IPAddr#wildcard_mask

# File tmp/rubies/ruby-3.4.1/lib/ipaddr.rb, line 497
def wildcard_mask
  case @family
  when Socket::AF_INET
    mask = IN4MASK ^ @mask_addr
  when Socket::AF_INET6
    mask = IN6MASK ^ @mask_addr
  else
    raise AddressFamilyError, "unsupported address family"
  end

  _to_string(mask)
end