factorial.hpp

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/** \file factorial.hpp
 * \brief Declares and defines the factorial function.
 * \ingroup gen_math_files
 * \author Jared R. Males (jaredmales@gmail.com)
 *
 */
 
//***********************************************************************//
// Copyright 2020 Jared R. Males (jaredmales@gmail.com)
//
// This file is part of mxlib.
//
// mxlib 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.
//
// mxlib 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 mxlib.  If not, see <http://www.gnu.org/licenses/>.
//***********************************************************************//
 
#ifndef mx_factorial_hpp
#define mx_factorial_hpp
 
#include <type_traits>
 
#ifdef MX_INCLUDE_BOOST
#include <boost/math/special_functions/factorials.hpp>
#endif
 
namespace mx
{
namespace math
{
namespace func
{
 
/// The factorial function.
/**
 * \ingroup functions
 */
template <typename T>
T factorial( T x /**< [in] the argument */ )
{
#ifdef MX_INCLUDE_BOOST
    return boost::math::factorial<T>( x );
#else
    static_assert(
        std::is_fundamental<T>::value || !std::is_fundamental<T>::value,
        "factorial<T> not specialized for type T, and MX_INCLUDE_BOOST is not defined, so I can't just use boost." );
    return 0;
#endif
}
 
template <>
float factorial<float>( float x );
 
template <>
double factorial<double>( double x );
 
template <>
long double factorial<long double>( long double x );
 
#ifdef HASQUAD
template <>
__float128 factorial<__float128>( __float128 x );
#endif
 
} // namespace func
} // namespace math
} // namespace mx
 
#endif // mx_factorial_hpp