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_NULL_MOVE, PH_TT_MOVES, PH_GOOD_CAPTURES, PH_KILLERS, PH_NONCAPTURES, PH_BAD_CAPTURES, PH_STOP};
44 const MovegenPhaseT MainSearchNoNullPhaseTable[] = { PH_TT_MOVES, PH_GOOD_CAPTURES, PH_KILLERS, PH_NONCAPTURES, PH_BAD_CAPTURES, PH_STOP};
45 const MovegenPhaseT LowSearchPhaseTable[] = { PH_TT_MOVES, PH_NULL_MOVE, PH_GOOD_CAPTURES, PH_KILLERS, PH_NONCAPTURES, PH_BAD_CAPTURES, PH_STOP};
46 const MovegenPhaseT EvasionsPhaseTable[] = { PH_EVASIONS, PH_STOP};
47 const MovegenPhaseT QsearchWithChecksPhaseTable[] = { PH_TT_MOVES, PH_QCAPTURES, PH_QCHECKS, PH_STOP};
48 const MovegenPhaseT QsearchWithoutChecksPhaseTable[] = { PH_TT_MOVES, PH_QCAPTURES, PH_STOP};
57 /// Constructor for the MovePicker class. Apart from the position for which
58 /// it is asked to pick legal moves, MovePicker also wants some information
59 /// to help it to return the presumably good moves first, to decide which
60 /// moves to return (in the quiescence search, for instance, we only want to
61 /// search captures, promotions and some checks) and about how important good
62 /// move ordering is at the current node.
64 MovePicker::MovePicker(const Position& p, Move ttm, Depth d,
65 const History& h, SearchStack* ss, bool useNullMove) : pos(p), H(h) {
66 ttMoves[0].move = ttm;
69 ttMoves[1].move = (ss->mateKiller == ttm)? MOVE_NONE : ss->mateKiller;
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(3 * OnePly))
86 phasePtr = useNullMove ? MainSearchPhaseTable : MainSearchNoNullPhaseTable;
87 else if (d > Depth(0))
88 phasePtr = useNullMove ? LowSearchPhaseTable : MainSearchNoNullPhaseTable;
89 else if (d == Depth(0))
90 phasePtr = QsearchWithChecksPhaseTable;
92 phasePtr = QsearchWithoutChecksPhaseTable;
99 /// MovePicker::go_next_phase() generates, scores and sorts the next bunch
100 /// of moves when there are no more moves to try for the current phase.
102 void MovePicker::go_next_phase() {
105 phase = *(++phasePtr);
113 lastMove = curMove + 2;
116 case PH_GOOD_CAPTURES:
117 lastMove = generate_captures(pos, moves);
119 std::sort(moves, lastMove);
124 lastMove = curMove + 2;
128 lastMove = generate_noncaptures(pos, moves);
130 std::sort(moves, lastMove);
133 case PH_BAD_CAPTURES:
134 // Bad captures SEE value is already calculated so just sort them
135 // to get SEE move ordering.
136 curMove = badCaptures;
137 lastMove = badCaptures + numOfBadCaptures;
138 std::sort(badCaptures, lastMove);
142 assert(pos.is_check());
143 lastMove = generate_evasions(pos, moves, pinned);
145 std::sort(moves, lastMove);
149 lastMove = generate_captures(pos, moves);
151 std::sort(moves, lastMove);
155 // Perhaps we should order moves move here? FIXME
156 lastMove = generate_non_capture_checks(pos, moves, dc);
169 /// MovePicker::score_captures(), MovePicker::score_noncaptures() and
170 /// MovePicker::score_evasions() assign a numerical move ordering score
171 /// to each move in a move list. The moves with highest scores will be
172 /// picked first by get_next_move().
174 void MovePicker::score_captures() {
175 // Winning and equal captures in the main search are ordered by MVV/LVA.
