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
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
namespace {
enum Stages {
- MAIN_SEARCH, GOOD_CAPTURES, KILLERS, GOOD_QUIETS, BAD_QUIETS, BAD_CAPTURES,
+ MAIN_SEARCH, GOOD_CAPTURES, KILLERS, QUIET, BAD_CAPTURES,
EVASION, ALL_EVASIONS,
QSEARCH_WITH_CHECKS, QCAPTURES_1, CHECKS,
QSEARCH_WITHOUT_CHECKS, QCAPTURES_2,
// 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.
+ // are few moves, e.g., the possible captures.
Move pick_best(ExtMove* begin, ExtMove* end)
{
std::swap(*begin, *std::max_element(begin, end));
/// 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::MovePicker(const Position& p, Move ttm, Depth d, Search::Stack* s)
+ : pos(p), ss(s), depth(d) {
assert(d > DEPTH_ZERO);
- endBadCaptures = moves + MAX_MOVES - 1;
- countermove = cm;
- ss = s;
-
- if (pos.checkers())
- stage = EVASION;
-
- else
- stage = MAIN_SEARCH;
+ Square prevSq = to_sq((ss-1)->currentMove);
+ countermove = pos.this_thread()->counterMoves[pos.piece_on(prevSq)][prevSq];
- ttMove = (ttm && pos.pseudo_legal(ttm) ? ttm : MOVE_NONE);
+ stage = pos.checkers() ? EVASION : MAIN_SEARCH;
+ ttMove = ttm && pos.pseudo_legal(ttm) ? ttm : MOVE_NONE;
endMoves += (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::MovePicker(const Position& p, Move ttm, Depth d, Square s)
+ : pos(p) {
assert(d <= DEPTH_ZERO);
ttm = MOVE_NONE;
}
- ttMove = (ttm && pos.pseudo_legal(ttm) ? ttm : MOVE_NONE);
+ ttMove = ttm && pos.pseudo_legal(ttm) ? ttm : MOVE_NONE;
endMoves += (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::MovePicker(const Position& p, Move ttm, Value th)
+ : pos(p), 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;
+ // In ProbCut we generate captures with SEE higher than the given threshold
+ ttMove = ttm
+ && pos.pseudo_legal(ttm)
+ && pos.capture(ttm)
+ && pos.see(ttm) > threshold ? ttm : MOVE_NONE;
endMoves += (ttMove != MOVE_NONE);
}
-/// score() assign a numerical value to each move in a move list. The moves with
+/// 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.
- // 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
+ // 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 in pick_move_from_list(). This way we save some SEE
- // calls in case we get a cutoff.
+ // 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))]
- - 200 * relative_rank(pos.side_to_move(), to_sq(m));
+ - Value(200 * relative_rank(pos.side_to_move(), to_sq(m)));
}
template<>
void MovePicker::score<QUIETS>() {
- Square prevSq = to_sq((ss-1)->currentMove);
- const HistoryStats& cmh = counterMovesHistory[pos.piece_on(prevSq)][prevSq];
+ 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();
for (auto& m : *this)
- m.value = history[pos.moved_piece(m)][to_sq(m)]
- + cmh[pos.moved_piece(m)][to_sq(m)] * 3;
+ 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 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.
+ // 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;
for (auto& m : *this)
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)];
+ m.value = history[pos.moved_piece(m)][to_sq(m)] + fromTo.get(c, m);
}
-/// generate_next_stage() generates, scores and sorts the next bunch of moves,
+/// generate_next_stage() generates, scores, and sorts the next bunch of moves
/// when there are no more moves to try for the current stage.
void MovePicker::generate_next_stage() {
+ assert(stage != STOP);
+
cur = moves;
switch (++stage) {
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;
+ killers[2] = countermove;
+ cur = killers;
+ endMoves = cur + 2 + (countermove != killers[0] && countermove != killers[1]);
break;
- case GOOD_QUIETS:
- endQuiets = endMoves = generate<QUIETS>(pos, moves);
+ case QUIET:
+ 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)
+ 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);
break;
case BAD_CAPTURES:
- // Just pick them in reverse order to get MVV/LVA ordering
+ // Just pick them in reverse order to get correct ordering
cur = moves + MAX_MOVES - 1;
endMoves = endBadCaptures;
break;
break;
case EVASION: case QSEARCH_WITH_CHECKS: case QSEARCH_WITHOUT_CHECKS:
- case PROBCUT: case RECAPTURE:
+ case PROBCUT: case RECAPTURE: case STOP:
stage = STOP;
- /* Fall through */
-
- case STOP:
- endMoves = cur + 1; // Avoid another generate_next_stage() call
break;
default:
}
}
+int MovePicker::see_sign() const
+{
+ return stage == GOOD_CAPTURES ? 1
+ : stage == BAD_CAPTURES ? -1 : 0;
+}
/// 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>() {
+
+Move MovePicker::next_move() {
Move move;
while (true)
{
- while (cur == endMoves)
+ while (cur == endMoves && stage != STOP)
generate_next_stage();
switch (stage) {
return move;
break;
- case GOOD_QUIETS: case BAD_QUIETS:
+ case QUIET:
move = *cur++;
if ( move != ttMove
&& move != killers[0]
case PROBCUT_CAPTURES:
move = pick_best(cur++, endMoves);
- if (move != ttMove && pos.see(move) > captureThreshold)
+ if (move != ttMove && pos.see(move) > threshold)
return move;
break;
}
}
}
-
-
-/// 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>(); }
projects / stockfish / blobdiff