Re: Unsigned Integer Restraint Errors

["Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>]

On 12 Mar 2007 12:13:26 -0700, frikk wrote:

> Thank you for the input. This leaves me with 2 questions:
> 1.  If my input is 2**35, wouldn't this still render the Integer type
> inaccurate? The goal is to be able to use 64 bit integers... I'm
> referring to your example of UNSIGNED_LONG_INT := UNSIGNED_LONG_INT
> (Integer'(X));

I don't understand what are you trying to achieve. Where the input comes
from, and what type it has. I see only two possibilities:

1. The input type is UNSIGNED_LONG_INT, where is the problem? It is in the
range. -5 in your example is not a number, it is an expression of
UNSIGNED_LONG_INT and its result is in the range of. If the semantics of
"-" bothers you, redefine it:

   function "-" (Left : UNSIGNED_LONG_INT) return UNSIGNED_LONG_INT is
   begin
      if Left = 0 then
         return Left;
      else
         raise Constraint_Error; -- No wrapping
      end if;
   end "-";

or else disallow it altogether:

   function "-" (Left : UNSIGNED_LONG_INT) return UNSIGNED_LONG_INT
       is abstract;

2. The type is some different type. You have to convert it to
UNSIGNED_LONG_INT and if its value is outside UNSIGNED_LONG_INT'Range you
will get Constraint_Error. Again, no problem in sight.

It is safe in all cases.

-------
When you use Integer, it is to expect that on most machines
Integer'Last<System.Max_Binary_Modulus. But, again, I probably don't
understand your problem, because I don't see in the first place why you
wanted to convert signed integers to modular integers. As Randy has already
suggested, declare it signed natural and enjoy range checks.

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de