qjuliancalendar.cpp

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// 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
 
#include "qglobal.h"
#include "qjuliancalendar_p.h"
#include "qromancalendar_data_p.h"
#include "qcalendarmath_p.h"
 
#include <QtCore/qdatetime.h>
 
QT_BEGIN_NAMESPACE
 
using namespace QRoundingDown;
 
QString QJulianCalendar::name() const
{
    return QStringLiteral("Julian");
}
 
QStringList QJulianCalendar::nameList()
{
    return { QStringLiteral("Julian") };
}
 
bool QJulianCalendar::isLeapYear(int year) const
{
    if (year == QCalendar::Unspecified || !year)
        return false;
 
    return qMod<4>(year < 0 ? year + 1 : year) == 0;
}
 
// Julian Day 0 was January the first in the proleptic Julian calendar's 4713 BC.
using namespace QRomanCalendrical;
// End a Julian four-year cycle on 1 BC's leap day (Gregorian Feb 27th):
constexpr qint64 JulianBaseJd = LeapDayGregorian1Bce - 2;
 
bool QJulianCalendar::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);
    *jd = qDiv<4>(FourYears * yearDays.year) + yearDays.days + day + JulianBaseJd;
    return true;
}
 
QCalendar::YearMonthDay QJulianCalendar::julianDayToDate(qint64 jd) const
{
    const auto year4Day = qDivMod<FourYears>(4 * (jd - JulianBaseJd) - 1);
    // Its remainder changes by 4 per day, except at roughly yearly quotient steps.
    const auto ymd = dayInYearToYmd(qDiv<4>(year4Day.remainder));
    const int y = year4Day.quotient + ymd.year;
    return QCalendar::YearMonthDay(y > 0 ? y : y - 1, ymd.month, ymd.day);
}
 
QT_END_NAMESPACE