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.
I understand the claims about accuracy, but the one about speed seems very surprising to me. Was your test specifically with denormals on not-so-recent hardware, or specifically when sqrt does a library call for errno? Otherwise, I have a hard time believing that 3 multiplications and 2 additions can be slower than 4 multiplications, 2 additions, plus a bunch of tests and divisions.
-- Marc Glisse
