#
# Return an array of bytes that correspond to an IPv6 netmask.
# The MSB is returned as the first byte.
#
sub make_netmask {
    my $mask = shift;
    return if $mask < 0 or $mask > 128;

    my @bytes;
    while ($mask > 0) {
	my $off = ($mask >= 8) ? 0 : (8 - $mask);
	push @bytes, (0xff << $off) & 0xff;
	$mask -= 8;
    }

    return @bytes;
}

sub output {
    my $mask = shift;
    my @bytes = make_netmask($mask);
    print "$mask = ", join(' ', map { sprintf "%02x", $_ } @bytes), "\n";
}

# Test some inputs
output(0);
output(3);
output(8);
output(9);
output(127);
output(128);

__OUTPUT__
0 = 
3 = e0
8 = ff
9 = ff 80
127 = ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff fe
128 = ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff