Re: bug in recCompress.c

[mrk@aps.anl.gov (Marty Kraimer)]

> From fgougna@sigx0.saclay.cea.fr Mon Feb 13 07:38 CST 1995
> Date: Mon, 13 Feb 95 14:39:42 GMT
> From: "F. Gougnaud" <fgougna@sigx0.saclay.cea.fr>
> To: tech-talk@aps.anl.gov
> Subject: bug in recCompress.c
> Content-Type> : > text> 
> Content-Length: 1100
> 
> 	Hi,
> 
> 	
> 
> 	I have corrected a bug in the recCompress.c file in EPICS release 3.11.
> 
> The AVERAGE algorithm doesn't work when the N field is greater than 1 (!)
> because the routine array_average() doesn't update the INX record's field.
> 
> The routine must be modified like this:
> 
> 	...
> 	/* do we need to calculate the result */
> 	inx++;
> 	if (pcompress->n<=0) pcompress->n=1;
> 	n = pcompress->n;
> 	pcompress->inx = inx;    <---- add this line
> 	if (inx<n) return(1);
> 	if (n>1) {
> 		pcompress->inx = 0;    <---- and this line
> 		psum = (double *)pcompress->sptr;
> 		multiplier = 1.0/((double)n);
> 		for (i = 0; i < nuse; i++, psum++)
> 	    		*psum = *psum * multiplier;
> 	}
> 	put_value(pcompress,pcompress->sptr,nuse);
> 	return(0);
> 
You must have an older version of epics. The current version, which appears
to be equivalent to your suggested changes has the code:


> A static int array_average(pcompress,psource,no_elements)
struct compressRecord	*pcompress;
double			*psource;
long			no_elements;
{
	long	i;
	long	nnow;
	long	nsam=pcompress->nsam;
	double	*psum;
	double	multiplier;
	long	inx=pcompress->inx;
	struct dbAddr *pdbAddr = (struct dbAddr *)(pcompress->inp.value.db_link.pdbAddr);
	long	ninp=pdbAddr->no_elements;
	long	nuse,n;

	nuse = nsam;
	if(nuse>ninp) nuse = ninp;
	nnow=nuse;
	if(nnow>no_elements) nnow=no_elements;
	psum = (double *)pcompress->sptr;

	/* add in the new waveform */
	if (inx == 0){
		for (i = 0; i < nnow; i++)
		    *psum++ = *psource++;
		for(i=nnow; i<nuse; i++) *psum++ = 0;
	}else{
		for (i = 0; i < nnow; i++)
		    *psum++ += *psource++;
	}

	/* do we need to calculate the result */
	inx++;
	if(pcompress->n<=0)pcompress->n=1;
	n = pcompress->n;
	if (inx<n) {
		pcompress->inx = inx;
		return(1);
	}
	if(n>1) {
		psum = (double *)pcompress->sptr;
		multiplier = 1.0/((double)n);
		for (i = 0; i < nuse; i++, psum++)
	    		*psum = *psum * multiplier;
	}
	put_value(pcompress,pcompress->sptr,nuse);
	pcompress->inx = 0;
	return(0);
}
>suggestion for the compress record type:
> 
> in 3.11 it's not possible to modify the N field of a compress record from
> an application. For that, the N field definition in the compressRecord.ascii
> file need to be changed like this:
> 
> (before)    "N to 1 Compression"     N    SPC_NOMOD  DBF_ULONG   ...
> (after)     "N to 1 Compression"     N    SPC_RESET  DBF_ULONG   ...
> 
> 
> 	Yves Lussignol.
> 

Good suggestion. I am making this change to this field and also to ALG.

Marty