Add support for the Islamic Civil calendar

This has its own locale data, extracted from CLDR. This data may
potentially be shared with other variants on the Islamic calendar, so
is handled by a separate base-class, QHijriCalendar, on which such
variants may base their implementations.

[ChangeLog][QtCore][QCalendar] Added support for the Islamic Civil
calendar, controlled by feature islamiccivilcalendar, with locale data
that can be shared with other implementations, controlled by feature
hijricalendar.

Fixes: QTBUG-56675
Change-Id: Idf32d3da7034baa8ec5e66ef847e59a8a2f31cbd
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>

1 files changed, 125 insertions, 0 deletions

diff --git a/src/corelib/time/qislamiccivilcalendar.cpp b/src/corelib/time/qislamiccivilcalendar.cpp
new file mode 100644
index 0000000000..27c93f5c00
--- /dev/null
+++ b/src/corelib/time/qislamiccivilcalendar.cpp
@@ -0,0 +1,125 @@
+/****************************************************************************
+**
+** Copyright (C) 2018 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
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+****************************************************************************/
+
+#include "qglobal.h"
+#include "qislamiccivilcalendar_p.h"
+#include "qcalendarmath_p.h"
+#include <QtCore/qmath.h>
+
+QT_BEGIN_NAMESPACE
+
+using namespace QRoundingDown;
+
+/*!
+  \since 5.14
+
+  \class QIslamicCivilCalendar
+  \inmodule QtCore
+  \brief Implements a commonly-used computed version of the Islamic calendar.
+
+  \section1 Civil Islamic Calendar
+
+  QIslamicCivilCalendar implements a tabular version of the Hijri calendar which
+  is known as the Islamic Civil Calendar. It has the same numbering of years and
+  months, but the months are determined by arithmetical rules rather than by
+  observation or astronomical calculations.
+
+  \section2 Calendar Organization
+
+  The civil calendar follows the usual tabular scheme of odd-numbered months and
+  the last month of each leap year being 30 days long, the rest being 29 days
+  long. Its determination of leap years follows a 30-year cycle, in each of
+  which the years 2, 5, 7, 10, 13, 16, 18, 21, 24, 26 and 29 are leap years.
+
+  \sa QJijriCalendar, QCalendar
+*/
+
+QIslamicCivilCalendar::QIslamicCivilCalendar()
+    : QHijriCalendar(QStringLiteral("Islamic Civil"), QCalendar::System::IslamicCivil)
+{
+    registerAlias(QStringLiteral("islamic-civil")); // CLDR name
+    registerAlias(QStringLiteral("islamicc")); // old CLDR name, still (2018) used by Mozilla
+    // Until we have a oncrete implementation that knows all the needed ephemerides:
+    registerAlias(QStringLiteral("Islamic"));
+}
+
+QString QIslamicCivilCalendar::name() const
+{
+    return QStringLiteral("Islamic Civil");
+}
+
+QCalendar::System QIslamicCivilCalendar::calendarSystem() const
+{
+    return QCalendar::System::IslamicCivil;
+}
+
+bool QIslamicCivilCalendar::isLeapYear(int year) const
+{
+    if (year == QCalendar::Unspecified)
+        return false;
+    if (year < 0)
+        ++year;
+    return qMod(year * 11 + 14, 30) < 11;
+}
+
+bool QIslamicCivilCalendar::dateToJulianDay(int year, int month, int day, qint64 *jd) const
+{
+    Q_ASSERT(jd);
+    if (!isDateValid(year, month, day))
+        return false;
+    if (year <= 0)
+        ++year;
+    *jd = qDiv(10631 * year - 10617, 30)
+            + qDiv(325 * month - 320, 11)
+            + day + 1948439;
+    return true;
+}
+
+QCalendar::YearMonthDay QIslamicCivilCalendar::julianDayToDate(qint64 jd) const
+{
+    const qint64 epoch = 1948440;
+    const int32_t k2 = 30 * (jd - epoch) + 15;
+    const int32_t k1 = 11 * qDiv(qMod(k2, 10631), 30) + 5;
+    int y = qDiv(k2, 10631) + 1;
+    const int month = qDiv(k1, 325) + 1;
+    const int day = qDiv(qMod(k1, 325), 11) + 1;
+    return QCalendar::YearMonthDay(y > 0 ? y : y - 1, month, day);
+}
+
+QT_END_NAMESPACE