The following code shows that the rounding mode of the sse2 FPU is altered by a
call to fmaf().

#include <stdio.h>
#include <float.h>
#include <math.h>

static  float res0, res1, res2, res3;
static  float half = 0.5f;

void chk( void ){
  res2 = res0 + half;		/* should round down to even */
  if( res2 == res0 ){ puts("OK1"); }else{ puts("Bad1"); }
  res3 = res1 + half;		/* should round up to even */
  if( res3 != res1 ){ puts("OK2"); }else{ puts("Bad2"); }
}

int main(void){

  res0 = FLT_EPSILON;
  res0++;
  res0--;
  res0 = 1.f / res0;		/* even; 1/EPSILON is a magic number */
  res1 = res0 + 1.f;		/* odd */

  chk();

  res2 = sinf( 1.f );		/* sse2 rounding is not altered */

  chk();

  res2 = fmaf( 1.f, 1.f, 1.f );	/* this messes up sse2 rounding */

  chk();

  return 0;
}


Hardware:  Intel Core 2 Duo in 32-bit mode
O.S.    :  Fedora Core 17 in 32-bit mode
Compiler:  gcc 4.7.0-2
Library :  glibc 2.15-32

Compiler options: -std=gnu11 -O0 -mfpmath=sse -msse2 -fno-builtin -frounding-math -mieee-fp -ffloat-store -fexcess-precision=standard