From: Shugo Maeda <shugo@...>
Date: 2009-11-10T11:52:11+09:00
Subject: [ruby-core:26658] Re: [Feature #2347] Math::INFINITY

Hi,

2009/11/10 Marc-Andre Lafortune <redmine@ruby-lang.org>:
> I'm quite ignorant about the differences between compilers and implementations (and I wouldn't mind remaining this way! ;-)
>
> The fact is, Ruby _already_ generates infinities. Line 2471 of numeric.c:
>
> #define infinite_value() ruby_div0(1.0)

FYI, I heard that some compilers doesn't permit zero divisions by
literals, but the following
code can be used to avoid the check:

  tmp = 1.0;
  inf = 1.0 / (tmp - tmp);

GNU Octave has more complicated code to generate an infinity:

        volatile double tmp_inf;

#if defined (SCO)
        volatile double tmp = 1.0;
        tmp_inf = 1.0 / (tmp - tmp);
#elif defined (__alpha__) && defined (__osf__)
        extern unsigned int DINFINITY[2];
        tmp_inf =  (*(X_CAST(double *, DINFINITY)));
#else
        double tmp = 1e+10;
        tmp_inf = tmp;
        for (;;)
          {
            tmp_inf *= 1e+10;
            if (tmp_inf == tmp)
              break;
            tmp = tmp_inf;
          }

-- 
Shugo Maeda