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(const Position& p, bool pvnode, Move ttm, Move mk,
65 Move k1, Move k2, Depth d) : pos(p) {
68 mateKiller = (mk == ttm)? MOVE_NONE : mk;
75 dc = p.discovered_check_candidates(p.side_to_move());
78 phaseIndex = EvasionsPhaseIndex;
79 else if (depth > Depth(0))
80 phaseIndex = MainSearchPhaseIndex;
81 else if (depth == Depth(0))
82 phaseIndex = QsearchWithChecksPhaseIndex;
84 phaseIndex = QsearchWithoutChecksPhaseIndex;
86 pinned = p.pinned_pieces(p.side_to_move());
92 /// MovePicker::get_next_move() is the most important method of the MovePicker
93 /// class. It returns a new legal move every time it is called, until there
94 /// are no more moves left of the types we are interested in.
96 Move MovePicker::get_next_move() {
102 // If we already have a list of generated moves, pick the best move from
103 // the list, and return it.
104 move = pick_move_from_list();
105 if (move != MOVE_NONE)
107 assert(move_is_ok(move));
113 switch (PhaseTable[phaseIndex]) {
116 if (ttMove != MOVE_NONE)
118 assert(move_is_ok(ttMove));
119 if (move_is_legal(pos, ttMove, pinned))
125 if (mateKiller != MOVE_NONE)
127 assert(move_is_ok(mateKiller));
128 if (move_is_legal(pos, mateKiller, pinned))
133 case PH_GOOD_CAPTURES:
134 numOfMoves = generate_captures(pos, moves);
139 case PH_BAD_CAPTURES:
140 badCapturesPicked = 0;
144 numOfMoves = generate_noncaptures(pos, moves);
150 assert(pos.is_check());
151 numOfMoves = generate_evasions(pos, moves);
157 numOfMoves = generate_captures(pos, moves);
163 numOfMoves = generate_checks(pos, moves, dc);
178 /// A variant of get_next_move() which takes a lock as a parameter, used to
179 /// prevent multiple threads from picking the same move at a split point.
181 Move MovePicker::get_next_move(Lock &lock) {
189 Move m = get_next_move();
198 /// MovePicker::score_captures(), MovePicker::score_noncaptures(),
199 /// MovePicker::score_evasions() and MovePicker::score_qcaptures() assign a
200 /// numerical move ordering score to each move in a move list. The moves
201 /// with highest scores will be picked first by pick_move_from_list().
203 void MovePicker::score_captures() {
204 // Winning and equal captures in the main search are ordered by MVV/LVA.
205 // Suprisingly, this appears to perform slightly better than SEE based
206 // move ordering. The reason is probably that in a position with a winning
207 // capture, capturing a more valuable (but sufficiently defended) piece
208 // first usually doesn't hurt. The opponent will have to recapture, and
209 // the hanging piece will still be hanging (except in the unusual cases
210 // where it is possible to recapture with the hanging piece). Exchanging
211 // big pieces before capturing a hanging piece probably helps to reduce
216 for (int i = 0; i < numOfMoves; i++)
219 seeValue = pos.see(m);
222 if (move_promotion(m))
223 moves[i].score = QueenValueMidgame;
225 moves[i].score = int(pos.midgame_value_of_piece_on(move_to(m)))
226 -int(pos.type_of_piece_on(move_from(m)));
228 moves[i].score = seeValue;
232 void MovePicker::score_noncaptures() {
233 // First score by history, when no history is available then use
234 // piece/square tables values. This seems to be better then a
235 // random choice when we don't have an history for any move.
239 for (int i = 0; i < numOfMoves; i++)
\r
244 hs = HistoryMax + 2;
\r
245 else if (m == killer2)
\r
246 hs = HistoryMax + 1;
\r
248 hs = H.move_ordering_score(pos.piece_on(move_from(m)), m);
\r
250 // Ensure moves in history are always sorted as first
\r
254 moves[i].score = hs + pos.mg_pst_delta(m);
\r
258 void MovePicker::score_evasions() {
260 for (int i = 0; i < numOfMoves; i++)
262 Move m = moves[i].move;
264 moves[i].score = 2*HistoryMax;
265 else if (!pos.square_is_empty(move_to(m)))
267 int seeScore = pos.see(m);
268 moves[i].score = (seeScore >= 0)? seeScore + HistoryMax : seeScore;
270 moves[i].score = H.move_ordering_score(pos.piece_on(move_from(m)), m);
272 // FIXME try psqt also here
275 void MovePicker::score_qcaptures() {
277 // Use MVV/LVA ordering
278 for (int i = 0; i < numOfMoves; i++)
280 Move m = moves[i].move;
281 if (move_promotion(m))
282 moves[i].score = QueenValueMidgame;
284 moves[i].score = int(pos.midgame_value_of_piece_on(move_to(m)))
285 -int(pos.type_of_piece_on(move_from(m)));
290 /// find_best_index() loops across the moves and returns index of
291 /// the highest scored one.
293 int MovePicker::find_best_index() {
295 int bestScore = -10000000, bestIndex = -1;
297 for (int i = movesPicked; i < numOfMoves; i++)
298 if (moves[i].score > bestScore)
301 bestScore = moves[i].score;
307 /// MovePicker::pick_move_from_list() picks the move with the biggest score
308 /// from a list of generated moves (moves[] or badCaptures[], depending on
309 /// the current move generation phase). It takes care not to return the
310 /// transposition table move if that has already been serched previously.
