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

[Joseph Myers]

On Tue, 27 Sep 2016, Jonathan Wakely wrote:

> 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.

Should I take it from this implementation that C++ is not concerned by 
certain considerations that would arise for C: spurious underflow 
exceptions from the scaling when some arguments much larger than others; 
spurious "invalid" exceptions from the comparisons when any argument is 
(quiet) NaN; handling of mixed (quiet) NaN and Inf arguments (where ISO C 
Annex F has Inf returned, not NaN)?

-- 
Joseph S. Myers
joseph@codesourcery.com