[Octave-bug-tracker] [bug #49667] Computing powers of complex numbers in 4.2.0 is slower than in 4.0.3

[Mike Miller]

Follow-up Comment #5, bug #49667 (project octave):

Correct, I believe it is because the std::pow(std::complex<T>, int) overload
was conditionally compiled out of existence in earlier versions of gcc when
using the -std=gnu++11 or -std=gnu++0x command-line option, but was available
when building in (previously the default) C++98 mode.

With gcc 5, the specialization was reinstated when building in C++11 mode, and
the performance is as it was.

I think a user on Ubuntu 14.04 or Mint 17 could confirm this by using gdb or
perf and showing that the inline function std::__complex_pow_unsigned is *not*
being called at all. But I've looked at this for about a half hour now and I'm
pretty convinced by inspection that this is the case.

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