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(const Position& p, bool pvnode, Move ttm, Move mk,
64 Move k1, Move k2, Depth d) : pos(p) {
67 mateKiller = (mk == ttm)? MOVE_NONE : mk;
74 dc = p.discovered_check_candidates(p.side_to_move());
77 phaseIndex = EvasionsPhaseIndex;
78 else if(depth > Depth(0))
79 phaseIndex = MainSearchPhaseIndex;
80 else if(depth == Depth(0))
81 phaseIndex = QsearchWithChecksPhaseIndex;
83 phaseIndex = QsearchWithoutChecksPhaseIndex;
85 pinned = p.pinned_pieces(p.side_to_move());
91 /// MovePicker::get_next_move() is the most important method of the MovePicker
92 /// class. It returns a new legal move every time it is called, until there
93 /// are no more moves left of the types we are interested in.
95 Move MovePicker::get_next_move() {
101 // If we already have a list of generated moves, pick the best move from
102 // the list, and return it:
103 move = pick_move_from_list();
104 if (move != MOVE_NONE)
106 assert(move_is_ok(move));
112 switch (PhaseTable[phaseIndex]) {
115 if (ttMove != MOVE_NONE)
117 assert(move_is_ok(ttMove));
118 if (generate_move_if_legal(pos, ttMove, pinned) != MOVE_NONE)
124 if (mateKiller != MOVE_NONE)
126 assert(move_is_ok(mateKiller));
127 if (generate_move_if_legal(pos, mateKiller, pinned) != MOVE_NONE)
132 case PH_GOOD_CAPTURES:
133 numOfMoves = generate_captures(pos, moves);
138 case PH_BAD_CAPTURES:
139 badCapturesPicked = 0;
143 numOfMoves = generate_noncaptures(pos, moves);
149 assert(pos.is_check());
150 numOfMoves = generate_evasions(pos, moves);
156 numOfMoves = generate_captures(pos, moves);
162 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();
199 /// MovePicker::score_captures(), MovePicker::score_noncaptures(),
200 /// MovePicker::score_evasions() and MovePicker::score_qcaptures() assign a
201 /// numerical move ordering score to each move in a move list. The moves
202 /// with highest scores will be picked first by
203 /// MovePicker::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 Move m = moves[i].move;
218 moves[i].score = pos.see(m);
219 if (moves[i].score >= 0)
221 moves[i].score = move_promotion(m) ? QueenValueMidgame
222 : int(pos.midgame_value_of_piece_on(move_to(m)))
223 -int(pos.type_of_piece_on(move_from(m)));
224 // FIXME second term seems wrong !
229 void MovePicker::score_noncaptures() {
231 for (int i = 0; i < numOfMoves; i++)
233 Move m = moves[i].move;
235 moves[i].score = HistoryMax + 2;
236 else if (m == killer2)
237 moves[i].score = HistoryMax + 1;
239 moves[i].score = H.move_ordering_score(pos.piece_on(move_from(m)), m);
241 // Ensure moves in history are always sorted as first
242 if (moves[i].score > 0)
243 moves[i].score += 1000;
245 moves[i].score += pos.mg_pst_delta(moves[i].move);
249 void MovePicker::score_evasions() {
251 for (int i = 0; i < numOfMoves; i++)
253 Move m = moves[i].move;
255 moves[i].score = 2*HistoryMax;
256 else if (!pos.square_is_empty(move_to(m)))
258 moves[i].score = pos.see(m);
259 if (moves[i].score >= 0)
260 moves[i].score += HistoryMax;
263 moves[i].score = H.move_ordering_score(pos.piece_on(move_from(m)), m);
265 // FIXME try psqt also here
268 void MovePicker::score_qcaptures() {
270 // Use MVV/LVA ordering.
271 for (int i = 0; i < numOfMoves; i++)
273 Move m = moves[i].move;
274 moves[i].score = move_promotion(m) ? QueenValueMidgame
275 : int(pos.midgame_value_of_piece_on(move_to(m)))
276 -int(pos.midgame_value_of_piece_on(move_to(m))) / 64;
277 // FIXME Why second term like that ???
282 /// MovePicker::pick_move_from_list() picks the move with the biggest score
283 /// from a list of generated moves (moves[] or badCaptures[], depending on
284 /// the current move generation phase). It takes care not to return the
285 /// transposition table move if that has already been serched previously.
286 /// While picking captures in the PH_GOOD_CAPTURES phase (i.e. while picking
287 /// non-losing captures in the main search), it moves all captures with
288 /// negative SEE values to the badCaptures[] array.
