try <<0:16/float>> of
    _ -> lists:keystore(erl_opts, 1, CONFIG, {erl_opts, case lists:keyfind(erl_opts, 1, CONFIG) of
                                                            {_, O} -> [{d, 'HAVE_float16'}|O];
                                                            _ -> [{d, 'HAVE_float16'}]
                                                        end})
catch
    error:badarg -> CONFIG
end.