From: Roger Pack <rogerpack2005@...>
Date: 2010-01-20T02:26:36+09:00
Subject: Re: Float Points error

> It is true that floats are approximations of real numbers but the issue 
> that most often trips people up is the conversion between the internal 
> binary representation and the external decimal representation.  More 
> specifically, by default Ruby doesn't show you the full precision 
> available in a float:
> 
>>> 1/3.0
> => 0.333333333333333
>>> "%0.60f" % (1/3.0)
> => "0.333333333333333314829616256247390992939472198486328125000000"


So currently ruby "doesn't show you the real floating point number"
which leads to surprising behavior, for example

>> (2.0 - 1.1) == 0.9
=> false

This has been changed in the latest dev trunk, to be more explicit 
(Float#to_s is totally explicit now).

>> 2.0 - 1.1
=> 0.8999999999999999
>> 0.9
=> 0.9
>> 2.0 - 1.1 == 0.9
=> false

Unfortunately this means that writing out to the screen used to be
>> puts 2.0 - 1.1
0.9

but is now
>> puts 2.0 - 1.1
0.8999999999999999

I have a proposal out to make Float#to_s be "the imprecise [old] way" 
and Float#inspect to be the new, precise way (split the 
functionality--it's currently the same).
Any feedback/preferences on this before I do anything in that regard?
-r
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