use Math::BigInt;
print bytearray_to_bigint(127,2);
use Data::Dumper;
sub bytearray_to_bigint {
    my @array = reverse @_;  #Big Endian
    my $result = Math::BigInt->new('0');
    foreach my $a (@array) {
        ($result <<= 8) += $a;
        # This alternative doesn't work:
        # $result = $result->blsft(8)->badd($a);
    }
    return $result;
}

##</code><code>##

@ulongs = unpack 'V*', $bytestring;