qislamiccivilcalendar.cpp

Go to the documentation of this file.

// 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 "qislamiccivilcalendar_p.h"
#include "qcalendarmath_p.h"
 
QT_BEGIN_NAMESPACE
 
using namespace QRoundingDown;
 
QString QIslamicCivilCalendar::name() const
{
    return QStringLiteral("Islamic Civil");
}
 
QStringList QIslamicCivilCalendar::nameList()
{
    return {
        QStringLiteral("Islamic Civil"),
        QStringLiteral("islamic-civil"), // CLDR name
        QStringLiteral("islamicc"), // old CLDR name, still (2018) used by Mozilla
        // Until we have a concrete implementation that knows all the needed ephemerides:
        QStringLiteral("Islamic"),
    };
}
 
bool QIslamicCivilCalendar::isLeapYear(int year) const
{
    if (year == QCalendar::Unspecified)
        return false;
    if (year < 0)
        ++year;
    return qMod<30>(year * 11 + 14) < 11;
}
 
// First day of first year (Gregorian 622 CE July 19th) is the base date here:
constexpr qint64 EpochJd = 1948440;
// Each 30 years has 11 leap years of 355 days and 19 ordinary years of 354:
constexpr unsigned ThirtyYears = 11 * 355 + 19 * 354;
// The first eleven months of the year alternate 30, 29, ..., 29, 30 days in length.
constexpr unsigned ElevenMonths = 6 * 30 + 5 * 29;
 
bool QIslamicCivilCalendar::dateToJulianDay(int year, int month, int day, qint64 *jd) const
{
    Q_ASSERT(jd);
    if (!isDateValid(year, month, day))
        return false;
 
    *jd = qDiv<30>(qint64(ThirtyYears) * (year > 0 ? year - 1 : year) + 14)
        + qDiv<11>(ElevenMonths * (month - 1) + 5)
        + day + EpochJd - 1;
    return true;
}
 
QCalendar::YearMonthDay QIslamicCivilCalendar::julianDayToDate(qint64 jd) const
{
    const auto year30Day = qDivMod<ThirtyYears>(30 * (jd - EpochJd) + 15);
    // Its remainder changes by 30 per day, except roughly yearly.
    const auto month11Day = qDivMod<ElevenMonths>(11 * qDiv<30>(year30Day.remainder) + 5);
    // Its remainder changes by 11 per day except roughly monthly.
    const int month = month11Day.quotient + 1;
    const int day = qDiv<11>(month11Day.remainder) + 1;
    const int y = year30Day.quotient + 1;
    return QCalendar::YearMonthDay(y > 0 ? y : y - 1, month, day);
}
 
QT_END_NAMESPACE