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) 2015-2017 Marco Costalba, Joona Kiiski, Gary Linscott, 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
namespace {
enum Stages {
- MAIN_SEARCH, CAPTURES_INIT, GOOD_CAPTURES, KILLERS, COUNTERMOVE, QUIET_INIT, QUIET, BAD_CAPTURES,
- EVASION, EVASIONS_INIT, ALL_EVASIONS,
- PROBCUT, PROBCUT_INIT, PROBCUT_CAPTURES,
- QSEARCH_WITH_CHECKS, QCAPTURES_1_INIT, QCAPTURES_1, QCHECKS,
- QSEARCH_NO_CHECKS, QCAPTURES_2_INIT, QCAPTURES_2,
- QSEARCH_RECAPTURES, QRECAPTURES
+ 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
};
// partial_insertion_sort() sorts moves in descending order up to and including
}
}
- // 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;
- }
-
} // namespace
/// search captures, promotions, and some checks) and how important good move
/// ordering is at the current node.
+/// MovePicker constructor for the main search
MovePicker::MovePicker(const Position& p, Move ttm, Depth d, const ButterflyHistory* mh,
- const PieceToHistory** ch, Move cm, Move* killers_p)
- : pos(p), mainHistory(mh), contHistory(ch), countermove(cm),
- killers{killers_p[0], killers_p[1]}, depth(d){
+ 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);
- stage = pos.checkers() ? EVASION : MAIN_SEARCH;
+ stage = pos.checkers() ? EVASION_TT : MAIN_TT;
ttMove = ttm && pos.pseudo_legal(ttm) ? ttm : MOVE_NONE;
stage += (ttMove == MOVE_NONE);
}
+/// MovePicker constructor for quiescence search
MovePicker::MovePicker(const Position& p, Move ttm, Depth d, const ButterflyHistory* mh,
- const PieceToHistory** ch, Square s)
- : pos(p), mainHistory(mh), contHistory(ch) {
+ 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_NO_CHECKS;
-
- else
- {
- stage = QSEARCH_RECAPTURES;
- recaptureSquare = s;
- return;
- }
-
- ttMove = ttm && pos.pseudo_legal(ttm) ? ttm : 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, Value th)
- : pos(p), threshold(th) {
+/// 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 captures with SEE higher than or equal to the given threshold
+ stage = PROBCUT_TT;
ttMove = ttm
- && pos.pseudo_legal(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() assigns 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, preferring
- // captures near our home rank. Surprisingly, this appears to perform slightly
- // better than SEE-based move ordering: exchanging big pieces before capturing
- // a hanging piece probably helps to reduce the subtree size.
- // In the 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, saving some SEE calls in case we get a cutoff.
for (auto& m : *this)
- m.value = PieceValue[MG][pos.piece_on(to_sq(m))]
- - Value(200 * relative_rank(pos.side_to_move(), to_sq(m)));
-}
+ if (Type == CAPTURES)
+ m.value = PieceValue[MG][pos.piece_on(to_sq(m))]
+ + (*captureHistory)[pos.moved_piece(m)][to_sq(m)][type_of(pos.piece_on(to_sq(m)))] / 8;
-template<>
-void MovePicker::score<QUIETS>() {
+ 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;
- for (auto& m : *this)
- m.value = (*mainHistory)[pos.side_to_move()][from_to(m)]
- + (*contHistory[0])[pos.moved_piece(m)][to_sq(m)]
- + (*contHistory[1])[pos.moved_piece(m)][to_sq(m)]
- + (*contHistory[3])[pos.moved_piece(m)][to_sq(m)];
+ 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<EVASIONS>() {
- // Try captures ordered by MVV/LVA, then non-captures ordered by stats heuristics
- for (auto& m : *this)
- if (pos.capture(m))
- m.value = PieceValue[MG][pos.piece_on(to_sq(m))]
- - Value(type_of(pos.moved_piece(m))) + (1 << 28);
- else
- m.value = (*mainHistory)[pos.side_to_move()][from_to(m)];
-}
+/// 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) {
+ while (cur < endMoves)
+ {
+ if (T == Best)
+ std::swap(*cur, *std::max_element(cur, endMoves));
-/// 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.
