maths.hpp

#ifndef __BIOMC_COMMON_MATHS__
#define __BIOMC_COMMON_MATHS__
 
#include <Kokkos_BitManipulation.hpp>
#include <Kokkos_MathematicalFunctions.hpp>
 
namespace CommonMaths
{
 
  template <bool use_kokkos_log>
  KOKKOS_INLINE_FUNCTION float
  _ln(float x)
    requires(!use_kokkos_log)
  {
    // NOLINTBEGIN
    // std::bit_cast keeps the same exact bit in the target type
    // better than unsafe C const
    unsigned int bx = Kokkos::bit_cast<unsigned int>(x);
    const unsigned int ex = bx >> 23;
    const signed int t
        = static_cast<signed int>(ex) - static_cast<signed int>(127);
    // unsigned int s = (t < 0) ? (-t) : t;
    bx = 1065353216 | (bx & 8388607);
    x = Kokkos::bit_cast<float>(bx);
    return -1.49278 + (2.11263 + (-0.729104 + 0.10969 * x) * x) * x
           + 0.6931471806 * t;
    // NOLINTEND
  }
 
  template <bool use_kokkos_log>
  KOKKOS_INLINE_FUNCTION float
  _ln(float x)
    requires(use_kokkos_log)
  {
    return Kokkos::log(x);
  }
 
} // namespace CommonMaths
#endif