mirror of
https://github.com/peterosterlund2/droidfish.git
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319 lines
9.1 KiB
C++
319 lines
9.1 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) 2008-2015 Marco Costalba, Joona Kiiski, Tord Romstad
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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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#include <cassert>
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#include "movepick.h"
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#include "thread.h"
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namespace {
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enum Stages {
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MAIN_SEARCH, GOOD_CAPTURES, KILLERS, GOOD_QUIETS, BAD_QUIETS, BAD_CAPTURES,
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EVASION, ALL_EVASIONS,
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QSEARCH_WITH_CHECKS, QCAPTURES_1, CHECKS,
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QSEARCH_WITHOUT_CHECKS, QCAPTURES_2,
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PROBCUT, PROBCUT_CAPTURES,
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RECAPTURE, RECAPTURES,
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STOP
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};
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// Our insertion sort, which is guaranteed to be stable, as it should be
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void insertion_sort(ExtMove* begin, ExtMove* end)
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{
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ExtMove tmp, *p, *q;
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for (p = begin + 1; p < end; ++p)
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{
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tmp = *p;
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for (q = p; q != begin && *(q-1) < tmp; --q)
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*q = *(q-1);
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*q = tmp;
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}
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}
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// pick_best() finds the best move in the range (begin, end) and moves it to
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// the front. It's faster than sorting all the moves in advance when there
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// are few moves e.g. the possible captures.
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Move pick_best(ExtMove* begin, ExtMove* end)
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{
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std::swap(*begin, *std::max_element(begin, end));
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return *begin;
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}
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} // namespace
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/// Constructors of the MovePicker class. As arguments we pass 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 how important good move
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/// ordering is at the current node.
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MovePicker::MovePicker(const Position& p, Move ttm, Depth d, const HistoryStats& h,
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const CounterMovesStats& cmh, Move cm, Search::Stack* s)
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: pos(p), history(h), counterMovesHistory(&cmh), ss(s), countermove(cm), depth(d) {
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assert(d > DEPTH_ZERO);
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stage = pos.checkers() ? EVASION : MAIN_SEARCH;
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ttMove = ttm && pos.pseudo_legal(ttm) ? ttm : MOVE_NONE;
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endMoves += (ttMove != MOVE_NONE);
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}
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MovePicker::MovePicker(const Position& p, Move ttm, Depth d,
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const HistoryStats& h, Square s)
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: pos(p), history(h), counterMovesHistory(nullptr) {
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assert(d <= DEPTH_ZERO);
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if (pos.checkers())
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stage = EVASION;
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else if (d > DEPTH_QS_NO_CHECKS)
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stage = QSEARCH_WITH_CHECKS;
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else if (d > DEPTH_QS_RECAPTURES)
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stage = QSEARCH_WITHOUT_CHECKS;
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else
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{
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stage = RECAPTURE;
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recaptureSquare = s;
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ttm = MOVE_NONE;
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}
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ttMove = ttm && pos.pseudo_legal(ttm) ? ttm : MOVE_NONE;
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endMoves += (ttMove != MOVE_NONE);
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}
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MovePicker::MovePicker(const Position& p, Move ttm, const HistoryStats& h, Value th)
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: pos(p), history(h), counterMovesHistory(nullptr), threshold(th) {
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assert(!pos.checkers());
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stage = PROBCUT;
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// In ProbCut we generate captures with SEE higher than the given threshold
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ttMove = ttm
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&& pos.pseudo_legal(ttm)
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&& pos.capture(ttm)
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&& pos.see(ttm) > threshold ? ttm : MOVE_NONE;
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endMoves += (ttMove != MOVE_NONE);
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}
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/// score() assigns a numerical value to each move in a move list. The moves with
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/// highest values will be picked first.
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template<>
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void MovePicker::score<CAPTURES>() {
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// Winning and equal captures in the main search are ordered by MVV, preferring
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// captures near our home rank. Surprisingly, this appears to perform slightly
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// better than SEE based move ordering: exchanging big pieces before capturing
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// a hanging piece probably helps to reduce the subtree size.
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// In main search we want to push captures with negative SEE values to the
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// badCaptures[] array, but instead of doing it now we delay until the move
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// has been picked up, saving some SEE calls in case we get a cutoff.
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for (auto& m : *this)
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m.value = PieceValue[MG][pos.piece_on(to_sq(m))]
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- Value(200 * relative_rank(pos.side_to_move(), to_sq(m)));
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}
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template<>
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void MovePicker::score<QUIETS>() {
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for (auto& m : *this)
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m.value = history[pos.moved_piece(m)][to_sq(m)]
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+ (*counterMovesHistory)[pos.moved_piece(m)][to_sq(m)];
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}
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template<>
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void MovePicker::score<EVASIONS>() {
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// Try winning and equal captures captures ordered by MVV/LVA, then non-captures
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// ordered by history value, then bad-captures and quiet moves with a negative
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// SEE ordered by SEE value.
