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).