From: Christian Luginbuehl <dinkel@...>
Date: 2007-08-20T04:06:44+09:00
Subject: Re: Float addition problem / Processor bug?

>> Is it a processor bug, a simple rounding problem or a ruby error?
> 
> The second one.  This is a standard rounding issue.  The short 
> explanation is that you see the numbers in decimal system while the 
> computer uses binary representation for floats.

I kind of knew it ;-) - but still thank you Robert for confirming!

>> How do I proceed?
> 
> Live with it or use other data types like BigDecimal or Rational.
> 
> [ SNIP irb code ]

I changed my app to use BigDecimal now and it works fine this way.

However I don't like this Float behaviour of Ruby. Especially that the 
String representation of such values looks correct, while testing for 
equality says 'false' - like this:

=== START irb output ===
irb(main):014:0> a = 2.95 + 2.95 + 2.95
=> 8.85
irb(main):015:0> puts a
8.85
=> nil
irb(main):016:0> puts a == 8.85
false
=> nil
=== END irb output ===

With whole numbers the conversion from Fixnum to Bignum is transparent 
to the user and makes life a lot easier. Wouldn't it be possible to have 
the same behaviour with floating point numbers?


Dinkel