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https://github.com/sockspls/badfish
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c8af7a867e
It is not useful becasue it is safe to call get_next_move() multiple times when phase == PH_STOP No functional change. Signed-off-by: Marco Costalba <mcostalba@gmail.com>
355 lines
11 KiB
C++
355 lines
11 KiB
C++
/*
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Stockfish, a UCI chess playing engine derived from Glaurung 2.1
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Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
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Copyright (C) 2008-2009 Marco Costalba
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Stockfish is free software: you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation, either version 3 of the License, or
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(at your option) any later version.
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Stockfish is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program. If not, see <http://www.gnu.org/licenses/>.
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*/
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////
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//// Includes
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////
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#include <cassert>
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#include "history.h"
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#include "movegen.h"
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#include "movepick.h"
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#include "search.h"
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#include "value.h"
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////
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//// Local definitions
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////
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namespace {
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enum MovegenPhase {
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PH_TT_MOVES, // Transposition table move and mate killer
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PH_GOOD_CAPTURES, // Queen promotions and captures with SEE values >= 0
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PH_KILLERS, // Killer moves from the current ply
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PH_NONCAPTURES, // Non-captures and underpromotions
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PH_BAD_CAPTURES, // Queen promotions and captures with SEE values < 0
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PH_EVASIONS, // Check evasions
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PH_QCAPTURES, // Captures in quiescence search
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PH_QCHECKS, // Non-capture checks in quiescence search
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PH_STOP
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};
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CACHE_LINE_ALIGNMENT
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const uint8_t MainSearchPhaseTable[] = { PH_TT_MOVES, PH_GOOD_CAPTURES, PH_KILLERS, PH_NONCAPTURES, PH_BAD_CAPTURES, PH_STOP};
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const uint8_t EvasionsPhaseTable[] = { PH_TT_MOVES, PH_EVASIONS, PH_STOP};
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const uint8_t QsearchWithChecksPhaseTable[] = { PH_TT_MOVES, PH_QCAPTURES, PH_QCHECKS, PH_STOP};
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const uint8_t QsearchWithoutChecksPhaseTable[] = { PH_TT_MOVES, PH_QCAPTURES, PH_STOP};
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}
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////
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//// Functions
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////
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/// Constructor for the MovePicker class. Apart from the position for which
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/// it is asked to pick legal moves, MovePicker also wants some information
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/// to help it to return the presumably good moves first, to decide which
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/// moves to return (in the quiescence search, for instance, we only want to
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/// search captures, promotions and some checks) and about how important good
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/// move ordering is at the current node.
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MovePicker::MovePicker(const Position& p, Move ttm, Depth d,
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const History& h, SearchStack* ss) : pos(p), H(h) {
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int searchTT = ttm;
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ttMoves[0].move = ttm;
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lastBadCapture = badCaptures;
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pinned = p.pinned_pieces(pos.side_to_move());
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if (ss && !p.is_check())
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{
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ttMoves[1].move = (ss->mateKiller == ttm)? MOVE_NONE : ss->mateKiller;
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searchTT |= ttMoves[1].move;
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killers[0].move = ss->killers[0];
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killers[1].move = ss->killers[1];
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} else
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ttMoves[1].move = killers[0].move = killers[1].move = MOVE_NONE;
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if (p.is_check())
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phasePtr = EvasionsPhaseTable;
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else if (d > Depth(0))
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phasePtr = MainSearchPhaseTable;
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else if (d == Depth(0))
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phasePtr = QsearchWithChecksPhaseTable;
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else
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phasePtr = QsearchWithoutChecksPhaseTable;
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phasePtr += !searchTT - 1;
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go_next_phase();
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}
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/// MovePicker::go_next_phase() generates, scores and sorts the next bunch
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/// of moves when there are no more moves to try for the current phase.
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void MovePicker::go_next_phase() {
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curMove = moves;
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phase = *(++phasePtr);
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switch (phase) {
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case PH_TT_MOVES:
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curMove = ttMoves;
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lastMove = curMove + 2;
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return;
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case PH_GOOD_CAPTURES:
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lastMove = generate_captures(pos, moves);
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score_captures();
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return;
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case PH_KILLERS:
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curMove = killers;
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lastMove = curMove + 2;
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return;
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case PH_NONCAPTURES:
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lastMove = generate_noncaptures(pos, moves);
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score_noncaptures();
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sort_moves(moves, lastMove);
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return;
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case PH_BAD_CAPTURES:
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// Bad captures SEE value is already calculated so just sort them
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// to get SEE move ordering.
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curMove = badCaptures;
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lastMove = lastBadCapture;
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return;
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case PH_EVASIONS:
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assert(pos.is_check());
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lastMove = generate_evasions(pos, moves);
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score_evasions();
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return;
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case PH_QCAPTURES:
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lastMove = generate_captures(pos, moves);
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score_captures();
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return;
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case PH_QCHECKS:
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// Perhaps we should order moves move here? FIXME
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lastMove = generate_non_capture_checks(pos, moves);
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return;
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case PH_STOP:
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lastMove = curMove + 1; // Avoids another go_next_phase() call
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return;
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default:
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assert(false);
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return;
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}
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}
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/// MovePicker::score_captures(), MovePicker::score_noncaptures() and
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/// MovePicker::score_evasions() assign a numerical move ordering score
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/// to each move in a move list. The moves with highest scores will be
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/// picked first by get_next_move().
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void MovePicker::score_captures() {
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// Winning and equal captures in the main search are ordered by MVV/LVA.
