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/>.
38 //// Local definitions
46 const MovegenPhaseT MainSearchPhaseTable[] = { PH_NULL_MOVE, PH_TT_MOVES, PH_GOOD_CAPTURES, PH_KILLERS, PH_NONCAPTURES, PH_BAD_CAPTURES, PH_STOP};
47 const MovegenPhaseT MainSearchNoNullPhaseTable[] = { PH_TT_MOVES, PH_GOOD_CAPTURES, PH_KILLERS, PH_NONCAPTURES, PH_BAD_CAPTURES, PH_STOP};
48 const MovegenPhaseT LowSearchPhaseTable[] = { PH_TT_MOVES, PH_GOOD_CAPTURES, PH_NULL_MOVE, PH_KILLERS, PH_NONCAPTURES, PH_BAD_CAPTURES, PH_STOP};
49 const MovegenPhaseT EvasionsPhaseTable[] = { PH_EVASIONS, PH_STOP};
50 const MovegenPhaseT QsearchWithChecksPhaseTable[] = { PH_TT_MOVES, PH_QCAPTURES, PH_QCHECKS, PH_STOP};
51 const MovegenPhaseT QsearchWithoutChecksPhaseTable[] = { PH_TT_MOVES, PH_QCAPTURES, PH_STOP};
60 /// Constructor for the MovePicker class. Apart from the position for which
61 /// it is asked to pick legal moves, MovePicker also wants some information
62 /// to help it to return the presumably good moves first, to decide which
63 /// moves to return (in the quiescence search, for instance, we only want to
64 /// search captures, promotions and some checks) and about how important good
65 /// move ordering is at the current node.
67 MovePicker::MovePicker(const Position& p, Move ttm, Depth d,
68 const History& h, SearchStack* ss, bool useNullMove) : pos(p), H(h) {
72 ttMoves[1] = (ss->mateKiller == ttm)? MOVE_NONE : ss->mateKiller;
73 killers[0] = ss->killers[0];
74 killers[1] = ss->killers[1];
76 ttMoves[1] = killers[0] = killers[1] = MOVE_NONE;
81 Color us = pos.side_to_move();
83 dc = p.discovered_check_candidates(us);
84 pinned = p.pinned_pieces(us);
87 phasePtr = EvasionsPhaseTable;
88 else if (d >= Depth(3 * OnePly))
89 phasePtr = useNullMove ? MainSearchPhaseTable : MainSearchNoNullPhaseTable;
90 else if (d > Depth(0))
91 phasePtr = useNullMove ? LowSearchPhaseTable : MainSearchNoNullPhaseTable;
92 else if (d == Depth(0))
93 phasePtr = QsearchWithChecksPhaseTable;
95 phasePtr = QsearchWithoutChecksPhaseTable;
102 /// MovePicker::go_next_phase() generates, scores and sorts the next bunch
103 /// of moves when there are no more moves to try for the currrent phase.
105 void MovePicker::go_next_phase() {
108 phase = *(++phasePtr);
115 case PH_GOOD_CAPTURES:
116 numOfMoves = generate_captures(pos, moves);
118 std::sort(moves, moves + numOfMoves);
125 numOfMoves = generate_noncaptures(pos, moves);
127 std::sort(moves, moves + numOfMoves);
130 case PH_BAD_CAPTURES:
131 // Bad captures SEE value is already calculated so just sort them
132 // to get SEE move ordering.
133 std::sort(badCaptures, badCaptures + numOfBadCaptures);
137 assert(pos.is_check());
138 numOfMoves = generate_evasions(pos, moves, pinned);
140 std::sort(moves, moves + numOfMoves);
144 numOfMoves = generate_captures(pos, moves);
146 std::sort(moves, moves + numOfMoves);
150 // Perhaps we should order moves move here? FIXME
151 numOfMoves = generate_non_capture_checks(pos, moves, dc);
164 /// MovePicker::score_captures(), MovePicker::score_noncaptures(),
165 /// MovePicker::score_evasions() and MovePicker::score_qcaptures() assign a
166 /// numerical move ordering score to each move in a move list. The moves
167 /// with highest scores will be picked first by pick_move_from_list().
169 void MovePicker::score_captures() {
170 // Winning and equal captures in the main search are ordered by MVV/LVA.
