where the move is grabbed
/// from the split point's shared MovePicker object. This function is not thread
/// safe so should be lock protected by the caller.
template<>
Move MovePicker::next_move<true>() { return ss->sp->mp->next_move<false>(); }