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);
180 /// A variant of get_next_move() which takes a lock as a parameter, used to
181 /// prevent multiple threads from picking the same move at a split point.
183 Move MovePicker::get_next_move(Lock &lock) {
191 Move m = get_next_move();
200 /// MovePicker::score_captures(), MovePicker::score_noncaptures(),
201 /// MovePicker::score_evasions() and MovePicker::score_qcaptures() assign a
202 /// numerical move ordering score to each move in a move list. The moves
203 /// with highest scores will be picked first by pick_move_from_list().
205 void MovePicker::score_captures() {
206 // Winning and equal captures in the main search are ordered by MVV/LVA.
207 // Suprisingly, this appears to perform slightly better than SEE based
208 // move ordering. The reason is probably that in a position with a winning
209 // capture, capturing a more valuable (but sufficiently defended) piece
210 // first usually doesn't hurt. The opponent will have to recapture, and
211 // the hanging piece will still be hanging (except in the unusual cases
212 // where it is possible to recapture with the hanging piece). Exchanging
213 // big pieces before capturing a hanging piece probably helps to reduce
215 for (int i = 0; i < numOfMoves; i++)
217 int seeValue = pos.see(moves[i].move);
220 if (move_promotion(moves[i].move))
221 moves[i].score = QueenValueMidgame;
223 moves[i].score = int(pos.midgame_value_of_piece_on(move_to(moves[i].move)))
224 -int(pos.type_of_piece_on(move_from(moves[i].move)));
226 moves[i].score = seeValue;
230 void MovePicker::score_noncaptures() {
232 for (int i = 0; i < numOfMoves; i++)
234 Move m = moves[i].move;
236 moves[i].score = HistoryMax + 2;
237 else if (m == killer2)
238 moves[i].score = HistoryMax + 1;
240 moves[i].score = H.move_ordering_score(pos.piece_on(move_from(m)), m);
244 void MovePicker::score_evasions() {
246 for (int i = 0; i < numOfMoves; i++)
248 Move m = moves[i].move;
250 moves[i].score = 2*HistoryMax;
251 else if (!pos.square_is_empty(move_to(m)))
253 int seeScore = pos.see(m);
254 moves[i].score = (seeScore >= 0)? seeScore + HistoryMax : seeScore;
256 moves[i].score = H.move_ordering_score(pos.piece_on(move_from(m)), m);
258 // FIXME try psqt also here
261 void MovePicker::score_qcaptures() {
263 // Use MVV/LVA ordering
264 for (int i = 0; i < numOfMoves; i++)
266 Move m = moves[i].move;
267 if (move_promotion(m))
268 moves[i].score = QueenValueMidgame;
270 moves[i].score = int(pos.midgame_value_of_piece_on(move_to(m)))
271 -int(pos.midgame_value_of_piece_on(move_to(m))) / 64;
276 /// find_best_index() loops across the moves and returns index of
\r
277 /// the highest scored one.
\r
279 int MovePicker::find_best_index() {
\r
281 int bestScore = -10000000, bestIndex = -1;
\r
283 for (int i = movesPicked; i < numOfMoves; i++)
\r
284 if (moves[i].score > bestScore)
\r
287 bestScore = moves[i].score;
\r
293 /// MovePicker::pick_move_from_list() picks the move with the biggest score
294 /// from a list of generated moves (moves[] or badCaptures[], depending on
295 /// the current move generation phase). It takes care not to return the
296 /// transposition table move if that has already been serched previously.
297 /// While picking captures in the PH_GOOD_CAPTURES phase (i.e. while picking
298 /// non-losing captures in the main search), it moves all captures with
299 /// negative SEE values to the badCaptures[] array.
301 Move MovePicker::pick_move_from_list() {
306 switch (PhaseTable[phaseIndex]) {
307 case PH_GOOD_CAPTURES:
308 assert(!pos.is_check());
309 assert(movesPicked >= 0);
311 while (movesPicked < numOfMoves)
313 int bestScore = -10000000;
315 for (int i = movesPicked; i < numOfMoves; i++)
317 if (moves[i].score < 0)
319 // Losing capture, move it to the badCaptures[] array
320 assert(numOfBadCaptures < 63);
321 badCaptures[numOfBadCaptures++] = moves[i];
322 moves[i--] = moves[--numOfMoves];
324 else if (moves[i].score > bestScore)
327 bestScore = moves[i].score;
330 if (bestIndex != -1) // Found a good capture
332 move = moves[bestIndex].move;
333 moves[bestIndex] = moves[movesPicked++];
335 && move != mateKiller
336 && pos.pl_move_is_legal(move, pinned))
343 assert(!pos.is_check());
344 assert(movesPicked >= 0);
346 while (movesPicked < numOfMoves)
348 // If this is a PV node or we have only picked a few moves, scan
349 // the entire move list for the best move. If many moves have already
350 // been searched and it is not a PV node, we are probably failing low
351 // anyway, so we just pick the first move from the list.
