2 Glaurung, a UCI chess playing engine.
3 Copyright (C) 2004-2008 Tord Romstad
5 Glaurung is free software: you can redistribute it and/or modify
6 it under the terms of the GNU General Public License as published by
7 the Free Software Foundation, either version 3 of the License, or
8 (at your option) any later version.
10 Glaurung is distributed in the hope that it will be useful,
11 but WITHOUT ANY WARRANTY; without even the implied warranty of
12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
13 GNU General Public License for more details.
15 You should have received a copy of the GNU General Public License
16 along with this program. If not, see <http://www.gnu.org/licenses/>.
34 //// Local definitions
41 MovePicker::MovegenPhase PhaseTable[32];
42 int MainSearchPhaseIndex;
43 int EvasionsPhaseIndex;
44 int QsearchWithChecksPhaseIndex;
45 int QsearchWithoutChecksPhaseIndex;
56 /// Constructor for the MovePicker class. Apart from the position for which
57 /// it is asked to pick legal moves, MovePicker also wants some information
58 /// to help it to return the presumably good moves first, to decide which
59 /// moves to return (in the quiescence search, for instance, we only want to
60 /// search captures, promotions and some checks) and about how important good
61 /// move ordering is at the current node.
63 MovePicker::MovePicker(Position &p, bool pvnode, Move ttm, Move mk,
64 Move k1, Move k2, Depth dpth) {
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() {
100 // If we already have a list of generated moves, pick the best move from
101 // the list, and return it:
102 move = this->pick_move_from_list();
103 if(move != MOVE_NONE) {
104 assert(move_is_ok(move));
110 switch(PhaseTable[phaseIndex]) {
113 if(ttMove != MOVE_NONE) {
114 assert(move_is_ok(ttMove));
115 Move m = generate_move_if_legal(*pos, ttMove, pinned);
124 if(mateKiller != MOVE_NONE) {
125 assert(move_is_ok(mateKiller));
126 Move m = generate_move_if_legal(*pos, mateKiller, pinned);
128 assert(m == mateKiller);
134 case PH_GOOD_CAPTURES:
135 // pinned = pos->pinned_pieces(pos->side_to_move());
136 numOfMoves = generate_captures(*pos, moves);
137 this->score_captures();
141 case PH_BAD_CAPTURES:
142 badCapturesPicked = 0;
146 numOfMoves = generate_noncaptures(*pos, moves);
147 this->score_noncaptures();
152 assert(pos->is_check());
153 // pinned = pos->pinned_pieces(pos->side_to_move());
154 numOfMoves = generate_evasions(*pos, moves);
155 this->score_evasions();
160 // pinned = pos->pinned_pieces(pos->side_to_move());
161 numOfMoves = generate_captures(*pos, moves);
162 this->score_qcaptures();
167 numOfMoves = generate_checks(*pos, moves, dc);
186 /// A variant of get_next_move() which takes a lock as a parameter, used to
187 /// prevent multiple threads from picking the same move at a split point.
189 Move MovePicker::get_next_move(Lock &lock) {
197 m = this->get_next_move();
206 /// MovePicker::number_of_moves() simply returns the numOfMoves member
207 /// variable. It is intended to be used in positions where the side to move
208 /// is in check, for detecting checkmates or situations where there is only
209 /// a single reply to check.
211 int MovePicker::number_of_moves() const {
216 /// MovePicker::score_captures(), MovePicker::score_noncaptures(),
217 /// MovePicker::score_evasions() and MovePicker::score_qcaptures() assign a
218 /// numerical move ordering score to each move in a move list. The moves
219 /// with highest scores will be picked first by
220 /// MovePicker::pick_move_from_list().
222 void MovePicker::score_captures() {
223 // Winning and equal captures in the main search are ordered by MVV/LVA.
224 // Suprisingly, this appears to perform slightly better than SEE based
225 // move ordering. The reason is probably that in a position with a winning
226 // capture, capturing a more valuable (but sufficiently defended) piece
227 // first usually doesn't hurt. The opponent will have to recapture, and
228 // the hanging piece will still be hanging (except in the unusual cases
229 // where it is possible to recapture with the hanging piece). Exchanging
230 // big pieces before capturing a hanging piece probably helps to reduce
232 for(int i = 0; i < numOfMoves; i++) {
233 int seeValue = pos->see(moves[i].move);
235 if(move_promotion(moves[i].move))
236 moves[i].score = QueenValueMidgame;
239 int(pos->midgame_value_of_piece_on(move_to(moves[i].move))) -
240 int(pos->type_of_piece_on(move_from(moves[i].move)));
243 moves[i].score = seeValue;
248 void MovePicker::score_noncaptures() {
250 bool all_zero = true;
251 for (int i = 0; i < numOfMoves; i++)
253 Move m = moves[i].move;
256 moves[i].score = HistoryMax + 2;
259 else if (m == killer2)
261 moves[i].score = HistoryMax + 1;
266 moves[i].score = H.move_ordering_score(pos->piece_on(move_from(m)), m);
267 if (all_zero && moves[i].score != 0)
274 // If we don't have at least one history score then
275 // try to order using psq tables difference between
276 // from square and to square.
