Re: calc and calcout records in EPICS 3.14.6

[Dirk Zimoch <dirk.zimoch@psi.ch>]

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