311 /// While picking captures in the PH_GOOD_CAPTURES phase (i.e. while picking
312 /// non-losing captures in the main search), it moves all captures with
313 /// negative SEE values to the badCaptures[] array.
315 Move MovePicker::pick_move_from_list() {
320 switch (PhaseTable[phaseIndex]) {
321 case PH_GOOD_CAPTURES:
322 assert(!pos.is_check());
323 assert(movesPicked >= 0);
325 while (movesPicked < numOfMoves)
327 int bestScore = -10000000;
329 for (int i = movesPicked; i < numOfMoves; i++)
331 if (moves[i].score < 0)
333 // Losing capture, move it to the badCaptures[] array
334 assert(numOfBadCaptures < 63);
335 badCaptures[numOfBadCaptures++] = moves[i];
336 moves[i--] = moves[--numOfMoves];
338 else if (moves[i].score > bestScore)
341 bestScore = moves[i].score;
344 if (bestIndex != -1) // Found a good capture
346 move = moves[bestIndex].move;
347 moves[bestIndex] = moves[movesPicked++];
349 && move != mateKiller
350 && pos.pl_move_is_legal(move, pinned))
357 assert(!pos.is_check());
358 assert(movesPicked >= 0);
360 while (movesPicked < numOfMoves)
362 // If this is a PV node or we have only picked a few moves, scan
363 // the entire move list for the best move. If many moves have already
364 // been searched and it is not a PV node, we are probably failing low
365 // anyway, so we just pick the first move from the list.
366 bestIndex = (pvNode || movesPicked < 12) ? find_best_index() : movesPicked;
370 move = moves[bestIndex].move;
371 moves[bestIndex] = moves[movesPicked++];
373 && move != mateKiller
374 && pos.pl_move_is_legal(move, pinned))
381 assert(pos.is_check());
382 assert(movesPicked >= 0);
384 while (movesPicked < numOfMoves)
386 bestIndex = find_best_index();
390 move = moves[bestIndex].move;
391 moves[bestIndex] = moves[movesPicked++];
397 case PH_BAD_CAPTURES:
398 assert(!pos.is_check());
399 assert(badCapturesPicked >= 0);
400 // It's probably a good idea to use SEE move ordering here, instead
401 // of just picking the first move. FIXME
402 while (badCapturesPicked < numOfBadCaptures)
404 move = badCaptures[badCapturesPicked++].move;
406 && move != mateKiller
407 && pos.pl_move_is_legal(move, pinned))
413 assert(!pos.is_check());
414 assert(movesPicked >= 0);
415 while (movesPicked < numOfMoves)
417 bestIndex = (movesPicked < 4 ? find_best_index() : movesPicked);
421 move = moves[bestIndex].move;
422 moves[bestIndex] = moves[movesPicked++];
423 // Remember to change the line below if we decide to hash the qsearch!
424 // Maybe also postpone the legality check until after futility pruning?
425 if (/* move != ttMove && */ pos.pl_move_is_legal(move, pinned))
432 assert(!pos.is_check());
433 assert(movesPicked >= 0);
434 // Perhaps we should do something better than just picking the first
436 while (movesPicked < numOfMoves)
438 move = moves[movesPicked++].move;
439 // Remember to change the line below if we decide to hash the qsearch!
440 if (/* move != ttMove && */ pos.pl_move_is_legal(move, pinned))
452 /// MovePicker::current_move_type() returns the type of the just
453 /// picked next move. It can be used in search to further differentiate
454 /// according to the current move type: capture, non capture, escape, etc.
455 MovePicker::MovegenPhase MovePicker::current_move_type() const {
457 return PhaseTable[phaseIndex];
461 /// MovePicker::init_phase_table() initializes the PhaseTable[],
462 /// MainSearchPhaseIndex, EvasionPhaseIndex, QsearchWithChecksPhaseIndex
463 /// and QsearchWithoutChecksPhaseIndex variables. It is only called once
464 /// during program startup, and never again while the program is running.
466 void MovePicker::init_phase_table() {
471 MainSearchPhaseIndex = i - 1;
472 PhaseTable[i++] = PH_TT_MOVE;
473 PhaseTable[i++] = PH_MATE_KILLER;
474 PhaseTable[i++] = PH_GOOD_CAPTURES;
475 // PH_KILLER_1 and PH_KILLER_2 are not yet used.
476 // PhaseTable[i++] = PH_KILLER_1;
477 // PhaseTable[i++] = PH_KILLER_2;
478 PhaseTable[i++] = PH_NONCAPTURES;
479 PhaseTable[i++] = PH_BAD_CAPTURES;
480 PhaseTable[i++] = PH_STOP;
483 EvasionsPhaseIndex = i - 1;
484 PhaseTable[i++] = PH_EVASIONS;
485 PhaseTable[i++] = PH_STOP;
487 // Quiescence search with checks
488 QsearchWithChecksPhaseIndex = i - 1;
489 PhaseTable[i++] = PH_QCAPTURES;
490 PhaseTable[i++] = PH_QCHECKS;
491 PhaseTable[i++] = PH_STOP;
493 // Quiescence search without checks
494 QsearchWithoutChecksPhaseIndex = i - 1;
495 PhaseTable[i++] = PH_QCAPTURES;
496 PhaseTable[i++] = PH_STOP;