On Wed, 28 Sep 2016, Jonathan Wakely wrote: > On 27/09/16 23:28 +0000, Joseph Myers wrote: > > 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)? > > The entire spec from the C++ draft is: Returns: √ x^2 + y^2 + z^2
As a further issue: even if you ignore exceptions and Annex F issues, and don't have NaN arguments, if you have an Inf argument it will be the largest, and so your code will do Inf/Inf, and so return NaN, if any argument is Inf (when obviously the correct answer in that case is Inf). -- Joseph S. Myers jos...@codesourcery.com
