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 Marco Costalba
6 Stockfish is free software: you can redistribute it and/or modify
7 it under the terms of the GNU General Public License as published by
8 the Free Software Foundation, either version 3 of the License, or
9 (at your option) any later version.
11 Stockfish is distributed in the hope that it will be useful,
12 but WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 GNU General Public License for more details.
16 You should have received a copy of the GNU General Public License
17 along with this program. If not, see <http://www.gnu.org/licenses/>.
35 //// Local definitions
42 MovePicker::MovegenPhase PhaseTable[32];
43 int MainSearchPhaseIndex;
44 int EvasionsPhaseIndex;
45 int QsearchWithChecksPhaseIndex;
46 int QsearchWithoutChecksPhaseIndex;
57 /// Constructor for the MovePicker class. Apart from the position for which
58 /// it is asked to pick legal moves, MovePicker also wants some information
59 /// to help it to return the presumably good moves first, to decide which
60 /// moves to return (in the quiescence search, for instance, we only want to
61 /// search captures, promotions and some checks) and about how important good
62 /// move ordering is at the current node.
64 MovePicker::MovePicker(Position& p, bool pvnode, Move ttm, Move mk,
65 Move k1, Move k2, Depth d) {
69 mateKiller = (mk == ttm)? MOVE_NONE : mk;
76 dc = p.discovered_check_candidates(p.side_to_move());
79 phaseIndex = EvasionsPhaseIndex;
80 else if (depth > Depth(0))
81 phaseIndex = MainSearchPhaseIndex;
82 else if (depth == Depth(0))
83 phaseIndex = QsearchWithChecksPhaseIndex;
85 phaseIndex = QsearchWithoutChecksPhaseIndex;
87 pinned = p.pinned_pieces(p.side_to_move());
93 /// MovePicker::get_next_move() is the most important method of the MovePicker
94 /// class. It returns a new legal move every time it is called, until there
95 /// are no more moves left of the types we are interested in.
97 Move MovePicker::get_next_move() {
103 // If we already have a list of generated moves, pick the best move from
104 // the list, and return it.
105 move = pick_move_from_list();
106 if (move != MOVE_NONE)
108 assert(move_is_ok(move));
114 switch (PhaseTable[phaseIndex]) {
116 if (ttMove != MOVE_NONE)
118 assert(move_is_ok(ttMove));
119 Move m = generate_move_if_legal(*pos, ttMove, pinned);
129 if (mateKiller != MOVE_NONE)
131 assert(move_is_ok(mateKiller));
132 Move m = generate_move_if_legal(*pos, mateKiller, pinned);
135 assert(m == mateKiller);
141 case PH_GOOD_CAPTURES:
142 numOfMoves = generate_captures(*pos, moves);
147 case PH_BAD_CAPTURES:
148 badCapturesPicked = 0;
152 numOfMoves = generate_noncaptures(*pos, moves);
158 assert(pos->is_check());
159 numOfMoves = generate_evasions(*pos, moves);
165 numOfMoves = generate_captures(*pos, moves);
171 numOfMoves = generate_checks(*pos, moves, dc);
188 /// A variant of get_next_move() which takes a lock as a parameter, used to
189 /// prevent multiple threads from picking the same move at a split point.
191 Move MovePicker::get_next_move(Lock &lock) {
210 /// MovePicker::score_captures(), MovePicker::score_noncaptures(),
211 /// MovePicker::score_evasions() and MovePicker::score_qcaptures() assign a
212 /// numerical move ordering score to each move in a move list. The moves
213 /// with highest scores will be picked first by pick_move_from_list().
215 void MovePicker::score_captures() {
216 // Winning and equal captures in the main search are ordered by MVV/LVA.