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// Suprisingly, this appears to perform slightly better than SEE based
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// move ordering. The reason is probably that in a position with a winning
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// capture, capturing a more valuable (but sufficiently defended) piece
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// first usually doesn't hurt. The opponent will have to recapture, and
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// the hanging piece will still be hanging (except in the unusual cases
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// where it is possible to recapture with the hanging piece). Exchanging
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// big pieces before capturing a hanging piece probably helps to reduce
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// the subtree size.
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// In main search we want to push captures with negative SEE values to
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// badCaptures[] array, but instead of doing it now we delay till when
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// the move has been picked up in pick_move_from_list(), this way we save
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// some SEE calls in case we get a cutoff (idea from Pablo Vazquez).
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Move m;
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// Use MVV/LVA ordering
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for (MoveStack* cur = moves; cur != lastMove; cur++)
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{
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m = cur->move;
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if (move_is_promotion(m))
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cur->score = QueenValueMidgame;
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else
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cur->score = pos.midgame_value_of_piece_on(move_to(m))
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- pos.type_of_piece_on(move_from(m));
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}
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}
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void MovePicker::score_noncaptures() {
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// First score by history, when no history is available then use
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// piece/square tables values. This seems to be better then a
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// random choice when we don't have an history for any move.
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Move m;
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Piece piece;
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Square from, to;
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int hs;
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for (MoveStack* cur = moves; cur != lastMove; cur++)
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{
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m = cur->move;
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from = move_from(m);
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to = move_to(m);
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piece = pos.piece_on(from);
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hs = H.move_ordering_score(piece, to);
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// Ensure history is always preferred to pst
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if (hs > 0)
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hs += 1000;
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// pst based scoring
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cur->score = hs + mg_value(pos.pst_delta(piece, from, to));
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}
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}
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void MovePicker::score_evasions() {
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// Try good captures ordered by MVV/LVA, then non-captures if
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// destination square is not under attack, ordered by history
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// value, and at the end bad-captures and non-captures with a
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// negative SEE. This last group is ordered by the SEE score.
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Move m;
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int seeScore;
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for (MoveStack* cur = moves; cur != lastMove; cur++)
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{
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m = cur->move;
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if ((seeScore = pos.see_sign(m)) < 0)
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cur->score = seeScore;
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else if (pos.move_is_capture(m))
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cur->score = pos.midgame_value_of_piece_on(move_to(m))
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- pos.type_of_piece_on(move_from(m)) + HistoryMax;
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else
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cur->score = H.move_ordering_score(pos.piece_on(move_from(m)), move_to(m));
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}
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}
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/// MovePicker::get_next_move() is the most important method of the MovePicker
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/// class. It returns a new legal move every time it is called, until there
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/// are no more moves left.
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/// It picks the move with the biggest score from a list of generated moves taking
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/// care not to return the tt move if has already been searched previously.
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Move MovePicker::get_next_move() {
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Move move;
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while (true)
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{
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while (curMove != lastMove)
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{
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switch (phase) {
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case PH_TT_MOVES:
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move = (curMove++)->move;
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if ( move != MOVE_NONE
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&& move_is_legal(pos, move, pinned))
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return move;
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break;
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case PH_GOOD_CAPTURES:
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move = pick_best(curMove++, lastMove).move;
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if ( move != ttMoves[0].move
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&& move != ttMoves[1].move
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&& pos.pl_move_is_legal(move, pinned))
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{
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// Check for a non negative SEE now
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int seeValue = pos.see_sign(move);
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if (seeValue >= 0)
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return move;
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// Losing capture, move it to the badCaptures[] array, note
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// that move has now been already checked for legality.
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assert(int(lastBadCapture - badCaptures) < 63);
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lastBadCapture->move = move;
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lastBadCapture->score = seeValue;
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lastBadCapture++;
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}
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break;
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case PH_KILLERS:
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move = (curMove++)->move;
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if ( move != MOVE_NONE
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&& move != ttMoves[0].move
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&& move != ttMoves[1].move
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&& move_is_legal(pos, move, pinned)
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&& !pos.move_is_capture(move))
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return move;
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break;
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case PH_NONCAPTURES:
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move = (curMove++)->move;
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if ( move != ttMoves[0].move
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&& move != ttMoves[1].move
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&& move != killers[0].move
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&& move != killers[1].move
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&& pos.pl_move_is_legal(move, pinned))
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return move;
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break;
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case PH_BAD_CAPTURES:
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move = pick_best(curMove++, lastMove).move;
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return move;
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case PH_EVASIONS:
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case PH_QCAPTURES:
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move = pick_best(curMove++, lastMove).move;
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if ( move != ttMoves[0].move
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&& pos.pl_move_is_legal(move, pinned))
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return move;
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break;
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case PH_QCHECKS:
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move = (curMove++)->move;
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if ( move != ttMoves[0].move
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&& pos.pl_move_is_legal(move, pinned))
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return move;
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break;
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case PH_STOP:
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return MOVE_NONE;
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default:
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assert(false);
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break;
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}
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}
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go_next_phase();
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}
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}
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/// A variant of get_next_move() which takes a lock as a parameter, used to
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/// prevent multiple threads from picking the same move at a split point.
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Move MovePicker::get_next_move(Lock &lock) {
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lock_grab(&lock);
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// Note that it is safe to call many times
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// get_next_move() when phase == PH_STOP
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Move m = get_next_move();
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lock_release(&lock);
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return m;
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}
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