#include <xmmintrin.h>
#define CPUID(f,ax,bx,cx,dx) __asm__ __volatile__ \
("cpuid": "=a" (ax), "=b" (bx), "=c" (cx), "=d" (dx) : "a" (f))
// denormal protection
static int set_DAZ_and_FTZ(int /*bool*/ on)
{
int sse_level = 0;
if(on)
{
unsigned long ax, bx, cx, dx;
CPUID(0x00,ax,bx,cx,dx);
CPUID(0x01,ax,bx,cx,dx);
if (dx & 0x02000000)
{
sse_level = 1;
// set FLUSH_TO_ZERO to ON and
// set round towards zero (RZ)
_mm_setcsr(_mm_getcsr() | 0x8000|0x6000);
if (dx & 0x04000000)
{
sse_level = 2;
if (cx & 0x00000001)
{
sse_level = 3;
// set DENORMALS_ARE_ZERO to ON
_mm_setcsr(_mm_getcsr() | 0x0040);
}
// we should have checked for AMD K8 without SSE3 here:
// if(AMD_K8_NO_SSE3)
// .. but I can't recall how to that :-/
}
}
} else
// clear underflow and precision flags
// and set DAZ and FTZ to OFF
// and restore round to nearest (RN)
_mm_setcsr(_mm_getcsr() & ~(0x0030|0x8000|0x0040|0x6000));
return sse_level;
}
On Wed, 2009-08-19 at 12:37 +0200, Tim Goetze wrote:
> [Conrad Berhörster]
> >But i try to understand, what happens here. Is the compiler overoptimizing
> >zeros.
>
> It'd be a lot more helpful to see the full source but from what you're
> writing I'd be willing to bet you're encountering denormals.
>
> Cheers, Tim
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