+ if (*cur != ttMove && filter())
+ return *cur++;
-Move MovePicker::next_move(bool skipQuiets) {
+ cur++;
+ }
+ return MOVE_NONE;
+}
- Move move;
+/// 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) {
+top:
switch (stage) {
- case MAIN_SEARCH: case EVASION: case QSEARCH_WITH_CHECKS:
- case QSEARCH_NO_CHECKS: case PROBCUT:
+ case MAIN_TT:
+ case EVASION_TT:
+ case QSEARCH_TT:
+ case PROBCUT_TT:
++stage;
return ttMove;
- case CAPTURES_INIT:
- endBadCaptures = cur = moves;
+ case CAPTURE_INIT:
+ case PROBCUT_INIT:
+ case QCAPTURE_INIT:
+ cur = endBadCaptures = moves;
endMoves = generate<CAPTURES>(pos, cur);
+
score<CAPTURES>();
++stage;
- /* fallthrough */
+ goto top;
- case GOOD_CAPTURES:
- while (cur < endMoves)
- {
- move = pick_best(cur++, endMoves);
- if (move != ttMove)
- {
- if (pos.see_ge(move))
- return move;
-
- // Losing capture, move it to the beginning of the array
- *endBadCaptures++ = move;
- }
- }
+ 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);
- ++stage;
- move = killers[0]; // First killer move
- if ( move != MOVE_NONE
- && move != ttMove
- && pos.pseudo_legal(move)
- && !pos.capture(move))
- return move;
- /* fallthrough */
+ // 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;
- case KILLERS:
++stage;
- move = killers[1]; // Second killer move
- if ( move != MOVE_NONE
- && move != ttMove
- && pos.pseudo_legal(move)
- && !pos.capture(move))
- return move;
/* fallthrough */
- case COUNTERMOVE:
+ case REFUTATION:
+ if (select<Next>([&](){ return *cur != MOVE_NONE
+ && !pos.capture(*cur)
+ && pos.pseudo_legal(*cur); }))
+ return *(cur - 1);
++stage;
- move = countermove;
- if ( move != MOVE_NONE
- && move != ttMove
- && move != killers[0]
- && move != killers[1]
- && pos.pseudo_legal(move)
- && !pos.capture(move))
- return move;
/* fallthrough */
case QUIET_INIT:
cur = endBadCaptures;
endMoves = generate<QUIETS>(pos, cur);
+
score<QUIETS>();
partial_insertion_sort(cur, endMoves, -4000 * depth / ONE_PLY);
++stage;
/* fallthrough */
case QUIET:
- while ( cur < endMoves
- && (!skipQuiets || cur->value >= VALUE_ZERO))
- {
- move = *cur++;
+ if ( !skipQuiets
+ && select<Next>([&](){return *cur != refutations[0].move
+ && *cur != refutations[1].move
+ && *cur != refutations[2].move;}))
+ return *(cur - 1);
+
+ // Prepare the pointers to loop over the bad captures
+ cur = moves;
+ endMoves = endBadCaptures;
- if ( move != ttMove
- && move != killers[0]
- && move != killers[1]
- && move != countermove)
- return move;
- }
++stage;
- cur = moves; // Point to beginning of bad captures
/* fallthrough */
- case BAD_CAPTURES:
- if (cur < endBadCaptures)
- return *cur++;
- break;
+ case BAD_CAPTURE:
+ return select<Next>([](){ return true; });
- case EVASIONS_INIT:
+ case EVASION_INIT:
cur = moves;
endMoves = generate<EVASIONS>(pos, cur);
+
score<EVASIONS>();
++stage;
/* fallthrough */
- case ALL_EVASIONS:
- while (cur < endMoves)
- {
- move = pick_best(cur++, endMoves);
- if (move != ttMove)
- return move;
- }
- break;
+ case EVASION:
+ return select<Best>([](){ return true; });
- case PROBCUT_INIT:
- cur = moves;
- endMoves = generate<CAPTURES>(pos, cur);
- score<CAPTURES>();
- ++stage;
- /* fallthrough */
+ case PROBCUT:
+ return select<Best>([&](){ return pos.see_ge(*cur, threshold); });
- case PROBCUT_CAPTURES:
- while (cur < endMoves)
- {
- move = pick_best(cur++, endMoves);
- if ( move != ttMove
- && pos.see_ge(move, threshold))
- return move;
- }
- break;
+ case QCAPTURE:
+ if (select<Best>([&](){ return depth > DEPTH_QS_RECAPTURES
+ || to_sq(*cur) == recaptureSquare; }))
+ return *(cur - 1);
+
+ // If we did not find any move and we do not try checks, we have finished
+ if (depth != DEPTH_QS_CHECKS)
+ return MOVE_NONE;
- case QCAPTURES_1_INIT: case QCAPTURES_2_INIT:
- cur = moves;
- endMoves = generate<CAPTURES>(pos, cur);
- score<CAPTURES>();
++stage;
/* fallthrough */
- case QCAPTURES_1: case QCAPTURES_2:
- while (cur < endMoves)
- {
- move = pick_best(cur++, endMoves);
- if (move != ttMove)
- return move;
- }
- if (stage == QCAPTURES_2)
- break;
+ case QCHECK_INIT:
cur = moves;
endMoves = generate<QUIET_CHECKS>(pos, cur);
- ++stage;
- /* fallthrough */
-
- case QCHECKS:
- while (cur < endMoves)
- {
- move = cur++->move;
- if (move != ttMove)
- return move;
- }
- break;
- case QSEARCH_RECAPTURES:
- cur = moves;
- endMoves = generate<CAPTURES>(pos, cur);
- score<CAPTURES>();
++stage;
/* fallthrough */
- case QRECAPTURES:
- while (cur < endMoves)
- {
- move = pick_best(cur++, endMoves);
- if (to_sq(move) == recaptureSquare)
- return move;
- }
- break;
-
- default:
- assert(false);
+ case QCHECK:
+ return select<Next>([](){ return true; });
}
- return MOVE_NONE;
+ assert(false);
+ return MOVE_NONE; // Silence warning
}
projects / stockfish / blobdiff