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 for (int i = 0; i < numOfMoves; i++)
252 Move m = moves[i].move;
254 moves[i].score = HistoryMax + 2;
255 else if (m == killer2)
256 moves[i].score = HistoryMax + 1;
258 moves[i].score = H.move_ordering_score(pos->piece_on(move_from(m)), m);
260 // Ensure moves in history are always sorted as first
261 if (moves[i].score > 0)
262 moves[i].score += 1000;
264 moves[i].score += pos->mg_pst_delta(moves[i].move);
268 void MovePicker::score_evasions() {
269 for(int i = 0; i < numOfMoves; i++) {
270 Move m = moves[i].move;
272 moves[i].score = 2*HistoryMax;
273 else if(!pos->square_is_empty(move_to(m))) {
274 int seeScore = pos->see(m);
275 moves[i].score = (seeScore >= 0)? seeScore + HistoryMax : seeScore;
278 moves[i].score = H.move_ordering_score(pos->piece_on(move_from(m)), m);
282 void MovePicker::score_qcaptures() {
283 // Use MVV/LVA ordering.
284 for(int i = 0; i < numOfMoves; i++) {
285 Move m = moves[i].move;
286 if(move_promotion(m))
287 moves[i].score = QueenValueMidgame;
290 int(pos->midgame_value_of_piece_on(move_to(m))) -
291 int(pos->midgame_value_of_piece_on(move_to(m))) / 64;
296 /// MovePicker::pick_move_from_list() picks the move with the biggest score
297 /// from a list of generated moves (moves[] or badCaptures[], depending on
298 /// the current move generation phase). It takes care not to return the
299 /// transposition table move if that has already been serched previously.
300 /// While picking captures in the PH_GOOD_CAPTURES phase (i.e. while picking
301 /// non-losing captures in the main search), it moves all captures with
302 /// negative SEE values to the badCaptures[] array.
304 Move MovePicker::pick_move_from_list() {
305 int bestScore = -10000000;
309 switch(PhaseTable[phaseIndex]) {
311 case PH_GOOD_CAPTURES:
312 assert(!pos->is_check());
313 assert(movesPicked >= 0);
314 while(movesPicked < numOfMoves) {
315 bestScore = -10000000;
317 for(int i = movesPicked; i < numOfMoves; i++) {
318 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) {
326 bestScore = moves[i].score;
329 if(bestIndex != -1) { // Found a good capture
330 move = moves[bestIndex].move;
\r
331 moves[bestIndex] = moves[movesPicked++];
332 if(move != ttMove && move != mateKiller &&
333 pos->move_is_legal(move, pinned))
340 assert(!pos->is_check());
341 assert(movesPicked >= 0);
342 while(movesPicked < numOfMoves) {
343 bestScore = -10000000;
345 // If this is a PV node or we have only picked a few moves, scan
346 // the entire move list for the best move. If many moves have already
347 // been searched and it is not a PV node, we are probably failing low
348 // anyway, so we just pick the first move from the list.
349 if(pvNode || movesPicked < 12) {
351 for(int i = movesPicked; i < numOfMoves; i++)
352 if(moves[i].score > bestScore) {
354 bestScore = moves[i].score;
358 bestIndex = movesPicked;
360 if(bestIndex != -1) {
361 move = moves[bestIndex].move;
\r
362 moves[bestIndex] = moves[movesPicked++];
363 if(move != ttMove && move != mateKiller &&
364 pos->move_is_legal(move, pinned))
371 assert(pos->is_check());
372 assert(movesPicked >= 0);
373 while(movesPicked < numOfMoves) {
374 bestScore = -10000000;
376 for(int i = movesPicked; i < numOfMoves; i++)
377 if(moves[i].score > bestScore) {
379 bestScore = moves[i].score;
382 if(bestIndex != -1) {
383 move = moves[bestIndex].move;
\r
384 moves[bestIndex] = moves[movesPicked++];
390 case PH_BAD_CAPTURES:
391 assert(!pos->is_check());
392 assert(badCapturesPicked >= 0);
393 // It's probably a good idea to use SEE move ordering here, instead
394 // of just picking the first move. FIXME
395 while(badCapturesPicked < numOfBadCaptures) {
396 move = badCaptures[badCapturesPicked++].move;
397 if(move != ttMove && move != mateKiller &&
398 pos->move_is_legal(move, pinned))
404 assert(!pos->is_check());
405 assert(movesPicked >= 0);
406 while(movesPicked < numOfMoves) {
407 bestScore = -10000000;
408 if(movesPicked < 4) {
410 for(int i = movesPicked; i < numOfMoves; i++)
411 if(moves[i].score > bestScore) {
413 bestScore = moves[i].score;
417 bestIndex = movesPicked;
419 if(bestIndex != -1) {
420 move = moves[bestIndex].move;
\r
421 moves[bestIndex] = moves[movesPicked++];
422 // Remember to change the line below if we decide to hash the qsearch!
423 // Maybe also postpone the legality check until after futility pruning?
424 if(/* move != ttMove && */ pos->move_is_legal(move, pinned))
431 assert(!pos->is_check());
432 assert(movesPicked >= 0);
433 // Perhaps we should do something better than just picking the first
435 while(movesPicked < numOfMoves) {
436 move = moves[movesPicked++].move;
437 // Remember to change the line below if we decide to hash the qsearch!
438 if(/* move != ttMove && */ pos->move_is_legal(move, pinned))
450 MovePicker::MovegenPhase MovePicker::current_move_type() const {
451 return PhaseTable[phaseIndex];
454 /// MovePicker::init_phase_table() initializes the PhaseTable[],
455 /// MainSearchPhaseIndex, EvasionPhaseIndex, QsearchWithChecksPhaseIndex
456 /// and QsearchWithoutChecksPhaseIndex variables. It is only called once
457 /// during program startup, and never again while the program is running.
459 void MovePicker::init_phase_table() {
463 MainSearchPhaseIndex = i - 1;
464 PhaseTable[i++] = PH_TT_MOVE;
465 PhaseTable[i++] = PH_MATE_KILLER;
466 PhaseTable[i++] = PH_GOOD_CAPTURES;
467 // PH_KILLER_1 and PH_KILLER_2 are not yet used.
468 // PhaseTable[i++] = PH_KILLER_1;
469 // PhaseTable[i++] = PH_KILLER_2;
470 PhaseTable[i++] = PH_NONCAPTURES;
471 PhaseTable[i++] = PH_BAD_CAPTURES;
472 PhaseTable[i++] = PH_STOP;
475 EvasionsPhaseIndex = i - 1;
476 PhaseTable[i++] = PH_EVASIONS;
477 PhaseTable[i++] = PH_STOP;
479 // Quiescence search with checks
480 QsearchWithChecksPhaseIndex = i - 1;
481 PhaseTable[i++] = PH_QCAPTURES;
482 PhaseTable[i++] = PH_QCHECKS;
483 PhaseTable[i++] = PH_STOP;
485 // Quiescence search without checks
486 QsearchWithoutChecksPhaseIndex = i - 1;
487 PhaseTable[i++] = PH_QCAPTURES;
488 PhaseTable[i++] = PH_STOP;