File: movepick.cpp

package info (click to toggle)
stockfish 12-2
  • links: PTS
  • area: main
  • in suites: bullseye, sid
  • size: 21,436 kB
  • sloc: cpp: 9,020; makefile: 740; ansic: 199; sh: 193
file content (264 lines) | stat: -rw-r--r-- 8,928 bytes parent folder | download
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
/*
  Stockfish, a UCI chess playing engine derived from Glaurung 2.1
  Copyright (C) 2004-2020 The Stockfish developers (see AUTHORS file)

  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 <cassert>

#include "movepick.h"

namespace {

  enum Stages {
    MAIN_TT, CAPTURE_INIT, GOOD_CAPTURE, REFUTATION, QUIET_INIT, QUIET, BAD_CAPTURE,
    EVASION_TT, EVASION_INIT, EVASION,
    PROBCUT_TT, PROBCUT_INIT, PROBCUT,
    QSEARCH_TT, QCAPTURE_INIT, QCAPTURE, QCHECK_INIT, QCHECK
  };

  // partial_insertion_sort() sorts moves in descending order up to and including
  // a given limit. The order of moves smaller than the limit is left unspecified.
  void partial_insertion_sort(ExtMove* begin, ExtMove* end, int limit) {

    for (ExtMove *sortedEnd = begin, *p = begin + 1; p < end; ++p)
        if (p->value >= limit)
        {
            ExtMove tmp = *p, *q;
            *p = *++sortedEnd;
            for (q = sortedEnd; q != begin && *(q - 1) < tmp; --q)
                *q = *(q - 1);
            *q = tmp;
        }
  }

} // namespace


/// 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 how important good move
/// ordering is at the current node.

/// MovePicker constructor for the main search
MovePicker::MovePicker(const Position& p, Move ttm, Depth d, const ButterflyHistory* mh, const LowPlyHistory* lp,
                       const CapturePieceToHistory* cph, const PieceToHistory** ch, Move cm, const Move* killers, int pl)
           : pos(p), mainHistory(mh), lowPlyHistory(lp), captureHistory(cph), continuationHistory(ch),
             ttMove(ttm), refutations{{killers[0], 0}, {killers[1], 0}, {cm, 0}}, depth(d), ply(pl) {

  assert(d > 0);

  stage = (pos.checkers() ? EVASION_TT : MAIN_TT) +
          !(ttm && pos.pseudo_legal(ttm));
}

/// MovePicker constructor for quiescence search
MovePicker::MovePicker(const Position& p, Move ttm, Depth d, const ButterflyHistory* mh,
                       const CapturePieceToHistory* cph, const PieceToHistory** ch, Square rs)
           : pos(p), mainHistory(mh), captureHistory(cph), continuationHistory(ch), ttMove(ttm), recaptureSquare(rs), depth(d) {

  assert(d <= 0);

  stage = (pos.checkers() ? EVASION_TT : QSEARCH_TT) +
           !(ttm && (depth > DEPTH_QS_RECAPTURES || to_sq(ttm) == recaptureSquare)
                 && pos.pseudo_legal(ttm));
}

/// MovePicker constructor for ProbCut: we generate captures with SEE greater
/// than or equal to the given threshold.
MovePicker::MovePicker(const Position& p, Move ttm, Value th, const CapturePieceToHistory* cph)
           : pos(p), captureHistory(cph), ttMove(ttm), threshold(th) {

  assert(!pos.checkers());

  stage = PROBCUT_TT + !(ttm && pos.capture(ttm)
                             && pos.pseudo_legal(ttm)
                             && pos.see_ge(ttm, threshold));
}

/// MovePicker::score() assigns a numerical value to each move in a list, used
/// for sorting. Captures are ordered by Most Valuable Victim (MVV), preferring
/// captures with a good history. Quiets moves are ordered using the histories.
template<GenType Type>
void MovePicker::score() {

  static_assert(Type == CAPTURES || Type == QUIETS || Type == EVASIONS, "Wrong type");

  for (auto& m : *this)
      if (Type == CAPTURES)
          m.value =  int(PieceValue[MG][pos.piece_on(to_sq(m))]) * 6
                   + (*captureHistory)[pos.moved_piece(m)][to_sq(m)][type_of(pos.piece_on(to_sq(m)))];

