duration_cast.hpp

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// SPDX-License-Identifier: BSL-1.0
 
#ifndef TETL_CHRONO_DURATION_CAST_HPP
#define TETL_CHRONO_DURATION_CAST_HPP
 
#include <etl/_chrono/duration.hpp>
#include <etl/_chrono/treat_as_floating_point.hpp>
#include <etl/_type_traits/bool_constant.hpp>
#include <etl/_type_traits/common_type.hpp>
#include <etl/_type_traits/is_arithmetic.hpp>
 
namespace etl::chrono {
 
namespace detail {
template <typename T>
struct is_duration : etl::false_type { };
 
template <typename Rep, typename Period>
struct is_duration<etl::chrono::duration<Rep, Period>> : etl::true_type { };
 
template <typename T>
inline constexpr auto is_duration_v = is_duration<T>::value;
 
template <typename ToDuration, typename CF, typename CR, bool NumIsOne = false, bool DenIsOne = false>
struct duration_cast_impl {
    template <typename Rep, typename Period>
    [[nodiscard]] static constexpr auto cast(duration<Rep, Period> const& duration)
        noexcept(is_arithmetic_v<Rep> and is_arithmetic_v<typename ToDuration::rep>) -> ToDuration
    {
        using to_rep = typename ToDuration::rep;
        return ToDuration(
            static_cast<to_rep>(static_cast<CR>(duration.count()) * static_cast<CR>(CF::num) / static_cast<CR>(CF::den))
        );
    }
};
 
template <typename ToDuration, typename CF, typename CR>
struct duration_cast_impl<ToDuration, CF, CR, true, false> {
    template <typename Rep, typename Period>
    [[nodiscard]] static constexpr auto cast(duration<Rep, Period> const& duration)
        noexcept(is_arithmetic_v<Rep> and is_arithmetic_v<typename ToDuration::rep>) -> ToDuration
    {
        using to_rep = typename ToDuration::rep;
        return ToDuration(static_cast<to_rep>(static_cast<CR>(duration.count()) / static_cast<CR>(CF::den)));
    }
};
 
template <typename ToDuration, typename CF, typename CR>
struct duration_cast_impl<ToDuration, CF, CR, false, true> {
    template <typename Rep, typename Period>
    [[nodiscard]] static constexpr auto cast(duration<Rep, Period> const& duration)
        noexcept(is_arithmetic_v<Rep> and is_arithmetic_v<typename ToDuration::rep>) -> ToDuration
    {
        using to_rep = typename ToDuration::rep;
        return ToDuration(static_cast<to_rep>(static_cast<CR>(duration.count()) * static_cast<CR>(CF::num)));
    }
};
 
template <typename ToDuration, typename CF, typename CR>
struct duration_cast_impl<ToDuration, CF, CR, true, true> {
    template <typename Rep, typename Period>
    [[nodiscard]] static constexpr auto cast(duration<Rep, Period> const& duration)
        noexcept(is_arithmetic_v<Rep> and is_arithmetic_v<typename ToDuration::rep>) -> ToDuration
    {
        using to_rep = typename ToDuration::rep;
        return ToDuration(static_cast<to_rep>(duration.count()));
    }
};
 
} // namespace detail

template <typename ToDur, typename Rep, typename Period>
    requires(detail::is_duration_v<ToDur>)
[[nodiscard]] constexpr auto duration_cast(duration<Rep, Period> const& duration)
    noexcept(is_arithmetic_v<Rep> and is_arithmetic_v<typename ToDur::rep>) -> ToDur
{
    using detail::duration_cast_impl;
    using cf   = ratio_divide<Period, typename ToDur::period>;
    using cr   = common_type_t<typename ToDur::rep, Rep, intmax_t>;
    using impl = duration_cast_impl<ToDur, cf, cr, cf::num == 1, cf::den == 1>;
    return impl::cast(duration);
}
 
} // namespace etl::chrono
 
#endif // TETL_CHRONO_DURATION_CAST_HPP