makeNullMove method

void makeNullMove()

Pass the turn to the opponent without moving (null-move pruning). Only the side to move and en-passant square change; the board is untouched. Never call when inCheck (the null side could be mated).

Implementation

void makeNullMove() {
  _undo.add(_Undo(-1, -1, castling, epSquare, halfmove));
  epSquare = -1;
  halfmove++;
  turn ^= 1;
}