Re: [Qemu-devel] [PATCH 02/14] Add various NaN-handling macros

[Aurelien Jarno <aurelien@aurel32.net>]

On Tue, Feb 03, 2009 at 12:19:09PM -0800, Nathan Froyd wrote:
> On Tue, Feb 03, 2009 at 08:41:14PM +0100, Aurelien Jarno wrote:
> > On Thu, Jan 22, 2009 at 12:44:02PM -0800, Nathan Froyd wrote:
> > > These simplify the implementation of the floating-point Altivec
> > > instructions and reduce clutter.
> > >  
> > > +#undef DO_HANDLE_NAN
> > > +#undef HANDLE_NAN1
> > > +#undef HANDLE_NAN2
> > > +#undef HANDLE_NAN3
> > >  #undef VECTOR_FOR_INORDER_I
> > >  #undef HI_IDX
> > >  #undef LO_IDX
> > 
> > This is something already handled by the softfloat code. You should use
> > set_default_nan_mode(1, &env->vec_status) to get this behavior. This
> > could probably done directly in the init code.
> 
> I saw the set_default_nan_mode and considered using it.  It doesn't give
> the same results as the above macros, though.  The Altivec specs say
> that if a particular input is a SNaN, then the output is the
> corresponding QNaN, not the default NaN for the platform.  The default
> NaN is only used in specific instances.  Also, QNaNs propagate through
> Altivec operations; using set_default_nan_mode would mean that the
> correct propagation no longer occurs.

Ok, I understand now, I have applied the patch. Thanks.

Aurelien

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