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() {
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 (generate_move_if_legal(*pos, ttMove, pinned) != MOVE_NONE)
125 if (mateKiller != MOVE_NONE)
127 assert(move_is_ok(mateKiller));
128 if (generate_move_if_legal(*pos, mateKiller, pinned) != MOVE_NONE)
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);
181 /// A variant of get_next_move() which takes a lock as a parameter, used to
182 /// prevent multiple threads from picking the same move at a split point.
184 Move MovePicker::get_next_move(Lock &lock) {
192 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
204 /// MovePicker::pick_move_from_list().
206 void MovePicker::score_captures() {
207 // Winning and equal captures in the main search are ordered by MVV/LVA.
208 // Suprisingly, this appears to perform slightly better than SEE based
209 // move ordering. The reason is probably that in a position with a winning
210 // capture, capturing a more valuable (but sufficiently defended) piece
211 // first usually doesn't hurt. The opponent will have to recapture, and
212 // the hanging piece will still be hanging (except in the unusual cases
213 // where it is possible to recapture with the hanging piece). Exchanging
214 // big pieces before capturing a hanging piece probably helps to reduce
216 for (int i = 0; i < numOfMoves; i++)
218 Move m = moves[i].move;
219 moves[i].score = pos->see(m);
220 if (moves[i].score >= 0)
222 moves[i].score = move_promotion(m) ? QueenValueMidgame
223 : int(pos->midgame_value_of_piece_on(move_to(m)))
224 -int(pos->type_of_piece_on(move_from(m)));
225 // FIXME second term seems wrong !
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);
242 // Ensure moves in history are always sorted as first
243 if (moves[i].score > 0)
244 moves[i].score += 1000;
246 moves[i].score += pos->mg_pst_delta(moves[i].move);
250 void MovePicker::score_evasions() {
252 for (int i = 0; i < numOfMoves; i++)
254 Move m = moves[i].move;
256 moves[i].score = 2*HistoryMax;
257 else if (!pos->square_is_empty(move_to(m)))
259 moves[i].score = pos->see(m);
260 if (moves[i].score >= 0)
261 moves[i].score += HistoryMax;
264 moves[i].score = H.move_ordering_score(pos->piece_on(move_from(m)), m);
266 // FIXME try psqt also here
269 void MovePicker::score_qcaptures() {
271 // Use MVV/LVA ordering.
272 for (int i = 0; i < numOfMoves; i++)
274 Move m = moves[i].move;
275 moves[i].score = move_promotion(m) ? QueenValueMidgame
276 : int(pos->midgame_value_of_piece_on(move_to(m)))
277 -int(pos->midgame_value_of_piece_on(move_to(m))) / 64;
278 // FIXME Why second term like that ???
283 /// MovePicker::pick_move_from_list() picks the move with the biggest score
284 /// from a list of generated moves (moves[] or badCaptures[], depending on
285 /// the current move generation phase). It takes care not to return the
286 /// transposition table move if that has already been serched previously.
287 /// While picking captures in the PH_GOOD_CAPTURES phase (i.e. while picking
288 /// non-losing captures in the main search), it moves all captures with
289 /// negative SEE values to the badCaptures[] array.
291 Move MovePicker::pick_move_from_list() {
293 int bestScore = -10000000;
297 switch (PhaseTable[phaseIndex]) {
299 case PH_GOOD_CAPTURES:
300 assert(!pos->is_check());
301 assert(movesPicked >= 0);
302 while (movesPicked < numOfMoves)
304 bestScore = -10000000;
306 for (int i = movesPicked; i < numOfMoves; i++)
308 if (moves[i].score < 0)
310 // Losing capture, move it to the badCaptures[] array
311 assert(numOfBadCaptures < 63);
312 badCaptures[numOfBadCaptures++] = moves[i];
313 moves[i--] = moves[--numOfMoves];
315 else if (moves[i].score > bestScore)
318 bestScore = moves[i].score;
321 if (bestIndex != -1) // Found a good capture
323 move = moves[bestIndex].move;
\r
324 moves[bestIndex] = moves[movesPicked++];
326 && move != mateKiller
327 && pos->move_is_legal(move, pinned))
334 assert(!pos->is_check());
335 assert(movesPicked >= 0);
336 while (movesPicked < numOfMoves)
338 // If this is a PV node or we have only picked a few moves, scan
339 // the entire move list for the best move. If many moves have already
340 // been searched and it is not a PV node, we are probably failing low
341 // anyway, so we just pick the first move from the list.
342 if (pvNode || movesPicked < 12)
344 bestScore = -10000000;
346 for (int i = movesPicked; i < numOfMoves; i++)
347 if(moves[i].score > bestScore)
350 bestScore = moves[i].score;
353 bestIndex = movesPicked;
357 move = moves[bestIndex].move;
\r
358 moves[bestIndex] = moves[movesPicked++];
360 && move != mateKiller
361 && pos->move_is_legal(move, pinned))
368 assert(pos->is_check());
369 assert(movesPicked >= 0);
370 while (movesPicked < numOfMoves)
372 bestScore = -10000000;
374 for (int i = movesPicked; i < numOfMoves; i++)
375 if (moves[i].score > bestScore)
378 bestScore = moves[i].score;
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)
397 move = badCaptures[badCapturesPicked++].move;
399 && move != mateKiller
400 && pos->move_is_legal(move, pinned))
406 assert(!pos->is_check());
407 assert(movesPicked >= 0);
408 while (movesPicked < numOfMoves)
410 bestScore = -10000000;
411 if (movesPicked < 4) // FIXME makes sens to score qcaps?
414 for (int i = movesPicked; i < numOfMoves; i++)
415 if(moves[i].score > bestScore)
418 bestScore = moves[i].score;
421 bestIndex = movesPicked;
425 move = moves[bestIndex].move;
\r
426 moves[bestIndex] = moves[movesPicked++];
427 // Remember to change the line below if we decide to hash the qsearch!
428 // Maybe also postpone the legality check until after futility pruning?
430 if (/* move != ttMove && */ pos->move_is_legal(move, pinned))
437 assert(!pos->is_check());
438 assert(movesPicked >= 0);
439 // Perhaps we should do something better than just picking the first
441 while (movesPicked < numOfMoves)
443 move = moves[movesPicked++].move;
444 // Remember to change the line below if we decide to hash the qsearch!
446 if (/* move != ttMove && */ pos->move_is_legal(move, pinned))
458 /// MovePicker::current_move_type() returns the type of the just
459 /// picked next move. It can be used in search to further differentiate
460 /// according to the current move type: capture, non capture, escape, etc.
461 MovePicker::MovegenPhase MovePicker::current_move_type() const {
462 return PhaseTable[phaseIndex];
466 /// MovePicker::init_phase_table() initializes the PhaseTable[],
467 /// MainSearchPhaseIndex, EvasionPhaseIndex, QsearchWithChecksPhaseIndex
468 /// and QsearchWithoutChecksPhaseIndex variables. It is only called once
469 /// during program startup, and never again while the program is running.
471 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;