Re: [Qemu-devel] [PATCH v1 03/14] softfloat: fix {min, max}nummag for same-abs-value inputs

["Alex Bennée" <alex.bennee@linaro.org>]

Emilio G. Cota <cota@braap.org> writes:

> Before 8936006 ("fpu/softfloat: re-factor minmax", 2018-02-21),
> we used to return +Zero for maxnummag(-Zero,+Zero); after that
> commit, we return -Zero.
>
> Fix it by making {min,max}nummag consistent with {min,max}num,
> deferring to the latter when the absolute value of the operands
> is the same.
>
> With this fix we now pass fp-test.
>
> Signed-off-by: Emilio G. Cota <cota@braap.org>

Reviewed-by: Alex Bennée <alex.bennee@linaro.org>

> ---
>  fpu/softfloat.c | 17 +++++++++--------
>  1 file changed, 9 insertions(+), 8 deletions(-)
>
> diff --git a/fpu/softfloat.c b/fpu/softfloat.c
> index e124df9..ee615a9 100644
> --- a/fpu/softfloat.c
> +++ b/fpu/softfloat.c
> @@ -1700,7 +1700,6 @@ static FloatParts minmax_floats(FloatParts a, FloatParts b, bool ismin,
>          return pick_nan(a, b, s);
>      } else {
>          int a_exp, b_exp;
> -        bool a_sign, b_sign;
>
>          switch (a.cls) {
>          case float_class_normal:
> @@ -1731,20 +1730,22 @@ static FloatParts minmax_floats(FloatParts a, FloatParts b, bool ismin,
>              break;
>          }
>
> -        a_sign = a.sign;
> -        b_sign = b.sign;
> -        if (ismag) {
> -            a_sign = b_sign = 0;
> +        if (ismag && (a_exp != b_exp || a.frac != b.frac)) {
> +            bool a_less = a_exp < b_exp;
> +            if (a_exp == b_exp) {
> +                a_less = a.frac < b.frac;
> +            }
> +            return a_less ^ ismin ? b : a;
>          }
>
> -        if (a_sign == b_sign) {
> +        if (a.sign == b.sign) {
>              bool a_less = a_exp < b_exp;
>              if (a_exp == b_exp) {
>                  a_less = a.frac < b.frac;
>              }
> -            return a_sign ^ a_less ^ ismin ? b : a;
> +            return a.sign ^ a_less ^ ismin ? b : a;
>          } else {
> -            return a_sign ^ ismin ? b : a;
> +            return a.sign ^ ismin ? b : a;
>          }
>      }
>  }


--
Alex Bennée