[Octave-bug-tracker] [bug #47775] realpow and sparse-xpow.cc-tst fails

[Lachlan Andrew]

Follow-up Comment #11, bug #47775 (project octave):

When I try to configure and make with "CXX="g++ -std=gnu++11", I get a compile
error:


In file included from ../libgnu/time.h:42:0,
                 from /usr/include/pthread.h:24,
                 from
/usr/include/x86_64-linux-gnu/c++/4.8/bits/gthr-default.h:35,
                 from /usr/include/x86_64-linux-gnu/c++/4.8/bits/gthr.h:148,
                 from /usr/include/c++/4.8/ext/atomicity.h:35,
                 from /usr/include/c++/4.8/bits/ios_base.h:39,
                 from /usr/include/c++/4.8/ios:42,
                 from /usr/include/c++/4.8/istream:38,
                 from /usr/include/c++/4.8/sstream:38,
                 from /usr/include/c++/4.8/complex:45,
                 from ../../liboctave/util/oct-cmplx.h:27,
                 from ../../liboctave/array/Array-C.cc:30:
../libgnu/stddef.h:93:3: error: conflicting declaration 'typedef union
max_align_t max_align_t'
 } max_align_t;


Any suggestions?

I'm completely happy with keeping the tight tolerances.

Oh, and I shouldn't have referred to [3,4] regarding tolerance. Those were for
the sparse-xpow test, but the same holds for an epsilon change in the exponent
(or base) used in the realpow test.  The point is that (IMHO) we shouldn't
rely on floating point libraries to distinguish between "integer" and
"non-integer"; they're "entitled" to assume all floating point values are
approximations, and to return approximations as results -- unless they are
documented to do otherwise.

Rather than blacklisting particular versions of tools or libraries, I think we
should write the integer-power case explicitly if the tolerance is
unacceptable.  It is compact and relatively fast in principle
(2log_2(exponent) multiplications).

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