#!/usr/bin/perl

use Math::BigInt;

my $hex = "0x000fffff7f00fffc";
my $dec = Math::BigInt->new($hex);

print "$hex = $dec\n";

# also works with even larger numbers...

$hex = "0x000fffff7f00fffc000fffff7f00fffc000fffff7f00fffc000fffff7f00fffc";
$dec = Math::BigInt->new($hex);

print "$hex = $dec\n";

__END__
0x000fffff7f00fffc = 4503597463175164
0x000fffff7f00fffc000fffff7f00fffc000fffff7f00fffc000fffff7f00fffc = 28269539451579875061911530748705190818470806058399246855690547914954833916