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) 2015-2018 Marco Costalba, Joona Kiiski, Gary Linscott, Tord Romstad
+ Copyright (C) 2015-2020 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_CAPTURES_INIT, PROBCUT_CAPTURES,
- QSEARCH, QCAPTURES_INIT, QCAPTURES, QCHECKS, 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
/// 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 CapturePieceToHistory* cph, const PieceToHistory** ch, Move cm, Move* killers_p)
- : pos(p), mainHistory(mh), captureHistory(cph), contHistory(ch), countermove(cm),
- killers{killers_p[0], killers_p[1]}, depth(d){
+MovePicker::MovePicker(const Position& p, Move ttm, Depth d, const ButterflyHistory* mh, const LowPlyHistory* lp,
+ const CapturePieceToHistory* cph, const PieceToHistory** ch, Move cm, Move* killers, int pl)
+ : pos(p), mainHistory(mh), lowPlyHistory(lp), captureHistory(cph), continuationHistory(ch),
+ ttMove(ttm), refutations{{killers[0], 0}, {killers[1], 0}, {cm, 0}}, depth(d), ply(pl) {
- assert(d > DEPTH_ZERO);
+ assert(d > 0);
- stage = pos.checkers() ? EVASION : MAIN_SEARCH;
- ttMove = ttm && pos.pseudo_legal(ttm) ? ttm : MOVE_NONE;
- stage += (ttMove == MOVE_NONE);
+ stage = (pos.checkers() ? EVASION_TT : MAIN_TT) +
+ !(ttm && pos.pseudo_legal(ttm));
}
/// MovePicker constructor for quiescence search
-MovePicker::MovePicker(const Position& p, Move ttm, Depth d, const ButterflyHistory* mh, const CapturePieceToHistory* cph, Square s)
- : pos(p), mainHistory(mh), captureHistory(cph), depth(d) {
-
- assert(d <= DEPTH_ZERO);
-
- if (pos.checkers())
- stage = EVASION;
-
- else if (d > DEPTH_QS_RECAPTURES)
- stage = QSEARCH;
+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), ttMove(ttm), recaptureSquare(rs), depth(d) {
- else
- {
- stage = QSEARCH_RECAPTURES;
- recaptureSquare = s;
- return;
- }
+ assert(d <= 0);
- ttMove = ttm && pos.pseudo_legal(ttm) ? ttm : MOVE_NONE;
- stage += (ttMove == MOVE_NONE);
+ stage = (pos.checkers() ? EVASION_TT : QSEARCH_TT) +
+ !(ttm && (depth > DEPTH_QS_RECAPTURES || to_sq(ttm) == recaptureSquare)
+ && pos.pseudo_legal(ttm));
}
-/// MovePicker constructor for ProbCut: we generate captures with SEE higher
+/// 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) {
+ : pos(p), captureHistory(cph), ttMove(ttm), threshold(th) {
assert(!pos.checkers());
- stage = PROBCUT;
- ttMove = ttm
- && pos.pseudo_legal(ttm)
- && pos.capture(ttm)
- && pos.see_ge(ttm, threshold) ? ttm : MOVE_NONE;
-
- stage += (ttMove == MOVE_NONE);
+ stage = PROBCUT_TT + !(ttm && pos.capture(ttm)
+ && pos.pseudo_legal(ttm)
+ && pos.see_ge(ttm, threshold));
}
-/// 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 are ordered using the histories.
+/// 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() {
for (auto& m : *this)
if (Type == CAPTURES)
- m.value = PieceValue[MG][pos.piece_on(to_sq(m))]
- + Value((*captureHistory)[pos.moved_piece(m)][to_sq(m)][type_of(pos.piece_on(to_sq(m)))]);
+ 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)]
- + (*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)];
+ m.value = (*mainHistory)[pos.side_to_move()][from_to(m)]
+ + 2 * (*continuationHistory[0])[pos.moved_piece(m)][to_sq(m)]
+ + 2 * (*continuationHistory[1])[pos.moved_piece(m)][to_sq(m)]
+ + 2 * (*continuationHistory[3])[pos.moved_piece(m)][to_sq(m)]
+ + (*continuationHistory[5])[pos.moved_piece(m)][to_sq(m)]
+ + (ply < MAX_LPH ? 4 * (*lowPlyHistory)[ply][from_to(m)] : 0);
else // Type == EVASIONS
{
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)] - (1 << 28);
+ m.value = (*mainHistory)[pos.side_to_move()][from_to(m)]
+ + (*continuationHistory[0])[pos.moved_piece(m)][to_sq(m)]
+ - (1 << 28);
}
}
-/// 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.
