Stockfish, a UCI chess playing engine derived from Glaurung 2.1
Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
Copyright (C) 2008-2015 Marco Costalba, Joona Kiiski, Tord Romstad
+ Copyright (C) 2015-2019 Marco Costalba, Joona Kiiski, Gary Linscott, Tord Romstad
Stockfish is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.
-
Stockfish is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
#include <cassert>
#include "movepick.h"
-#include "thread.h"
namespace {
enum Stages {
- MAIN_SEARCH, GOOD_CAPTURES, KILLERS, GOOD_QUIETS, BAD_QUIETS, BAD_CAPTURES,
- EVASION, ALL_EVASIONS,
- QSEARCH_WITH_CHECKS, QCAPTURES_1, CHECKS,
- QSEARCH_WITHOUT_CHECKS, QCAPTURES_2,
- PROBCUT, PROBCUT_CAPTURES,
- RECAPTURE, RECAPTURES,
- STOP
+ MAIN_TT, CAPTURE_INIT, GOOD_CAPTURE, REFUTATION, QUIET_INIT, QUIET, BAD_CAPTURE,
+ EVASION_TT, EVASION_INIT, EVASION,
+ PROBCUT_TT, PROBCUT_INIT, PROBCUT,
+ QSEARCH_TT, QCAPTURE_INIT, QCAPTURE, QCHECK_INIT, QCHECK
};
- // Our insertion sort, which is guaranteed to be stable, as it should be
- void insertion_sort(ExtMove* begin, ExtMove* end)
- {
- ExtMove tmp, *p, *q;
-
- for (p = begin + 1; p < end; ++p)
- {
- tmp = *p;
- for (q = p; q != begin && *(q-1) < tmp; --q)
- *q = *(q-1);
- *q = tmp;
- }
- }
-
- // pick_best() finds the best move in the range (begin, end) and moves it to
- // the front. It's faster than sorting all the moves in advance when there
- // are few moves e.g. the possible captures.
- Move pick_best(ExtMove* begin, ExtMove* end)
- {
- std::swap(*begin, *std::max_element(begin, end));
- return *begin;
+ // partial_insertion_sort() sorts moves in descending order up to and including
+ // a given limit. The order of moves smaller than the limit is left unspecified.
+ void partial_insertion_sort(ExtMove* begin, ExtMove* end, int limit) {
+
+ for (ExtMove *sortedEnd = begin, *p = begin + 1; p < end; ++p)
+ if (p->value >= limit)
+ {
+ ExtMove tmp = *p, *q;
+ *p = *++sortedEnd;
+ for (q = sortedEnd; q != begin && *(q - 1) < tmp; --q)
+ *q = *(q - 1);
+ *q = tmp;
+ }
}
} // namespace
/// Constructors of the MovePicker class. As arguments we pass information
/// to help it to return the (presumably) good moves first, to decide which
/// moves to return (in the quiescence search, for instance, we only want to
-/// search captures, promotions and some checks) and how important good move
+/// search captures, promotions, and some checks) and how important good move
/// ordering is at the current node.
