factorial.hpp

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#pragma once
 
#include "NumCpp/Core/Internal/StlAlgorithms.hpp"
#include "NumCpp/Core/Types.hpp"
#include "NumCpp/NdArray.hpp"
 
#ifndef NUMCPP_NO_USE_BOOST
#include "boost/math/special_functions/factorials.hpp"
#endif
 
#include <limits>
 
namespace nc::special
{
    //============================================================================
    // Method Description:
    inline double factorial(uint32 inValue)
    {
#ifndef NUMCPP_NO_USE_BOOST
        if (inValue <= boost::math::max_factorial<double>::value)
        {
            return boost::math::factorial<double>(inValue);
        }
 
        return std::numeric_limits<double>::infinity();
#else
        double result = 1.;
        for (uint32 i = 2; i <= inValue; ++i)
        {
            result *= static_cast<double>(i);
        }
 
        return result;
#endif
    }
 
    //============================================================================
    // Method Description:
    inline NdArray<double> factorial(const NdArray<uint32>& inArray)
    {
        NdArray<double> returnArray(inArray.shape());
 
        stl_algorithms::transform(inArray.cbegin(),
                                  inArray.cend(),
                                  returnArray.begin(),
                                  [](uint32 inValue) -> double { return factorial(inValue); });
 
        return returnArray;
    }
} // namespace nc::special