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// 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 "qgregoriancalendar_p.h"
#include "qcalendarmath_p.h"
#include <QtCore/qdatetime.h>
QT_BEGIN_NAMESPACE
using namespace QRoundingDown;
// Verification that QRoundingDown::qDivMod() works correctly:
static_assert(qDivMod<2>(-86400).quotient == -43200);
static_assert(qDivMod<2>(-86400).remainder == 0);
static_assert(qDivMod<86400>(-86400).quotient == -1);
static_assert(qDivMod<86400>(-86400).remainder == 0);
static_assert(qDivMod<86400>(-86401).quotient == -2);
static_assert(qDivMod<86400>(-86401).remainder == 86399);
static_assert(qDivMod<86400>(-100000).quotient == -2);
static_assert(qDivMod<86400>(-100000).remainder == 72800);
static_assert(qDivMod<86400>(-172799).quotient == -2);
static_assert(qDivMod<86400>(-172799).remainder == 1);
static_assert(qDivMod<86400>(-172800).quotient == -2);
static_assert(qDivMod<86400>(-172800).remainder == 0);
// Uncomment to verify error on bad denominator is clear and intelligible:
// static_assert(qDivMod<1>(17).remainder == 0);
// static_assert(qDivMod<0>(17).remainder == 0);
// static_assert(qDivMod<std::numeric_limits<unsigned>::max()>(17).remainder == 0);
/*!
\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<7>(jd) + 1;
}
bool QGregorianCalendar::dateToJulianDay(int year, int month, int day, qint64 *jd) const
{
return julianFromParts(year, month, day, jd);
}
QCalendar::YearMonthDay QGregorianCalendar::julianDayToDate(qint64 jd) const
{
return partsFromJulian(jd);
}
int QGregorianCalendar::yearStartWeekDay(int year)
{
// Equivalent to weekDayOfJulian(julianForParts({year, 1, 1})
const int y = year - (year < 0 ? 800 : 801);
return qMod<7>(y + qDiv<4>(y) - qDiv<100>(y) + qDiv<400>(y)) + 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;
}
/*
* 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).
*
* The source given uses 4801 BCE as base date; the following adjusts that by
* 4800 years to simplify part of the arithmetic (and match more closely what we
* do for Milankovic).
*/
using namespace QRomanCalendrical;
// End a Gregorian four-century cycle on 1 BC's leap day:
constexpr qint64 BaseJd = LeapDayGregorian1Bce;
// Every four centures there are 97 leap years:
constexpr unsigned FourCenturies = 400 * 365 + 97;
bool QGregorianCalendar::julianFromParts(int year, int month, int day, qint64 *jd)
{
Q_ASSERT(jd);
if (!validParts(year, month, day))
return false;
const auto yearDays = yearMonthToYearDays(year, month);
const qint64 y = yearDays.year;
const qint64 fromYear = 365 * y + qDiv<4>(y) - qDiv<100>(y) + qDiv<400>(y);
*jd = fromYear + yearDays.days + day + BaseJd ;
return true;
}
QCalendar::YearMonthDay QGregorianCalendar::partsFromJulian(qint64 jd)
{
const qint64 dayNumber = jd - BaseJd;
const qint64 century = qDiv<FourCenturies>(4 * dayNumber - 1);
const int dayInCentury = dayNumber - qDiv<4>(FourCenturies * century);
const int yearInCentury = qDiv<FourYears>(4 * dayInCentury - 1);
const int dayInYear = dayInCentury - qDiv<4>(FourYears * yearInCentury);
const int m = qDiv<FiveMonths>(5 * dayInYear - 3);
Q_ASSERT(m < 12 && m >= 0);
// That m is a month adjusted to March = 0, with Jan = 10, Feb = 11 in the previous year.
const int yearOffset = m < 10 ? 0 : 1;
const int y = 100 * century + yearInCentury + yearOffset;
const int month = m + 3 - 12 * yearOffset;
const int day = dayInYear - qDiv<5>(FiveMonths * m + 2);
// Adjust for no year 0
return QCalendar::YearMonthDay(y > 0 ? y : y - 1, month, day);
}
QT_END_NAMESPACE
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