-MovePicker::MovePicker(const Position& p, Move ttm, Depth d, const HistoryStats& h, const CounterMovesHistoryStats& cmh,
- Move cm, Search::Stack* s) : pos(p), history(h), counterMovesHistory(cmh), depth(d) {
+/// MovePicker constructor for the main search
+MovePicker::MovePicker(const Position& p, Move ttm, Depth d, const ButterflyHistory* mh,
+ const CapturePieceToHistory* cph, const PieceToHistory** ch, Move cm, Move* killers)
+ : pos(p), mainHistory(mh), captureHistory(cph), continuationHistory(ch),
+ refutations{{killers[0], 0}, {killers[1], 0}, {cm, 0}}, depth(d) {
assert(d > DEPTH_ZERO);
- endBadCaptures = moves + MAX_MOVES - 1;
- countermove = cm;
- ss = s;
-
- if (pos.checkers())
- stage = EVASION;
-
- else
- stage = MAIN_SEARCH;
-
- ttMove = (ttm && pos.pseudo_legal(ttm) ? ttm : MOVE_NONE);
- endMoves += (ttMove != MOVE_NONE);
+ stage = pos.checkers() ? EVASION_TT : MAIN_TT;
+ ttMove = ttm && pos.pseudo_legal(ttm) ? ttm : MOVE_NONE;
+ stage += (ttMove == MOVE_NONE);
}
-MovePicker::MovePicker(const Position& p, Move ttm, Depth d, const HistoryStats& h, const CounterMovesHistoryStats& cmh,
- Square s) : pos(p), history(h), counterMovesHistory(cmh) {
+/// MovePicker constructor for quiescence search
+MovePicker::MovePicker(const Position& p, Move ttm, Depth d, const ButterflyHistory* mh,
+ const CapturePieceToHistory* cph, const PieceToHistory** ch, Square rs)
+ : pos(p), mainHistory(mh), captureHistory(cph), continuationHistory(ch), recaptureSquare(rs), depth(d) {
assert(d <= DEPTH_ZERO);
- if (pos.checkers())
- stage = EVASION;
-
- else if (d > DEPTH_QS_NO_CHECKS)
- stage = QSEARCH_WITH_CHECKS;
-
- else if (d > DEPTH_QS_RECAPTURES)
- stage = QSEARCH_WITHOUT_CHECKS;
-
- else
- {
- stage = RECAPTURE;
- recaptureSquare = s;
- ttm = MOVE_NONE;
- }
-
- ttMove = (ttm && pos.pseudo_legal(ttm) ? ttm : MOVE_NONE);
- endMoves += (ttMove != MOVE_NONE);
+ stage = pos.checkers() ? EVASION_TT : QSEARCH_TT;
+ ttMove = ttm
+ && (depth > DEPTH_QS_RECAPTURES || to_sq(ttm) == recaptureSquare)
+ && pos.pseudo_legal(ttm) ? ttm : MOVE_NONE;
+ stage += (ttMove == MOVE_NONE);
}
-MovePicker::MovePicker(const Position& p, Move ttm, const HistoryStats& h, const CounterMovesHistoryStats& cmh, PieceType pt)
- : pos(p), history(h), counterMovesHistory(cmh) {
+/// MovePicker constructor for ProbCut: we generate captures with SEE greater
+/// than or equal to the given threshold.
+MovePicker::MovePicker(const Position& p, Move ttm, Value th, const CapturePieceToHistory* cph)
+ : pos(p), captureHistory(cph), threshold(th) {
assert(!pos.checkers());
- stage = PROBCUT;
-
- // In ProbCut we generate only captures that are better than the parent's
- // captured piece.
- captureThreshold = PieceValue[MG][pt];
- ttMove = (ttm && pos.pseudo_legal(ttm) ? ttm : MOVE_NONE);
-
- if (ttMove && (!pos.capture(ttMove) || pos.see(ttMove) <= captureThreshold))
- ttMove = MOVE_NONE;
-
- endMoves += (ttMove != MOVE_NONE);
+ stage = PROBCUT_TT;
+ ttMove = ttm
+ && pos.capture(ttm)
+ && pos.pseudo_legal(ttm)
+ && pos.see_ge(ttm, threshold) ? ttm : MOVE_NONE;
+ stage += (ttMove == MOVE_NONE);
}
+/// MovePicker::score() assigns a numerical value to each move in a list, used
+/// for sorting. Captures are ordered by Most Valuable Victim (MVV), preferring
+/// captures with a good history. Quiets moves are ordered using the histories.
+template<GenType Type>
+void MovePicker::score() {
+
+ static_assert(Type == CAPTURES || Type == QUIETS || Type == EVASIONS, "Wrong type");
-/// score() assign a numerical value to each move in a move list. The moves with
-/// highest values will be picked first.
-template<>
-void MovePicker::score<CAPTURES>() {
- // Winning and equal captures in the main search are ordered by MVV.
