Long double alignment test

[Neil Turton <neilt+rsp@chiark.greenend.org.uk>]

Brett Cundal writes:
 > The issue is with a test for long double alignment which reports an
 > incorrect value on ia64 (and probably other archs).
 > [...]
 > Anyone know if this works?

The code which was posted doesn't use the long double type, which
makes the idea of it giving the alignment of that type somewhat
doubtful.  A processor could have special alignment issues to do with
long doubles which don't show up in long, double or void* (due to a
weird floating point unit).

I believe that the "if" condition is never false because "f" contains
two unions and two chars, so its size is greater than that of two
unions (by at least two chars) and therefore not equal.  As a result,
it seems to give the alignment of the union, which is the maximum
alignment of the three types inside.

I prefer the code below.  Enjoy!

Cheers, Neil.

#include <stdio.h>

#define ALIGN_OF(t) \
  ((int)(sizeof(  \
     struct {  \
       char c;  \
       t x;  \
     })  \
   - sizeof(t) ))

int main()
{
  printf("char: %d\n", ALIGN_OF(char));
  printf("short: %d\n", ALIGN_OF(short));
  printf("int: %d\n", ALIGN_OF(int));
  printf("long: %d\n", ALIGN_OF(long));
  printf("long long: %d\n", ALIGN_OF(long long));
  printf("void*: %d\n", ALIGN_OF(void*));
  printf("float: %d\n", ALIGN_OF(float));
  printf("double: %d\n", ALIGN_OF(double));
  printf("long double: %d\n", ALIGN_OF(long double));
  return 0;
}