math: fix fmaf not to depend on FE_TOWARDZERO

src/math/fmaf.c

@@ -77,17 +77,16 @@ float fmaf(float x, float y, float z)
 	 * If result is inexact, and exactly halfway between two float values,
 	 * we need to adjust the low-order bit in the direction of the error.
 	 */
-#ifdef FE_TOWARDZERO
-	fesetround(FE_TOWARDZERO);
-#endif
-	volatile double vxy = xy;  /* XXX work around gcc CSE bug */
-	double adjusted_result = vxy + z;
-	fesetround(FE_TONEAREST);
-	if (result == adjusted_result) {
-		u.f = adjusted_result;
+	double err;
+	int neg = u.i >> 63;
+	if (neg == (z > xy))
+		err = xy - result + z;
+	else
+		err = z - result + xy;
+	if (neg == (err < 0))
 		u.i++;
-		adjusted_result = u.f;
-	}
-	z = adjusted_result;
+	else
+		u.i--;
+	z = u.f;
 	return z;
 }