Re: [Qemu-devel] [PATCH v2 1/5] target-tricore: Added FTOUZ instruction

[Richard Henderson]

On 11/08/2016 04:12 PM, Bastian Koppelmann wrote:
> On 11/08/2016 04:06 PM, Richard Henderson wrote:
> > On 11/08/2016 02:37 PM, Bastian Koppelmann wrote:
> > > Consider 0x836d4e86 as an input which is clearly negative, however
> > > float_flag_invalid is not set. The hardware on the other hand does set
> > > it.
> >
> > Hmm.  This is -0x1.da9d0cp-121.  Softfloat claims that we should round
> > to zero first, and only if the result is still < 0, raise invalid.
> > Which does sound plausible as a common behaviour.
>
> TriCore does it the other way round.
>
> > Does your hardware raise invalid for true -0.0, i.e. 0x80000000?
>
> No, -0.0 does not raise invalid.

Then I suppose the check should look like

  flags = f_get_excp_flags(env);
  if (flags & float_flag_invalid) {
    flags &= ~float_flag_inexact;
  } else if (float32_lt_quiet(f_arg, 0, &env->status)) {
    flags = float_flag_invalid;
  }
  if (flags) {
    f_update_psw_flags(env, flags);
  }

Note that the 0.0 that you use is truncated to 0 by C for the uint32_t argument.


r~