julian_conversions.hpp

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// SPDX-License-Identifier: MIT
#pragma once
#ifndef TIME_SHIELD_HEADER_ASTRONOMY_JULIAN_CONVERSIONS_HPP_INCLUDED
#define TIME_SHIELD_HEADER_ASTRONOMY_JULIAN_CONVERSIONS_HPP_INCLUDED
 
 
#include <time_shield/core.hpp>
 
#include <cmath>
#include <cstdint>
 
namespace time_shield {
 
    namespace detail {
 
        inline jd_t gregorian_dmy_to_jd_unchecked(double day, int64_t month, int64_t year) noexcept {
            if (month == 1 || month == 2) {
                year -= 1;
                month += 12;
            }
            const double a = std::floor(static_cast<double>(year) / 100.0);
            const double b = 2.0 - a + std::floor(a / 4.0);
            const double jd = std::floor(365.25 * (static_cast<double>(year) + 4716.0))
                            + std::floor(30.6000001 * (static_cast<double>(month) + 1.0))
                            + day + b - 1524.5;
            return static_cast<jd_t>(jd);
        }
 
        inline jdn_t gregorian_dmy_to_jdn_unchecked(int64_t day, int64_t month, int64_t year) noexcept {
            const int64_t a = (14LL - month) / 12LL;
            const int64_t y = year + 4800LL - a;
            const int64_t m = month + 12LL * a - 3LL;
            const int64_t jdn = day
                              + (153LL * m + 2LL) / 5LL
                              + 365LL * y
                              + y / 4LL
                              - y / 100LL
                              + y / 400LL
                              - 32045LL;
            return static_cast<jdn_t>(jdn);
        }
 
        inline double day_fraction_from_hms(
                int hour,
                int minute,
                int second,
                int millisecond) noexcept {
            return (static_cast<double>(hour) / 24.0) +
                   (static_cast<double>(minute) / (24.0 * 60.0)) +
                   ((static_cast<double>(second) + static_cast<double>(millisecond) / 1000.0)
                     / static_cast<double>(SEC_PER_DAY));
        }
 
    } // namespace detail
 
    inline jd_t fts_to_jd(fts_t ts) noexcept {
        return static_cast<jd_t>(2440587.5)
             + static_cast<jd_t>(ts) / static_cast<jd_t>(SEC_PER_DAY);
    }
 
    inline jd_t ts_to_jd(ts_t ts) noexcept {
        return fts_to_jd(static_cast<fts_t>(ts));
    }
 
    inline jd_t gregorian_ymd_to_jd(
            year_t year,
            int month,
            int day,
            int hour = 0,
            int minute = 0,
            int second = 0,
            int millisecond = 0) noexcept {
        return detail::gregorian_dmy_to_jd_unchecked(
                static_cast<double>(day) + detail::day_fraction_from_hms(hour, minute, second, millisecond),
                static_cast<int64_t>(month),
                static_cast<int64_t>(year));
    }
 
    inline mjd_t fts_to_mjd(fts_t ts) noexcept {
        return static_cast<mjd_t>(fts_to_jd(ts) - 2400000.5);
    }
 
    inline mjd_t ts_to_mjd(ts_t ts) noexcept {
        return static_cast<mjd_t>(fts_to_mjd(static_cast<fts_t>(ts)));
    }
 
    inline jdn_t gregorian_ymd_to_jdn(year_t year, int month, int day) noexcept {
        return detail::gregorian_dmy_to_jdn_unchecked(
                static_cast<int64_t>(day),
                static_cast<int64_t>(month),
                static_cast<int64_t>(year));
    }
 
    inline bool try_gregorian_ymd_to_jd(
            year_t year,
            int month,
            int day,
            int hour,
            int minute,
            int second,
            int millisecond,
            jd_t& out) noexcept {
        if (!is_valid_date(year, month, day) || !is_valid_time(hour, minute, second, millisecond)) {
            return false;
        }
        out = gregorian_ymd_to_jd(year, month, day, hour, minute, second, millisecond);
        return true;
    }
 
    inline bool try_gregorian_ymd_to_jdn(
            year_t year,
            int month,
            int day,
            jdn_t& out) noexcept {
        if (!is_valid_date(year, month, day)) {
            return false;
        }
        const int64_t a = (14LL - static_cast<int64_t>(month)) / 12LL;
        const int64_t y = static_cast<int64_t>(year) + 4800LL - a;
        const int64_t m = static_cast<int64_t>(month) + 12LL * a - 3LL;
        const int64_t jdn = static_cast<int64_t>(day)
                          + (153LL * m + 2LL) / 5LL
                          + 365LL * y
                          + y / 4LL
                          - y / 100LL
                          + y / 400LL
                          - 32045LL;
        if (jdn < 0) {
            return false;
        }
        out = static_cast<jdn_t>(jdn);
        return true;
    }
 
} // namespace time_shield
 
#endif // TIME_SHIELD_HEADER_ASTRONOMY_JULIAN_CONVERSIONS_HPP_INCLUDED