math.hpp

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//~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~//
// Copyright (c) Lawrence Livermore National Security, LLC and other
// RAJA Project Developers. See top-level LICENSE and COPYRIGHT
// files for dates and other details. No copyright assignment is required
// to contribute to RAJA.
//
// SPDX-License-Identifier: (BSD-3-Clause)
//~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~//
 
#ifndef RAJA_util_math_HPP
#define RAJA_util_math_HPP
 
#include "RAJA/config.hpp"
 
#include <type_traits>
#include <climits>
 
namespace RAJA
{
 
template<typename T, std::enable_if_t<std::is_integral<T>::value>* = nullptr>
RAJA_HOST_DEVICE RAJA_INLINE constexpr T log2(T n) noexcept
{
  T result = 0;
  if (n > 0)
  {
    while (n >>= 1)
    {
      ++result;
    }
  }
  return result;
}
 
template<typename T, std::enable_if_t<std::is_integral<T>::value>* = nullptr>
RAJA_HOST_DEVICE RAJA_INLINE constexpr T next_pow2(T n) noexcept
{
  --n;
  for (size_t s = 1; s < CHAR_BIT * sizeof(T); s *= 2)
  {
    n |= n >> s;
  }
  ++n;
  return n;
}
 
template<typename T, std::enable_if_t<std::is_integral<T>::value>* = nullptr>
RAJA_HOST_DEVICE RAJA_INLINE constexpr T prev_pow2(T n) noexcept
{
  if (n < 0) return 0;
  for (size_t s = 1; s < CHAR_BIT * sizeof(T); s *= 2)
  {
    n |= n >> s;
  }
  return n - (n >> 1);
}
 
template<typename L,
         typename R,
         std::enable_if_t<std::is_integral<L>::value &&
                          std::is_integral<R>::value>* = nullptr>
RAJA_HOST_DEVICE RAJA_INLINE constexpr auto power_of_2_mod(L lhs,
                                                           R rhs) noexcept
{
  return lhs & (rhs - R(1));
}
 
}  // namespace RAJA
 
#endif