Re: [Bug-gsl] gsl-1.12 make check failure with gcc-4.4.1

[Brian Gough]

At Tue, 11 Aug 2009 12:29:46 +0000,
Tasos Drosopoulos wrote:
> make[2]: Entering directory `/home/drososa/gsl-1.12/integration'
> FAIL: qawc(f459) elist (1.83292424966307774e-15 observed vs 
> 1.83308294820715351e-15 expected) [744]
> FAIL: test
> ...
> 
> The error disappears when I compile with CFLAGS="-O" indicating an 
> overaggressive optimization (perhaps? on the side of the  gcc-4.4.1 
> compiler). I observed a similar pattern in the past with gcc-4.3.2 which 
> was fixed with gcc-4.3.3 (the one I am using now for my everyday work).
> 
> If anyone has a Linux system using the same compiler please verify the 
> above. If the FAIL persists someone should inform the gcc people. I 
> would like to upgrade to a more recent gcc provided I can still do my 
> work (based heavily on gsl).

Thanks for the bug report.  I don't think this is a bug in GCC, rather
the test is probably too strict and doesn't account for differences in
the integration algorithm caused by rounding errors and optimisation.

We should probably increase the test tolerance on this -- it would be
interesting to know exactly where the difference is coming from first
though, by comparing all the intermediate results at the two
optimisation levels.  This should be as simple as putting some
breakpoints (or print statements) in qc25c for each computation of
abserr.

-- 
Brian Gough
(GSL Maintainer)

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