From: Jeff Schwab <jeff@...>
Date: 2009-04-29T05:30:02+09:00
Subject: Re: Detecting -0.0

Thomas B. wrote:
> Hello.
> 
> I have a simple question - how to detect if a variable contains a Float
> of value -0.0? Is there any special method for this, or any comparison
> that distinguishes negative zero from a the regular zero?

NB: I'm not sure how portable this is.

def negative_zero?(number)
   inverse = 1 / number.to_f
   inverse < 0 && inverse.infinite? ? true : false
end

[ 0.0, # false
  -0.0, # true
  -1.0, # false
   1.0  # false
].each do |f|
   puts negative_zero?(f)
end