+ # 50-move rule. Note that castle does not reset the counter, per FIDE rules.
+ my $castling = (lc($piece) eq 'k' && abs($from_col - $to_col) > 1) || # King moves two squares.
+ ($piece eq 'K' && $dest_piece eq 'R') || # Chess960-style king-takes-rook.
+ ($piece eq 'k' && $dest_piece eq 'r');
+ if (!$castling && (lc($piece) eq 'p' || $dest_piece ne '-')) {