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39
40#include "qgregoriancalendar_p.h"
41#include "qcalendarmath_p.h"
42#include <QtCore/qdatetime.h>
43
44QT_BEGIN_NAMESPACE
45
46using namespace QRoundingDown;
47
48/*!
49 \since 5.14
50
51 \class QGregorianCalendar
52 \inmodule QtCore
53 \brief The QGregorianCalendar class implements the Gregorian calendar.
54
55 \section1 The Gregorian Calendar
56
57 The Gregorian calendar is a refinement of the earlier Julian calendar,
58 itself a late form of the Roman calendar. It is widely used.
59
60 \sa QRomanCalendar, QJulianCalendar, QCalendar
61*/
62
63QGregorianCalendar::QGregorianCalendar()
64 : QRomanCalendar(QStringLiteral("Gregorian"), QCalendar::System::Gregorian)
65{
66 registerAlias(QStringLiteral("gregory"));
67}
68
69QString QGregorianCalendar::name() const
70{
71 return QStringLiteral("Gregorian");
72}
73
74QCalendar::System QGregorianCalendar::calendarSystem() const
75{
76 return QCalendar::System::Gregorian;
77}
78
79bool QGregorianCalendar::isLeapYear(int year) const
80{
81 return leapTest(year);
82}
83
84bool QGregorianCalendar::leapTest(int year)
85{
86 if (year == QCalendar::Unspecified)
87 return false;
88
89 // No year 0 in Gregorian calendar, so -1, -5, -9 etc are leap years
90 if (year < 1)
91 ++year;
92
93 return year % 4 == 0 && (year % 100 != 0 || year % 400 == 0);
94}
95
96// Duplicating code from QRomanCalendar, but inlining isLeapYear() as leapTest():
97int QGregorianCalendar::monthLength(int month, int year)
98{
99 if (month < 1 || month > 12)
100 return 0;
101
102 if (month == 2)
103 return leapTest(year) ? 29 : 28;
104
105 return 30 | ((month & 1) ^ (month >> 3));
106}
107
108bool QGregorianCalendar::validParts(int year, int month, int day)
109{
110 return year && 0 < day && day <= monthLength(month, year);
111}
112
113int QGregorianCalendar::weekDayOfJulian(qint64 jd)
114{
115 return qMod(jd, 7) + 1;
116}
117
118bool QGregorianCalendar::dateToJulianDay(int year, int month, int day, qint64 *jd) const
119{
120 return julianFromParts(year, month, day, jd);
121}
122
123bool QGregorianCalendar::julianFromParts(int year, int month, int day, qint64 *jd)
124{
125 Q_ASSERT(jd);
126 if (!validParts(year, month, day))
127 return false;
128
129 if (year < 0)
130 ++year;
131
132 /*
133 * Math from The Calendar FAQ at http://www.tondering.dk/claus/cal/julperiod.php
134 * This formula is correct for all julian days, when using mathematical integer
135 * division (round to negative infinity), not c++11 integer division (round to zero)
136 */
137 int a = month < 3 ? 1 : 0;
138 qint64 y = qint64(year) + 4800 - a;
139 int m = month + 12 * a - 3;
140 *jd = day + qDiv(153 * m + 2, 5) - 32045
141 + 365 * y + qDiv(y, 4) - qDiv(y, 100) + qDiv(y, 400);
142 return true;
143}
144
145QCalendar::YearMonthDay QGregorianCalendar::julianDayToDate(qint64 jd) const
146{
147 return partsFromJulian(jd);
148}
149
150QCalendar::YearMonthDay QGregorianCalendar::partsFromJulian(qint64 jd)
151{
152 /*
153 * Math from The Calendar FAQ at http://www.tondering.dk/claus/cal/julperiod.php
154 * This formula is correct for all julian days, when using mathematical integer
155 * division (round to negative infinity), not c++11 integer division (round to zero)
156 */
157 qint64 a = jd + 32044;
158 qint64 b = qDiv(4 * a + 3, 146097);
159 int c = a - qDiv(146097 * b, 4);
160
161 int d = qDiv(4 * c + 3, 1461);
162 int e = c - qDiv(1461 * d, 4);
163 int m = qDiv(5 * e + 2, 153);
164
165 int y = 100 * b + d - 4800 + qDiv(m, 10);
166
167 // Adjust for no year 0
168 int year = y > 0 ? y : y - 1;
169 int month = m + 3 - 12 * qDiv(m, 10);
170 int day = e - qDiv(153 * m + 2, 5) + 1;
171
172 return QCalendar::YearMonthDay(year, month, day);
173}
174
175QT_END_NAMESPACE
176