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/>.
36 //// Local definitions
42 PH_TT_MOVES, // Transposition table move and mate killer
43 PH_GOOD_CAPTURES, // Queen promotions and captures with SEE values >= 0
44 PH_KILLERS, // Killer moves from the current ply
45 PH_NONCAPTURES, // Non-captures and underpromotions
46 PH_BAD_CAPTURES, // Queen promotions and captures with SEE values < 0
47 PH_EVASIONS, // Check evasions
48 PH_QCAPTURES, // Captures in quiescence search
49 PH_QCHECKS, // Non-capture checks in quiescence search
54 const uint8_t MainSearchPhaseTable[] = { PH_TT_MOVES, PH_GOOD_CAPTURES, PH_KILLERS, PH_NONCAPTURES, PH_BAD_CAPTURES, PH_STOP};
55 const uint8_t EvasionsPhaseTable[] = { PH_EVASIONS, PH_STOP};
56 const uint8_t QsearchWithChecksPhaseTable[] = { PH_TT_MOVES, PH_QCAPTURES, PH_QCHECKS, PH_STOP};
57 const uint8_t QsearchWithoutChecksPhaseTable[] = { PH_TT_MOVES, PH_QCAPTURES, PH_STOP};
66 /// Constructor for the MovePicker class. Apart from the position for which
67 /// it is asked to pick legal moves, MovePicker also wants some information
68 /// to help it to return the presumably good moves first, to decide which
69 /// moves to return (in the quiescence search, for instance, we only want to
70 /// search captures, promotions and some checks) and about how important good
71 /// move ordering is at the current node.
73 MovePicker::MovePicker(const Position& p, Move ttm, Depth d,
74 const History& h, SearchStack* ss) : pos(p), H(h) {
76 ttMoves[0].move = ttm;
78 lastBadCapture = badCaptures;
82 ttMoves[1].move = (ss->mateKiller == ttm)? MOVE_NONE : ss->mateKiller;
83 searchTT |= ttMoves[1].move;
84 killers[0].move = ss->killers[0];
85 killers[1].move = ss->killers[1];
87 ttMoves[1].move = killers[0].move = killers[1].move = MOVE_NONE;
89 pinned = p.pinned_pieces(pos.side_to_move());
92 phasePtr = EvasionsPhaseTable;
93 else if (d > Depth(0))
94 phasePtr = MainSearchPhaseTable + !searchTT;
95 else if (d == Depth(0))
96 phasePtr = QsearchWithChecksPhaseTable + !searchTT;
98 phasePtr = QsearchWithoutChecksPhaseTable + !searchTT;
105 /// MovePicker::go_next_phase() generates, scores and sorts the next bunch
106 /// of moves when there are no more moves to try for the current phase.
108 void MovePicker::go_next_phase() {
111 phase = *(++phasePtr);
116 lastMove = curMove + 2;
119 case PH_GOOD_CAPTURES:
120 lastMove = generate_captures(pos, moves);
126 lastMove = curMove + 2;
130 lastMove = generate_noncaptures(pos, moves);
132 sort_moves(moves, lastMove);
135 case PH_BAD_CAPTURES:
136 // Bad captures SEE value is already calculated so just sort them
137 // to get SEE move ordering.
138 curMove = badCaptures;
139 lastMove = lastBadCapture;
143 assert(pos.is_check());
144 lastMove = generate_evasions(pos, moves);
149 lastMove = generate_captures(pos, moves);
154 // Perhaps we should order moves move here? FIXME
155 lastMove = generate_non_capture_checks(pos, moves);
159 lastMove = curMove + 1; // hack to be friendly for get_next_move()
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 = pos.midgame_value_of_piece_on(move_to(m))
198 - 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() {
229 // Always try ttMove as first. Then try good captures ordered
230 // by MVV/LVA, then non-captures if destination square is not
231 // under attack, ordered by history value, and at the end
232 // bad-captures and non-captures with a negative SEE. This
233 // last group is ordered by the SEE score.
237 for (MoveStack* cur = moves; cur != lastMove; cur++)
240 if (m == ttMoves[0].move)
241 cur->score = 2 * HistoryMax;
242 else if ((seeScore = pos.see_sign(m)) < 0)
243 cur->score = seeScore;
244 else if (pos.move_is_capture(m))
245 cur->score = pos.midgame_value_of_piece_on(move_to(m))
246 - pos.type_of_piece_on(move_from(m)) + HistoryMax;
248 cur->score = H.move_ordering_score(pos.piece_on(move_from(m)), move_to(m));
252 /// MovePicker::get_next_move() is the most important method of the MovePicker
253 /// class. It returns a new legal move every time it is called, until there
254 /// are no more moves left.
255 /// It picks the move with the biggest score from a list of generated moves taking
256 /// care not to return the tt move if has already been searched previously.
258 Move MovePicker::get_next_move() {
260 assert(!pos.is_check() || *phasePtr == PH_EVASIONS || *phasePtr == PH_STOP);
261 assert( pos.is_check() || *phasePtr != PH_EVASIONS);
267 while (curMove != lastMove)
272 move = (curMove++)->move;
273 if ( move != MOVE_NONE
274 && move_is_legal(pos, move, pinned))
278 case PH_GOOD_CAPTURES:
279 move = pick_best(curMove++, lastMove).move;
280 if ( move != ttMoves[0].move
281 && move != ttMoves[1].move
282 && pos.pl_move_is_legal(move, pinned))
284 // Check for a non negative SEE now
285 int seeValue = pos.see_sign(move);
289 // Losing capture, move it to the badCaptures[] array, note
290 // that move has now been already checked for legality.
291 assert(int(lastBadCapture - badCaptures) < 63);
292 lastBadCapture->move = move;
293 lastBadCapture->score = seeValue;
299 move = (curMove++)->move;
300 if ( move != MOVE_NONE
301 && move != ttMoves[0].move
302 && move != ttMoves[1].move
303 && move_is_legal(pos, move, pinned)
304 && !pos.move_is_capture(move))
309 move = (curMove++)->move;
310 if ( move != ttMoves[0].move
311 && move != ttMoves[1].move
312 && move != killers[0].move
313 && move != killers[1].move
314 && pos.pl_move_is_legal(move, pinned))
318 case PH_BAD_CAPTURES:
319 move = pick_best(curMove++, lastMove).move;
323 move = pick_best(curMove++, lastMove).move;
324 if (pos.pl_move_is_legal(move, pinned))
329 move = pick_best(curMove++, lastMove).move;
330 if ( move != ttMoves[0].move
331 && pos.pl_move_is_legal(move, pinned))
336 move = (curMove++)->move;
337 if ( move != ttMoves[0].move
338 && pos.pl_move_is_legal(move, pinned))
354 /// A variant of get_next_move() which takes a lock as a parameter, used to
355 /// prevent multiple threads from picking the same move at a split point.
357 Move MovePicker::get_next_move(Lock &lock) {
365 Move m = get_next_move();