Experimental Physics and
Industrial Control System

Dirk Zimoch <[email protected]> · Tue, 16 Nov 2004 09:30:33 +0100

Hi,
some time ago, I noticed a bug in the ccppc for Tornado 2 running on Linux.
gcc version gcc-2.96 (2.96+) 19990621 AltiVec
I got the sources from SNS.
When used with -O, the compiler produces buggy floating point code. I
noticed that forst in the calcout record, because instead of =, it
calculates <= or so.
I reported the problem to Dave Thompson, but got no fix so far.
Hello Dave,
I have dowloaded your Tornado 2.2 cross compiler for Linux and built EPICS3.13 with it.
Unfortunately, I found a serious bug: The calc record didn't work any more!
The simple CALC "A=B" behaves like "A<=B" what I found very strange. I found that I only had the problem when using the -O compiler flag. Without optimization, everything is fine.
I guess that the bug also leads to a lot of other errors.

I tracked the problem down to:
double a,b,c;
a=1;
b=2;
c=(a==b);
results in 1.0000 !
But
double a,b,c;
int i;
a=1;
b=2;
i=(a==b);
c=i;
result to 0.0000 as expected.
The problem is independent of EPICS. I just compiled the attached C-file with 'ccppc -c -O comptest.c' and loaded the object code on a MVME5100 IOC with only vxWorks running.
The generated assembler code looks different from the code generated on Solaris.
Have you ever seen this? What's going wrong? Can you fix it?

Best regards
Dirk

My solution is not to use the -O2 optimize flag.
Dirk

Geoff Savage wrote:

Hi,
We noticed some changed behaviour in calc and calcout records from
v3.13.4 to v3.14.6 and were unable to identify the cause. Take a simple
calc record, maybe too simple:

record(calc,"CTL_TEST_66/CALC") {

field(CALC, "1=0")

field(SCAN, "1 second")

}

In v3.13.4 VAL is the expected value of zero. In v3.14.6 VAL is one.
The same applies for the calcout record.
What are we missing?
Geoff

--
Dr. Dirk Zimoch
Swiss Light Source
Paul Scherrer Institut
Computing and Controls
phone +41 56 310 5182
fax   +41 56 310 4413

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System