DenseVector/Serial/Morpheus_Reduction_Impl.hpp

 
#ifndef MORPHEUS_DENSEVECTOR_SERIAL_REDUCTION_IMPL_HPP
#define MORPHEUS_DENSEVECTOR_SERIAL_REDUCTION_IMPL_HPP
 
#include <Morpheus_Macros.hpp>
#if defined(MORPHEUS_ENABLE_SERIAL)
 
#include <Morpheus_SpaceTraits.hpp>
#include <Morpheus_FormatTraits.hpp>
#include <Morpheus_FormatTags.hpp>
#include <Morpheus_Spaces.hpp>
 
namespace Morpheus {
namespace Impl {
 
// Compute sum reduction using Kahan summation for an accurate sum of large
// arrays. http://en.wikipedia.org/wiki/Kahan_summation_algorithm
template <typename ExecSpace, typename Vector>
typename Vector::value_type reduce(
    const Vector& in, typename Vector::size_type size,
    typename std::enable_if_t<
        Morpheus::is_dense_vector_format_container_v<Vector> &&
        Morpheus::has_custom_backend_v<ExecSpace> &&
        Morpheus::has_serial_execution_space_v<ExecSpace> &&
        Morpheus::has_access_v<ExecSpace, Vector>>* = nullptr) {
  using value_type = typename Vector::value_type;
  using size_type  = typename Vector::size_type;
  value_type sum   = in[0];
  value_type c     = (value_type)0.0;
 
  for (size_type i = 1; i < size; i++) {
    value_type y = in[i] - c;
    value_type t = sum + y;
    c            = (t - sum) - y;
    sum          = t;
  }
 
  return sum;
}
 
}  // namespace Impl
}  // namespace Morpheus
 
#endif  // MORPHEUS_ENABLE_SERIAL
#endif  // MORPHEUS_DENSEVECTOR_SERIAL_REDUCTION_IMPL_HPP