217 // Suprisingly, this appears to perform slightly better than SEE based
218 // move ordering. The reason is probably that in a position with a winning
219 // capture, capturing a more valuable (but sufficiently defended) piece
220 // first usually doesn't hurt. The opponent will have to recapture, and
221 // the hanging piece will still be hanging (except in the unusual cases
222 // where it is possible to recapture with the hanging piece). Exchanging
223 // big pieces before capturing a hanging piece probably helps to reduce
225 for (int i = 0; i < numOfMoves; i++)
227 int seeValue = pos->see(moves[i].move);
230 if (move_promotion(moves[i].move))
231 moves[i].score = QueenValueMidgame;
233 moves[i].score = int(pos->midgame_value_of_piece_on(move_to(moves[i].move)))
234 -int(pos->type_of_piece_on(move_from(moves[i].move)));
236 moves[i].score = seeValue;
240 void MovePicker::score_noncaptures() {
242 for (int i = 0; i < numOfMoves; i++)
244 Move m = moves[i].move;
246 moves[i].score = HistoryMax + 2;
247 else if (m == killer2)
248 moves[i].score = HistoryMax + 1;
250 moves[i].score = H.move_ordering_score(pos->piece_on(move_from(m)), m);
254 void MovePicker::score_evasions() {
256 for (int i = 0; i < numOfMoves; i++)
258 Move m = moves[i].move;
260 moves[i].score = 2*HistoryMax;
261 else if(!pos->square_is_empty(move_to(m)))
263 int seeScore = pos->see(m);
264 moves[i].score = (seeScore >= 0)? seeScore + HistoryMax : seeScore;
266 moves[i].score = H.move_ordering_score(pos->piece_on(move_from(m)), m);
268 // FIXME try psqt also here
271 void MovePicker::score_qcaptures() {
273 // Use MVV/LVA ordering
274 for (int i = 0; i < numOfMoves; i++)
276 Move m = moves[i].move;
277 if (move_promotion(m))
278 moves[i].score = QueenValueMidgame;
280 moves[i].score = int(pos->midgame_value_of_piece_on(move_to(m)))
281 -int(pos->midgame_value_of_piece_on(move_to(m))) / 64;
286 /// MovePicker::pick_move_from_list() picks the move with the biggest score
287 /// from a list of generated moves (moves[] or badCaptures[], depending on
288 /// the current move generation phase). It takes care not to return the
289 /// transposition table move if that has already been serched previously.
290 /// While picking captures in the PH_GOOD_CAPTURES phase (i.e. while picking
291 /// non-losing captures in the main search), it moves all captures with
292 /// negative SEE values to the badCaptures[] array.
294 Move MovePicker::pick_move_from_list() {
296 int bestScore = -10000000;
300 switch (PhaseTable[phaseIndex]) {
301 case PH_GOOD_CAPTURES:
302 assert(!pos->is_check());
303 assert(movesPicked >= 0);
305 while (movesPicked < numOfMoves)
307 bestScore = -10000000;
309 for (int i = movesPicked; i < numOfMoves; i++)
311 if (moves[i].score < 0)
313 // Losing capture, move it to the badCaptures[] array
314 assert(numOfBadCaptures < 63);
315 badCaptures[numOfBadCaptures++] = moves[i];
316 moves[i--] = moves[--numOfMoves];
318 else if (moves[i].score > bestScore)
321 bestScore = moves[i].score;
324 if (bestIndex != -1) // Found a good capture
326 move = moves[bestIndex].move;
327 moves[bestIndex] = moves[movesPicked++];
329 && move != mateKiller
330 && pos->move_is_legal(move, pinned))
337 assert(!pos->is_check());
338 assert(movesPicked >= 0);
340 while (movesPicked < numOfMoves)
342 bestScore = -10000000;
344 // If this is a PV node or we have only picked a few moves, scan
345 // the entire move list for the best move. If many moves have already
346 // been searched and it is not a PV node, we are probably failing low
347 // anyway, so we just pick the first move from the list.
