From: Christoph Rippel <crippel@...>
Date: 2001-03-29T18:13:33+09:00
Subject: [ruby-talk:13315] A subtle Hash bug

Hi,

I recently run into the the following bug 
   
(-0.0).eql? (0.0)        #  => true
(-0.0).hash == (0.0).hash # => false

The reason for this that the hashing algorithm of float converts a double
into a string and builds a hash key from this string. This does not work 
for (-0.0) and (0.0) because their bit pattern are different but the gcc 
at least claims that (in C )
               -0.0 == 0.0 # => true. 
If one wants to fix this one has explicitly check for the -0.0 bit pattern. 
The other possibility is to declare that 
 
          -0.0.eql 0.0  # => false  

in which case one has to check for the -0.0 pattern in the #eql? method 
which is actually better IMO. 


Christoph