Re: Long double alignment test

[Goswin von Brederlow <brederlo@informatik.uni-tuebingen.de>]

Brett Cundal <bcundal@cundal.net> writes:

> Mentors,
>
> This may be a full-on d-devel question, but I'll start out here.
>
> I'm maintaining GNU Smalltalk, which is having problems building on
> most 64-bit platforms. I'm having difficulty tracking these problems
> down, so I'm asking for some assistance from anyone who has access to
> these platforms (any DD, I believe).
>
> The issue is with a test for long double alignment which reports an
> incorrect value on ia64 (and probably other archs). On a RedHat
> mailing list I have found the following code which is claimed to
> correctly detect long double alignment:
>
> http://sources.redhat.com/ml/autoconf/1999-07/msg00002.html
>
> struct foo {
>     union align {
>         double d;
>         long l;
>         void *p;
>     } u;
>     char c;
> };
>
> int main() {
>     struct foo f[2];
>
>     printf("sizeof(foo)=%ld\n", (long) sizeof(struct foo));
>     printf("sizeof(align)=%ld\n", (long) sizeof(union align));
>     printf("sizeof(f2)=%ld\n", (long) sizeof(f));
>
>     if( 2*sizeof(union align) != sizeof(f) ) {
>         printf("union may be aligned on %ld byte boundaries.\n",
>             (long)(sizeof(struct foo) - sizeof(union align)));
>         return 1;
>     }
>
>     printf("union must be aligned on %ld byte boundaries.\n",
>         (long)sizeof(union align));
>     return 0;
> }
>
> Anyone know if this works? Could someone please run this on each of
> the archs we support (particularly ia64) and report the results to me?
>
> Does anyone have any better code for discovering alignment? I'm
> surprised this isn't common enough that there would be a stock
> solution.

Debian-amd64:

sizeof(foo)=16
sizeof(align)=8
sizeof(f2)=32
union may be aligned on 8 byte boundaries.

>
> Thanks in advance,
>
> -- Brett

MfG
        Goswin