From: Todd Benson <caduceass@...>
Date: 2008-10-28T02:09:46+09:00
Subject: Re: float equality

On Mon, Oct 27, 2008 at 11:50 AM, guille lists <guilledist@gmail.com> wrote:
> Hi,
>
> sorry if this is a very naive question (I'm new to ruby), but I
> haven't found an explication yet. When comparing to floats in ruby I
> came across this:
>
>>> a = 0.1
> => 0.1
>>> b = 1 - 0.9
> => 0.1
>>> a == b
> => false
>>> a > b
> => true
>>> a < b
> => false
>>> a <=> b
> => 1
>
> I'm a bit lost here, shouldn't (0.1) and (1 - 0.9) be equals regarding
> the == operator? I also found that for example 0.3 == (0.2 + 0.1)
> returns false, etc.

Most people will  point you to this:
http://en.wikipedia.org/wiki/Floating_point_arithmetic

There are several ways around it (using BigDecimal, Rational, Integers, etc.)

Totally off-topic, but has any one figured out exactly why 1/9
(0.111...) plus 8/9 (0.888...) is 1 instead of 0.999... :-)

Todd