# 0.0 sign
**URL:** https://rubytalk.org/t/0-0-sign/11372
**Category:** ruby-talk
**Created:** [5 May 2004 17:33 UTC](https://rubytalk.org/t/0-0-sign/11372 "2004-05-05T17:33:52Z")
**Posts on this page:** 10
**Page:** 1
### Author:  [@Elias\_Athanasopoulos](https://rubytalk.org/u/Elias_Athanasopoulos)
#### Post date: [5 May 2004 17:33 UTC](https://rubytalk.org/t/0-0-sign/11372/1 "2004-05-05T17:33:52Z")
Hello!
I don’t know if this is intentional, but is there a reason
that 0.0 holds the sign?
tiny = 0.0000000000000000001
inf = 1/tiny
a = 1/inf
b = -1/inf
p a, b, (a-b), (a+b)
a = -1/inf
b = 1/inf
p a, b, (a-b), (a+b)
I can hardly imagine you can use it somehow; OTOH it can
make the output a little uglier. 🙂
I checked Python and altough 0.0 carries the sign it is not
used in the results of subtraction/addition, as it is in Ruby.
Regards,
> **···**
>
> –
> University of Athens I bet the human brain
> Physics Department is a kludge --Marvin Minsky
>
> — /home/elathan/hacking/ruby/numeric.c.orig 2004-05-05 00:18:12.000000000 +0300
> +++ /home/elathan/hacking/ruby/numeric.c 2004-05-05 00:18:41.000000000 +0300
> @@ -502,6 +502,7 @@
> avalue = fabs(value);
> if (avalue == 0.0) {
> fmt = “%.1f”;
>
> - value = avalue;
> }
> else if (avalue \< 1.0e-3) {
> d1 = avalue;
---
### Author:  [@Mark\_Hubbart](https://rubytalk.org/u/Mark_Hubbart)
#### Post date: [5 May 2004 19:28 UTC](https://rubytalk.org/t/0-0-sign/11372/2 "2004-05-05T19:28:36Z")
IEEE 754 (floating point arithmetic standard) specifies negative zero
for floats. For more explanation, see
[http://www.obtuse.com/resources/negative\_zero.html](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
> **···**
>
> 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?
---
### Author:  [@Tobias1](https://rubytalk.org/u/Tobias1)
#### Post date: [5 May 2004 22:13 UTC](https://rubytalk.org/t/0-0-sign/11372/3 "2004-05-05T22:13:57Z")
What I find much more problematic than 0.0 having a sign is that ruby treats
0.0000000000000000001 == 0.0 as true.
If I’ve counted correct that should be 1 \* 10^-19. Doubles can represent
Numbers down to approx. 10^-300.
1e-300 == 0.0 is false in ruby, as it should be.
There must be a bug in the interpreter, where it reads Float literals.
Tobias
---
### Author:  [@Elias\_Athanasopoulos](https://rubytalk.org/u/Elias_Athanasopoulos)
#### Post date: [6 May 2004 07:17 UTC](https://rubytalk.org/t/0-0-sign/11372/4 "2004-05-06T07:17:17Z")
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.
Regards,
> **···**
>
> 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](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
>
> –
> University of Athens I bet the human brain
> Physics Department is a kludge --Marvin Minsky
---
### Author:  [@Mark\_Hubbart](https://rubytalk.org/u/Mark_Hubbart)
#### Post date: [5 May 2004 22:31 UTC](https://rubytalk.org/t/0-0-sign/11372/5 "2004-05-05T22:31:29Z")
For me, it cuts off after 1e-17:
0.000\_000\_000\_000\_000\_01
==\>1e-17
0.000\_000\_000\_000\_000\_001
==\>0.0
I’m not sure it’s a bug in float parsing, since you can go:
1e-18
==\>1e-18
1e-300
==\>1e-300
…which would be preferable to typing in all those zeros anyway. But I
would be curious to know why they decided to truncate long float
literals?
–Mark
> **···**
>
> On May 5, 2004, at 3:13 PM, Tobias Peters wrote:
>
> > What I find much more problematic than 0.0 having a sign is that ruby
> > treats
> >
> > 0.0000000000000000001 == 0.0 as true.
> >
> > If I’ve counted correct that should be 1 \* 10^-19. Doubles can
> > represent Numbers down to approx. 10^-300.
> >
> > 1e-300 == 0.0 is false in ruby, as it should be.
> >
> > There must be a bug in the interpreter, where it reads Float literals.
