Re: Endianness independance

["Warren W. Gay VE3WWG" <ve3wwg@cogeco.ca>]

Simon Wright wrote:
> "Warren W. Gay VE3WWG" <ve3wwg@cogeco.ca> writes:
>>If you look carefully at GLADE, you will notice that all that is
>>being done there is "byte swapping". There is more to independent
>>network formats than that (it just happens to work with _most_
>>modern platforms at the moment).
> 
> I don't know what version of GLADE you are looking at, but the code
> for 3.15p does a lot more than this. I am no expert as to whether it
> achieves the purpose or not on eg a VAX (but I don't believe that GNAT
> supports VAXes anyway).
> 
> This is reading a single-length Float from the net:
> 
>    function I_F (Stream : access RST) return Float is
>       I       : constant Precision := Single;
>       E_Size  : Integer  renames Fields (I).E_Size;
>       E_Bias  : Integer  renames Fields (I).E_Bias;
>       E_Last  : Integer  renames Fields (I).E_Last;
>       F_Size  : Integer  renames Fields (I).F_Size;
>       F_Mask  : SE       renames Fields (I).F_Mask;
>       E_Bytes : SEO      renames Fields (I).E_Bytes;
>       F_Bytes : SEO      renames Fields (I).F_Bytes;
> 
>       E : Unsigned;
>       P : Boolean;
>       X : Float;
>       S : SEA (1 .. F_L);
>       L : SEO;
> 
>    begin
>       Ada.Streams.Read (Stream.all, S, L);
> 
>       if L /= S'Last then
>          raise Data_Error;
>       end if;
> 
>       --  Extract Fraction, Exponent and Sign.
>       X := Float (S (F_L + 1 - F_Bytes) and F_Mask);
>       for N in F_L + 2 - F_Bytes .. F_L loop
>          X := X * FB + Float (S (N));
>       end loop;
>       X := Scaling (X, -F_Size); --  Float
...
>    end I_F;

Well Simon, I have to admit this sure looks a lot different
than the code I remember looking at. I havn't reviewed this
in great detail, but obviously there is more than byte
swapping here. I am sure that the last time I looked was
pre 3.15p.

I am actually rather happy to see this level of support.

It would be best if the format supported was XDR, but without
more investigation, I cannot say here and now if this is
it (XDR support would make Ada more easily able to speak
on equal network terms with existing RPC C code). However,
simply guaranteeing that the format is compatible
between two GLADE sessions is good enough for most purposes
that I would personally have in mind.

Thanks for pointing this out. Warren.
-- 
Warren W. Gay VE3WWG
http://home.cogeco.ca/~ve3wwg