Re: Altivec + 16 byte alignment

[Daniel Egger <degger@fhm.edu>]

On Tue, 2003-02-11 at 11:07, Gianni Tedesco wrote:

> gcc version 2.95.4 20010319 (prerelease/franzo/20011204)

Please do yourself a favour and ditch that Motorola crap. Gcc supports
AltiVec natively since 3.1 and does a much better job at things similar
to your problem.

Your problem is fixed by supplying the -mabi=altivec switch to gcc 3.1
or later as demonstrated by the following dump program:

struct vector {
  float x,y,z,w;
}__attribute__((aligned(16)));
                                                                                
int main (void)
{
  short a = 0;
  struct vector b = {1, 2, 3};
  int c = 4;
  struct vector d = {4, 5, 6};
  printf ("address: %p\n", &a);
  printf ("address: %p\n", &b);
  printf ("address: %p\n", &c);
  printf ("address: %p\n", &d);
}


egger@sonja:~$ gcc  -o test test.c
egger@sonja:~$ ./test
address: 0x7ffff9a8
address: 0x7ffff9b0
address: 0x7ffff9c0
address: 0x7ffff9c8

egger@sonja:~$ gcc  -mabi=altivec -o test test.c
egger@sonja:~$ ./test
address: 0x7ffff9a8
address: 0x7ffff9b0
address: 0x7ffff9c0
address: 0x7ffff9d0

> PS. Is there any documentation about the vector support directly in C? I
> hear gcc3 has that feature.

Check back with altivec.h in gcc 3.1 or later. The C implementation is
horrible though compared to the C++ one realized with overloading.

--
Servus,
       Daniel