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

[Robert A Duff <bobduff@shell01.TheWorld.com>]

Jean-Pierre Rosen <rosen@adalog.fr> writes:

> 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.

That's all true, if we're just talking about Ada.

But we're talking about translating Pascal into Ada.
I was making the implicit assumption that Pascal's
Integer is the same as Ada's Integer, which is
likely true.

If that's true, then we must presume that the Pascal
programmer already made sure that calculations won't
overflow, so they won't overflow in Ada Integer, either.
Or else there's a bug in the Pascal code,
and we're going to translate that into the same
bug in the Ada code.

If you don't like the above assumption, then I'd say
the correct translation is:

    type Pascal_Integer is range ...;
    subtype T is Pascal_Integer range A..B;

where the rangs of Pascal_Integer is chosen to
match the Pascal compiler -- obviously you have
to know something about the Pascal compiler.

Either way (whether we use Integer or a special
Pascal_Integer), there's no need to analyze the
program for overflow, and do things like the 2*B
you suggest -- that's not the job of a Pascal-to-Ada
translator!

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

I'm all for it.  ;-)

- Bob