[rrd-developers] Re: Representation of NAN and INF

Alex van den Bogaerdt alex at slot.hollandcasino.nl
Thu Jul 26 04:37:28 MEST 2001

Matt Zimmerman wrote:
> Mathematically speaking, 1.0/0.0 is undefined while 0.0/0.0 is indeterminate,
> and those do not mean the same thing.  From a programming standards
> perspective, as far as I know, IEEE 754 says that there are multiple
> permissible representations for NaN and infinity (not all bits are defined).
> So there are values for which, within rrdtool:
> isnan(x) && x != DNAN
> and
> isinf(x) && x != DINF

Good to know.

> I would hope that rrdtool only uses these macros to obtain reasonable values to
> use in its internal storage format, and not for any comparisons (where the IEEE
> functions should be used).

A quick scan doesn't reveal any such comparisons.  I'll check more careful
later on.

> As long as this is true, the expressions for DNAN and DINF are a perfectly
> valid way to obtain some values which will satisfy finite/isnan/isinf in the
> expected ways:  IEEE defines that isnan(0.0/0.0) and isinf(1.0/0.0) will both
> be true.

Do you also happen to know the official way to handle isnan(1.0/0.0) ?

> I missed the original post...is there some compiler which is not handling these
> expressions correctly?

It was about porting to VB OCX or something alike.  I don't know if it
was asked because it fails in VB or not.

 / alex at slot.hollandcasino.nl                  alex at ergens.op.het.net \
| work                                                         private |
| My employer is capable of speaking therefore I speak only for myself |
| Technical questions sent directly to me will be nuked. Use the list. | 
| http://faq.mrtg.org/                                                 |
| http://rrdtool.eu.org  --> tutorial                                  |

Unsubscribe mailto:rrd-developers-request at list.ee.ethz.ch?subject=unsubscribe
Help        mailto:rrd-developers-request at list.ee.ethz.ch?subject=help
Archive     http://www.ee.ethz.ch/~slist/rrd-developers
WebAdmin    http://www.ee.ethz.ch/~slist/lsg2.cgi

More information about the rrd-developers mailing list