Experimental Physics and
Industrial Control System

Andrew Johnson <[email protected]> · Mon, 12 Apr 2010 17:43:51 -0500

On Monday 12 April 2010 17:12:45 Ralph Lange wrote:
>
> I just learned that the recently introduced VAL keyword does not
> (quoting the Record Reference Manual) return "the current contents of
> the VAL field" but rather "the current contents of this expression's
> result".

That sentence was obviously written assuming that the result would be assigned 
to the VAL field, which was always true for the Calc record but not for the 
Calcout.  The VAL keyword could be added because calcPerform() takes a pointer 
to the double where it should put the result, so it assumes that the previous 
value is still available.

> Which means, that inside a calcout record's OCAL expression, VAL refers
> to OVAL, not VAL.
> Which means you can not use VAL inside OCAL to refer to the result of
> the CALC expression, but have to repeat the CALC expression inside OCAL
> to get the same value.
>
> Which (in my case) makes the OCAL expression more than 40 characters
> long, which doesn't work.

If you have a spare input and enough space in the CALC expression you could 
assign the CALC result to that variable using the := operator, then it will be 
available to use in your OCAL expression:

CALC: L:=<expression>;L
OCAL: <expression using L>

> Should we change the behaviour or the documentation?

My first though was that we have to change the documentation of the Calcout 
record, but I guess it would be possible to assign prec->oval = prec->val 
before evaluating OCAL.  However if someone does understand how the VAL 
keyword works they might already be relying on the existing behaviour.

I think I'd be happier just fixing the documentation.

- Andrew
-- 
The best FOSS code is written to be read by other humans -- Harald Welte

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System