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LibChess: Only save hash of board state for repetition checking

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This more than doubles the number of nodes that MCTS can search for a
given time limit, and greatly reduces memory usage.
This commit is contained in:
Peter Elliott 2021-06-19 14:49:53 -06:00 • committed by Andreas Kling
parent 675b8ba995
commit 57bb4d1aec
2 changed files with 9 additions and 10 deletions
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7
Userland/Libraries/LibChess/Chess.h
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@ -172,7 +172,8 @@ private:
bool m_black_can_castle_kingside { true };
bool m_black_can_castle_queenside { true };
HashMap<Board, int> m_previous_states;
// We trust that hash collisions will not happen to save lots of memory and time.
HashMap<unsigned, int> m_previous_states;
Vector<Move> m_moves;
friend struct Traits<Board>;
};
@ -276,7 +277,7 @@ void Board::generate_moves(Callback callback, Color color) const
template<>
struct AK::Traits<Chess::Piece> : public GenericTraits<Chess::Piece> {
static unsigned hash(Chess::Piece piece)
static unsigned hash(const Chess::Piece& piece)
{
return pair_int_hash(static_cast<u32>(piece.color), static_cast<u32>(piece.type));
}
@ -284,7 +285,7 @@ struct AK::Traits<Chess::Piece> : public GenericTraits<Chess::Piece> {
template<>
struct AK::Traits<Chess::Board> : public GenericTraits<Chess::Board> {
static unsigned hash(Chess::Board chess)
static unsigned hash(const Chess::Board chess)
{
unsigned hash = 0;
hash = pair_int_hash(hash, static_cast<u32>(chess.m_white_can_castle_queenside));