# File lib/ipaddress/ipv6.rb, line 724
    def initialize(str)
      string, netmask = str.split("/")
      if string =~ /\./ # IPv4 in dotted decimal form
        @ipv4 = IPAddress::IPv4.extract(string)
      else # IPv4 in hex form
        groups = IPAddress::IPv6.groups(string)
        @ipv4 = IPAddress::IPv4.parse_u32((groups[-2]<< 16)+groups[-1])
      end
      super("::ffff:#{@ipv4.to_ipv6}/#{netmask}")
    end