Format File Sizes

display.erl

-module(display).
-export([format/1,format/2]).

format(Num) -> format(Num, 2).

format(Num, Precision) ->
  Abs = abs(Num),
  TB = math:pow(10,12),
  GB = math:pow(10,9),
  MB = math:pow(10,6),
  KB = math:pow(10,3),
  {Suffix, Value} =
    if
      Abs >= TB ->
        {"TB", Abs/TB};
      Abs < TB, Abs >= GB ->
        {"GB", Abs/GB};
      Abs < GB, Abs >= MB ->
        {"MB", Abs/MB};
      Abs < MB, Abs >= KB ->
        {"KB", Abs/KB};
      true ->
        {"B", Abs}
    end,
  io_lib:format("~." ++ integer_to_list(Precision) ++ "f~s",[Value, Suffix]).

%% for logging, I end up doing lists:flatten on this output