IPAddr#link_local_unicast?

# File tmp/rubies/ruby-4.1.0-preview1/lib/ipaddr.rb, line 337
def link_local?
  case @family
  when Socket::AF_INET
    (@addr & 0xffff0000 == 0xa9fe0000) && prefix >= 16 # 169.254.0.0/16
  when Socket::AF_INET6
    (@addr & 0xffc0_0000_0000_0000_0000_0000_0000_0000 == 0xfe80_0000_0000_0000_0000_0000_0000_0000) && prefix >= 10 || # fe80::/10
      (@addr >> 32 == 0xffff && (
        (@addr & 0xffff0000 == 0xa9fe0000) && prefix >= 112 # ::ffff:169.254.0.0/112 (169.254.0.0/16)
      ))
  else
    raise AddressFamilyError, "unsupported address family"
  end
end