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From: Robert Dewar <robert_dewar@my-deja.com>
Subject: Re: OS Bindings (was: Where is the elusive jump command?)
Date: 2000/04/12
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Date: 2000-04-12T00:00:00+00:00
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In article <8csjs8$o2p3@ftp.kvaerner.com>,
  "Tarjei T. Jensen" <tarjei.jensen@kvaerner.com> wrote:
> In most cases where an unsigned type like size_t is used it is
> apropriate to translate it to an unsigned integer of some sort
> and not a modular type.

Maybe so, C unlike Ada does not have this possibility, so it
is indeed possible that the above is right. For example if
we see in C

  unsigned char q;

it maybe that the best Ada translation is

  type q is range 0 .. 255;
  for q'size use 8;

but I still don't see the complaint, wrapping types like
unsigned in C are useful in Ada and in C, and we have always
have unsigned types in the sense of the above declaration of
q in Ada.

But I see the point you are making now. I still don't really
see why you don't like the modular types, they seem useful
and clear to me. After all Java decided it was all they needed
:-)

> Arithmetic operations which causes wraparound are most likely
> errors and should be caught.

OK, but this really has nothing to do with type checking, which
is why I was confused by your original post. But if you want
this kind of range checking, then of course do NOT use a modular
type to model the C type.

> Now I have to remember to check interface.C when I get home,
> to check verify that the definition of int, short and long in
> gnat has C semantics.

Not sure what you mean here. In C, overflow for such types
makes the program execution undefined, in Ada, the semantics
is the same as C except in this undefined case, where Ada
defines that CE must be raised.


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