Experimental Physics and
Industrial Control System

Benjamin Franksen <[email protected]> · Tue, 4 Nov 2014 14:17:45 +0100

On Tuesday 04 November 2014 13:41:00 Ralph Lange wrote:
> Hello Götz,
>
> On 04/11/2014 13:32, Goetz Pfeiffer wrote:
> > another problem is that DRVL and DRVH seem to be ignored for NaN.
> >
> > The following record;
> >
> > record(ao,"UE56ID3R:BaseParGapTrs") {
> >
> >      field(ASG,"USERCTL")
> >      field(DRVH,"0.1")
> >      field(DRVL,"0")
> >      field(LINR,"NO CONVERSION")
> >      field(OIF,"Full")
> >      field(PREC,"4")
> >
> > }
> >
> > for example can be set to NaN (at least for Epics Base 3.14.8).
>
> Comparisons between numbers and non-numbers (such as NaN) are
> undefined.

I am quite sure neither the C standard(s) nor IEEE 754 say this is
undefined. Rather, IIRC, comparisons involving NaN always result in a
FALSE value, including the test for equality of a variable with itself.

> What is your suggestion on how to check limits for a
> non-number without using comparisons?

The more interesting question is: what should the resulting VAL be, if
not NaN?

Cheers
Ben
--
"Make it so they have to reboot after every typo." ― Scott Adams

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Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System