linuxaudio.org

#include  
#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:

quoted text
> [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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