anchor.diff:  roundtrip_enc(Mod, Type, Value, ExpectedValue) ->
       {ok,Encoded} = Mod:encode(Type, Value),
       {ok,ExpectedValue} = Mod:decode(Type, Encoded),
  +    test_ber_indefinite(Mod, Type, Encoded, ExpectedValue),
       Encoded.
   
   %%%
  
positive.code: hex2num(C) when $0 =< C, C =< $9 -> C - $0;
  hex2num(C) when $A =< C, C =< $F -> C - $A + 10;
  hex2num(C) when $a =< C, C =< $f -> C - $a + 10.
  
negative.code: roundtrip(Mod, Type, Value, ExpectedValue) ->
      {ok,Encoded} = Mod:encode(Type, Value),
      {ok,ExpectedValue} = Mod:decode(Type, Encoded),
      test_ber_indefinite(Mod, Type, Encoded, ExpectedValue),
      ok.
  
  roundtrip_enc(Mod, Type, Value) ->
  