2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
4 Copyright (C) 2008-2009 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.
12 Stockfish is distributed in the hope that it will be useful,
13 but WITHOUT ANY WARRANTY; without even the implied warranty of
14 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
15 GNU General Public License for more details.
17 You should have received a copy of the GNU General Public License
18 along with this program. If not, see <http://www.gnu.org/licenses/>.
37 //// Local definitions
43 const MovegenPhaseT MainSearchPhaseTable[] = { PH_TT_MOVES, PH_GOOD_CAPTURES, PH_KILLERS, PH_NONCAPTURES, PH_BAD_CAPTURES, PH_STOP};
44 const MovegenPhaseT EvasionsPhaseTable[] = { PH_EVASIONS, PH_STOP};
45 const MovegenPhaseT QsearchWithChecksPhaseTable[] = { PH_TT_MOVES, PH_QCAPTURES, PH_QCHECKS, PH_STOP};
46 const MovegenPhaseT QsearchWithoutChecksPhaseTable[] = { PH_TT_MOVES, PH_QCAPTURES, PH_STOP};
55 /// Constructor for the MovePicker class. Apart from the position for which
56 /// it is asked to pick legal moves, MovePicker also wants some information
57 /// to help it to return the presumably good moves first, to decide which
58 /// moves to return (in the quiescence search, for instance, we only want to
59 /// search captures, promotions and some checks) and about how important good
60 /// move ordering is at the current node.
62 MovePicker::MovePicker(const Position& p, Move ttm, Depth d,
63 const History& h, SearchStack* ss) : pos(p), H(h) {
65 ttMoves[0].move = ttm;
68 ttMoves[1].move = (ss->mateKiller == ttm)? MOVE_NONE : ss->mateKiller;
69 searchTT |= ttMoves[1].move;
70 killers[0].move = ss->killers[0];
71 killers[1].move = ss->killers[1];
73 ttMoves[1].move = killers[0].move = killers[1].move = MOVE_NONE;
78 Color us = pos.side_to_move();
80 dc = p.discovered_check_candidates(us);
81 pinned = p.pinned_pieces(us);
84 phasePtr = EvasionsPhaseTable;
85 else if (d > Depth(0))
86 phasePtr = MainSearchPhaseTable + !searchTT;
87 else if (d == Depth(0))
88 phasePtr = QsearchWithChecksPhaseTable + !searchTT;
90 phasePtr = QsearchWithoutChecksPhaseTable + !searchTT;
97 /// MovePicker::go_next_phase() generates, scores and sorts the next bunch
98 /// of moves when there are no more moves to try for the current phase.
100 void MovePicker::go_next_phase() {
103 phase = *(++phasePtr);
108 lastMove = curMove + 2;
111 case PH_GOOD_CAPTURES:
112 lastMove = generate_captures(pos, moves);
114 std::sort(moves, lastMove);
119 lastMove = curMove + 2;
123 lastMove = generate_noncaptures(pos, moves);
125 std::sort(moves, lastMove);
128 case PH_BAD_CAPTURES:
129 // Bad captures SEE value is already calculated so just sort them
130 // to get SEE move ordering.
131 curMove = badCaptures;
132 lastMove = badCaptures + numOfBadCaptures;
133 std::sort(badCaptures, lastMove);
137 assert(pos.is_check());
138 lastMove = generate_evasions(pos, moves, pinned);
140 std::sort(moves, lastMove);
144 lastMove = generate_captures(pos, moves);
146 std::sort(moves, lastMove);
150 // Perhaps we should order moves move here? FIXME
151 lastMove = generate_non_capture_checks(pos, moves, dc);
155 lastMove = curMove + 1; // hack to be friendly for get_next_move()
165 /// MovePicker::score_captures(), MovePicker::score_noncaptures() and
166 /// MovePicker::score_evasions() assign a numerical move ordering score
167 /// to each move in a move list. The moves with highest scores will be
168 /// picked first by get_next_move().
170 void MovePicker::score_captures() {
171 // Winning and equal captures in the main search are ordered by MVV/LVA.
