QDateTime: Remove Julian Calendar

Convert QDate to only use Gregorian calendar and not Julian calendar
before 1582.  In future the Julian can be used via proper calendar
classes.

Change-Id: I547a3550332057a0ab1be616706630b6afaceffc
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

1 files changed, 36 insertions, 129 deletions

diff --git a/src/corelib/tools/qdatetime.cpp b/src/corelib/tools/qdatetime.cpp
index e05eb371dd..8649690c72 100644
--- a/src/corelib/tools/qdatetime.cpp
+++ b/src/corelib/tools/qdatetime.cpp
@@ -82,7 +82,7 @@ enum {
     MSECS_PER_HOUR = 3600000,
     SECS_PER_MIN = 60,
     MSECS_PER_MIN = 60000,
-    JULIAN_DAY_FOR_EPOCH = 2440588 // result of julianDayFromGregorianDate(1970, 1, 1)
+    JULIAN_DAY_FOR_EPOCH = 2440588 // result of julianDayFromDate(1970, 1, 1)
 };
 
 static inline QDate fixedDate(int y, int m, int d)
@@ -92,66 +92,41 @@ static inline QDate fixedDate(int y, int m, int d)
     return result;
 }
 
-static inline qint64 julianDayFromGregorianDate(qint64 year, int month, int day)
+static inline qint64 julianDayFromDate(qint64 year, int month, int day)
 {
-    // Gregorian calendar starting from October 15, 1582
+    // Gregorian calendar
     // Algorithm from Henry F. Fliegel and Thomas C. Van Flandern
+
+    if (year < 0)
+        ++year;
+
     return (1461 * (year + 4800 + (month - 14) / 12)) / 4
            + (367 * (month - 2 - 12 * ((month - 14) / 12))) / 12
            - (3 * ((year + 4900 + (month - 14) / 12) / 100)) / 4
            + day - 32075;
 }
 
-static qint64 julianDayFromDate(qint64 year, int month, int day)
-{
-    if (year > 1582 || (year == 1582 && (month > 10 || (month == 10 && day >= 15)))) {
-        return julianDayFromGregorianDate(year, month, day);
-    } else if (year < 1582 || (year == 1582 && (month < 10 || (month == 10 && day <= 4)))) {
-        // Julian calendar until October 4, 1582
-        // Algorithm from Frequently Asked Questions about Calendars by Claus Toendering
-        if (year < 0)
-            ++year;
-        int a = (14 - month) / 12;
-        return (153 * (month + (12 * a) - 3) + 2) / 5
-               + (1461 * (year + 4800 - a)) / 4
-               + day - 32083;
-    } else {
-        // the day following October 4, 1582 is October 15, 1582
-        return std::numeric_limits<qint64>::min(); // i.e. nullJd()
-    }
-}
-
 static void getDateFromJulianDay(qint64 julianDay, int *year, int *month, int *day)
 {
     int y, m, d;
 
