[boost] [math] mark constants as constexpr

Subject: [boost] [math] mark constants as constexpr
From: Lakshay Garg (lakshayg373_at_[hidden])
Date: 2017-08-21 05:33:28

Hello all

The boost.math library stores quite a few constants for improving
performance of various operations (example:
boost/math/special_functions/detail/unchecked_factorial.hpp). I was
wondering if marking these constants as constexpr would be desirable.

Please provide feedback / suggestions so that I can get started :)

Lakshay