+/// 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) {
-Move MovePicker::next_move(bool skipQuiets) {
+ while (cur < endMoves)
+ {
+ if (T == Best)
+ std::swap(*cur, *std::max_element(cur, endMoves));
+
+ if (*cur != ttMove && filter())
+ return *cur++;
- Move move;
+ cur++;
+ }
+ return MOVE_NONE;
+}
+/// 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: case PROBCUT:
+ case MAIN_TT:
+ case EVASION_TT:
+ case QSEARCH_TT:
+ case PROBCUT_TT:
++stage;
return ttMove;
- case CAPTURES_INIT:
- case PROBCUT_CAPTURES_INIT:
- case QCAPTURES_INIT:
- case QSEARCH_RECAPTURES:
- endBadCaptures = cur = moves;
+ case CAPTURE_INIT:
+ case PROBCUT_INIT:
+ case QCAPTURE_INIT:
+ cur = endBadCaptures = moves;
endMoves = generate<CAPTURES>(pos, cur);
+
score<CAPTURES>();
++stage;
+ goto top;
- // Rebranch at the top of the switch via a recursive call
- return next_move(skipQuiets);
+ case GOOD_CAPTURE:
+ if (select<Best>([&](){
+ return pos.see_ge(*cur, Value(-69 * cur->value / 1024)) ?
+ // Move losing capture to endBadCaptures to be tried later
+ true : (*endBadCaptures++ = *cur, false); }))
+ return *(cur - 1);
- case GOOD_CAPTURES:
- while (cur < endMoves)
- {
- move = pick_best(cur++, endMoves);
- if (move != ttMove)
- {
- if (pos.see_ge(move, Value(-55 * (cur-1)->value / 1024)))
- return move;
-
- // Losing capture, move it to the beginning of the array
- *endBadCaptures++ = move;
- }
- }
+ // Prepare the pointers to loop over the refutations array
+ cur = std::begin(refutations);
+ endMoves = std::end(refutations);
- ++stage;
- move = killers[0]; // First killer move
- if ( move != MOVE_NONE
- && move != ttMove
- && pos.pseudo_legal(move)
- && !pos.capture(move))
- return move;
- /* fallthrough */
+ // 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);
+ if (!skipQuiets)
+ {
+ cur = endBadCaptures;
+ endMoves = generate<QUIETS>(pos, cur);
+
+ score<QUIETS>();
+ partial_insertion_sort(cur, endMoves, -3000 * depth);
+ }
+
++stage;
/* fallthrough */
case QUIET:
- if (!skipQuiets)
- while (cur < endMoves)
- {
- move = *cur++;
-
- if ( move != ttMove
- && move != killers[0]
- && move != killers[1]
- && move != countermove)
- return move;
- }
+ 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;
+
++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_CAPTURES:
- while (cur < endMoves)
- {
- move = pick_best(cur++, endMoves);
- if ( move != ttMove
- && pos.see_ge(move, threshold))
- return move;
- }
- break;
+ case PROBCUT:
+ return select<Best>([&](){ return pos.see_ge(*cur, threshold); });
+
+ 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:
- while (cur < endMoves)
- {
- move = pick_best(cur++, endMoves);
- if (move != ttMove)
- return move;
- }
- if (depth <= DEPTH_QS_NO_CHECKS)
- break;
- 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 QCHECK_INIT:
+ cur = moves;
+ endMoves = generate<QUIET_CHECKS>(pos, cur);
- case QRECAPTURES:
- while (cur < endMoves)
- {
- move = *cur++;
- if (to_sq(move) == recaptureSquare)
- return move;
- }
- break;
+ ++stage;
+ /* fallthrough */
- default:
- assert(false);
+ case QCHECK:
+ return select<Next>([](){ return true; });
}
- return MOVE_NONE;
+ assert(false);
+ return MOVE_NONE; // Silence warning
}
projects / stockfish / blobdiff