use strict;
use warnings;
use Time::HiRes qw( time );

my $start = time();

open (my $file, '<', $ARGV[0]) or die 'cannot open $file: $!';
binmode($file);

open (my $reversedFile, '+>', "$ARGV[0].swap");
binmode($reversedFile);

my($data, $n);

 while (($n = read $file, $data, 4096) != 0) {
	print $reversedFile pack("v*", unpack("n*", $data));
	}
	
my $end = time();
my $runtime = sprintf("%.16s", $end - $start);
print $runtime;