#!/usr/local/bin/perl5.6.2
use Math::BigInt;

BEGIN {
    if (!exists &Math::BigInt::as_hex) {
        *Math::BigInt::as_hex = sub {
            my $i = shift;
            my $hex = '';
            do {
                my $mod = $i % 16;
                $hex .= sprintf("%x", $mod);
            } while $i = $i / 16;
            scalar reverse $hex;
        }
    }
}

$z = new Math::BigInt("1234567890"x 3);
print $z->as_hex();