---
### Author:  [@NAKAMURA\_Hiroshi1](https://rubytalk.org/u/NAKAMURA_Hiroshi1)
#### Post date: [6 May 2004 07:26 UTC](https://rubytalk.org/t/0-0-sign/11372/6 "2004-05-06T07:26:30Z")
Hi,
Elias Athanasopoulos wrote:
> 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.
Check XSDFloat implementation at xsd/datatypes.rb in ruby \> 1.8.1 or
[http://www.ruby-lang.org/cgi-bin/cvsweb.cgi/lib/soap4r/lib/xsd/datatypes.rb?rev=1.13](http://www.ruby-lang.org/cgi-bin/cvsweb.cgi/lib/soap4r/lib/xsd/datatypes.rb?rev=1.13)
I hope this helps.
Regards,
// NaHi
---
### Author:  [@Mark\_Hubbart](https://rubytalk.org/u/Mark_Hubbart)
#### Post date: [6 May 2004 08:52 UTC](https://rubytalk.org/t/0-0-sign/11372/7 "2004-05-06T08:52:46Z")
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
> **···**
>
> 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](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.
---
### Author:  [@Zsban\_Ambrus](https://rubytalk.org/u/Zsban_Ambrus)
#### Post date: [6 May 2004 13:20 UTC](https://rubytalk.org/t/0-0-sign/11372/8 "2004-05-06T13:20:46Z")
I think this might be a bug in the C library, not ruby. Don’t take this for
sure however.
Why I think this is because something similar seems to occur in Perl too.
I’ve written a japh “[http://www.perlmonks.com/index.pl?node\_id=330784](http://www.perlmonks.com/index.pl?node_id=330784)”.
I’ve checked that it works on machines with either endianness (linux-ix86
and sun4-solaris-sparc). However, I’ve got reports saying that it won’t
work on their machine. One report,
“[Re: Fun with duff's device and AUTOLOAD](http://www.perlmonks.com/index.pl?node_id=331720)” looks especially as if
the last few digits of the floating point literals in the code were ignored.
That last report was on a winnt machine, but it’s also said that it doesn’t
work on solaris.
Please tell me on what platform and OS did you get the above results.
ambrus
> **···**
>
> On Thu, May 06, 2004 at 07:13:57AM +0900, Tobias Peters wrote:
>
> > What I find much more problematic than 0.0 having a sign is that ruby treats
> >
> > 0.0000000000000000001 == 0.0 as true.
> >
> > If I’ve counted correct that should be 1 \* 10^-19. Doubles can represent
> > Numbers down to approx. 10^-300.
> >
> > 1e-300 == 0.0 is false in ruby, as it should be.
> >
> > There must be a bug in the interpreter, where it reads Float literals.
> >
> > Tobias
---
### Author:  [@Elias\_Athanasopoulos](https://rubytalk.org/u/Elias_Athanasopoulos)
#### Post date: [6 May 2004 09:18 UTC](https://rubytalk.org/t/0-0-sign/11372/9 "2004-05-06T09:18:44Z")
Ok, got it! Very nice. 🙂 Thanx.
Regards,
> **···**
>
> On Thu, May 06, 2004 at 05:52:46PM +0900, Mark Hubbart wrote:
>
> > class Numeric
> > def negative?()
> > zero? ? (1.0/self \< 0) : (self \< 0)
> > end
> > end
> > ==\>nil
> > -0.0.negative?
> > ==\>true
> > 0.0.negative?
> > ==\>false
>
> –
> University of Athens I bet the human brain
> Physics Department is a kludge --Marvin Minsky
---
### Author:  [@Yukihiro\_Matsumoto2](https://rubytalk.org/u/Yukihiro_Matsumoto2)
#### Post date: [6 May 2004 14:08 UTC](https://rubytalk.org/t/0-0-sign/11372/10 "2004-05-06T14:08:20Z")
Hi,
> **···**
>
> In message “Re: Bug in Float literal (1e-19 == 0) Re: 0.0 sign” on 04/05/06, “Zsban Ambrus” [ambrus@math.bme.hu](mailto:ambrus@math.bme.hu) writes:
>
> > > 0.0000000000000000001 == 0.0 as true.
>
> > I think this might be a bug in the C library, not ruby. Don’t take this for
> > sure however.
>
> It’s a bug in strtod(), but Ruby uses its own strtod() implementation.
> H.Yamamoto submitted the fix in [ruby-dev:23465].
>
> ```
> matz.
>
> ```