Experimental Physics and
Industrial Control System

Dirk Zimoch <[email protected]> · Wed, 05 Nov 2014 14:43:04 +0100

On 04.11.2014 14:37, [email protected] wrote:

From: Ralph Lange [mailto:[email protected]]

Comparisons between numbers and non-numbers (such as NaN) are
undefined.

Not quite: comparisons involving NaN are defined to always return false.  This means that a test of the form

	if (prec->drvl <= value && value <= prec->drvh)
	    // accept value
	else
	    // reject value

would have the desired effect (and setting a drv limit would cause all values to be rejected!)

Note that the intent of DRVH and DRVL is not to reject values but to

truncate the range. So a value larger than DRVH is not ignored but

replaced by DRVH. As argued before, NaN is never larger than DRVH, thus

the value is accepted.

Dirk

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

We also found that you can type "NaN" at any entry field in DM2K

which

writes NaN directly to the PV.

NaN, -inf and +inf are valid values for a double. Why would you reject
entering valid values in entry fields?

Cheers,
~Ralph

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System