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
It doesn't mention "without undue overflow or underflow" as the C
standard does for hypot(x, y). Handling those conditions would of
course be nice, but I'm not capable of doing so, and I'd rather have a
poor implementation than none.
p0030r0 had "In addition to the two-argument versions of certain math
functions in <cmath> and its float and long double overloads, C++ adds
three-argument versions of these functions that follow similar semantics
as their two-argument counterparts."
One could interpret that as an intent to follow the C semantics. On the
other hand, the paper mentions speed and convenience as the main selling
points. Maybe LWG could clarify the intent?
--
Marc Glisse
