From: "Berger, Daniel" <Daniel.Berger@...>
Date: 2005-04-05T02:50:16+09:00
Subject: Re: Math.sqrt(NaN) behaves differently on windows and linux



> -----Original Message-----
> From: Dave Baldwin [mailto:dave.baldwin@3dlabs.com] 
> Sent: Monday, April 04, 2005 6:50 AM
> To: ruby-talk ML
> Subject: Re: Math.sqrt(NaN) behaves differently on windows and linux
> 
> 
> 
> On 4 Apr 2005, at 12:48, Geert Fannes wrote:
> 
> > Hello, the following statement gives different results on 
> windows and
> > linux:
> > Linux:
> >
> > irb(main):003:0> Math.sqrt(0.0/0.0)
> >
> > *     NaN
> >
> Mac OS X gives this result.
> 
> > Windows:
> >
> > irb(main):002:0> Math.sqrt(0.0/0.0)
> >
> > Errno::EDOM: Domain error - sqrt
> >
> >         from (irb):2:in `sqrt'
> >
> >         from (irb):2
> >
> > I guess this is not as it should be. Which is the correct way to 
> > handle NaNs?
> >
> > How can I generate NaN without using the trick 0.0/0.0. Why 
> does 0/0 
> > give a ZeroDivisionError and 0.0/0.0 a NaN
> >
> >
> 0/0 is integer division and all bit patterns are used.
> 0.0/0.0 is floating point division and for IEEE floating 
> point numbers 
> the result is defined by the standard to be NaN.  Bit 
> patterns has been 
> reserved to all information like this to be encoded in the number.
> 
> Can't help you with what Windows is doing or how to generate 
> a NaN more 
> cleanly from Ruby.  It would be very simple to generate one 
> as part of 
> a C extension.
> 
> Dave.
> 
> >
> > Greetings,
> >
> > Geert Fannes.

From what I'm reading at
http://www.opengroup.org/onlinepubs/009695399/functions/sqrt.html, it
appears that in this case, Windows is, in fact, doing the right thing
(though see below).  From the text:

"For finite values of x < -0, a domain error shall occur, and either a
NaN (if supported), or an implementation-defined value shall be
returned."

It looks to me like *nix is only returning NaN, but isn't actually
raising an error while Windows is raising an error, but is not returning
NaN.

begin
   x = Math.sqrt(0.0/0.0)
rescue Errno::EDOM => err
   puts "X is: #{x}" # Should be NaN
   puts "Error: #{err}"
   raise
end

I'd say this is a bug all the way around.

Regards,

Dan