From: Charles Mills <cmills@...>
Date: 2004-09-02T03:40:43+09:00
Subject: Re: invisible Infinity

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
....
 > 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.