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softfloat: Add float_muladd_suppress_add_product_zero

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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>
This commit is contained in:
Richard Henderson 2024-12-08 09:13:45 -06:00
parent 72330260cd
commit 82f898f3b6
3 changed files with 11 additions and 1 deletions
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4
fpu/softfloat-parts.c.inc
View file

@ -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;

3
fpu/softfloat.c
View file

@ -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))) {

5
include/fpu/softfloat.h
View file

@ -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,
};
/*----------------------------------------------------------------------------