int_pow.hpp

Go to the documentation of this file.

/*
 * Copyright (C) 2010-2022 The ESPResSo project
 * Copyright (C) 2002,2003,2004,2005,2006,2007,2008,2009,2010
 *   Max-Planck-Institute for Polymer Research, Theory Group
 *
 * This file is part of ESPResSo.
 *
 * ESPResSo is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * ESPResSo is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */
 
#pragma once
 
#include "utils/device_qualifier.hpp"
 
namespace Utils {
/**
 * \brief Calculate integer powers.
 * This functions calculates x^n, where
 * n is a positive integer that is known
 * at compile time. It uses exponentiation by
 * squaring to construct an efficient function.
 */
template <unsigned n, typename T> DEVICE_QUALIFIER constexpr T int_pow(T x) {
  if constexpr (n == 0) {
    return T{1};
  }
  if constexpr (n == 1) {
    return x;
  }
  if constexpr (n % 2 == 0) {
    return int_pow<n / 2, T>(x * x);
  }
  return x * int_pow<(n - 1) / 2, T>(x * x);
}
} // namespace Utils