277 for (int i = 0; i < numOfMoves; i++)
278 moves[i].score = pos->mg_pst_delta(moves[i].move);
281 void MovePicker::score_evasions() {
282 for(int i = 0; i < numOfMoves; i++) {
283 Move m = moves[i].move;
285 moves[i].score = 2*HistoryMax;
286 else if(!pos->square_is_empty(move_to(m))) {
287 int seeScore = pos->see(m);
288 moves[i].score = (seeScore >= 0)? seeScore + HistoryMax : seeScore;
291 moves[i].score = H.move_ordering_score(pos->piece_on(move_from(m)), m);
295 void MovePicker::score_qcaptures() {
296 // Use MVV/LVA ordering.
297 for(int i = 0; i < numOfMoves; i++) {
298 Move m = moves[i].move;
299 if(move_promotion(m))
300 moves[i].score = QueenValueMidgame;
303 int(pos->midgame_value_of_piece_on(move_to(m))) -
304 int(pos->midgame_value_of_piece_on(move_to(m))) / 64;
309 /// MovePicker::pick_move_from_list() picks the move with the biggest score
310 /// from a list of generated moves (moves[] or badCaptures[], depending on
311 /// the current move generation phase). It takes care not to return the
312 /// transposition table move if that has already been serched previously.
313 /// While picking captures in the PH_GOOD_CAPTURES phase (i.e. while picking
314 /// non-losing captures in the main search), it moves all captures with
315 /// negative SEE values to the badCaptures[] array.
317 Move MovePicker::pick_move_from_list() {
318 int bestScore = -10000000;
322 switch(PhaseTable[phaseIndex]) {
324 case PH_GOOD_CAPTURES:
325 assert(!pos->is_check());
326 assert(movesPicked >= 0);
327 while(movesPicked < numOfMoves) {
328 bestScore = -10000000;
330 for(int i = movesPicked; i < numOfMoves; i++) {
331 if(moves[i].score < 0) {
332 // Losing capture, move it to the badCaptures[] array
333 assert(numOfBadCaptures < 63);
334 badCaptures[numOfBadCaptures++] = moves[i];
335 moves[i--] = moves[--numOfMoves];
337 else if(moves[i].score > bestScore) {
339 bestScore = moves[i].score;
342 if(bestIndex != -1) { // Found a good capture
343 move = moves[bestIndex].move;
\r
344 moves[bestIndex] = moves[movesPicked++];
345 if(move != ttMove && move != mateKiller &&
346 pos->move_is_legal(move, pinned))
353 assert(!pos->is_check());
354 assert(movesPicked >= 0);
355 while(movesPicked < numOfMoves) {
356 bestScore = -10000000;
358 // If this is a PV node or we have only picked a few moves, scan
359 // the entire move list for the best move. If many moves have already
360 // been searched and it is not a PV node, we are probably failing low
361 // anyway, so we just pick the first move from the list.
362 if(pvNode || movesPicked < 12) {
364 for(int i = movesPicked; i < numOfMoves; i++)
365 if(moves[i].score > bestScore) {
367 bestScore = moves[i].score;
371 bestIndex = movesPicked;
373 if(bestIndex != -1) {
374 move = moves[bestIndex].move;
\r
375 moves[bestIndex] = moves[movesPicked++];
376 if(move != ttMove && move != mateKiller &&
377 pos->move_is_legal(move, pinned))
384 assert(pos->is_check());
385 assert(movesPicked >= 0);
386 while(movesPicked < numOfMoves) {
387 bestScore = -10000000;
389 for(int i = movesPicked; i < numOfMoves; i++)
390 if(moves[i].score > bestScore) {
392 bestScore = moves[i].score;
395 if(bestIndex != -1) {
396 move = moves[bestIndex].move;
\r
397 moves[bestIndex] = moves[movesPicked++];
403 case PH_BAD_CAPTURES:
404 assert(!pos->is_check());
405 assert(badCapturesPicked >= 0);
406 // It's probably a good idea to use SEE move ordering here, instead
407 // of just picking the first move. FIXME
408 while(badCapturesPicked < numOfBadCaptures) {
409 move = badCaptures[badCapturesPicked++].move;
410 if(move != ttMove && move != mateKiller &&
411 pos->move_is_legal(move, pinned))
417 assert(!pos->is_check());
418 assert(movesPicked >= 0);
419 while(movesPicked < numOfMoves) {
420 bestScore = -10000000;
421 if(movesPicked < 4) {
423 for(int i = movesPicked; i < numOfMoves; i++)
424 if(moves[i].score > bestScore) {
426 bestScore = moves[i].score;
430 bestIndex = movesPicked;
432 if(bestIndex != -1) {
433 move = moves[bestIndex].move;
\r
434 moves[bestIndex] = moves[movesPicked++];
435 // Remember to change the line below if we decide to hash the qsearch!
436 // Maybe also postpone the legality check until after futility pruning?
437 if(/* move != ttMove && */ pos->move_is_legal(move, pinned))
444 assert(!pos->is_check());
445 assert(movesPicked >= 0);
446 // Perhaps we should do something better than just picking the first
448 while(movesPicked < numOfMoves) {
449 move = moves[movesPicked++].move;
450 // Remember to change the line below if we decide to hash the qsearch!
451 if(/* move != ttMove && */ pos->move_is_legal(move, pinned))
463 MovePicker::MovegenPhase MovePicker::current_move_type() const {
464 return PhaseTable[phaseIndex];
467 /// MovePicker::init_phase_table() initializes the PhaseTable[],
468 /// MainSearchPhaseIndex, EvasionPhaseIndex, QsearchWithChecksPhaseIndex
469 /// and QsearchWithoutChecksPhaseIndex variables. It is only called once
470 /// during program startup, and never again while the program is running.
472 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;