- // Suprisingly, this appears to perform slightly better than SEE based
- // move ordering. The reason is probably that in a position with a winning
- // capture, capturing a valuable (but sufficiently defended) piece
- // first usually doesn't hurt. The opponent will have to recapture, and
- // the hanging piece will still be hanging (except in the unusual cases
- // where it is possible to recapture with the hanging piece). Exchanging
- // big pieces before capturing a hanging piece probably helps to reduce
- // the subtree size.
- // In main search we want to push captures with negative SEE values to the
- // badCaptures[] array, but instead of doing it now we delay until the move
- // has been picked up in pick_move_from_list(). This way we save some SEE
- // calls in case we get a cutoff.
for (auto& m : *this)
- m.value = PieceValue[MG][pos.piece_on(to_sq(m))]
- - 200 * relative_rank(pos.side_to_move(), to_sq(m));
+ if (Type == CAPTURES)
+ m.value = int(PieceValue[MG][pos.piece_on(to_sq(m))]) * 6
+ + (*captureHistory)[pos.moved_piece(m)][to_sq(m)][type_of(pos.piece_on(to_sq(m)))];
+
+ else if (Type == QUIETS)
+ m.value = (*mainHistory)[pos.side_to_move()][from_to(m)]
+ + (*continuationHistory[0])[pos.moved_piece(m)][to_sq(m)]
+ + (*continuationHistory[1])[pos.moved_piece(m)][to_sq(m)]
+ + (*continuationHistory[3])[pos.moved_piece(m)][to_sq(m)]
+ + (*continuationHistory[5])[pos.moved_piece(m)][to_sq(m)] / 2;
+
+ else // Type == EVASIONS
+ {
+ if (pos.capture(m))
+ m.value = PieceValue[MG][pos.piece_on(to_sq(m))]
+ - Value(type_of(pos.moved_piece(m)));
+ else
+ m.value = (*mainHistory)[pos.side_to_move()][from_to(m)]
+ + (*continuationHistory[0])[pos.moved_piece(m)][to_sq(m)]
+ - (1 << 28);
+ }
}
-template<>
-void MovePicker::score<QUIETS>() {
+/// MovePicker::select() returns the next move satisfying a predicate function.
+/// It never returns the TT move.
+template<MovePicker::PickType T, typename Pred>
+Move MovePicker::select(Pred filter) {
- Square prevSq = to_sq((ss-1)->currentMove);
- const HistoryStats& cmh = counterMovesHistory[pos.piece_on(prevSq)][prevSq];
+ while (cur < endMoves)
+ {
+ if (T == Best)
+ std::swap(*cur, *std::max_element(cur, endMoves));
- for (auto& m : *this)
- m.value = history[pos.moved_piece(m)][to_sq(m)]
- + cmh[pos.moved_piece(m)][to_sq(m)] * 3;
+ if (*cur != ttMove && filter())
+ return *cur++;
+
+ cur++;
+ }
+ return MOVE_NONE;
}
-template<>
-void MovePicker::score<EVASIONS>() {
- // Try good captures ordered by MVV/LVA, then non-captures if destination square
- // is not under attack, ordered by history value, then bad-captures and quiet
- // moves with a negative SEE. This last group is ordered by the SEE value.
- Value see;
+/// MovePicker::next_move() is the most important method of the MovePicker class. It
+/// returns a new pseudo legal move every time it is called until there are no more
+/// moves left, picking the move with the highest score from a list of generated moves.
+Move MovePicker::next_move(bool skipQuiets) {
- for (auto& m : *this)
- if ((see = pos.see_sign(m)) < VALUE_ZERO)
- m.value = see - HistoryStats::Max; // At the bottom
-
- else if (pos.capture(m))
- m.value = PieceValue[MG][pos.piece_on(to_sq(m))]
- - Value(type_of(pos.moved_piece(m))) + HistoryStats::Max;
- else
- m.value = history[pos.moved_piece(m)][to_sq(m)];
-}
+top:
+ switch (stage) {
+ case MAIN_TT:
+ case EVASION_TT:
+ case QSEARCH_TT:
+ case PROBCUT_TT:
+ ++stage;
+ return ttMove;
-/// generate_next_stage() generates, scores and sorts the next bunch of moves,
-/// when there are no more moves to try for the current stage.
