[m-rev.] for review: putback of 8-bit values to binary input streams

[Julien Fischer]

Hi Peter,

On Fri, 5 Oct 2018, Peter Wang wrote:

> On Fri, 5 Oct 2018 02:36:11 +0000 (UTC), Julien Fischer <jfischer at opturion.com> wrote:
>>
>> For review by anyone.
>>
>> -------------------------------------
>>
>> Putback of 8-bit values to binary input streams.
>>
>> Support direct putback of int8 and uint8 values to binary input streams
>> instead of via the bottom 8 bits of an int value.
>>
>> library/io.m:
>>      Add putback_{int8,uint8}/[34].
>>
>>      Add stream type class instances for putback streams binary_input_stream
>>      with int8 and uint8.
>>
>> tests/hard_coded/Mmakefile:
>> tests/hard_coded/putback_binary_int8.{m,exp}:
>> tests/hard_coded/putback_binary_uint8.{m,exp}:
>>      Add tests of the above.
>>
>> Julien.
>>
>> diff --git a/library/io.m b/library/io.m
>> index 20af25a..b3356ff 100644
>> --- a/library/io.m
>> +++ b/library/io.m
>> @@ -1014,6 +1014,20 @@
>>   :- pred putback_byte(io.binary_input_stream::in, int::in, io::di, io::uo)
>>       is det.
>
> The description for putback_byte itself does not describe the behaviour
> for out-of-range values.

It's supposed to be the bottom 8 bits of the int, which is what we say
elsewhere for predicates that deal with "bytes".  I've added sentence
to that end.

>> +    % As above, but un-reads an int8 instead of a byte represented by
>> +    % the bottom 8 bits of an int.
>> +    %
>> +:- pred putback_int8(int8::in, io::di, io::uo) is det.
>> +:- pred putback_int8(io.binary_input_stream::in, int8::in, io::di, io::uo)
>> +    is det.
>
> The comment should be more specific, something like:
>
>    Un-reads a byte, where the byte value is the 8 bits of the int8
>    reinterpreted as a uint8.

How this?

     Like putback_byte, but where the byte value un-read is the 8 bits
     of the int8 reinterpreted as a uint8.

> (where the reference manual has defined int8 to use two's complement
> representation)

I don't think it's worth duplicating what the refence manual says here.

Julien.