CIDR in/out net calculation

netmask.erl

-module(netmask).
-export([in_network/3]).

in_network(Net, CIDR, IP)
  when is_binary(Net), is_binary(IP), is_integer(CIDR) ->
    <<NetworkPrefix:CIDR/bits, _/bits>> = Net,
    case IP of
        <<NetworkPrefix:CIDR/bits, _Host/bits>> ->
            in_net;
        _ -> not_in_net
    end.