diff options
Diffstat (limited to 'src/corelib/tools/qdatetime.cpp')
| -rw-r--r-- | src/corelib/tools/qdatetime.cpp | 106 |
1 files changed, 54 insertions, 52 deletions
diff --git a/src/corelib/tools/qdatetime.cpp b/src/corelib/tools/qdatetime.cpp index e463ba9c4e..56dc0fade9 100644 --- a/src/corelib/tools/qdatetime.cpp +++ b/src/corelib/tools/qdatetime.cpp @@ -93,47 +93,67 @@ static inline QDate fixedDate(int y, int m, int d) return result; } -static inline qint64 julianDayFromDate(qint64 year, int month, int day) +static inline qint64 floordiv(qint64 a, qint64 b) { - // Gregorian calendar - // Algorithm from Henry F. Fliegel and Thomas C. Van Flandern + return (a - (a < 0 ? b-1 : 0)) / b; +} + +static inline qint64 floordiv(qint64 a, int b) +{ + return (a - (a < 0 ? b-1 : 0)) / b; +} +static inline int floordiv(int a, int b) +{ + return (a - (a < 0 ? b-1 : 0)) / b; +} + +static inline qint64 julianDayFromDate(int year, int month, int day) +{ + // Adjust for no year 0 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; +/* + * 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) + */ + int a = floordiv(14 - month, 12); + qint64 y = (qint64)year + 4800 - a; + int m = month + 12 * a - 3; + return day + floordiv(153 * m + 2, 5) + 365 * y + floordiv(y, 4) - floordiv(y, 100) + floordiv(y, 400) - 32045; } -static void getDateFromJulianDay(qint64 julianDay, int *year, int *month, int *day) +static void getDateFromJulianDay(qint64 julianDay, int *yearp, int *monthp, int *dayp) { - int y, m, d; +/* + * 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) + */ + qint64 a = julianDay + 32044; + qint64 b = floordiv(4 * a + 3, 146097); + int c = a - floordiv(146097 * b, 4); + + int d = floordiv(4 * c + 3, 1461); + int e = c - floordiv(1461 * d, 4); + int m = floordiv(5 * e + 2, 153); - // 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; + int day = e - floordiv(153 * m + 2, 5) + 1; + int month = m + 3 - 12 * floordiv(m, 10); + int year = 100 * b + d - 4800 + floordiv(m, 10); - if (y<= 0) - --y; + // Adjust for no year 0 + if (year <= 0) + --year ; - if (year) - *year = y; - if (month) - *month = m; - if (day) - *day = d; + if (yearp) + *yearp = year; + if (monthp) + *monthp = month; + if (dayp) + *dayp = day; } @@ -225,14 +245,8 @@ static QString fmtDateTime(const QString& f, const QTime* dt = 0, const QDate* d QDate::toJulianDay() and can be set using QDate::fromJulianDay(). The range of dates able to be stored by QDate as a Julian Day number is - limited for convenience from std::numeric_limits<qint64>::min() / 2 to - std::numeric_limits<qint64>::max() / 2, which on most platforms means - from around 2.5 quadrillion BCE to around 2.5 quadrillion CE, effectively - covering the full range of astronomical time. The range of Julian Days - able to be accurately converted to and from valid YMD form Dates is - restricted to 1 January 4800 BCE to 31 December 1400000 CE due to - shortcomings in the available conversion formulas. Conversions outside this - range are not guaranteed to be correct. This may change in the future. + for technical reasons limited to between -784350574879 and 784354017364, + which means from before 2 billion BCE to after 2 billion CE. \sa QTime, QDateTime, QDateEdit, QDateTimeEdit, QCalendarWidget */ @@ -859,9 +873,6 @@ QString QDate::toString(const QString& format) const If the specified date is invalid, the QDate object is set to be invalid. - Note that any date before 4800 BCE or after about 1.4 million CE - may not be accurately stored. - \sa isValid() */ bool QDate::setDate(int year, int month, int day) @@ -882,9 +893,6 @@ bool QDate::setDate(int year, int month, int day) Returns 0 if the date is invalid. - Note that any date before 4800 BCE or after about 1.4 million CE - may not be accurately stored. - \sa year(), month(), day(), isValid() */ void QDate::getDate(int *year, int *month, int *day) @@ -2100,14 +2108,8 @@ int QTime::elapsed() const QDate::toJulianDay() and can be set using QDate::fromJulianDay(). The range of dates able to be stored by QDate as a Julian Day number is - limited for convenience from std::numeric_limits<qint64>::min() / 2 to - std::numeric_limits<qint64>::max() / 2, which on most platforms means - from around 2.5 quadrillion BCE to around 2.5 quadrillion CE, effectively - covering the full range of astronomical time. The range of Julian Days - able to be accurately converted to and from valid YMD form Dates is - restricted to 1 January 4800 BCE to 31 December 1400000 CE due to - shortcomings in the available conversion formulas. Conversions outside this - range are not guaranteed to be correct. This may change in the future. + for technical reasons limited to between -784350574879 and 784354017364, + which means from before 2 billion BCE to after 2 billion CE. \section2 Use of System Timezone |