Re: How do you bitwise operations in Ada '83 and '95

[Colin Paul Gloster <Colin_Paul_Gloster@ACM.org>]

On Thu, 20 Jul 2006, Georg Bauhaus wrote:

"On Thu, 2006-07-20 at 15:08 +0200, Colin Paul Gloster wrote:

>  the returned value from function 
> Shift_Left  (Value : Unsigned_96; Amount : Natural) return Unsigned_96 
> can not be assigned to a variable of type Time is mod 2 ** 96 without 
> conversion.

type Time is new Unsigned_96;

In fact,
  type Time is private;
and then the above."

No, actually you need a subtype for your example but I accept your point 
is still valid. Uncomment the following comments for a compilation error.
procedure Subtype_Instead_Of_Type is
   type T1 is range 0..19;
   --type T2 is new T1;
   subtype ST is T1;
   V1 : T1;
   --V2 : T2;
   V3 : ST;
begin
   V1 := 7;
   --V2 := V1;
   V3 := V1;
end;


"[..]
But if an algorithm is about shifting bits really, then why
not use the subprograms that say "Shift_zzzz" in their names, and
that were made for shifting bits?"

If you can and all the platforms you wish to have the program on allow it, 
it could be done. Another question is, why did the Ada 95 standard and the 
Ada 2005 standard provide those functions in such a form which is less 
general than Ada's multiplication and power operators and C's shift 
operators?

" If there is room for even more than 96 bits in modular 
numbers, [..]"

Whereas if the largest Interfaces.Unsigned_n is smaller than needed...