176 // Suprisingly, this appears to perform slightly better than SEE based
177 // move ordering. The reason is probably that in a position with a winning
178 // capture, capturing a more valuable (but sufficiently defended) piece
179 // first usually doesn't hurt. The opponent will have to recapture, and
180 // the hanging piece will still be hanging (except in the unusual cases
181 // where it is possible to recapture with the hanging piece). Exchanging
182 // big pieces before capturing a hanging piece probably helps to reduce
184 // In main search we want to push captures with negative SEE values to
185 // badCaptures[] array, but instead of doing it now we delay till when
186 // the move has been picked up in pick_move_from_list(), this way we save
187 // some SEE calls in case we get a cutoff (idea from Pablo Vazquez).
190 // Use MVV/LVA ordering
191 for (MoveStack* cur = moves; cur != lastMove; cur++)
194 if (move_is_promotion(m))
195 cur->score = QueenValueMidgame;
197 cur->score = int(pos.midgame_value_of_piece_on(move_to(m)))
198 -int(pos.type_of_piece_on(move_from(m)));
202 void MovePicker::score_noncaptures() {
203 // First score by history, when no history is available then use
204 // piece/square tables values. This seems to be better then a
205 // random choice when we don't have an history for any move.
211 for (MoveStack* cur = moves; cur != lastMove; cur++)
216 piece = pos.piece_on(from);
217 hs = H.move_ordering_score(piece, to);
219 // Ensure history is always preferred to pst
224 cur->score = hs + pos.pst_delta<Position::MidGame>(piece, from, to);
228 void MovePicker::score_evasions() {
232 for (MoveStack* cur = moves; cur != lastMove; cur++)
235 if (m == ttMoves[0].move)
236 cur->score = 2 * HistoryMax;
237 else if (!pos.square_is_empty(move_to(m)))
239 int seeScore = pos.see(m);
240 cur->score = seeScore + (seeScore >= 0 ? HistoryMax : 0);
242 cur->score = H.move_ordering_score(pos.piece_on(move_from(m)), move_to(m));
246 /// MovePicker::get_next_move() is the most important method of the MovePicker
247 /// class. It returns a new legal move every time it is called, until there
248 /// are no more moves left.
249 /// It picks the move with the biggest score from a list of generated moves taking
250 /// care not to return the tt move if that has already been serched previously.
252 Move MovePicker::get_next_move() {
254 assert(!pos.is_check() || *phasePtr == PH_EVASIONS || *phasePtr == PH_STOP);
255 assert( pos.is_check() || *phasePtr != PH_EVASIONS);
266 while (curMove != lastMove)
268 Move move = (curMove++)->move;
269 if ( move != MOVE_NONE
270 && move_is_legal(pos, move, pinned))
275 case PH_GOOD_CAPTURES:
276 while (curMove != lastMove)
278 Move move = (curMove++)->move;
279 if ( move != ttMoves[0].move
280 && move != ttMoves[1].move
281 && pos.pl_move_is_legal(move, pinned))
283 // Check for a non negative SEE now
284 int seeValue = pos.see_sign(move);
288 // Losing capture, move it to the badCaptures[] array, note
289 // that move has now been already checked for legality.
290 assert(numOfBadCaptures < 63);
291 badCaptures[numOfBadCaptures].move = move;
292 badCaptures[numOfBadCaptures++].score = seeValue;
298 while (curMove != lastMove)
300 Move move = (curMove++)->move;
301 if ( move != MOVE_NONE
302 && move != ttMoves[0].move
303 && move != ttMoves[1].move
304 && move_is_legal(pos, move, pinned)
305 && !pos.move_is_capture(move))
311 while (curMove != lastMove)
313 Move move = (curMove++)->move;
314 if ( move != ttMoves[0].move
315 && move != ttMoves[1].move
316 && move != killers[0].move
317 && move != killers[1].move
318 && pos.pl_move_is_legal(move, pinned))
324 case PH_BAD_CAPTURES:
325 if (curMove != lastMove)
326 return (curMove++)->move;
331 while (curMove != lastMove)
333 Move move = (curMove++)->move;
334 // Maybe postpone the legality check until after futility pruning?
335 if ( move != ttMoves[0].move
336 && pos.pl_move_is_legal(move, pinned))
352 /// A variant of get_next_move() which takes a lock as a parameter, used to
353 /// prevent multiple threads from picking the same move at a split point.
355 Move MovePicker::get_next_move(Lock &lock) {
363 Move m = get_next_move();