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39
40 #include "qglobal.h"
41 #include "qjuliancalendar_p.h"
42 #include "qromancalendar_data_p.h"
43 #include "qcalendarmath_p.h"
44 #include <QtCore/qmath.h>
45 #include <QtCore/qlocale.h>
46 #include <QtCore/qdatetime.h>
47
48 QT_BEGIN_NAMESPACE
49
50 using namespace QRoundingDown;
51
52 /*!
53 \since 5.14
54
55 \class QJulianCalendar
56 \inmodule QtCore
57 \brief The QJulianCalendar class provides Julian calendar system
58 implementation.
59
60 \section1 Julian Calendar
61
62 The Julian calendar, proposed by Julius Caesar in 46 BC (708 AUC), was a
63 reform of the Roman calendar. It took effect on 1 January 45 BC (AUC 709),
64 by edict. It was the predominant calendar in the Roman world, most of
65 Europe, and in European settlements in the Americas and elsewhere, until it
66 was refined and gradually replaced by the Gregorian calendar,
67 promulgated in 1582 by Pope Gregory XIII.
68
69 The Julian calendar gains against the mean tropical year at the rate of one
70 day in 128 years. For the Gregorian calendar, the figure is one day in
71 3030 years. The difference in the average length of the year
72 between Julian (365.25 days) and Gregorian (365.2425 days) is 0.002%.
73
74 Source: \l {https://en.wikipedia.org/wiki/Julian_calendar}{Wikipedia page on
75 Julian Calendar}
76 */
77
QJulianCalendar()78 QJulianCalendar::QJulianCalendar()
79 : QRomanCalendar(QStringLiteral("Julian"), QCalendar::System::Julian) {}
80
name() const81 QString QJulianCalendar::name() const
82 {
83 return QStringLiteral("Julian");
84 }
85
calendarSystem() const86 QCalendar::System QJulianCalendar::calendarSystem() const
87 {
88 return QCalendar::System::Julian;
89 }
90
isLeapYear(int year) const91 bool QJulianCalendar::isLeapYear(int year) const
92 {
93 if (year == QCalendar::Unspecified || !year)
94 return false;
95
96 return qMod(year < 0 ? year + 1 : year, 4) == 0;
97 }
98
99 // Julian Day 0 was January the first in the proleptic Julian calendar's 4713 BC
100
dateToJulianDay(int year,int month,int day,qint64 * jd) const101 bool QJulianCalendar::dateToJulianDay(int year, int month, int day, qint64 *jd) const
102 {
103 Q_ASSERT(jd);
104 if (!isDateValid(year, month, day))
105 return false;
106 if (year < 0)
107 ++year;
108 const qint64 c0 = month < 3 ? -1 : 0;
109 const qint64 j1 = qDiv(1461 * (year + c0), 4);
110 const qint64 j2 = qDiv(153 * month - 1836 * c0 - 457, 5);
111 *jd = j1 + j2 + day + 1721117;
112 return true;
113 }
114
julianDayToDate(qint64 jd) const115 QCalendar::YearMonthDay QJulianCalendar::julianDayToDate(qint64 jd) const
116 {
117 const qint64 y2 = jd - 1721118;
118 const qint64 k2 = 4 * y2 + 3;
119 const qint64 k1 = 5 * qDiv(qMod(k2, 1461), 4) + 2;
120 const qint64 x1 = qDiv(k1, 153);
121 const qint64 c0 = qDiv(x1 + 2, 12);
122 const int y = qint16(qDiv(k2, 1461) + c0);
123 const int month = quint8(x1 - 12 * c0 + 3);
124 const int day = qDiv(qMod(k1, 153), 5) + 1;
125 return QCalendar::YearMonthDay(y > 0 ? y : y - 1, month, day);
126 }
127
128 QT_END_NAMESPACE
129