Experimental Physics and
Industrial Control System

[email protected] (Tim Mooney) · Mon, 7 Jul 1997 16:14:26 -0500

Andrew Johnson writes...

> > BAD:
> > 
> > grecord(calc,"$(Ring):BXBCM:TEMPA") {
> >         field(SCAN,"10 second")
> >         field(CALC,"( (A&C) >> 3 ) - B")
> > ...
> 
> The thing which I see as significant in these differences is that Ron
> has taken the literal "3" out of the expression and put it into the
> input D instead.  I have been aware for some time that literals aren't
> always accepted in CALC expressions (but some work fine -- thats the
> wierd thing about it).  I suspect this may be the area of the problem,
> but I'm only guessing.  It may relate to a literal with an adjacent
> space, which matches where Rozelle's saw the error being reported.

Your exactly right.

Literals (i.e., FLOAT_PT_CONST's in postfix.c) aren't accepted in CALC
expressions when they are preceded by a space.  This is because literals
are parsed twice, and the second parse doesn't accept spaces.  (The first
parse, which all expression elements undergo, does handle leading spaces.)

If the line marked below is added to postfix.c, the problem goes away.

-----excerpt from postfix.c-----------
long postfix(pinfix,ppostfix,perror)
.
.
.
	    case FLOAT_PT_CONST:
		if (!operand_needed){
		    *perror = 5;
		    return(-1);
		}

		/* add constant to the expression */
		*ppostfix++ = pelement->code;
		pposthold = ppostfix;

		pinfix-=no_bytes;
>>>----->	while (*pinfix == ' ') *ppostfix++ = *pinfix++;
		while (TRUE) {
.
.
.
---------------------------------------

Tim Mooney
Beamline Controls & Data Acquisition
Advanced Photon Source
Argonne National Lab

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System