-    if (julianDay >= 2299161) {
-        // Gregorian calendar starting from October 15, 1582
-        // This algorithm is from Henry F. Fliegel and Thomas C. Van Flandern
-        qint64 ell, n, i, j;  //TODO These will need to be bigger to prevent overflow!!!
-        ell = julianDay + 68569;
-        n = (4 * ell) / 146097;
-        ell = ell - (146097 * n + 3) / 4;
-        i = (4000 * (ell + 1)) / 1461001;
-        ell = ell - (1461 * i) / 4 + 31;
-        j = (80 * ell) / 2447;
-        d = ell - (2447 * j) / 80;
-        ell = j / 11;
-        m = j + 2 - (12 * ell);
-        y = 100 * (n - 49) + i + ell;
-    } else {
-        // Julian calendar until October 4, 1582
-        // Algorithm from Frequently Asked Questions about Calendars by Claus Toendering
-        julianDay += 32082;
-        qint64 dd = (4 * julianDay + 3) / 1461;  //TODO These may need to be bigger to prevent overflow!!!
-        qint64 ee = julianDay - (1461 * dd) / 4;  //TODO These may need to be bigger to prevent overflow!!!
-        qint64 mm = ((5 * ee) + 2) / 153;  //TODO These may need to be bigger to prevent overflow!!!
-        d = ee - (153 * mm + 2) / 5 + 1;
-        m = mm + 3 - 12 * (mm / 10);
-        y = dd - 4800 + (mm / 10);
-        if (y <= 0)
-            --y;
-    }
+    // Gregorian calendar
+    // This algorithm is from Henry F. Fliegel and Thomas C. Van Flandern
+    qint64 ell, n, i, j;  //TODO These will need to be bigger to prevent overflow!!!
+    ell = julianDay + 68569;
+    n = (4 * ell) / 146097;
+    ell = ell - (146097 * n + 3) / 4;
+    i = (4000 * (ell + 1)) / 1461001;
+    ell = ell - (1461 * i) / 4 + 31;
+    j = (80 * ell) / 2447;
+    d = ell - (2447 * j) / 80;
+    ell = j / 11;
+    m = j + 2 - (12 * ell);
+    y = 100 * (n - 49) + i + ell;
+
+    if (y<= 0)
+        --y;
+
     if (year)
         *year = y;
     if (month)
@@ -197,12 +172,10 @@ static QString fmtDateTime(const QString& f, const QTime* dt = 0, const QDate* d
 
 
     A QDate object contains a calendar date, i.e. year, month, and day
-    numbers, in the Gregorian calendar. (see \l{QDate G and J} {Use of
-    Gregorian and Julian Calendars} for dates prior to 15 October
-    1582). It can read the current date from the system clock. It
-    provides functions for comparing dates, and for manipulating
-    dates. For example, it is possible to add and subtract days,
-    months, and years to dates.
+    numbers, in the Gregorian calendar. It can read the current date
+    from the system clock. It provides functions for comparing dates,
+    and for manipulating dates. For example, it is possible to add
+    and subtract days, months, and years to dates.
 
     A QDate object is typically created either by giving the year,
     month, and day numbers explicitly. Note that QDate interprets two
@@ -233,26 +206,6 @@ static QString fmtDateTime(const QString& f, const QTime* dt = 0, const QDate* d
 
     \section1
 
-    \target QDate G and J
-    \section2 Use of Gregorian and Julian Calendars
-
-    QDate uses the Gregorian calendar in all locales, beginning
-    on the date 15 October 1582. For dates up to and including 4
-    October 1582, the Julian calendar is used.  This means there is a
-    10-day gap in the internal calendar between the 4th and the 15th
-    of October 1582. When you use QDateTime for dates in that epoch,
-    the day after 4 October 1582 is 15 October 1582, and the dates in
-    the gap are invalid.
-
-    The Julian to Gregorian changeover date used here is the date when
-    the Gregorian calendar was first introduced, by Pope Gregory
-    XIII. That change was not universally accepted and some localities
-    only executed it at a later date (if at all).  QDateTime
-    doesn't take any of these historical facts into account. If an
-    application must support a locale-specific dating system, it must
-    do so on its own, remembering to convert the dates using the
-    Julian day.
-
     \section2 No Year 0
 
     There is no year 0. Dates in that year are considered invalid. The
@@ -985,11 +938,6 @@ QDate QDate::addDays(qint64 ndays) const
     resulting month/year, this function will return a date that is the
     latest valid date.
 
-    \warning QDate has a date hole around the days introducing the
-    Gregorian calendar (the days 5 to 14 October 1582, inclusive, do
-    not exist). If the calculation ends in one of those days, QDate
-    will return either October 4 or October 15.
-
     \sa addDays() addYears()
 */
 
@@ -1039,10 +987,6 @@ QDate QDate::addMonths(int nmonths) const
         // yes, adjust the date by +1 or -1 years
         y += increasing ? +1 : -1;
 
-    // did we end up in the Gregorian/Julian conversion hole?
-    if (y == 1582 && m == 10 && d > 4 && d < 15)
-        d = increasing ? 15 : 4;
-
     return fixedDate(y, m, d);
 }
 
