sub hex2 {
    my $str = shift;
    $str =~ s/^(0x|x)//;
    if (length $str) {
        if ($str =~ /([^0-9a-f])/i) {
            die "hex2: Illegal hexadecimal digit found: '$1'";
        }
        else {
            return hex $str;
        }
    }
    else {
        die "hex2: No chars found after stripping leading 0x or x";
    }
}