[PATCH] Don't calculate with NaN when on 100% o2

[Dirk Hohndel]

On Mon, 2014-03-17 at 13:05 -0700, Linus Torvalds wrote:
> On Mon, Mar 17, 2014 at 12:25 PM, Anton Lundin <glance at acc.umu.se> wrote:
> > Fixes: 465
> 
> Actually, probably only on x86.
> 
> >                 double ratio = (double)fhe / (1000.0 - fo2);
> > +               /* if we have 100% o2, ratio is nan */
> > +               if (isnan(ratio))
> > +                       ratio = 0;
> 
> There's no real reason to think that division by zero always returns
> NaN. On some platforms or settings it might well just trap.
> 
> In fact, it might be a good idea to have a debug mode to *make* it
> trap with something like
> 
>         feenableexcept(FE_DIVBYZERO | FE_OVERFLOW);
> 
> which could help us find these things more easily (that
> feenableexcept() is a glibc extension, though, I forget how to do this
> "for real").
> 
> So it's probably safer to just do
> 
>         ratio = fo2 === 1000 ? 0 : (double)fhe / (1000 - fo2);

The triple '=' is something I know from javascript :-)

I really don't want Anton's patch. Linus hasn't submitted a better
patch. I could just take both of them and merge them.

The choices, the choices...

I think I'll do my own patch without using the javascript extension to
C :-)

/D