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) 2015-2016 Marco Costalba, Joona Kiiski, Gary Linscott, Tord Romstad
+ Copyright (C) 2015-2018 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
#include <cassert>
#include "movepick.h"
-#include "thread.h"
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, KILLER0, KILLER1, COUNTERMOVE, 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;
+ // Helper filter used with select_move()
+ const auto Any = [](){ return true; };
+
+ // 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
/// 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, Search::Stack* s)
- : pos(p), ss(s), 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_p)
+ : pos(p), mainHistory(mh), captureHistory(cph), contHistory(ch),
+ refutations{killers_p[0], killers_p[1], cm}, depth(d){
assert(d > DEPTH_ZERO);
- Square prevSq = to_sq((ss-1)->currentMove);
- countermove = pos.this_thread()->counterMoves[pos.piece_on(prevSq)][prevSq];
-
- 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::MovePicker(const Position& p, Move ttm, Depth d, Square s)
- : pos(p) {
+/// MovePicker constructor for quiescence search
+MovePicker::MovePicker(const Position& p, Move ttm, Depth d, const ButterflyHistory* mh,
+ const CapturePieceToHistory* cph, Square rs)
+ : pos(p), mainHistory(mh), captureHistory(cph), 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
+ && pos.pseudo_legal(ttm)
+ && (depth > DEPTH_QS_RECAPTURES || to_sq(ttm) == recaptureSquare) ? 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 higher
+/// 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 the given threshold
+ stage = PROBCUT_TT;
ttMove = ttm
&& pos.pseudo_legal(ttm)
&& pos.capture(ttm)
- && pos.see(ttm) > threshold ? ttm : MOVE_NONE;
-
+ && 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() {
-/// 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)));
-}
-
-template<>
-void MovePicker::score<QUIETS>() {
-
- const HistoryStats& history = pos.this_thread()->history;
- const FromToStats& fromTo = pos.this_thread()->fromTo;
-
- const CounterMoveStats* cm = (ss-1)->counterMoves;
- const CounterMoveStats* fm = (ss-2)->counterMoves;
- const CounterMoveStats* f2 = (ss-4)->counterMoves;
-
- Color c = pos.side_to_move();
+ static_assert(Type == CAPTURES || Type == QUIETS || Type == EVASIONS, "Wrong type");
for (auto& m : *this)
- m.value = history[pos.moved_piece(m)][to_sq(m)]
- + (cm ? (*cm)[pos.moved_piece(m)][to_sq(m)] : VALUE_ZERO)
- + (fm ? (*fm)[pos.moved_piece(m)][to_sq(m)] : VALUE_ZERO)
- + (f2 ? (*f2)[pos.moved_piece(m)][to_sq(m)] : VALUE_ZERO)
- + fromTo.get(c, m);
-}
-
-template<>
-void MovePicker::score<EVASIONS>() {
- // Try winning and equal captures ordered by MVV/LVA, then non-captures ordered
- // by history value, then bad captures and quiet moves with a negative SEE ordered
- // by SEE value.
- const HistoryStats& history = pos.this_thread()->history;
- const FromToStats& fromTo = pos.this_thread()->fromTo;
- Color c = pos.side_to_move();
- Value see;
+ 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)))];
- for (auto& m : *this)
- if ((see = pos.see_sign(m)) < VALUE_ZERO)
- m.value = see - HistoryStats::Max; // At the bottom
+ 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)];
- 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)] + fromTo.get(c, 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)] - (1 << 28);
+ }
}
+/// MovePicker::select_move() returns the next move satisfying a predicate function
+template<PickType T, typename Pred>
+Move MovePicker::select_move(Pred filter) {
+
+ while (cur < endMoves)
+ {
+ if (T == BEST_SCORE)
+ 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.
+ move = *cur++;
-Move MovePicker::next_move() {
+ if (move != ttMove && filter())
+ return move;
+ }
+ return move = 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. It picks 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:
+ case CAPTURE_INIT:
+ case PROBCUT_INIT:
+ case QCAPTURE_INIT:
endBadCaptures = cur = moves;
endMoves = generate<CAPTURES>(pos, cur);
score<CAPTURES>();
++stage;
+ goto top;
- case GOOD_CAPTURES:
- while (cur < endMoves)
- {
- move = pick_best(cur++, endMoves);
- if (move != ttMove)
- {
- if (pos.see_sign(move) >= VALUE_ZERO)
- return move;
-
- // Losing capture, move it to the beginning of the array
- *endBadCaptures++ = move;
- }
- }
-
- ++stage;
- move = ss->killers[0]; // First killer move
- if ( move != MOVE_NONE
- && move != ttMove
- && pos.pseudo_legal(move)
- && !pos.capture(move))
+ case GOOD_CAPTURE:
+ if (select_move<BEST_SCORE>([&](){ return pos.see_ge(move, Value(-55 * (cur-1)->value / 1024)) ?
