Re: AI12-0218: What is the portable representation clause for processing IETF packets on little-endian machines?

["Jeffrey R. Carter" <spam.jrcarter.not@spam.not.acm.org>]

On 05/12/2018 09:08 AM, Simon Wright wrote:
> 
> I saw the example. I stand by my statement that it's confusing.

I agree that the terminology is not intuitive.

> 
> Not quite the same, but I think I showed upthread a conversion that does
> this:
> 
>     function To_Fixed_32_16 (S : Four_Byte_Slice) return Fixed_32_16 is
>        function Convert is new Ada.Unchecked_Conversion (Four_Byte_Slice,
>                                                          Fixed_32_16);
>     begin
>        if Big_Endian then
>           return Convert (S);
>        else
>           return Convert ((1 => S (4),
>                            2 => S (3),
>                            3 => S (2),
>                            4 => S (1)));
>        end if;
>     end To_Fixed_32_16;

For the case where it does swapping, I don't see that this is very different 
from my version, at least if the intention is to go from Integer to Integer, 
which is what I thought you were asking. I used change-of-representation to get 
the swapping and this does the swapping itself, and this hides one of the 
unchecked conversions. My version was intended to allow conversion in both 
directions, while this seems to only go one way. I used Ada 83 to show that such 
change-of-representation was in the language then, and you're using a more 
recent version.

-- 
Jeff Carter
"Death awaits you all, with nasty, big, pointy teeth!"
Monty Python & the Holy Grail
20