gistfile1.hrl

-module(base32).
-export([encode/1, decode/1]).

encode(Binary) ->
  encode(Binary, <<>>).

encode(<<>>, To) -> To;
encode(<<B:1>>, To) -> <<To/binary, (symbol(B)), "====">>;
encode(<<B:2>>, To) -> <<To/binary, (symbol(B)), "=">>;
encode(<<B:3>>, To) -> <<To/binary, (symbol(B)), "=======">>;
encode(<<B:4>>, To) -> <<To/binary, (symbol(B)), "===">>;
encode(<<B:5/integer, Rest/bitstring>>, To) ->
  encode(Rest, <<To/binary, (symbol(B)):8/integer>>).

decode(Binary) ->
  decode(Binary, <<>>).

decode(<<>>, To) -> To;
decode(<<B:8, "====">>, To) -> <<To/binary, (B-1):1>>;
decode(<<B:8, "=">>, To) -> <<To/binary, (B-1):2>>;
decode(<<B:8, "=======">>, To) -> <<To/binary, (B-1):3>>;
decode(<<B:8, "===">>, To) -> <<To/binary, (B-1):4>>;
decode(<<B:8, Rest/binary>>, To) ->
  decode(Rest, <<To/binary, (value(B)):5>>).

symbol(B) when B >= 0 andalso B =< 25 -> $A + B;
symbol(B) when B < 32                 -> $2 + B - 26.

value(B) when B >= $A andalso B =< $Z -> B - $A;
value(B) when B >= $2 andalso B =< $9 -> B + 26 - $2.