Remove O(N^2) algorithm from repeated field extraction.

In messages with many values for a repeated field, lists:reverse/1 is
called many times, resulting in large amounts of garbage and an
unreasonable amount of time spent in decoding. This moves the list
reversal until the end of the decoding, only once per repeated field.

src/pokemon_pb.erl

@@ -100,7 +100,7 @@ decode(pikachu, Bytes) when is_binary(Bytes) ->
     Decoded = decode(Bytes, Types, Defaults),
     to_record(pikachu, Decoded).
 
-decode(<<>>, _, Acc) -> Acc;
+decode(<<>>, Types, Acc) -> reverse_repeated_fields(Acc, Types);
 decode(Bytes, Types, Acc) ->
     {ok, FNum} = protobuffs:next_field_num(Bytes),
     case lists:keyfind(FNum, 1, Types) of
@@ -125,12 +125,12 @@ decode(Bytes, Types, Acc) ->
                 true ->
                     case lists:keytake(FNum, 1, Acc) of
                         {value, {FNum, Name, List}, Acc1} ->
-                            decode(Rest1, Types, [{FNum, Name, lists:reverse([int_to_enum(Type,Value1)|lists:reverse(List)])}|Acc1]);
+                            decode(Rest1, Types, [{FNum, Name, [int_to_enum(Type,Value1)|List]}|Acc1]);
                         false ->
                             decode(Rest1, Types, [{FNum, Name, [int_to_enum(Type,Value1)]}|Acc])
                     end;
                 false ->
-		                decode(Rest1, Types, [{FNum, Name, int_to_enum(Type,Value1)}|Acc])
+                    decode(Rest1, Types, [{FNum, Name, int_to_enum(Type,Value1)}|Acc])
             end;
         false ->
             case lists:keyfind('$extensions', 2, Acc) of
@@ -147,6 +147,20 @@ decode(Bytes, Types, Acc) ->
             end
     end.
 
+reverse_repeated_fields(FieldList, Types) ->
+    [ begin
+          case lists:keyfind(FNum, 1, Types) of
+              {FNum, Name, _Type, Opts} ->
+                  case lists:member(repeated, Opts) of
+                      true ->
+                          {FNum, Name, lists:reverse(Value)};
+                      _ ->
+                          Field
+                  end;
+              _ -> Field
+          end
+      end || {FNum, Name, Value}=Field <- FieldList ].
+
 unpack_value(Binary, string) when is_binary(Binary) ->
     binary_to_list(Binary);
 unpack_value(Value, _) -> Value.