-0.0 treated as negative?

-0.0 treated as negative?

[Bill Schottstaedt]

I just noticed a case where -0.0 is apparently negative:

scheme@(guile-user)> (/ 1.0 0.0)
+inf.0
scheme@(guile-user)> (/ -1.0 0.0)
-inf.0
scheme@(guile-user)> (/ 1.0 -0.0)   
-inf.0
scheme@(guile-user)> (/ -1.0 -0.0)
+inf.0
scheme@(guile-user)> (negative? -0.0)
#f

And here's a separate oddity:

scheme@(guile-user)> (expt #t 0)
1

Re: -0.0 treated as negative?

[Andy Wingo]

Hi Bill,

On Mon 07 Jun 2010 16:00, "Bill Schottstaedt" <bil@ccrma.Stanford.EDU> writes:

> I just noticed a case where -0.0 is apparently negative:
>
> scheme@(guile-user)> (/ 1.0 -0.0)   
> -inf.0
> scheme@(guile-user)> (negative? -0.0)
> #f

Interesting. R5RS seems to be mute on negative zeros. The behavior of
negative? is correct according to R6RS, and the result (/ 1.0 -0.0)
follows IEEE 754, I think; so while odd, it does not seem to be a bug.
Let me know if I'm missing something here.

> scheme@(guile-user)> (expt #t 0)
> 1

Haha, that's amusing :) Will fix. 

Andy
-- 
http://wingolog.org/

Re: -0.0 treated as negative?

[Bill Schottstaedt]

Here's a slightly better example:

scheme@(guile-user)> (< (/ 1.0 -0.0) -1e100 1e100 (/ 1.0 0.0))
#t

Re: -0.0 treated as negative?

[Bill Schottstaedt]

I find this issue has been discussed elsewhere and:

"However, the IEEE committee decided that the advantages of utilizing the sign of zero outweighed the 
disadvantages."

humph.  Another committee covers itself with glory.

Re: -0.0 treated as negative?

[Bill Schottstaedt]

> Let me know if I'm missing something here.

Independent of standards, it means your arithmetic is inconsistent:

scheme@(guile-user)> (= -0.0 0.0)
#t
scheme@(guile-user)> (= +inf.0 +inf.0)
#t
scheme@(guile-user)> (= 1.0 1.0)
#t
scheme@(guile-user)> (= (/ 1.0 0.0) +inf.0)
#t
scheme@(guile-user)> (= (/ 1.0 0.0) (/ 1.0 -0.0))
#f