/// Calculate zobrist key from current board position. This should only be used after setting board from fen; during search the key should be updated incrementally.
public static ulong CalculateZobristKey(Board board)
{
ulong zobristKey = 0;
for (int squareIndex = 0; squareIndex < 64; squareIndex++)
{
if (board.Square[squareIndex] != 0)
{
int pieceType = Piece.PieceType(board.Square[squareIndex]);
int pieceColour = Piece.Colour(board.Square[squareIndex]);
zobristKey ^= piecesArray[pieceType, (pieceColour == Piece.White) ? Board.WhiteIndex : Board.BlackIndex, squareIndex];
}
}
int epIndex = (int)(board.currentGameState >> 4) & 15;
if (epIndex != -1)
{
zobristKey ^= enPassantFile[epIndex];
}
if (board.ColourToMove == Piece.Black)
{
zobristKey ^= sideToMove;
}
zobristKey ^= castlingRights[board.currentGameState & 0b1111];
