addr.exs

defmodule Addr do
  def extract_subnet(addr, mask) when is_binary(addr) and is_binary(mask) do
    <<converted_addr::integer-big-size(32)>> = addr
    <<converted_mask::integer-big-size(32)>> = mask
    subnet = Bitwise.band(converted_addr, converted_mask)

    <<octet1::integer-big-size(8), octet2::integer-big-size(8), octet3::integer-big-size(8),
      octet4::integer-big-size(8)>> = <<subnet::integer-big-size(32)>>

    {octet1, octet2, octet3, octet4}
  end
end