diff options
| author | Edward Welbourne <edward.welbourne@qt.io> | 2023-01-23 20:05:57 +0100 |
|---|---|---|
| committer | Edward Welbourne <edward.welbourne@qt.io> | 2023-01-31 17:35:13 +0100 |
| commit | 0e653246b163adb58d0fd955f45aaefc8a506443 (patch) | |
| tree | 86bbe132b7c982242d459fccb04fe92cfe08f632 /src | |
| parent | 5a91b734f2ac42df694c8052eaaf39c03c7cfab0 (diff) | |
Shift the base date for the Gregorian calendar's calculations
Internally it was using the start of March 4801 BCE and then adjusting
the year by 4800; instead, use the start of March 1 BCE and save those
adjustments. This incidentally aligns better with the Milankovic
calendar's calculations.
Change-Id: Ic64b4e1d4f65bbf1973a77f830e68f05f7949f4d
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Diffstat (limited to 'src')
| -rw-r--r-- | src/corelib/time/qgregoriancalendar.cpp | 12 |
1 files changed, 8 insertions, 4 deletions
diff --git a/src/corelib/time/qgregoriancalendar.cpp b/src/corelib/time/qgregoriancalendar.cpp index 846a115446..904b23434c 100644 --- a/src/corelib/time/qgregoriancalendar.cpp +++ b/src/corelib/time/qgregoriancalendar.cpp @@ -162,6 +162,10 @@ int QGregorianCalendar::yearSharingWeekDays(QDate date) * 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). */ bool QGregorianCalendar::julianFromParts(int year, int month, int day, qint64 *jd) @@ -174,16 +178,16 @@ bool QGregorianCalendar::julianFromParts(int year, int month, int day, qint64 *j ++year; int a = month < 3 ? 1 : 0; - qint64 y = qint64(year) + 4800 - a; + qint64 y = qint64(year) - a; int m = month + 12 * a - 3; - *jd = day + qDiv<5>(153 * m + 2) - 32045 + *jd = day + qDiv<5>(153 * m + 2) + 1721119 + 365 * y + qDiv<4>(y) - qDiv<100>(y) + qDiv<400>(y); return true; } QCalendar::YearMonthDay QGregorianCalendar::partsFromJulian(qint64 jd) { - qint64 a = jd + 32044; + qint64 a = jd - 1721120; qint64 b = qDiv<146097>(4 * a + 3); int c = a - qDiv<4>(146097 * b); @@ -191,7 +195,7 @@ QCalendar::YearMonthDay QGregorianCalendar::partsFromJulian(qint64 jd) int e = c - qDiv<4>(1461 * d); int m = qDiv<153>(5 * e + 2); - int y = 100 * b + d - 4800 + qDiv<10>(m); + int y = 100 * b + d + qDiv<10>(m); // Adjust for no year 0 int year = y > 0 ? y : y - 1; |