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/****************************************************************************
**
** Copyright (C) 2021 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 "qgregoriancalendar_p.h"
#include "qcalendarmath_p.h"
#include <QtCore/qdatetime.h>
QT_BEGIN_NAMESPACE
using namespace QRoundingDown;
/*!
\since 5.14
\class QGregorianCalendar
\inmodule QtCore
\brief The QGregorianCalendar class implements the Gregorian calendar.
\section1 The Gregorian Calendar
The Gregorian calendar is a refinement of the earlier Julian calendar,
itself a late form of the Roman calendar. It is widely used.
\sa QRomanCalendar, QJulianCalendar, QCalendar
*/
QString QGregorianCalendar::name() const
{
return QStringLiteral("Gregorian");
}
QStringList QGregorianCalendar::nameList()
{
return {
QStringLiteral("Gregorian"),
QStringLiteral("gregory"),
};
}
bool QGregorianCalendar::isLeapYear(int year) const
{
return leapTest(year);
}
bool QGregorianCalendar::leapTest(int year)
{
if (year == QCalendar::Unspecified)
return false;
// No year 0 in Gregorian calendar, so -1, -5, -9 etc are leap years
if (year < 1)
++year;
return year % 4 == 0 && (year % 100 != 0 || year % 400 == 0);
}
// Duplicating code from QRomanCalendar, but inlining isLeapYear() as leapTest():
int QGregorianCalendar::monthLength(int month, int year)
{
if (month < 1 || month > 12)
return 0;
if (month == 2)
return leapTest(year) ? 29 : 28;
return 30 | ((month & 1) ^ (month >> 3));
}
bool QGregorianCalendar::validParts(int year, int month, int day)
{
return year && 0 < day && day <= monthLength(month, year);
}
int QGregorianCalendar::weekDayOfJulian(qint64 jd)
{
return qMod(jd, 7) + 1;
}
bool QGregorianCalendar::dateToJulianDay(int year, int month, int day, qint64 *jd) const
{
return julianFromParts(year, month, day, jd);
}
bool QGregorianCalendar::julianFromParts(int year, int month, int day, qint64 *jd)
{
Q_ASSERT(jd);
if (!validParts(year, month, day))
return false;
if (year < 0)
++year;
/*
* Math from The Calendar FAQ at http://www.tondering.dk/claus/cal/julperiod.php
* This formula is correct for all julian days, when using mathematical integer
* division (round to negative infinity), not c++11 integer division (round to zero)
*/
int a = month < 3 ? 1 : 0;
qint64 y = qint64(year) + 4800 - a;
int m = month + 12 * a - 3;
*jd = day + qDiv(153 * m + 2, 5) - 32045
+ 365 * y + qDiv(y, 4) - qDiv(y, 100) + qDiv(y, 400);
return true;
}
int QGregorianCalendar::yearStartWeekDay(int year)
{
// Equivalent to weekDayOfJulian(julianForParts({year, 1, 1})
const int y = year - (year < 0 ? 800 : 801);
return qMod(y + qDiv(y, 4) - qDiv(y, 100) + qDiv(y, 400), 7) + 1;
}
int QGregorianCalendar::yearSharingWeekDays(QDate date)
{
// Returns a post-epoch year, no later than 2400, that has the same pattern
// of week-days (in the proleptic Gregorian calendar) as the year in which
// the given date falls. This will be the year in question if it's in the
// given range. Otherwise, the returned year's last two (decimal) digits
// won't coincide with the month number or day-of-month of the given date.
// For positive years, except when necessary to avoid such a clash, the
// returned year's last two digits shall coincide with those of the original
// year.
// Needed when formatting dates using system APIs with limited year ranges
// and possibly only a two-digit year. (The need to be able to safely
// replace the two-digit form of the returned year with a suitable form of
// the true year, when they don't coincide, is why the last two digits are
// treated specially.)
static_assert((400 * 365 + 97) % 7 == 0);
// A full 400-year cycle of the Gregorian calendar has 97 + 400 * 365 days;
// as 365 is one more than a multiple of seven and 497 is a multiple of
// seven, that full cycle is a whole number of weeks. So adding a multiple
// of four hundred years should get us a result that meets our needs.
const int year = date.year();
int res = (year < 1970
? 2400 - (2000 - (year < 0 ? year + 1 : year)) % 400
: year > 2399 ? 2000 + (year - 2000) % 400 : year);
Q_ASSERT(res > 0);
if (res != year) {
const int lastTwo = res % 100;
if (lastTwo == date.month() || lastTwo == date.day()) {
Q_ASSERT(lastTwo && !(lastTwo & ~31));
// Last two digits of these years are all > 31:
static constexpr int usual[] = { 2198, 2199, 2098, 2099, 2399, 2298, 2299 };
static constexpr int leaps[] = { 2396, 2284, 2296, 2184, 2196, 2084, 2096 };
// Indexing is: first day of year's day-of-week, Monday = 0, one less
// than Qt's, as it's simpler to subtract one than to s/7/0/.
res = (leapTest(year) ? leaps : usual)[yearStartWeekDay(year) - 1];
}
Q_ASSERT(QDate(res, 1, 1).dayOfWeek() == QDate(year, 1, 1).dayOfWeek());
Q_ASSERT(QDate(res, 12, 31).dayOfWeek() == QDate(year, 12, 31).dayOfWeek());
}
Q_ASSERT(res >= 1970 && res <= 2400);
return res;
}
QCalendar::YearMonthDay QGregorianCalendar::julianDayToDate(qint64 jd) const
{
return partsFromJulian(jd);
}
QCalendar::YearMonthDay QGregorianCalendar::partsFromJulian(qint64 jd)
{
/*
* Math from The Calendar FAQ at http://www.tondering.dk/claus/cal/julperiod.php
* This formula is correct for all julian days, when using mathematical integer
* division (round to negative infinity), not c++11 integer division (round to zero)
*/
qint64 a = jd + 32044;
qint64 b = qDiv(4 * a + 3, 146097);
int c = a - qDiv(146097 * b, 4);
int d = qDiv(4 * c + 3, 1461);
int e = c - qDiv(1461 * d, 4);
int m = qDiv(5 * e + 2, 153);
int y = 100 * b + d - 4800 + qDiv(m, 10);
// Adjust for no year 0
int year = y > 0 ? y : y - 1;
int month = m + 3 - 12 * qDiv(m, 10);
int day = e - qDiv(153 * m + 2, 5) + 1;
return QCalendar::YearMonthDay(year, month, day);
}
QT_END_NAMESPACE
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