factorial.h

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/* Copyright (c) 2008-2022 the MRtrix3 contributors.
 *
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/.
 *
 * Covered Software is provided under this License on an "as is"
 * basis, without warranty of any kind, either expressed, implied, or
 * statutory, including, without limitation, warranties that the
 * Covered Software is free of defects, merchantable, fit for a
 * particular purpose or non-infringing.
 * See the Mozilla Public License v. 2.0 for more details.
 *
 * For more details, see http://www.mrtrix.org/.
 */
 
#ifndef __math_factorial_h__
#define __math_factorial_h__
 
#include <functional>
#include <limits>
 
namespace MR
{
  namespace Math
  {
 
 
    template <typename T>
    T factorial (const T i) {
      if (i < 2) {
        return T(1);
      } else if (i == std::numeric_limits<T>::max()) {
        return i;
      } else {
        const T multiplier = factorial<T>(i-1);
        const T result = i * multiplier;
        if (result / multiplier == i)
          return result;
        else
          return std::numeric_limits<T>::max();
      }
    };
 
 
  }
}
 
#endif