172 // Suprisingly, this appears to perform slightly better than SEE based
173 // move ordering. The reason is probably that in a position with a winning
174 // capture, capturing a more valuable (but sufficiently defended) piece
175 // first usually doesn't hurt. The opponent will have to recapture, and
176 // the hanging piece will still be hanging (except in the unusual cases
177 // where it is possible to recapture with the hanging piece). Exchanging
178 // big pieces before capturing a hanging piece probably helps to reduce
180 // In main search we want to push captures with negative SEE values to
181 // badCaptures[] array, but instead of doing it now we delay till when
182 // the move has been picked up in pick_move_from_list(), this way we save
183 // some SEE calls in case we get a cutoff (idea from Pablo Vazquez).
186 // Use MVV/LVA ordering
187 for (MoveStack* cur = moves; cur != lastMove; cur++)
190 if (move_is_promotion(m))
191 cur->score = QueenValueMidgame;
193 cur->score = int(pos.midgame_value_of_piece_on(move_to(m)))
194 -int(pos.type_of_piece_on(move_from(m)));
198 void MovePicker::score_noncaptures() {
199 // First score by history, when no history is available then use
200 // piece/square tables values. This seems to be better then a
201 // random choice when we don't have an history for any move.
207 for (MoveStack* cur = moves; cur != lastMove; cur++)
212 piece = pos.piece_on(from);
213 hs = H.move_ordering_score(piece, to);
215 // Ensure history is always preferred to pst
220 cur->score = hs + pos.pst_delta<Position::MidGame>(piece, from, to);
224 void MovePicker::score_evasions() {
228 for (MoveStack* cur = moves; cur != lastMove; cur++)
231 if (m == ttMoves[0].move)
232 cur->score = 2 * HistoryMax;
233 else if (!pos.square_is_empty(move_to(m)))
235 int seeScore = pos.see(m);
236 cur->score = seeScore + (seeScore >= 0 ? HistoryMax : 0);
238 cur->score = H.move_ordering_score(pos.piece_on(move_from(m)), move_to(m));
242 /// MovePicker::get_next_move() is the most important method of the MovePicker
243 /// class. It returns a new legal move every time it is called, until there
244 /// are no more moves left.
245 /// It picks the move with the biggest score from a list of generated moves taking
246 /// care not to return the tt move if that has already been serched previously.
248 Move MovePicker::get_next_move() {
250 assert(!pos.is_check() || *phasePtr == PH_EVASIONS || *phasePtr == PH_STOP);
251 assert( pos.is_check() || *phasePtr != PH_EVASIONS);
257 while (curMove != lastMove)
259 move = (curMove++)->move;
264 if ( move != MOVE_NONE
265 && move_is_legal(pos, move, pinned))
269 case PH_GOOD_CAPTURES:
270 if ( move != ttMoves[0].move
271 && move != ttMoves[1].move
272 && pos.pl_move_is_legal(move, pinned))
274 // Check for a non negative SEE now
275 int seeValue = pos.see_sign(move);
279 // Losing capture, move it to the badCaptures[] array, note
280 // that move has now been already checked for legality.
281 assert(numOfBadCaptures < 63);
282 badCaptures[numOfBadCaptures].move = move;
283 badCaptures[numOfBadCaptures++].score = seeValue;
288 if ( move != MOVE_NONE
289 && move != ttMoves[0].move
290 && move != ttMoves[1].move
291 && move_is_legal(pos, move, pinned)
292 && !pos.move_is_capture(move))
297 if ( move != ttMoves[0].move
298 && move != ttMoves[1].move
299 && move != killers[0].move
300 && move != killers[1].move
301 && pos.pl_move_is_legal(move, pinned))
306 case PH_BAD_CAPTURES:
311 // Maybe postpone the legality check until after futility pruning?
312 if ( move != ttMoves[0].move
313 && pos.pl_move_is_legal(move, pinned))
329 /// A variant of get_next_move() which takes a lock as a parameter, used to
330 /// prevent multiple threads from picking the same move at a split point.
332 Move MovePicker::get_next_move(Lock &lock) {
340 Move m = get_next_move();