[rrd-users] Correct implementation of IF

[Alex van den Bogaerdt]

Owen DeLong wrote:

> > I doubt that "IF" will do the right thing here.  The source for
> > 1.1.x doesn't seem to check for unknowns and even worse, it seems
> > to handle them as "true".  Better make sure and use then "UN"
> > statement here.
> > 
> He's right again. :-(

When in doubt, read the source :)

Anyway, I think that the IF function should only return the first
value if the condition is a finite value and if the condition != false.
So, both infinite and unknown values should be equivalent to false.

We have:  condition,a,b,IF and this works correctly for conditions
that are finite numbers.  Please review the table below and discuss
what would be the correct implementation.

condition | return value
----------+-------------
-infinite | -infinite or unknown or a or b ?
+infinite | +infinite or unknown or a or b ?
 unknown  |              unknown or a or b ?
 <0       | return a
==0       | return b
 >0       | return a

cheers,
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