Re: [xml] XPath Infinities

[Daniel Veillard <veillard redhat com>]

On Sun, Apr 29, 2001 at 07:24:10AM -1000, Ray Strode wrote:
> >  double SetNaN()
> >  {
> >    return 0.0 / 0.0;
> >  }
> Actually, that may segfault on RedHat, too.  It's very specific,
> it only allows it when the variable is being initialized to it.
> It SIGFPE's any other way.  So double NaN = 0.0/0.0 will work, 
> but double NaN = SetNaN(), double NaN = 0/0,and double NaN; NaN /= 0.0, 
> won't.

  yep, what I ultimately want is the following sequence of code:
    save 0/1/-1 to an FP
    divide this FP by the value 0
it is impossible to avoid compiler "optimization", except maybe by calling
a function which would do the divide by 0 (compiler are unlikely to try
to solve this at compilation time. So the solution is probably to do something
like:

/* keeping the function public to absolutely avoid the compiler from trying
   global optimization on this. */

float xmlXPathDivideBy(float f, float fzero) {
    float ret;
#ifdef HAVE_SIGNAL
#ifdef SIGFPE
#ifdef SIG_IGN
    void (*sighandler)(int);
    sighandler = signal(SIGFPE, SIG_IGN);
#endif
#endif
#endif
   ret = f / fzero;
#ifdef HAVE_SIGNAL
#ifdef SIGFPE
#ifdef SIG_IGN
   signal(SIGFPE, sighandler);
#endif
#endif
#endif
}

xmlXPathInit()
...
   float f, fzero;

   f = 0/1/-1;
   fzero = 0.0;
   f = xmlXPathDivideByZero(f, fzero);
...

NB: restauring the signal is really important for libxml to be seen as a 
    well behaved library :-)

If both of you could check this solution I think it's the best to do
(should work with MS compiler too).

Daniel

-- 
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