Re: Selective suppression of warnings --- gnat on GNU/Linux

[Jean-Pierre Rosen <rosen@adalog.fr>]

Robert A Duff a �crit :
> 1.    subtype T is Integer range A..B;
> 2.    type T is new Integer range A..B;
> 3.    type T is range A..B;
> [...] 
> Option 3 is questionable, because of overflow semantics for intermediate
> results in expressions.  In Pascal, if you say (X+Y)/2, it won't
> overflow if X+Y is in Integer, but not in A..B.  Same is True in Ada for
> option 2, but not necessarily for option 3.
Oh no! Option 2 has exactly the same problem, you just hope that by 
forcing your type to have the same number of bits as Integer (a type you 
know nothing about), there will be enough room for your computations...

If you are worried about overflows (and you use only additions), the 
proper declarations are:
type Big_Enough is range A .. 2*B;
subtype T is Big_Enough range A .. B;

Of course, if you compute more than single additions, a real analysis 
has to be done to determine the bounds of Big_Enough.

By all means, please, let's get rid of Integer!

-- 
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            J-P. Rosen (rosen@adalog.fr)
Visit Adalog's web site at http://www.adalog.fr