Re: [PATCH 45/76] target/arm: Implement FPCR.AH semantics for scalar FMIN/FMAX

[Peter Maydell]

On Sun, 26 Jan 2025 at 12:44, Richard Henderson
<richard.henderson@linaro.org> wrote:
>
> On 1/24/25 08:28, Peter Maydell wrote:
> > diff --git a/target/arm/tcg/helper-a64.c b/target/arm/tcg/helper-a64.c
> > index 05036089dd7..406d76e1129 100644
> > --- a/target/arm/tcg/helper-a64.c
> > +++ b/target/arm/tcg/helper-a64.c
> > @@ -399,6 +399,42 @@ float32 HELPER(fcvtx_f64_to_f32)(float64 a, 
> > float_status *fpst)
> >       return r;
> >   }
> >
> > +/*
> > + * AH=1 min/max have some odd special cases:
> > + * comparing two zeroes (even of different sign), (NaN, anything),
> > + * or (anything, NaN) should return the second argument (possibly
> > + * squashed to zero).
> > + * Also, denormal outputs are not squashed to zero regardless of FZ or 
> > FZ16.
> > + */
> > +#define AH_MINMAX_HELPER(NAME, CTYPE, FLOATTYPE, MINMAX)                \
> > +    CTYPE HELPER(NAME)(CTYPE a, CTYPE b, float_status *fpst)            \
> > +    {                                                                   \
> > +        bool save;                                                      \
> > +        CTYPE r;                                                        \
> > +        a = FLOATTYPE ## _squash_input_denormal(a, fpst);               \
> > +        b = FLOATTYPE ## _squash_input_denormal(b, fpst);               \
> > +        if (FLOATTYPE ## _is_zero(a) && FLOATTYPE ## _is_zero(b)) {     \
>
> The comment says "even of different sign", the pseudocode explicitly checks 
> different
> sign.  But of course if they're the same sign a and b are indistinguishable.  
> Perhaps
> slightly different wording?

Sure. I changed from "(even of different sign)" to
"(regardless of sign)". Let me know if you have a
more specific tweak you'd like.

thanks
-- PMM