From: Hal Fulton <hal9000@...>
Date: 2004-10-28T05:36:22+09:00
Subject: Re: Rounding error, (100.0 * 9.95).to_i == 994

Jason DiCioccio wrote:
> 
> I'm confused now..  100.0 * 9.95 is clearly 995.  So what exactly is the 
> issue with floating point numbers is making this come out to 
> 994.999999999983 (or wahtever ;))?  If every language is plagued by this 
> problem, then I'd be curious to know the history behind it..
> 

:) It's not history, it's math.

Here's the short explanation.

Remember repeating decimals, which you learned about in elementary school?
For example, 1/3 = 0.33333... can't be expressed in a finite number of
digits.

Likewise 0.95 can't be expressed in a finite number of (binary) digits.
When you convert it to binary, it repeats infinitely.


Hal