Re: [Qemu-devel] [PATCH 4/5] target-ppc: use the softfloat float32_muladd function

[Aurelien Jarno <aurelien@aurel32.net>]

On Sun, Sep 09, 2012 at 10:51:20AM +0100, Peter Maydell wrote:
> On 8 September 2012 22:12, Aurelien Jarno <aurelien@aurel32.net> wrote:
> > +#define VARITHFPFMA(suffix, type)                                       \
> > +    void helper_v##suffix(CPUPPCState *env, ppc_avr_t *r, ppc_avr_t *a, \
> > +                           ppc_avr_t *b, ppc_avr_t *c)                  \
> > +    {                                                                   \
> > +        int i;                                                          \
> > +        for (i = 0; i < ARRAY_SIZE(r->f); i++) {                        \
> > +            r->f[i] = float32_muladd(a->f[i], c->f[i], b->f[i],         \
> > +                                     type, &env->vec_status);           \
> > +        }                                                               \
> > +    }
> > +VARITHFPFMA(maddfp, 0);
> > +VARITHFPFMA(nmsubfp, float_muladd_negate_result);
> > +#undef VARITHFPFMA
> > +
> >  #define VARITHSAT_CASE(type, op, cvt, element)                          \
> >      {                                                                   \
> >          type result = (type)a->element[i] op (type)b->element[i];       \
> > -void helper_vnmsubfp(CPUPPCState *env, ppc_avr_t *r, ppc_avr_t *a,
> > -                     ppc_avr_t *b, ppc_avr_t *c)
> > -{
> > -    int i;
> > -
> > -    for (i = 0; i < ARRAY_SIZE(r->f); i++) {
> > -        HANDLE_NAN3(r->f[i], a->f[i], b->f[i], c->f[i]) {
> > -            /* Need to do the computation is higher precision and round
> > -             * once at the end.  */
> > -            float64 af, bf, cf, t;
> > -
> > -            af = float32_to_float64(a->f[i], &env->vec_status);
> > -            bf = float32_to_float64(b->f[i], &env->vec_status);
> > -            cf = float32_to_float64(c->f[i], &env->vec_status);
> > -            t = float64_mul(af, cf, &env->vec_status);
> > -            t = float64_sub(t, bf, &env->vec_status);
> > -            t = float64_chs(t);
> > -            r->f[i] = float64_to_float32(t, &env->vec_status);
> > -        }
> > -    }
> > -}
> 
> I mentioned this in my comment on the other patch, but just to attach
> it to the right patch for the benefit of the archives:
> the code here for vnmsub is (correctly) doing a subtraction of bf
> and then negating the final result, so you need to pass float_muladd
> the flags negate_result | negate_c, not just negate_result.
> 

Correct, or alternatively it could use negate_product. I'll send an
updated patch later.


-- 
Aurelien Jarno	                        GPG: 1024D/F1BCDB73
aurelien@aurel32.net                 http://www.aurel32.net