On 09/11/10 14:26, Mehmet Erol Sanliturk wrote:
On Sat, Sep 11, 2010 at 5:43 AM, Andrew Brampton
<brampton+free...@gmail.com <mailto:brampton%2bfree...@gmail.com>> wrote:
On 11 September 2010 10:28, O. Hartmann
<ohart...@mail.zedat.fu-berlin.de
<mailto:ohart...@mail.zedat.fu-berlin.de>> wrote:
>
> Dear Sirs,
>
> you see me a kind of desperate. I wrote my own a small piece of
 software in
> C, calculating the orbit and position of astronomical objects,
astroids, in
> a heliocentric coordinate system from Keplerian orbital elements.
So far.
> The software calculates the set of points of an ellipse based upon
> ephemeridal datas taken from the Minor Planet Cataloge. Again, so
far,
> everything all right. The set of points of an orbit is all right and
> correct. But when it comes to positions at a specific time, then
I loose
> hair!
>
> Compiling this piece of software with FreeBSD's gcc (V4.2) and
clang (clang
> devel) on my private and lab's FreeBSD boxes (both most recent
FreeBSD
> 8.1/amd64), this program does well, the calculated orbital
positions are
> very close to professional applications or observational checks.
But when
> compiling the sources with gcc44 or gcc45 (same source, same
CFLAG setting,
> mostly no CFLAGS set), then there is a great discrepancy.
Sometimes when
> plotting positions, the results plotted seconds before differs
from the most
> recent. The ellipses are allways correct, but the position of a
single point
> at a specific time isn't correct.
>
> I use the GNU autotools to build the package.
>
> I suspekt miscompilations in memory alloction or in some time- or
> mathematical functions like sin, cos.
>
> before I digg deeper I'd like to ask the community for some hints
how to
> hunt down such a problem.
>
> regards,
> Oliver
Sounds a cool project. I suspect you are miss-using a feature of C or
are using uninitialised memory, and with gcc44/45's more aggressive
optimisations it is getting it wrong. I have three suggestions
1) Use valgrind to check if it finds anything wrong when running your
program. Check both the good and the bad builds.
2) If your program is made up of multiple C files, then try compiling
all of the C files with gcc42, but just one at a time with gcc44. This
way will help you track down exactly which C file has "the bug".
3) Finally do some printf debugging to find the first line of code
that is generating the wrong value.
I hope these suggestions help.
Andrew
Another check may be to use Sun Studio C and or Fortran compilers .
These can be used in Linux ( Linux version of Sun Studio )Â and/or
OpenSolaris or Solaris ( Solaris version of SunStudio ( both in x86 ,
x86_64 , Sparc )Â ( all of them are ( Solaris , OpenSolaris , Sun
Studio , Linux  )  free ) . All of them are freely downloadable from
www.sun.com <http://www.sun.com> and/or www.opensolaris.com
<http://www.opensolaris.com> ( these sites or their pages may be
redirected to www.oracle.com <http://www.oracle.com> owned pages ) .
Personally I tried GCC compilers , but I found that they are very
unreliable . Now I am using Sun Studio compilers in OpenSolaris and
Linux , and never GCC compilers .Â
Thank you very much .
Mehmet Erol Sanliturk
Â
Hello.
Well, the only other architectures I have access to are Linux boxes.
clang ist a very nice compiler since its syntax checking is formidable.
But its code is slow and there seems no OpenMP support at the moment.
Oliver
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