171 // Suprisingly, this appears to perform slightly better than SEE based
172 // move ordering. The reason is probably that in a position with a winning
173 // capture, capturing a more valuable (but sufficiently defended) piece
174 // first usually doesn't hurt. The opponent will have to recapture, and
175 // the hanging piece will still be hanging (except in the unusual cases
176 // where it is possible to recapture with the hanging piece). Exchanging
177 // big pieces before capturing a hanging piece probably helps to reduce
179 // In main search we want to push captures with negative SEE values to
180 // badCaptures[] array, but instead of doing it now we delay till when
181 // the move has been picked up in pick_move_from_list(), this way we save
182 // some SEE calls in case we get a cutoff (idea from Pablo Vazquez).
185 // Use MVV/LVA ordering
186 for (int i = 0; i < numOfMoves; i++)
189 if (move_is_promotion(m))
190 moves[i].score = QueenValueMidgame;
192 moves[i].score = int(pos.midgame_value_of_piece_on(move_to(m)))
193 -int(pos.type_of_piece_on(move_from(m)));
197 void MovePicker::score_noncaptures() {
198 // First score by history, when no history is available then use
199 // piece/square tables values. This seems to be better then a
200 // random choice when we don't have an history for any move.
205 for (int i = 0; i < numOfMoves; i++)
207 from = move_from(moves[i].move);
208 to = move_to(moves[i].move);
209 piece = pos.piece_on(from);
210 hs = H.move_ordering_score(piece, to);
212 // Ensure history is always preferred to pst
217 moves[i].score = hs + pos.pst_delta<Position::MidGame>(piece, from, to);
221 void MovePicker::score_evasions() {
223 for (int i = 0; i < numOfMoves; i++)
225 Move m = moves[i].move;
227 moves[i].score = 2*HistoryMax;
228 else if (!pos.square_is_empty(move_to(m)))
230 int seeScore = pos.see(m);
231 moves[i].score = (seeScore >= 0)? seeScore + HistoryMax : seeScore;
233 moves[i].score = H.move_ordering_score(pos.piece_on(move_from(m)), move_to(m));
237 /// MovePicker::get_next_move() is the most important method of the MovePicker
238 /// class. It returns a new legal move every time it is called, until there
239 /// are no more moves left.
240 /// It picks the move with the biggest score from a list of generated moves taking
241 /// care not to return the tt move if that has already been serched previously.
243 Move MovePicker::get_next_move() {
245 assert(movesPicked >= 0);
246 assert(!pos.is_check() || *phasePtr == PH_EVASIONS || *phasePtr == PH_STOP);
247 assert( pos.is_check() || *phasePtr != PH_EVASIONS);
258 while (movesPicked < 2) {
259 Move move = ttMoves[movesPicked++];
260 if ( move != MOVE_NONE
261 && move_is_legal(pos, move, pinned))
266 case PH_GOOD_CAPTURES:
267 while (movesPicked < numOfMoves)
269 Move move = moves[movesPicked++].move;
270 if ( move != ttMoves[0]
271 && move != ttMoves[1]
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;
289 while (movesPicked < 2) {
290 Move move = killers[movesPicked++];
291 if ( move != MOVE_NONE
292 && move != ttMoves[0]
293 && move != ttMoves[1]
294 && move_is_legal(pos, move, pinned)
295 && !pos.move_is_capture(move))
301 while (movesPicked < numOfMoves)
303 Move move = moves[movesPicked++].move;
304 if ( move != ttMoves[0]
305 && move != ttMoves[1]
306 && move != killers[0]
307 && move != killers[1]
308 && pos.pl_move_is_legal(move, pinned))
314 if (movesPicked < numOfMoves)
315 return moves[movesPicked++].move;
318 case PH_BAD_CAPTURES:
319 if (movesPicked < numOfBadCaptures)
320 return badCaptures[movesPicked++].move;
325 while (movesPicked < numOfMoves)
327 Move move = moves[movesPicked++].move;
328 // Maybe postpone the legality check until after futility pruning?
329 if ( move != ttMoves[0]
330 && pos.pl_move_is_legal(move, pinned))
347 /// A variant of get_next_move() which takes a lock as a parameter, used to
348 /// prevent multiple threads from picking the same move at a split point.
350 Move MovePicker::get_next_move(Lock &lock) {
358 Move m = get_next_move();