From: Mark Hubbart <discord@...>
Date: 2004-05-06T17:52:46+09:00
Subject: Re: 0.0 sign


On May 6, 2004, at 12:17 AM, Elias Athanasopoulos wrote:

> On Thu, May 06, 2004 at 04:28:36AM +0900, Mark Hubbart wrote:
>>
>> On May 5, 2004, at 10:33 AM, Elias Athanasopoulos wrote:
>>
>>> Hello!
>>>
>>> I don't know if this is intentional, but is there a reason
>>> that 0.0 holds the sign?
>>
>> IEEE 754 (floating point arithmetic standard) specifies negative zero
>> for floats. For more explanation, see
>> http://www.obtuse.com/resources/negative_zero.html
>>
>> if a mathematical result too small for your hardware to compute is
>> returned, you can determine whether it was on the negative side, or 
>> the
>> positive side.
>>
>>   def really_complex_function(num)
>>     num/1_000_000_000_000_000_000.0
>>   end
>>     ==>nil
>>   really_complex_function(  0.000_000_000_000_000_000_1 )
>>     ==>0.0
>>   really_complex_function( -0.000_000_000_000_000_000_1 )
>>    ==>-0.0
>
> Yes, but how can you distinguish them *inside* your code? Since
> 0.0 == -0.0, 0.0 === -0.0 and even 0.0.eql?(-0.0) is true.

   1/0.0 > 0
     ==>true
   1/-0.0 > 0
     ==>false

0.0 and -0.0 are considered equal. They only retain the sign for the 
case where you need to check it. If you divide 1 by a suspicious zero, 
you'll get either Infinity or -Infinity. Or, if you need to check a 
lot:

   class Numeric
     def negative?()
       zero? ? (1.0/self < 0) : (self < 0)
     end
   end
     ==>nil
   -0.0.negative?
     ==>true
   0.0.negative?
     ==>false

cheers,
--Mark