++ /* Sanity check: ensure that our length is at least 22 bytes, that
++ * IPv4MaskLen is <= 32, 6rdPrefixLen <= 128 and that the sum of
++ * (32 - IPv4MaskLen) + 6rdPrefixLen is less than or equal to 128.
++ * If any of these requirements is not fulfilled, return with empty
++ * value.
++ */
++ if ((len >= 22) && (*option <= 32) && (*(option+1) <= 128) &&
++ (((32 - *option) + *(option+1)) <= 128))
++ {
++ /* IPv4MaskLen */
++ dest += sprintf(dest, "%u ", *option++);
++ len--;