Find the smallest CIDR block that contains two IPAddrs, in Ruby.

IPAddr_union.rb

require "ipaddr"

class IPAddr
  # Returns the ipaddr representing the smallest CIDR block that includes both
  # ipaddrs.
  def union(other)
    addr = @addr
    coerced = coerce_other(other).to_i
    prefixlen = self.ipv4? ? 32 : 128
    while addr != coerced
        addr = addr >> 1
        coerced = coerced >> 1
        prefixlen -= 1
    end
    return self.clone.mask!(prefixlen)
  end

end

# whois 1.64.0.0
inetnum = "1.164.0.0 - 1.164.255.255"
a1, a2 = inetnum.split("-").map{|s| IPAddr.new s.strip}
puts a1.union(a2).inspect

This uses an O(n) algorithm. In theory you could use binary search but I'm not sure if it would be worth it.