@@ -1332,14 +1276,10 @@ QDate QDate::fromString(const QString &string, const QString &format)
 
 bool QDate::isValid(int year, int month, int day)
 {
-    // there is no year 0 in the Julian calendar
+    // there is no year 0 in the Gregorian calendar
     if (year == 0)
         return false;
 
-    // passage from Julian to Gregorian calendar
-    if (year == 1582 && month == 10 && day > 4 && day < 15)
-        return false;
-
     return (day > 0 && month > 0 && month <= 12) &&
            (day <= monthDays[month] || (day == 29 && month == 2 && isLeapYear(year)));
 }
@@ -1353,14 +1293,11 @@ bool QDate::isValid(int year, int month, int day)
 
 bool QDate::isLeapYear(int y)
 {
-    if (y < 1582) {
-        if ( y < 1) {  // No year 0 in Julian calendar, so -1, -5, -9 etc are leap years
-            ++y;
-        }
-        return y % 4 == 0;
-    } else {
-        return (y % 4 == 0 && y % 100 != 0) || y % 400 == 0;
-    }
+    // No year 0 in Gregorian calendar, so -1, -5, -9 etc are leap years
+    if ( y < 1)
+        ++y;
+
+    return (y % 4 == 0 && y % 100 != 0) || y % 400 == 0;
 }
 
 /*! \fn static QDate QDate::fromJulianDay(int jd)
@@ -2088,26 +2025,6 @@ int QTime::elapsed() const
 
     \section1
 
-    \target QDateTime G and J
-    \section2 Use of Gregorian and Julian Calendars
-
-    QDate uses the Gregorian calendar in all locales, beginning
-    on the date 15 October 1582. For dates up to and including 4
-    October 1582, the Julian calendar is used.  This means there is a
-    10-day gap in the internal calendar between the 4th and the 15th
-    of October 1582. When you use QDateTime for dates in that epoch,
-    the day after 4 October 1582 is 15 October 1582, and the dates in
-    the gap are invalid.
-
-    The Julian to Gregorian changeover date used here is the date when
-    the Gregorian calendar was first introduced, by Pope Gregory
-    XIII. That change was not universally accepted and some localities
-    only executed it at a later date (if at all).  QDateTime
-    doesn't take any of these historical facts into account. If an
-    application must support a locale-specific dating system, it must
-    do so on its own, remembering to convert the dates using the
-    Julian day.
-
     \section2 No Year 0
 
     There is no year 0. Dates in that year are considered invalid. The
@@ -2134,16 +2051,6 @@ int QTime::elapsed() const
     shortcomings in the available conversion formulas. Conversions outside this
     range are not guaranteed to be correct. This may change in the future.
 
-    The Gregorian calendar was introduced in different places around
-    the world on different dates. QDateTime uses QDate to store the
-    date, so it uses the Gregorian calendar for all locales, beginning
-    on the date 15 October 1582. For dates up to and including 4
-    October 1582, QDateTime uses the Julian calendar.  This means
-    there is a 10-day gap in the QDateTime calendar between the 4th
-    and the 15th of October 1582. When you use QDateTime for dates in
-    that epoch, the day after 4 October 1582 is 15 October 1582, and
-    the dates in the gap are invalid.
-
     \section2
     Use of System Timezone
 
@@ -3052,8 +2959,8 @@ qint64 QDateTime::currentMSecsSinceEpoch()
     GetSystemTime(&st);
 
     return msecsFromDecomposed(st.wHour, st.wMinute, st.wSecond, st.wMilliseconds) +
-            qint64(julianDayFromGregorianDate(st.wYear, st.wMonth, st.wDay)
-                   - julianDayFromGregorianDate(1970, 1, 1)) * Q_INT64_C(86400000);
+            qint64(julianDayFromDate(st.wYear, st.wMonth, st.wDay)
+                   - julianDayFromDate(1970, 1, 1)) * Q_INT64_C(86400000);
 }
 
 #elif defined(Q_OS_UNIX)