+ // Move losing capture to endBadCaptures to be tried later
+ true : (*endBadCaptures++ = move, false); }))
return move;
- case KILLERS:
+ // If the countermove is the same as a killer, skip it
+ if ( refutations[0] == refutations[2]
+ || refutations[1] == refutations[2])
+ refutations[2] = MOVE_NONE;
++stage;
- move = ss->killers[1]; // Second killer move
- if ( move != MOVE_NONE
- && move != ttMove
- && pos.pseudo_legal(move)
- && !pos.capture(move))
- return move;
+ /* fallthrough */
+ case KILLER0:
+ case KILLER1:
case COUNTERMOVE:
- ++stage;
- move = countermove;
- if ( move != MOVE_NONE
- && move != ttMove
- && move != ss->killers[0]
- && move != ss->killers[1]
- && pos.pseudo_legal(move)
- && !pos.capture(move))
- return move;
+ while (stage <= COUNTERMOVE)
+ {
+ move = refutations[ stage++ - KILLER0];
+ if ( move != MOVE_NONE
+ && move != ttMove
+ && pos.pseudo_legal(move)
+ && !pos.capture(move))
+ return move;
+ }
+ /* fallthrough */
case QUIET_INIT:
cur = endBadCaptures;
endMoves = generate<QUIETS>(pos, cur);
score<QUIETS>();
- if (depth < 3 * ONE_PLY)
- {
- ExtMove* goodQuiet = std::partition(cur, endMoves, [](const ExtMove& m)
- { return m.value > VALUE_ZERO; });
- insertion_sort(cur, goodQuiet);
- } else
- insertion_sort(cur, endMoves);
+ partial_insertion_sort(cur, endMoves, -4000 * depth / ONE_PLY);
++stage;
+ /* fallthrough */
case QUIET:
- while (cur < endMoves)
- {
- move = *cur++;
- if ( move != ttMove
- && move != ss->killers[0]
- && move != ss->killers[1]
- && move != countermove)
- return move;
- }
+ if ( !skipQuiets
+ && select_move<NEXT>([&](){return move != refutations[0]
+ && move != refutations[1]
+ && move != refutations[2];}))
+ return move;
+
+ // Point to beginning and end of 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_move<NEXT>(Any);
- case EVASIONS_INIT:
+ case EVASION_INIT:
cur = moves;
endMoves = generate<EVASIONS>(pos, cur);
- if (endMoves - cur - (ttMove != MOVE_NONE) > 1)
- score<EVASIONS>();
+ 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_move<BEST_SCORE>(Any);
- case PROBCUT_INIT:
- cur = moves;
- endMoves = generate<CAPTURES>(pos, cur);
- score<CAPTURES>();
- ++stage;
+ case PROBCUT:
+ return select_move<BEST_SCORE>([&](){ return pos.see_ge(move, threshold); });
- case PROBCUT_CAPTURES:
- while (cur < endMoves)
- {
- move = pick_best(cur++, endMoves);
- if ( move != ttMove
- && pos.see(move) > threshold)
- return move;
- }
- break;
+ case QCAPTURE:
+ if (select_move<BEST_SCORE>([&](){ return depth > DEPTH_QS_RECAPTURES
+ || to_sq(move) == recaptureSquare; }))
+ return move;
- case QCAPTURES_1_INIT: case QCAPTURES_2_INIT:
- cur = moves;
- endMoves = generate<CAPTURES>(pos, cur);
- score<CAPTURES>();
- ++stage;
+ // 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: case QCAPTURES_2:
- while (cur < endMoves)
- {
- move = pick_best(cur++, endMoves);
- if (move != ttMove)
- return move;
- }
- if (stage == QCAPTURES_2)
- 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 QSEARCH_RECAPTURES:
+ case QCHECK_INIT:
cur = moves;
- endMoves = generate<CAPTURES>(pos, cur);
- score<CAPTURES>();
+ endMoves = generate<QUIET_CHECKS>(pos, cur);
++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_move<NEXT>(Any);
}
- return MOVE_NONE;
+ assert(false);
+ return MOVE_NONE; // Silence warning
}
projects / stockfish / blobdiff