[Plplot-devel] We apparently now have floating-point consistency which we should take advantage of for testing purposes

[Alan W. I. <ir...@be...>]

I just made a wonderful discovery today as a result of a thread on the
MinGW/MSYS mailing list where a guy claimed that he generated
consistent unrounded floating-point results with gcc and other
compilers (Borland and MSVC?) for massive (many hours) floating-point
computations regardless of the optimizations for those compilers (so
long as he stuck with the usual simple numerical -O optimizations and
didn't use exotic optimization parameters).  That contradicted all I
"knew" from our experience several years ago where even changing the
simple optimization level from -O0 to -O1 affected our PostScript
results. So I made a new test today and indeed the -O0 and -O3 results
agree exactly for all our standard C examples using gcc (Debian
4.9.2-10).  So that result is consistent with his.  Furthermore, if
his more general result really does hold up for all C compilers
accessible to us, that is going to be a huge breakthrough in our
testing (i.e., we should be able to generate and distribute a tarball
of SVG or PostScript results that every platform should be able to
reproduce exactly).

Anyhow, after the current release is completed I plan to circulate
such a tarball to developers here to see whether we do really get the
same C results for all our standard examples for all compilers
accessible to us.  And if that consistency is confirmed, then some
substantial changes in our testing procedure should be implemented
that take advantage of that new floating-point consistency capability
of C compilers.

Alan
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Alan W. Irwin

Astronomical research affiliation with Department of Physics and Astronomy,
University of Victoria (astrowww.phys.uvic.ca).

Programming affiliations with the FreeEOS equation-of-state
implementation for stellar interiors (freeeos.sf.net); the Time
Ephemerides project (timeephem.sf.net); PLplot scientific plotting
software package (plplot.sf.net); the libLASi project
(unifont.org/lasi); the Loads of Linux Links project (loll.sf.net);
and the Linux Brochure Project (lbproject.sf.net).
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Linux-powered Science
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