      else if (Type == QUIETS)
          m.value =      (*mainHistory)[pos.side_to_move()][from_to(m)]
                   + 2 * (*continuationHistory[0])[pos.moved_piece(m)][to_sq(m)]
                   + 2 * (*continuationHistory[1])[pos.moved_piece(m)][to_sq(m)]
                   + 2 * (*continuationHistory[3])[pos.moved_piece(m)][to_sq(m)]
                   +     (*continuationHistory[5])[pos.moved_piece(m)][to_sq(m)]
                   + (ply < MAX_LPH ? std::min(4, depth / 3) * (*lowPlyHistory)[ply][from_to(m)] : 0);

      else // Type == EVASIONS
      {
          if (pos.capture(m))
              m.value =  PieceValue[MG][pos.piece_on(to_sq(m))]
                       - Value(type_of(pos.moved_piece(m)));
          else
              m.value =  (*mainHistory)[pos.side_to_move()][from_to(m)]
                       + (*continuationHistory[0])[pos.moved_piece(m)][to_sq(m)]
                       - (1 << 28);
      }
}

/// MovePicker::select() returns the next move satisfying a predicate function.
/// It never returns the TT move.
template<MovePicker::PickType T, typename Pred>
Move MovePicker::select(Pred filter) {

  while (cur < endMoves)
  {
      if (T == Best)
          std::swap(*cur, *std::max_element(cur, endMoves));

      if (*cur != ttMove && filter())
          return *cur++;

      cur++;
  }
  return MOVE_NONE;
}

/// 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, picking the move with the highest score from a list of generated moves.
Move MovePicker::next_move(bool skipQuiets) {

top:
  switch (stage) {

  case MAIN_TT:
  case EVASION_TT:
  case QSEARCH_TT:
  case PROBCUT_TT:
      ++stage;
      return ttMove;

  case CAPTURE_INIT:
  case PROBCUT_INIT:
  case QCAPTURE_INIT:
      cur = endBadCaptures = moves;
      endMoves = generate<CAPTURES>(pos, cur);

      score<CAPTURES>();
      ++stage;
      goto top;

  case GOOD_CAPTURE:
      if (select<Best>([&](){
                       return pos.see_ge(*cur, Value(-69 * cur->value / 1024)) ?
                              // Move losing capture to endBadCaptures to be tried later
                              true : (*endBadCaptures++ = *cur, false); }))
          return *(cur - 1);

      // Prepare the pointers to loop over the refutations array
      cur = std::begin(refutations);
      endMoves = std::end(refutations);

      // If the countermove is the same as a killer, skip it
      if (   refutations[0].move == refutations[2].move
          || refutations[1].move == refutations[2].move)
          --endMoves;

      ++stage;
      [[fallthrough]];

  case REFUTATION:
      if (select<Next>([&](){ return    *cur != MOVE_NONE
                                    && !pos.capture(*cur)
                                    &&  pos.pseudo_legal(*cur); }))
          return *(cur - 1);
      ++stage;
      [[fallthrough]];

  case QUIET_INIT:
      if (!skipQuiets)
      {
          cur = endBadCaptures;
          endMoves = generate<QUIETS>(pos, cur);

          score<QUIETS>();
          partial_insertion_sort(cur, endMoves, -3000 * depth);
      }

      ++stage;
      [[fallthrough]];

  case QUIET:
      if (   !skipQuiets
          && select<Next>([&](){return   *cur != refutations[0].move
                                      && *cur != refutations[1].move
                                      && *cur != refutations[2].move;}))
          return *(cur - 1);

      // Prepare the pointers to loop over the bad captures
      cur = moves;
      endMoves = endBadCaptures;

      ++stage;
      [[fallthrough]];

  case BAD_CAPTURE:
      return select<Next>([](){ return true; });

  case EVASION_INIT:
      cur = moves;
      endMoves = generate<EVASIONS>(pos, cur);

      score<EVASIONS>();
      ++stage;
      [[fallthrough]];

  case EVASION:
      return select<Best>([](){ return true; });

  case PROBCUT:
      return select<Best>([&](){ return pos.see_ge(*cur, threshold); });

  case QCAPTURE:
      if (select<Best>([&](){ return   depth > DEPTH_QS_RECAPTURES
                                    || to_sq(*cur) == recaptureSquare; }))
          return *(cur - 1);

      // If we did not find any move and we do not try checks, we have finished
      if (depth != DEPTH_QS_CHECKS)
          return MOVE_NONE;

      ++stage;
      [[fallthrough]];

  case QCHECK_INIT:
      cur = moves;
      endMoves = generate<QUIET_CHECKS>(pos, cur);

      ++stage;
      [[fallthrough]];

  case QCHECK:
      return select<Next>([](){ return true; });
  }

  assert(false);
  return MOVE_NONE; // Silence warning
}