From: Mohammad Khan <mkhan@...>
Date: 2004-09-02T05:08:44+09:00
Subject: Re: invisible Infinity

On Wed, 2004-09-01 at 15:55, Kristof Bastiaensen wrote:
> On Thu, 02 Sep 2004 04:25:57 +0900, Mohammad Khan wrote:
> 
> > On Wed, 2004-09-01 at 15:22, Mohammad Khan wrote:
> >> If you take a look in numeric.c
> >> 
> >> 
> >> /*
> >>  *  call-seq:
> >>  *     flt.to_s    => string
> >>  *
> >>  *  Returns a string containing a representation of self. As well as a *
> >>   fixed or exponential form of the number, the call may return * 
> >>  ``<code>NaN</code>'', ``<code>Infinity</code>'', and * 
> >>  ``<code>-Infinity</code>''.
> >>  */
> >>                                                                                                                                                              
> >> static VALUE
> >> flo_to_s(flt)
> >>     VALUE flt;
> >> {
> >>     char buf[32];
> >>     char *fmt = "%.15g";
> >>     double value = RFLOAT(flt)->value;
> >>     double avalue, d1, d2;
> >>                                                                                                                                                              
> >>     if (isinf(value))
> >>         return rb_str_new2(value < 0 ? "-Infinity" : "Infinity");
> >>     else if(isnan(value))
> >>         return rb_str_new2("NaN");
> >>                                                                                                                                                              
> >>     avalue = fabs(value);
> >>     if (avalue == 0.0) {
> >>         fmt = "%.1f";
> >>     }
> >>     else if (avalue < 1.0e-3) {
> >>         d1 = avalue;
> >>         while (d1 < 1.0) d1 *= 10.0;
> >>         d1 = modf(d1, &d2);
> >>         if (d1 == 0) fmt = "%.1e";
> >>     }
> >>     else if (avalue >= 1.0e15) {
> >>         d1 = avalue;
> >>         while (d1 > 10.0) d1 /= 10.0;
> >>         d1 = modf(d1, &d2);
> >>         if (d1 == 0) fmt = "%.1e";
> >>         else fmt = "%.16e";
> >>     }
> >>     else if ((d1 = modf(value, &d2)) == 0) {
> >>         fmt = "%.1f";
> >>     }
> >>     sprintf(buf, fmt, value);
> >>                                                                                                                                                              
> >>     return rb_str_new2(buf);
> >> }
> >> }
> >> Infinity and -Infinity is String and it is just a representation. It is
> >> definitely, not a Constant.
> >> 
> >> I am wrong, correct me please.
> > 
> > I meant,
> > If I am wrong, correct me please.
> > 
> 
> I am not sure if this is what you meant, but Infinity is not a string:
> 
> (10.0/0).class
> => Float
> 
> (10.0/0).to_s.class
> => String

irb(main):001:0> a = 10.0/0
=> Infinity
irb(main):002:0> b = -20.0/0
=> -Infinity

I said, Infinity and -Infinity is just a String representation of Float,
not a Constant.

regards
Mohammad


> 
> Regards,
> KB