print different dwords between two files

cmpbin.pl

use strict;
use warnings;
use IO::File;
sub readbin {
    my $fn= shift;
    my $fh= IO::File->new($fn, "r") or die "$fn: $!\n";
    binmode $fh;
    my $data;
    $fh->read($data, -s $fn);
    $fh->close();
    return $data;
}
if (@ARGV!=2) {
    die "Usage: cmpbin file1 file2\n";
}
my ($fn1, $fn2)= @ARGV;
my $f1= readbin($fn1);
my $f2= readbin($fn2);

for (my $ofs= 0 ; $ofs < length($f1) && $ofs < length($f2) ; $ofs+=4)
{
    if (substr($f1,$ofs,4) ne substr($f2,$ofs,4)) {
        my ($l,$r)= unpack("VV", substr($f1,$ofs,4).substr($f2,$ofs,4));
        printf("%08lx: %08lx %08lx  xor=%08x  sub=%08x %s  %s\n", $ofs, $l, $r, $l^$r, ($l-$r)&0xFFFFFFFF, disp(substr($f1,$ofs,4)), disp(substr($f2,$ofs,4)));
    }
}
if (length($f1) < length($f2)) {
    printf("%08x: EOF on %s\n", length($f1), $fn1);
}
elsif (length($f1) > length($f2)) {
    printf("%08x: EOF on %s\n", length($f2), $fn2);
}

sub disp {
    my $x= shift;
    $x =~ s/[\x00-\x1f\x7f-\xff]/./g;
    return $x;
}