Unsigned int ?!

Unsigned int ?!

[Luc MAZARDO]

I would like to get the "caml unsigned int value" of an "unsigned int C
value". Is there a way to do this ??

I do the following, and it fails ...


---toto_stub.c---
value toto(void)
{
  return Val_int(get()); 
}
------------

---toto.mli---
val toto : unit -> int ;;
------------

---toto.ml---
external toto : unit -> int = "toto";;
-------------

---test.c---
<<some stuff>>

printf("%d\n", toto()); /* unsigned int: --> 3 */

<<some stuff>>
-----------


---test.ml---
let t = toto () ;;
val t : int = -924646501 /* uh ?? */
-------------


-- 
Luc Mazardo
http://OCamlSDL.sourceforge.net
Gnu Emacs:flame.el Don't you realise that Michael Jackson is a cool
dude?

Re: Unsigned int ?!

[Xavier Leroy]

> I would like to get the "caml unsigned int value" of an "unsigned int C
> value". Is there a way to do this ??
> I do the following, and it fails ...

I tried to reproduce the problem from your (incomplete) code snippet,
and everything worked fine.  If you have a complete (self-contained)
program that reproduces the problem, please send it to
caml-bugs@inria.fr.

As for the unsigned vs. signed issue, it's just two ways to view the
same bit patterns: the most significant bit of the unsigned int becomes
the sign bit of the signed int.  So, for "small enough" unsigned ints,
you will see them as the corresponding Caml int; large unsigned ints
wrap around.

- Xavier Leroy

Re: Unsigned int ?!

[thierry BRAVIER]

Luc MAZARDO a écrit:

> I would like to get the "caml unsigned int value" of an "unsigned int C
> value". Is there a way to do this ??
>
> I do the following, and it fails ...
>
> ---toto_stub.c---
> value toto(void)
> {
>   return Val_int(get());
> }
> ------------

I think you should add:
value toto_external (value unit) { /* unit is  necessary for this external
function */
   return toto ();
}

> ---toto.mli---
> val toto : unit -> int ;;
> ------------
>
> ---toto.ml---
> external toto : unit -> int = "toto";;

Here you would rather write:
external toto : unit -> int = "toto_external";;

Anyway whether your version fails, returns a wrong result or anything else
cannot be predicted
since it is related to the function call protocol of your machine.

Or maybe I am wrong since I did not try this on my computer  :-)

Hope this helps.

Thierry Bravier