qmilankoviccalendar.cpp

++ // Copyright (C) 2021 The Qt Company Ltd.

++ // SPDX-License-Identifier: LicenseRef-Qt-Commercial OR LGPL-3.0-only OR GPL-2.0-only OR GPL-3.0-only

++ // Qt-Security score:significant reason:default

++

++ #include "qglobal.h"

++ #include "qmilankoviccalendar_p.h"

++ #include "qcalendarmath_p.h"

++

++ #include <QtCore/qdatetime.h>

++

++ QT_BEGIN_NAMESPACE

++

++ using namespace QRoundingDown;

++

++ /*!

++     \since 5.14

++     \internal

++

++     \class QMilankovicCalendar

++     \inmodule QtCore

++     \brief The QMilankovicCalendar class provides Milanković calendar system

++     implementation.

++

++     The Revised Julian calendar, also known as the Milanković calendar, or,

++     less formally, new calendar, is a calendar, developed and proposed by the

++     Serbian scientist Milutin Milanković in 1923, which effectively discontinued

++     the 340 years of divergence between the naming of dates sanctioned by those

++     Eastern Orthodox churches adopting it and the Gregorian calendar that has

++     come to predominate worldwide. This calendar was intended to replace the

++     ecclesiastical calendar based on the Julian calendar hitherto in use by all

++     of the Eastern Orthodox Church. The Revised Julian calendar temporarily

++     aligned its dates with the Gregorian calendar proclaimed in 1582 by Pope

++     Gregory XIII for adoption by the Christian world. The calendar has been

++     adopted by the Orthodox churches of Constantinople, Albania, Alexandria,

++     Antioch, Bulgaria, Cyprus, Greece, Poland, and Romania.

++

++     Source: \l {https://en.wikipedia.org/wiki/Revised_Julian_calendar}{Wikipedia

++     page on Milanković Calendar}

++  */

++

++ QString QMilankovicCalendar::name() const

++ {

++     return QStringLiteral("Milankovic");

++ }

++

++ QStringList QMilankovicCalendar::nameList()

++ {

++     return { QStringLiteral("Milankovic") };

++ }

++

++ bool QMilankovicCalendar::isLeapYear(int year) const

++ {

++     if (year == QCalendar::Unspecified)

++         return false;

++     if (year <= 0)

++         ++year;

++     if (qMod<4>(year))

++         return false;

++     const auto yeardm = qDivMod<100>(year);

++     if (yeardm.remainder == 0) {

++         const qint16 century = qMod<9>(yeardm.quotient);

++         if (century != 2 && century != 6)

++             return false;

++     }

++     return true;

++ }

++

++ using namespace QRomanCalendrical;

++ // End a Milankovic nine-century cycle on 1 BC, Feb 28 (Gregorian Feb 29):

++ constexpr qint64 MilankovicBaseJd = LeapDayGregorian1Bce;

++ // Leap years every 4 years, except for 7 turn-of-century years per nine centuries:

++ constexpr unsigned NineCenturies = 365 * 900 + 900 / 4 - 7;

++ // When the turn-of-century is a leap year, the century has 25 leap years in it:

++ constexpr unsigned LeapCentury = 365 * 100 + 25;

++

++ bool QMilankovicCalendar::dateToJulianDay(int year, int month, int day, qint64 *jd) const

++ {

++     Q_ASSERT(jd);

++     if (!isDateValid(year, month, day))

++         return false;

++

++     const auto yearDays = yearMonthToYearDays(year, month);

++     const auto centuryYear = qDivMod<100>(yearDays.year);

++     const qint64 fromYear = qDiv<9>(NineCenturies * centuryYear.quotient + 6)

++                           + qDiv<100>(LeapCentury * centuryYear.remainder);

++     *jd = fromYear + yearDays.days + day + MilankovicBaseJd;

++     return true;

++ }

++

++ QCalendar::YearMonthDay QMilankovicCalendar::julianDayToDate(qint64 jd) const

++ {

++     using Bound = std::numeric_limits<int>;

++     constexpr qint64 maxInt = Bound::max();

++

++     const auto century9Day = qDivMod<NineCenturies>(9 * (jd - MilankovicBaseJd) - 7);

++     // Its remainder changes by 9 per day, except roughly once per century.

++     const auto year100Day = qDivMod<LeapCentury>(100 * qDiv<9>(century9Day.remainder) + 99);

++     // Its remainder changes by 100 per day, except roughly once per year.

++     const auto ymd = dayInYearToYmd(qDiv<100>(year100Day.remainder));

++

++     const qint64 y = 100 * century9Day.quotient + year100Day.quotient + ymd.year;

++     // We'll be subtracting 1 if negative, so -maxInt is the lower bound, not Bound::min().

++     if (y > maxInt || y < -maxInt)

++         return {};

++

++     int year = static_cast<int>(y);

++     return QCalendar::YearMonthDay(year > 0 ? year : year - 1, ymd.month, ymd.day);

++ }

++

++ QT_END_NAMESPACE

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