Re: [eigen] fix double-promotion in 3.3 Core/SpecialFunctions.h

[Christoph Hertzberg <chtz@xxxxxxxxxxxxxxxxxxxxxxxx>]

On 2016-05-04 23:21, Christoph Hertzberg wrote:
> I will also add the -Wdouble-promotion to our standard compile-flags. It
> looks like our code was mostly clean with regard to that (except some
> test-code which I will fix now).

It turned out to be a bit more changes than I expected, but I finished 
it just now. Some things I noticed:

std::pow(float, int) actually gets promoted to std::pow(double, double). 
This is especially bad for std::pow(x, 2). Inside Eigen we can use 
numext::abs2(x) instead (and we already did most of the time, as far as 
I noticed).

We have quite a lot of Scalar(EIGEN_PI) now. We could implement either 
scalar_traits<Scalar>::pi() or a numext::pi class with a templated 
conversion operator:
  struct pi {
    template<class Scalar>
    operator Scalar() const { return Scalar(EIGEN_PI); }
  };
The first would also have the advantage to allow higher-precision pi for 
custom scalar types (like mpreal).
The second way would allow nicer code (and we could combine both, of 
course).


Christoph





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