From: Mohammad Khan <mkhan@...>
Date: 2004-09-02T04:25:57+09:00
Subject: Re: invisible Infinity

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.



> --
> Mohammad
> 
> 
> On Wed, 2004-09-01 at 15:05, Brian Schroeder wrote:
> > On Wed, 01 Sep 2004 18:05:43 +0000, gabriele renzi wrote:
> > 
> > > Hi gurus and nubys,
> > > 
> > > I wonder, if you divide a Float by zero, you get Infinity:
> > >  >> a=10.0/0
> > > => Infinity
> > > 
> > > 
> > > and you can even write code using Infinity like:
> > >  >> 0.upto(a) do |x| p x end
> > > 0
> > > 1
> > > 2
> > > 3
> > > ..
> > > 
> > > but if you try to access it directly you can't:
> > >  >> Infinity
> > > NameError: uninitialized constant Infinity
> > >          from (irb):4
> > > 
> > > Should we be able to access Infinity directly? It seem a strange
> > > unexplicable behaviour to me, that it exists but is not normally
> > > accessible.
> > 
> > 
> > I also was surprised, that Infinity is no predefined constant, as I used
> > it in some algorithm where I needed to fill an Array with infinity, then
> > iteratively reducing the values. In these cases infinity is much better
> > than nil as a special value because it can be compared.
> > 
> > So I declared 1.0/0.0 as Infinity and ready. But I regard it as against
> > the pols.
> > 
> > Greetings,
> > 
> > Brian
-- 
Mohammad Khan <mkhan@lextranet.com>
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