348 if (pvNode || movesPicked < 12)
351 for (int i = movesPicked; i < numOfMoves; i++)
352 if (moves[i].score > bestScore)
355 bestScore = moves[i].score;
358 bestIndex = movesPicked;
362 move = moves[bestIndex].move;
363 moves[bestIndex] = moves[movesPicked++];
365 && move != mateKiller
366 && pos->move_is_legal(move, pinned))
373 assert(pos->is_check());
374 assert(movesPicked >= 0);
376 while (movesPicked < numOfMoves)
378 bestScore = -10000000;
380 for (int i = movesPicked; i < numOfMoves; i++)
381 if(moves[i].score > bestScore)
384 bestScore = moves[i].score;
389 move = moves[bestIndex].move;
390 moves[bestIndex] = moves[movesPicked++];
396 case PH_BAD_CAPTURES:
397 assert(!pos->is_check());
398 assert(badCapturesPicked >= 0);
399 // It's probably a good idea to use SEE move ordering here, instead
400 // of just picking the first move. FIXME
401 while (badCapturesPicked < numOfBadCaptures)
403 move = badCaptures[badCapturesPicked++].move;
405 && move != mateKiller
406 && pos->move_is_legal(move, pinned))
412 assert(!pos->is_check());
413 assert(movesPicked >= 0);
414 while (movesPicked < numOfMoves)
416 bestScore = -10000000;
420 for (int i = movesPicked; i < numOfMoves; i++)
421 if(moves[i].score > bestScore)
424 bestScore = moves[i].score;
427 bestIndex = movesPicked;
431 move = moves[bestIndex].move;
432 moves[bestIndex] = moves[movesPicked++];
433 // Remember to change the line below if we decide to hash the qsearch!
434 // Maybe also postpone the legality check until after futility pruning?
435 if (/* move != ttMove && */ pos->move_is_legal(move, pinned))
442 assert(!pos->is_check());
443 assert(movesPicked >= 0);
444 // Perhaps we should do something better than just picking the first
446 while (movesPicked < numOfMoves)
448 move = moves[movesPicked++].move;
449 // Remember to change the line below if we decide to hash the qsearch!
450 if (/* move != ttMove && */ pos->move_is_legal(move, pinned))
461 MovePicker::MovegenPhase MovePicker::current_move_type() const {
463 return PhaseTable[phaseIndex];
466 /// MovePicker::init_phase_table() initializes the PhaseTable[],
467 /// MainSearchPhaseIndex, EvasionPhaseIndex, QsearchWithChecksPhaseIndex
468 /// and QsearchWithoutChecksPhaseIndex variables. It is only called once
469 /// during program startup, and never again while the program is running.
471 void MovePicker::init_phase_table() {
476 MainSearchPhaseIndex = i - 1;
477 PhaseTable[i++] = PH_TT_MOVE;
478 PhaseTable[i++] = PH_MATE_KILLER;
479 PhaseTable[i++] = PH_GOOD_CAPTURES;
480 // PH_KILLER_1 and PH_KILLER_2 are not yet used.
481 // PhaseTable[i++] = PH_KILLER_1;
482 // PhaseTable[i++] = PH_KILLER_2;
483 PhaseTable[i++] = PH_NONCAPTURES;
484 PhaseTable[i++] = PH_BAD_CAPTURES;
485 PhaseTable[i++] = PH_STOP;
488 EvasionsPhaseIndex = i - 1;
489 PhaseTable[i++] = PH_EVASIONS;
490 PhaseTable[i++] = PH_STOP;
492 // Quiescence search with checks
493 QsearchWithChecksPhaseIndex = i - 1;
494 PhaseTable[i++] = PH_QCAPTURES;
495 PhaseTable[i++] = PH_QCHECKS;
496 PhaseTable[i++] = PH_STOP;
498 // Quiescence search without checks
499 QsearchWithoutChecksPhaseIndex = i - 1;
500 PhaseTable[i++] = PH_QCAPTURES;
501 PhaseTable[i++] = PH_STOP;