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LibChess: Only save hash of board state for repetition checking
This more than doubles the number of nodes that MCTS can search for a given time limit, and greatly reduces memory usage.
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sideshowbarker
2024-07-18 11:38:27 +09:00
Author: https://github.com/petelliott Commit: https://github.com/SerenityOS/serenity/commit/57bb4d1aec9 Pull-request: https://github.com/SerenityOS/serenity/pull/8209 Reviewed-by: https://github.com/awesomekling
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@ -579,14 +579,12 @@ bool Board::apply_move(const Move& move, Color color)
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bool Board::apply_illegal_move(const Move& move, Color color)
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{
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Board clone = *this;
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clone.m_previous_states = {};
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clone.m_moves = {};
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auto state = Traits<Board>::hash(*this);
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auto state_count = 0;
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if (m_previous_states.contains(clone))
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state_count = m_previous_states.get(clone).value();
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if (m_previous_states.contains(state))
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state_count = m_previous_states.get(state).value();
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m_previous_states.set(clone, state_count + 1);
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m_previous_states.set(state, state_count + 1);
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m_moves.append(move);
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m_turn = opposing_color(color);
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@ -758,7 +756,7 @@ Board::Result Board::game_result() const
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if (m_moves_since_capture == 50 * 2)
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return Result::FiftyMoveRule;
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auto repeats = m_previous_states.get(*this);
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auto repeats = m_previous_states.get(Traits<Board>::hash(*this));
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if (repeats.has_value()) {
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if (repeats.value() == 3)
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return Result::ThreeFoldRepetition;
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@ -172,7 +172,8 @@ private:
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bool m_black_can_castle_kingside { true };
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bool m_black_can_castle_queenside { true };
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HashMap<Board, int> m_previous_states;
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// We trust that hash collisions will not happen to save lots of memory and time.
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HashMap<unsigned, int> m_previous_states;
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Vector<Move> m_moves;
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friend struct Traits<Board>;
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};
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@ -276,7 +277,7 @@ void Board::generate_moves(Callback callback, Color color) const
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template<>
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struct AK::Traits<Chess::Piece> : public GenericTraits<Chess::Piece> {
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static unsigned hash(Chess::Piece piece)
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static unsigned hash(const Chess::Piece& piece)
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{
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return pair_int_hash(static_cast<u32>(piece.color), static_cast<u32>(piece.type));
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}
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@ -284,7 +285,7 @@ struct AK::Traits<Chess::Piece> : public GenericTraits<Chess::Piece> {
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template<>
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struct AK::Traits<Chess::Board> : public GenericTraits<Chess::Board> {
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static unsigned hash(Chess::Board chess)
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static unsigned hash(const Chess::Board chess)
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{
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unsigned hash = 0;
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hash = pair_int_hash(hash, static_cast<u32>(chess.m_white_can_castle_queenside));
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