Re: Any examples of Byte Ordering Functions

[Jeffrey Carter <spam@spam.com>]

tmoran@acm.org wrote:

>   type source is record
>     a,b,c,d : bytes;
>   end record;
>   for source use record
>     a at 0 range 0 .. 7;
>     b at 1 range 0 .. 7;
>     c at 2 range 0 .. 7;
>     d at 3 range 0 .. 7;
>   end record;

for Source'Size use 32;

is probably a good idea, too.

>   type target is record
>     d,c,b,a : bytes;
>   end record;

Even better,

type Target is new Source;

This creates conversions named Source and Target that reorder your bytes 
for you automatically.

>   for target use record
>     d at 0 range 0 .. 7;
>     c at 1 range 0 .. 7;
>     b at 2 range 0 .. 7;
>     a at 3 range 0 .. 7;
>   end record;

A derived type may have a different representation than its parent.

A size clause here would be a good idea, too.

>   type dword is new interfaces.integer_32;
>   type swapped_dword is new interfaces.integer_32;
> 
>   function split_dword is new ada.unchecked_conversion(dword, source);
>   function make_swapped is new ada.unchecked_conversion(target, swapped_dword);
> 
>   function byte_swap(input : dword) return swapped_dword is
>     s : constant source := split_dword(input);
>   begin
>     return make_swapped(target'(a=>s.d, b=>s.c, c=>s.b, d=>s.a));
>   end byte_swap;

return Make_Swapped (Target (S) );

-- 
Jeff Carter
"You cheesy lot of second-hand electric donkey-bottom biters."
Monty Python & the Holy Grail
14