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+/****************************************************************************
+**
+** Copyright (C) 2018 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of the QtCore module of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:LGPL$
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and The Qt Company. For licensing terms
+** and conditions see https://www.qt.io/terms-conditions. For further
+** information use the contact form at https://www.qt.io/contact-us.
+**
+** GNU Lesser General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU Lesser
+** General Public License version 3 as published by the Free Software
+** Foundation and appearing in the file LICENSE.LGPL3 included in the
+** packaging of this file. Please review the following information to
+** ensure the GNU Lesser General Public License version 3 requirements
+** will be met: https://www.gnu.org/licenses/lgpl-3.0.html.
+**
+** GNU General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU
+** General Public License version 2.0 or (at your option) the GNU General
+** Public license version 3 or any later version approved by the KDE Free
+** Qt Foundation. The licenses are as published by the Free Software
+** Foundation and appearing in the file LICENSE.GPL2 and LICENSE.GPL3
+** included in the packaging of this file. Please review the following
+** information to ensure the GNU General Public License requirements will
+** be met: https://www.gnu.org/licenses/gpl-2.0.html and
+** https://www.gnu.org/licenses/gpl-3.0.html.
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#include "qglobal.h"
+#include "qjuliancalendar_p.h"
+#include "qromancalendar_data_p.h"
+#include "qcalendarmath_p.h"
+#include <QtCore/qmath.h>
+#include <QtCore/qlocale.h>
+#include <QtCore/qdatetime.h>
+
+QT_BEGIN_NAMESPACE
+
+using namespace QRoundingDown;
+
+/*!
+    \since 5.14
+
+    \class QJulianCalendar
+    \inmodule QtCore
+    \brief The QJulianCalendar class provides Julian calendar system
+    implementation.
+
+    \section1 Julian Calendar
+
+    The Julian calendar, proposed by Julius Caesar in 46 BC (708 AUC), was a
+    reform of the Roman calendar. It took effect on 1 January 45 BC (AUC 709),
+    by edict. It was the predominant calendar in the Roman world, most of
+    Europe, and in European settlements in the Americas and elsewhere, until it
+    was refined and gradually replaced by the Gregorian calendar,
+    promulgated in 1582 by Pope Gregory XIII.
+
+    The Julian calendar gains against the mean tropical year at the rate of one
+    day in 128 years. For the Gregorian calendar, the figure is one day in
+    3030 years. The difference in the average length of the year
+    between Julian (365.25 days) and Gregorian (365.2425 days) is 0.002%.
+
+    Source: \l {https://en.wikipedia.org/wiki/Julian_calendar}{Wikipedia page on
+    Julian Calendar}
+ */
+
+QJulianCalendar::QJulianCalendar()
+    : QRomanCalendar(QStringLiteral("Julian"), QCalendar::System::Julian) {}
+
+QString QJulianCalendar::name() const
+{
+    return QStringLiteral("Julian");
+}
+
+QCalendar::System QJulianCalendar::calendarSystem() const
+{
+    return QCalendar::System::Julian;
+}
+
+bool QJulianCalendar::isLeapYear(int year) const
+{
+    if (year == QCalendar::Unspecified || !year)
+        return false;
+
+    return qMod(year < 0 ? year + 1 : year, 4) == 0;
+}
+
+// Julian Day 0 was January the first in the proleptic Julian calendar's 4713 BC
+
+bool QJulianCalendar::dateToJulianDay(int year, int month, int day, qint64 *jd) const
+{
+    Q_ASSERT(jd);
+    if (!isDateValid(year, month, day))
+        return false;
+    if (year < 0)
+        ++year;
+    const qint64 c0 = month < 3 ? -1 : 0;
+    const qint64 j1 = qDiv(1461 * (year + c0), 4);
+    const qint64 j2 = qDiv(153 * month - 1836 * c0 - 457, 5);
+    *jd = j1 + j2 + day + 1721117;
+    return true;
+}
+
+QCalendar::YearMonthDay QJulianCalendar::julianDayToDate(qint64 jd) const
+{
+    const qint64 y2 = jd - 1721118;
+    const qint64 k2 = 4 * y2 + 3;
+    const qint64 k1 = 5 * qDiv(qMod(k2, 1461), 4) + 2;
+    const qint64 x1 = qDiv(k1, 153);
+    const qint64 c0 = qDiv(x1 + 2, 12);
+    const int y = qint16(qDiv(k2, 1461) + c0);
+    const int month = quint8(x1 - 12 * c0 + 3);
+    const int day = qDiv(qMod(k1, 153), 5) + 1;
+    return QCalendar::YearMonthDay(y > 0 ? y : y - 1, month, day);
+}
+
+QT_END_NAMESPACE