In my software SSE2 emulation I am currently using this sort of approach
to extract data fields out of __m128i and __m128d vectors:
#define EMM_SINT4(a) ((int *)&(a))
static __inline __m128i __attribute__((__always_inline__))
_mm_slli_epi32 (__m128i __A, int __B)
{
__v4si __tmp = {
EMM_SINT4(__A)[0] << __B,
EMM_SINT4(__A)[1] << __B,
EMM_SINT4(__A)[2] << __B,
EMM_SINT4(__A)[3] << __B};
return (__m128i)__tmp;
}
This works fine when testing one _mm function at a time, but does not
work reliably in real programs unless -O0 is used. I think at least
part of the problem is that once the function is inlined the parameter
__A is in some cases a register variable, and the pointer method is not
valid there. To get around that I'm think of introducing an explicit
local variable, like this:
static __inline __m128i __attribute__((__always_inline__))
_mm_slli_epi32 (__m128i __A, int __B)
{
__m128i A = __A;
__v4si __tmp = {
EMM_SINT4(A)[0] << __B,
EMM_SINT4(A)[1] << __B,
EMM_SINT4(A)[2] << __B,
EMM_SINT4(A)[3] << __B};
return (__m128i)__tmp;
}
I'm not sure that will work all the time either. The only other
approach I an aware of would be something like this:
#typedef union {
__m128i vi;
__m128d vd;
int s[4];
unsigned int us[4];
/* etc. for other types */
} emm_universal ;
#define EMM_SINT4(a) (a).s
static __inline __m128i __attribute__((__always_inline__))
_mm_slli_epi32 (__m128i __A, int __B)
{
emm_universal A;
A.vi = __A;
__v4si __tmp = {
EMM_SINT4(A)[0] << __B,
EMM_SINT4(A)[1] << __B,
EMM_SINT4(A)[2] << __B,
EMM_SINT4(A)[3] << __B};
return (__m128i)__tmp;
}
The union approach seems to be just a different a way to spin the
pointer operations. For gcc in particular, is one approach or the other
to be preferred and why?
Thanks,
David Mathog
[email protected]
Manager, Sequence Analysis Facility, Biology Division, Caltech
