Re: how to tell 64 vs 32 bit architecture ?

On Fri, Sep 07, 2007 at 02:50:21PM +0300, Giorgos Keramidas wrote:
> On 2007-09-07 00:09, Luigi Rizzo <rizzo_at_icir.org> wrote:
> >On Fri, Sep 07, 2007 at 01:26:47AM +0300, Giorgos Keramidas wrote:
> >>On 2007-09-06 11:10, Luigi Rizzo <rizzo_at_icir.org> wrote:
> >>> hi,
> >>> i was wondering what is the proper way to tell a 64 vs 32 bit
> >>> architecture.
> >>>
> >>> I see that some code in sys/ uses  ' #ifdef __LP64__ ' but i am not
> >>> sure if this is generic enough (ie not gcc or FreeBSD specific),
> >>> and also suitable for userland (i.e. works on linux or other platforms
> >>> as well).
> >>
> >> This is usually needed to differentiate between a feature "X" which
> >> behaves differently in amd64 vs. i386 vs. sparc vs. sparc64, etc.
> >
> > i am actually looking at pointer sizes, as i need to do some pointer
> > manipulation going through intptr_t, and need to know that in the
> > preprocessor because some constants need to be 32 or 64 bit depending
> > on that, and are not trivial (i.e. not 0, 1 or something i can build
> > with size-agnostic expressions)
> 
> An intptr_t can safely hold any void pointer value, and C99 says:
> 
> %     7.18.1.4 Integer types capable of holding object pointers
> %
> % 1   The following type designates a signed integer type with the
> %     property that any valid pointer to void can be converted to
> %     this type, then converted back to pointer to void, and the
> %     result will compare equal to the original pointer:
> %
> %         intptr_t
> 
> What sort of manipulation?  Can this sort of manipulation be written in
> a way that uses sizeof(intptr_t) instead of 4, 8, or preprocessor magic?

i need to do this:

#ifdef BUILT_FOR_64BIT_POINTERS
#define	MY_MAGIC	0xdeadbeefd00de123	/* 64 bit */
#else
#define	MY_MAGIC	0xdeadbeef		/* 32 bit */

If you know of a way to implement this without preprocessor
magic, i am all ears. If the values were simpler (eg all ones or so)
i could have used ~((unitptr_t)0) but this is not the case here

cheers
luigi