From: Stefano Crocco <stefano.crocco@...>
Date: 2009-04-11T00:14:00+09:00
Subject: Re: Float.finite ?

Alle Friday 10 April 2009, Aldric Giacomoni ha scritto:
> How does one use .finite? effectively? I tried with (1.0/3).finite? =>
> true... I tried with BigDecimal.. Still true. I'm pretty sure these numbers
> aren't finite. How do I make this work?

According to the ri documentation, Float#finite? only returns false if self is 
not inifinite and self.nan? is false. For example,

(1/0.0).finite?
=> false

What you wanted to know is whether the number has a finite or infinite number 
of decimal digits. Unfortunately, I don't think such a method exists. You 
can't do that with floats, because all floats have a finite number of decimal 
digits (you can't very well store infinite digits in your computer's memory, 
after all). I suppose it can be done with the Rational class, but you'd have 
to write the method yourself. Here's a simple example of how this could be 
done:

require 'rational'

class Rational

  def finite_digits?
    d = denominator
    return false if d % 2 !=0 and d % 5 != 0
    d = d / 2 while d % 2 ==0
    d = d / 5 while d % 5 == 0
    d == 1
  end
  
end

Stefano