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diff --git a/src/corelib/time/qmilankoviccalendar.cpp b/src/corelib/time/qmilankoviccalendar.cpp
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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 "qmilankoviccalendar_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 QMilankovicCalendar
+    \inmodule QtCore
+    \brief The QMilankovicCalendar class provides Milanković calendar system
+    implementation.
+
+    \section1
+
+    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}
+ */
+
+QMilankovicCalendar::QMilankovicCalendar()
+    : QRomanCalendar(QStringLiteral("Milankovic"), QCalendar::System::Milankovic) {}
+
+QString QMilankovicCalendar::name() const
+{
+    return QStringLiteral("Milankovic");
+}
+
+QCalendar::System QMilankovicCalendar::calendarSystem() const
+{
+    return QCalendar::System::Milankovic;
+}
+
+bool QMilankovicCalendar::isLeapYear(int year) const
+{
+    if (year == QCalendar::Unspecified)
+        return false;
+    if (year <= 0)
+        ++year;
+    if (qMod(year, 4))
+        return false;
+    if (qMod(year, 100) == 0) {
+        const qint16 century = qMod(qDiv(year, 100), 9);
+        if (century != 2 && century != 6)
+            return false;
+    }
+    return true;
+}
+
+bool QMilankovicCalendar::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 qint16 c0 = month < 3 ? -1 : 0;
+    const qint16 x1 = month - 12 * c0 - 3;
+    const qint16 x4 = year + c0;
+    const qint16 x3 = qDiv(x4, 100);
+    const qint16 x2 = qMod(x4, 100);
+    *jd = qDiv(328718 * x3 + 6, 9)
+        + qDiv(36525 * x2 , 100)
+        + qDiv(153 * x1 + 2 , 5)
+        + day + 1721119;
+    return true;
+}
+
+QCalendar::YearMonthDay  QMilankovicCalendar::julianDayToDate(qint64 jd) const
+{
+    const qint64 k3 = 9 * (jd - 1721120) + 2;
+    const qint64 x3 = qDiv(k3, 328718);
+    const qint64 k2 = 100 * qDiv(qMod(k3, 328718), 9) + 99;
+    const qint64 k1 = qDiv(qMod(k2, 36525), 100) * 5 + 2;
+    const qint64 x2 = qDiv(k2, 36525);
+    const qint64 x1 = qDiv(5 * qDiv(qMod(k2, 36525), 100) + 2, 153);
+    const qint64 c0 = qDiv(x1 + 2, 12);
+    const int y = 100 * x3 + x2 + c0;
+    const int month = 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