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

Alex van den Bogaerdt alex at slot.hollandcasino.nl
Wed Jul 25 16:54:25 MEST 2001

Dan McGinn-Combs wrote:

> I note in the C source that these two pseudo-numbers have representation
> defined in terms of the particular float scheme used with the C compiler:
> #define DNAN    ((double)(0.0/0.0))
> #define DINF    ((double)(1.0/0.0))
> Apparently, these two representations come out different. However, in the
> math I studied, "anything" divided by 0 is still ... like Undefined. And so
> 0/0 is the same as 1/0 and both are illegal.

For real mathematics this statement is entirely true.  However, in C
there is some IEEE standard that defines the float (and double) number
format and I *think* (so: not sure) this also defines the behaviour
when dividing by zero.

> So as I'm migrating the code to a (gasp!) VB OCX file, I'm trying to figure
> out what this has to be.

Just make sure the functions "isfinite()", "isnan()" and "isinf()" return
the proper result and you should be fine.

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