From: Mohammad Khan <mkhan@...>
Date: 2004-09-02T03:47:58+09:00
Subject: Re: invisible Infinity

On Wed, 2004-09-01 at 14:40, Charles Mills wrote:
> On Sep 1, 2004, at 11:10 AM, 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
> > ...
> >
> 
>  > a = 10.0/0
> => Infinity
>  > b = 10.0/0
> => Infinity
>  > a < b
> => false
>  > c = 2**1024

Also:

irb(main):004:0> a == b
=> true

so.. Infinity is Infinity !!
:-)



> ....
>  > c.to_f
> (irb):10: warning: Bignum out of Float range
> => Infinity
> 
> ...so your example won't go forever.  Eventually it will hit 'Infinity' 
> and stop.  (I think)
> So maybe having access to Infinity is a bad thing??
> -Charlie
> 
> If y is a double rb_big_cmp(x, y) converts x to a double (infinity if 
> the Bignum is greator than max double) and calls rb_dbl_cmp()
> 
> numeric.c:
> 02323 static VALUE
> 02324 int_upto(from, to)
> 02325     VALUE from, to;
> 02326 {
> 02327     if (FIXNUM_P(from) && FIXNUM_P(to)) {
> 02328       long i, end;
> 02329
> 02330       end = FIX2LONG(to);
> 02331       for (i = FIX2LONG(from); i <= end; i++) {
> 02332           rb_yield(LONG2FIX(i));
> 02333       }
> 02334     }
> 02335     else {
> 02336       VALUE i = from, c;
> 02337
> 02338       while (!(c = rb_funcall(i, '>', 1, to))) {
> 02339           rb_yield(i);
> 02340           i = rb_funcall(i, '+', 1, INT2FIX(1));
> 02341       }
> 02342       if (NIL_P(c)) rb_cmperr(i, to);
> 02343     }
> 02344     return from;
> 02345 }
> 
> 00691 VALUE
> 00692 rb_dbl_cmp(a, b)
> 00693     double a, b;
> 00694 {
> 00695     if (isnan(a) || isnan(b)) return Qnil;
> 00696     if (a == b) return INT2FIX(0);
> 00697     if (a > b) return INT2FIX(1);
> 00698     if (a < b) return INT2FIX(-1);
> 00699     return Qnil;
> 00700 }
> 
> >
> > 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.
-- 
Mohammad Khan <mkhan@lextranet.com>
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