[PATCH] Define 3-argument overloads of std::hypot for C++17 (P0030R1)

[Rainer Orth]

Hi Jonathan,

> This adds the new 3D std::hypot() functions. This implementation seems
> to be faster than the naïve sqrt(x*x + y*y + z*z) implementation, or
> hypot(hypot(x, y), z), and should be a bit more accurate at very large
> or very small values due to reducing the arguments by the largest one.
> Improvements welcome though, as this is not my forte.
>
> The test might not be very good, but tests some small integer values
> and some other values where accuracy is lost for one or other of the
> alternative implementations mentioned above. If this FAILs for some
> 32-bit targets we might need to adjust the tolerances or the
> dg-options.
>
> 	* doc/xml/manual/status_cxx2017.xml: Update status.
> 	* include/c_global/cmath (hypot): Add three-dimensional overloads.
> 	* testsuite/26_numerics/headers/cmath/hypot.cc: New.
>
> Tested powerpc64le-linux and x86_64-linux, committed to trunk.

the new test currently FAILs on Solaris 12 (both SPARC and x86):

+FAIL: 26_numerics/headers/cmath/hypot.cc (test for excess errors)
+WARNING: 26_numerics/headers/cmath/hypot.cc compilation failed to produce execu
table

Excess errors:
/vol/gcc/src/hg/trunk/local/libstdc++-v3/testsuite/26_numerics/headers/cmath/hypot.cc:38: error: no matching function for call to 'hypot(double, double, double)'
/vol/gcc/src/hg/trunk/local/libstdc++-v3/testsuite/26_numerics/headers/cmath/hypot.cc:38: error: no matching function for call to 'hypot(double, double, double)'
/vol/gcc/src/hg/trunk/local/libstdc++-v3/testsuite/26_numerics/headers/cmath/hypot.cc:38: error: template argument 2 is invalid

and many more.

	Rainer

-- 
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Rainer Orth, Center for Biotechnology, Bielefeld University