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Value see;
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for (auto& m : *this)
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if ((see = pos.see_sign(m)) < VALUE_ZERO)
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m.value = see - HistoryStats::Max; // At the bottom
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else if (pos.capture(m))
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m.value = PieceValue[MG][pos.piece_on(to_sq(m))]
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- Value(type_of(pos.moved_piece(m))) + HistoryStats::Max;
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else
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m.value = history[pos.moved_piece(m)][to_sq(m)];
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}
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/// generate_next_stage() generates, scores and sorts the next bunch of moves,
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/// when there are no more moves to try for the current stage.
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void MovePicker::generate_next_stage() {
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assert(stage != STOP);
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cur = moves;
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switch (++stage) {
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case GOOD_CAPTURES: case QCAPTURES_1: case QCAPTURES_2:
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case PROBCUT_CAPTURES: case RECAPTURES:
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endMoves = generate<CAPTURES>(pos, moves);
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score<CAPTURES>();
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break;
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case KILLERS:
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killers[0] = ss->killers[0];
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killers[1] = ss->killers[1];
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killers[2] = countermove;
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cur = killers;
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endMoves = cur + 2 + (countermove != killers[0] && countermove != killers[1]);
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break;
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case GOOD_QUIETS:
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endQuiets = endMoves = generate<QUIETS>(pos, moves);
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score<QUIETS>();
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endMoves = std::partition(cur, endMoves, [](const ExtMove& m) { return m.value > VALUE_ZERO; });
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insertion_sort(cur, endMoves);
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break;
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case BAD_QUIETS:
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cur = endMoves;
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endMoves = endQuiets;
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if (depth >= 3 * ONE_PLY)
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insertion_sort(cur, endMoves);
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break;
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case BAD_CAPTURES:
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// Just pick them in reverse order to get correct ordering
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cur = moves + MAX_MOVES - 1;
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endMoves = endBadCaptures;
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break;
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case ALL_EVASIONS:
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endMoves = generate<EVASIONS>(pos, moves);
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if (endMoves - moves > 1)
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score<EVASIONS>();
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break;
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case CHECKS:
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endMoves = generate<QUIET_CHECKS>(pos, moves);
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break;
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case EVASION: case QSEARCH_WITH_CHECKS: case QSEARCH_WITHOUT_CHECKS:
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case PROBCUT: case RECAPTURE: case STOP:
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stage = STOP;
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break;
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default:
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assert(false);
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}
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}
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/// next_move() is the most important method of the MovePicker class. It returns
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/// a new pseudo legal move every time it is called, until there are no more moves
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/// left. It picks the move with the biggest value from a list of generated moves
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/// taking care not to return the ttMove if it has already been searched.
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Move MovePicker::next_move() {
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Move move;
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while (true)
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{
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while (cur == endMoves && stage != STOP)
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generate_next_stage();
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switch (stage) {
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case MAIN_SEARCH: case EVASION: case QSEARCH_WITH_CHECKS:
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case QSEARCH_WITHOUT_CHECKS: case PROBCUT:
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++cur;
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return ttMove;
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case GOOD_CAPTURES:
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move = pick_best(cur++, endMoves);
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if (move != ttMove)
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{
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if (pos.see_sign(move) >= VALUE_ZERO)
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return move;
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// Losing capture, move it to the tail of the array
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*endBadCaptures-- = move;
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}
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break;
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case KILLERS:
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move = *cur++;
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if ( move != MOVE_NONE
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&& move != ttMove
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&& pos.pseudo_legal(move)
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&& !pos.capture(move))
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return move;
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break;
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case GOOD_QUIETS: case BAD_QUIETS:
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move = *cur++;
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if ( move != ttMove
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&& move != killers[0]
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&& move != killers[1]
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&& move != killers[2])
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return move;
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break;
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case BAD_CAPTURES:
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return *cur--;
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case ALL_EVASIONS: case QCAPTURES_1: case QCAPTURES_2:
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move = pick_best(cur++, endMoves);
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if (move != ttMove)
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return move;
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break;
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case PROBCUT_CAPTURES:
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move = pick_best(cur++, endMoves);
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if (move != ttMove && pos.see(move) > threshold)
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return move;
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break;
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case RECAPTURES:
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move = pick_best(cur++, endMoves);
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if (to_sq(move) == recaptureSquare)
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return move;
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break;
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case CHECKS:
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move = *cur++;
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if (move != ttMove)
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return move;
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break;
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case STOP:
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return MOVE_NONE;
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default:
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assert(false);
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}
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}
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}
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