+ case CAPTURE_INIT:
+ case PROBCUT_INIT:
+ case QCAPTURE_INIT:
+ cur = endBadCaptures = moves;
+ endMoves = generate<CAPTURES>(pos, cur);
-void MovePicker::generate_next_stage() {
+ score<CAPTURES>();
+ ++stage;
+ goto top;
+
+ case GOOD_CAPTURE:
+ if (select<Best>([&](){
+ return pos.see_ge(*cur, Value(-55 * cur->value / 1024)) ?
+ // Move losing capture to endBadCaptures to be tried later
+ true : (*endBadCaptures++ = *cur, false); }))
+ return *(cur - 1);
+
+ // Prepare the pointers to loop over the refutations array
+ cur = std::begin(refutations);
+ endMoves = std::end(refutations);
+
+ // If the countermove is the same as a killer, skip it
+ if ( refutations[0].move == refutations[2].move
+ || refutations[1].move == refutations[2].move)
+ --endMoves;
+
+ ++stage;
+ /* fallthrough */
+
+ case REFUTATION:
+ if (select<Next>([&](){ return *cur != MOVE_NONE
+ && !pos.capture(*cur)
+ && pos.pseudo_legal(*cur); }))
+ return *(cur - 1);
+ ++stage;
+ /* fallthrough */
+
+ case QUIET_INIT:
+ if (!skipQuiets)
+ {
+ cur = endBadCaptures;
+ endMoves = generate<QUIETS>(pos, cur);
+
+ score<QUIETS>();
+ partial_insertion_sort(cur, endMoves, -4000 * depth / ONE_PLY);
+ }
- cur = moves;
+ ++stage;
+ /* fallthrough */
- switch (++stage) {
+ case QUIET:
+ if ( !skipQuiets
+ && select<Next>([&](){return *cur != refutations[0].move
+ && *cur != refutations[1].move
+ && *cur != refutations[2].move;}))
+ return *(cur - 1);
- case GOOD_CAPTURES: case QCAPTURES_1: case QCAPTURES_2:
- case PROBCUT_CAPTURES: case RECAPTURES:
- endMoves = generate<CAPTURES>(pos, moves);
- score<CAPTURES>();
- break;
-
- case KILLERS:
- cur = killers;
- endMoves = cur + 2;
-
- killers[0] = ss->killers[0];
- killers[1] = ss->killers[1];
- killers[2].move = MOVE_NONE;
-
- // Be sure countermoves are different from killers
- if ( countermove != killers[0]
- && countermove != killers[1])
- *endMoves++ = countermove;
- break;
-
- case GOOD_QUIETS:
- endQuiets = endMoves = generate<QUIETS>(pos, moves);
- score<QUIETS>();
- endMoves = std::partition(cur, endMoves, [](const ExtMove& m) { return m.value > VALUE_ZERO; });
- insertion_sort(cur, endMoves);
- break;
-
- case BAD_QUIETS:
- cur = endMoves;
- endMoves = endQuiets;
- if (depth >= 3 * ONE_PLY)
- insertion_sort(cur, endMoves);
- break;
-
- case BAD_CAPTURES:
- // Just pick them in reverse order to get MVV/LVA ordering
- cur = moves + MAX_MOVES - 1;
+ // Prepare the pointers to loop over the bad captures
+ cur = moves;
endMoves = endBadCaptures;
- break;
- case ALL_EVASIONS:
- endMoves = generate<EVASIONS>(pos, moves);
- if (endMoves - moves > 1)
- score<EVASIONS>();
- break;
+ ++stage;
+ /* fallthrough */
- case CHECKS:
- endMoves = generate<QUIET_CHECKS>(pos, moves);
- break;
+ case BAD_CAPTURE:
+ return select<Next>([](){ return true; });
- case EVASION: case QSEARCH_WITH_CHECKS: case QSEARCH_WITHOUT_CHECKS:
- case PROBCUT: case RECAPTURE:
- stage = STOP;
- /* Fall through */
+ case EVASION_INIT:
+ cur = moves;
+ endMoves = generate<EVASIONS>(pos, cur);
- case STOP:
- endMoves = cur + 1; // Avoid another generate_next_stage() call
- break;
+ score<EVASIONS>();
+ ++stage;
+ /* fallthrough */
- default:
- assert(false);
- }
-}
+ case EVASION:
+ return select<Best>([](){ return true; });
+ case PROBCUT:
+ return select<Best>([&](){ return pos.see_ge(*cur, threshold); });
-/// next_move() is the most important method of the MovePicker class. It returns
-/// a new pseudo legal move every time it is called, until there are no more moves
-/// left. It picks the move with the biggest value from a list of generated moves
-/// taking care not to return the ttMove if it has already been searched.