290 Move MovePicker::pick_move_from_list() {
292 int bestScore = -10000000;
296 switch (PhaseTable[phaseIndex]) {
298 case PH_GOOD_CAPTURES:
299 assert(!pos.is_check());
300 assert(movesPicked >= 0);
301 while (movesPicked < numOfMoves)
303 bestScore = -10000000;
305 for (int i = movesPicked; i < numOfMoves; i++)
307 if (moves[i].score < 0)
309 // Losing capture, move it to the badCaptures[] array
310 assert(numOfBadCaptures < 63);
311 badCaptures[numOfBadCaptures++] = moves[i];
312 moves[i--] = moves[--numOfMoves];
314 else if (moves[i].score > bestScore)
317 bestScore = moves[i].score;
320 if (bestIndex != -1) // Found a good capture
322 move = moves[bestIndex].move;
\r
323 moves[bestIndex] = moves[movesPicked++];
325 && move != mateKiller
326 && pos.move_is_legal(move, pinned))
333 assert(!pos.is_check());
334 assert(movesPicked >= 0);
335 while (movesPicked < numOfMoves)
337 // If this is a PV node or we have only picked a few moves, scan
338 // the entire move list for the best move. If many moves have already
339 // been searched and it is not a PV node, we are probably failing low
340 // anyway, so we just pick the first move from the list.
341 if (pvNode || movesPicked < 12)
343 bestScore = -10000000;
345 for (int i = movesPicked; i < numOfMoves; i++)
346 if(moves[i].score > bestScore)
349 bestScore = moves[i].score;
352 bestIndex = movesPicked;
356 move = moves[bestIndex].move;
\r
357 moves[bestIndex] = moves[movesPicked++];
359 && move != mateKiller
360 && pos.move_is_legal(move, pinned))
367 assert(pos.is_check());
368 assert(movesPicked >= 0);
369 while (movesPicked < numOfMoves)
371 bestScore = -10000000;
373 for (int i = movesPicked; i < numOfMoves; i++)
374 if (moves[i].score > bestScore)
377 bestScore = moves[i].score;
382 move = moves[bestIndex].move;
\r
383 moves[bestIndex] = moves[movesPicked++];
389 case PH_BAD_CAPTURES:
390 assert(!pos.is_check());
391 assert(badCapturesPicked >= 0);
392 // It's probably a good idea to use SEE move ordering here, instead
393 // of just picking the first move. FIXME
394 while (badCapturesPicked < numOfBadCaptures)
396 move = badCaptures[badCapturesPicked++].move;
398 && move != mateKiller
399 && pos.move_is_legal(move, pinned))
405 assert(!pos.is_check());
406 assert(movesPicked >= 0);
407 while (movesPicked < numOfMoves)
409 bestScore = -10000000;
410 if (movesPicked < 4) // FIXME makes sens to score qcaps?
413 for (int i = movesPicked; i < numOfMoves; i++)
414 if(moves[i].score > bestScore)
417 bestScore = moves[i].score;
420 bestIndex = movesPicked;
424 move = moves[bestIndex].move;
\r
425 moves[bestIndex] = moves[movesPicked++];
426 // Remember to change the line below if we decide to hash the qsearch!
427 // Maybe also postpone the legality check until after futility pruning?
429 if (/* move != ttMove && */ pos.move_is_legal(move, pinned))
436 assert(!pos.is_check());
437 assert(movesPicked >= 0);
438 // Perhaps we should do something better than just picking the first
440 while (movesPicked < numOfMoves)
442 move = moves[movesPicked++].move;
443 // Remember to change the line below if we decide to hash the qsearch!
445 if (/* move != ttMove && */ pos.move_is_legal(move, pinned))
457 /// MovePicker::current_move_type() returns the type of the just
458 /// picked next move. It can be used in search to further differentiate
459 /// according to the current move type: capture, non capture, escape, etc.
460 MovePicker::MovegenPhase MovePicker::current_move_type() const {
461 return PhaseTable[phaseIndex];
465 /// MovePicker::init_phase_table() initializes the PhaseTable[],
466 /// MainSearchPhaseIndex, EvasionPhaseIndex, QsearchWithChecksPhaseIndex
467 /// and QsearchWithoutChecksPhaseIndex variables. It is only called once
468 /// during program startup, and never again while the program is running.
470 void MovePicker::init_phase_table() {
475 MainSearchPhaseIndex = i - 1;
476 PhaseTable[i++] = PH_TT_MOVE;
477 PhaseTable[i++] = PH_MATE_KILLER;
478 PhaseTable[i++] = PH_GOOD_CAPTURES;
479 // PH_KILLER_1 and PH_KILLER_2 are not yet used.
480 // PhaseTable[i++] = PH_KILLER_1;
481 // PhaseTable[i++] = PH_KILLER_2;
482 PhaseTable[i++] = PH_NONCAPTURES;
483 PhaseTable[i++] = PH_BAD_CAPTURES;
484 PhaseTable[i++] = PH_STOP;
487 EvasionsPhaseIndex = i - 1;
488 PhaseTable[i++] = PH_EVASIONS;
489 PhaseTable[i++] = PH_STOP;
491 // Quiescence search with checks
492 QsearchWithChecksPhaseIndex = i - 1;
493 PhaseTable[i++] = PH_QCAPTURES;
494 PhaseTable[i++] = PH_QCHECKS;
495 PhaseTable[i++] = PH_STOP;
497 // Quiescence search without checks
498 QsearchWithoutChecksPhaseIndex = i - 1;
499 PhaseTable[i++] = PH_QCAPTURES;
500 PhaseTable[i++] = PH_STOP;