352 bestIndex = (pvNode || movesPicked < 12) ? find_best_index() : movesPicked;
356 move = moves[bestIndex].move;
357 moves[bestIndex] = moves[movesPicked++];
359 && move != mateKiller
360 && pos.pl_move_is_legal(move, pinned))
367 assert(pos.is_check());
368 assert(movesPicked >= 0);
370 while (movesPicked < numOfMoves)
372 bestIndex = find_best_index();
376 move = moves[bestIndex].move;
377 moves[bestIndex] = moves[movesPicked++];
383 case PH_BAD_CAPTURES:
384 assert(!pos.is_check());
385 assert(badCapturesPicked >= 0);
386 // It's probably a good idea to use SEE move ordering here, instead
387 // of just picking the first move. FIXME
388 while (badCapturesPicked < numOfBadCaptures)
390 move = badCaptures[badCapturesPicked++].move;
392 && move != mateKiller
393 && pos.pl_move_is_legal(move, pinned))
399 assert(!pos.is_check());
400 assert(movesPicked >= 0);
401 while (movesPicked < numOfMoves)
403 bestIndex = (movesPicked < 4 ? find_best_index() : movesPicked);
407 move = moves[bestIndex].move;
408 moves[bestIndex] = moves[movesPicked++];
409 // Remember to change the line below if we decide to hash the qsearch!
410 // Maybe also postpone the legality check until after futility pruning?
411 if (/* move != ttMove && */ pos.pl_move_is_legal(move, pinned))
418 assert(!pos.is_check());
419 assert(movesPicked >= 0);
420 // Perhaps we should do something better than just picking the first
422 while (movesPicked < numOfMoves)
424 move = moves[movesPicked++].move;
425 // Remember to change the line below if we decide to hash the qsearch!
426 if (/* move != ttMove && */ pos.pl_move_is_legal(move, pinned))
438 /// MovePicker::current_move_type() returns the type of the just
\r
439 /// picked next move. It can be used in search to further differentiate
\r
440 /// according to the current move type: capture, non capture, escape, etc.
441 MovePicker::MovegenPhase MovePicker::current_move_type() const {
443 return PhaseTable[phaseIndex];
447 /// MovePicker::init_phase_table() initializes the PhaseTable[],
448 /// MainSearchPhaseIndex, EvasionPhaseIndex, QsearchWithChecksPhaseIndex
449 /// and QsearchWithoutChecksPhaseIndex variables. It is only called once
450 /// during program startup, and never again while the program is running.
452 void MovePicker::init_phase_table() {
457 MainSearchPhaseIndex = i - 1;
458 PhaseTable[i++] = PH_TT_MOVE;
459 PhaseTable[i++] = PH_MATE_KILLER;
460 PhaseTable[i++] = PH_GOOD_CAPTURES;
461 // PH_KILLER_1 and PH_KILLER_2 are not yet used.
462 // PhaseTable[i++] = PH_KILLER_1;
463 // PhaseTable[i++] = PH_KILLER_2;
464 PhaseTable[i++] = PH_NONCAPTURES;
465 PhaseTable[i++] = PH_BAD_CAPTURES;
466 PhaseTable[i++] = PH_STOP;
469 EvasionsPhaseIndex = i - 1;
470 PhaseTable[i++] = PH_EVASIONS;
471 PhaseTable[i++] = PH_STOP;
473 // Quiescence search with checks
474 QsearchWithChecksPhaseIndex = i - 1;
475 PhaseTable[i++] = PH_QCAPTURES;
476 PhaseTable[i++] = PH_QCHECKS;
477 PhaseTable[i++] = PH_STOP;
479 // Quiescence search without checks
480 QsearchWithoutChecksPhaseIndex = i - 1;
481 PhaseTable[i++] = PH_QCAPTURES;
482 PhaseTable[i++] = PH_STOP;