-template<>
-Move MovePicker::next_move<false>() {
+ case QCAPTURE:
+ if (select<Best>([&](){ return depth > DEPTH_QS_RECAPTURES
+ || to_sq(*cur) == recaptureSquare; }))
+ return *(cur - 1);
- Move move;
-
- while (true)
- {
- while (cur == endMoves)
- generate_next_stage();
-
- switch (stage) {
-
- case MAIN_SEARCH: case EVASION: case QSEARCH_WITH_CHECKS:
- case QSEARCH_WITHOUT_CHECKS: case PROBCUT:
- ++cur;
- return ttMove;
-
- case GOOD_CAPTURES:
- move = pick_best(cur++, endMoves);
- if (move != ttMove)
- {
- if (pos.see_sign(move) >= VALUE_ZERO)
- return move;
-
- // Losing capture, move it to the tail of the array
- *endBadCaptures-- = move;
- }
- break;
-
- case KILLERS:
- move = *cur++;
- if ( move != MOVE_NONE
- && move != ttMove
- && pos.pseudo_legal(move)
- && !pos.capture(move))
- return move;
- break;
-
- case GOOD_QUIETS: case BAD_QUIETS:
- move = *cur++;
- if ( move != ttMove
- && move != killers[0]
- && move != killers[1]
- && move != killers[2])
- return move;
- break;
-
- case BAD_CAPTURES:
- return *cur--;
-
- case ALL_EVASIONS: case QCAPTURES_1: case QCAPTURES_2:
- move = pick_best(cur++, endMoves);
- if (move != ttMove)
- return move;
- break;
-
- case PROBCUT_CAPTURES:
- move = pick_best(cur++, endMoves);
- if (move != ttMove && pos.see(move) > captureThreshold)
- return move;
- break;
-
- case RECAPTURES:
- move = pick_best(cur++, endMoves);
- if (to_sq(move) == recaptureSquare)
- return move;
- break;
-
- case CHECKS:
- move = *cur++;
- if (move != ttMove)
- return move;
- break;
-
- case STOP:
+ // If we did not find any move and we do not try checks, we have finished
+ if (depth != DEPTH_QS_CHECKS)
return MOVE_NONE;
- default:
- assert(false);
- }
- }
-}
+ ++stage;
+ /* fallthrough */
+ case QCHECK_INIT:
+ cur = moves;
+ endMoves = generate<QUIET_CHECKS>(pos, cur);
-/// Version of next_move() to use at split point nodes where the move is grabbed
-/// from the split point's shared MovePicker object. This function is not thread
-/// safe so must be lock protected by the caller.
-template<>
-Move MovePicker::next_move<true>() { return ss->splitPoint->movePicker->next_move<false>(); }
+ ++stage;
+ /* fallthrough */
+
+ case QCHECK:
+ return select<Next>([](){ return true; });
+ }
+
+ assert(false);
+ return MOVE_NONE; // Silence warning
+}
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