round.hpp

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// SPDX-License-Identifier: BSD-2-Clause
 
#ifndef pRC_CORE_VALUE_FUNCTIONS_ROUND_H
#define pRC_CORE_VALUE_FUNCTIONS_ROUND_H
 
#include <cmath>
 
#include <prc/core/basic/functions/ipow.hpp>
#include <prc/core/value/functions/div.hpp>
#include <prc/core/value/functions/mul.hpp>
#include <prc/core/value/type_traits.hpp>
 
namespace pRC
{
    template<std::int64_t D = 0, class T, If<IsFloat<T>> = 0>
    static inline constexpr auto round(T const &a)
    {
        if constexpr(D >= 0)
        {
            constexpr T scale = iPow(Size(10), Size(D));
            return Float(std::round((a * scale)())) / scale;
        }
        else
        {
            constexpr T scale = iPow(Size(10), Size(-D));
            auto aSign = sign(a);
            auto aAbs = abs(a);
            auto rem = fmod(aAbs, scale);
            if(pRC::unit<T>(2) * rem >= scale)
            {
                return aSign * (aAbs - rem + scale);
            }
            else
            {
                return aSign * (aAbs - rem);
            }
        }
    }
 
    template<std::int64_t D = 0, class T, If<IsInteger<T>> = 0>
    static inline constexpr auto round(T const &a)
    {
        if constexpr(D >= 0)
        {
            return a;
        }
        else
        {
            constexpr T scale = iPow(Size(10), Size(-D));
            auto aSign = sign(a);
            auto aAbs = abs(a);
            auto rem = aAbs % scale;
            if(pRC::unit<T>(2) * rem >= scale)
            {
                return aSign * (aAbs - rem + scale);
            }
            else
            {
                return aSign * (aAbs - rem);
            }
        }
    }
}
#endif // pRC_CORE_VALUE_FUNCTIONS_ROUND_H