@@ -120,11 +120,16 @@ bfloat16 bfloat16_squash_input_denormal(bfloat16 a, float_status *status);
| Using these differs from negating an input or output before calling
| the muladd function in that this means that a NaN doesn't have its
| sign bit inverted before it is propagated.
+|
+| With float_muladd_suppress_add_product_zero, if A or B is zero
+| such that the product is a true zero, then return C without addition.
+| This preserves the sign of C when C is +/- 0. Used for Hexagon.
*----------------------------------------------------------------------------*/
enum {
float_muladd_negate_c = 1,
float_muladd_negate_product = 2,
float_muladd_negate_result = 4,
+ float_muladd_suppress_add_product_zero = 8,
};
/*----------------------------------------------------------------------------
@@ -2274,6 +2274,9 @@ float32_muladd(float32 xa, float32 xb, float32 xc, int flags, float_status *s)
if (unlikely(!can_use_fpu(s))) {
goto soft;
}
+ if (unlikely(flags & float_muladd_suppress_add_product_zero)) {
+ goto soft;
+ }
float32_input_flush3(&ua.s, &ub.s, &uc.s, s);
if (unlikely(!f32_is_zon3(ua, ub, uc))) {
@@ -615,7 +615,9 @@ static FloatPartsN *partsN(muladd_scalbn)(FloatPartsN *a, FloatPartsN *b,
goto return_normal;
}
if (c->cls == float_class_zero) {
- if (a->sign != c->sign) {
+ if (flags & float_muladd_suppress_add_product_zero) {
+ a->sign = c->sign;
+ } else if (a->sign != c->sign) {
goto return_sub_zero;
}
goto return_zero;
Certain Hexagon instructions suppress changes to the result when the product of fma() is a true zero. Signed-off-by: Richard Henderson <richard.henderson@linaro.org> --- include/fpu/softfloat.h | 5 +++++ fpu/softfloat.c | 3 +++ fpu/softfloat-parts.c.inc | 4 +++- 3 files changed, 11 insertions(+), 1 deletion(-)