date.cxx

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#include <comphelper/date.hxx>
 
#include <cassert>
 
namespace comphelper::date
{
// Once upon a time the number of days we internally handled in tools' class
// Date was limited to MAX_DAYS 3636532. That changed with a full 16-bit year.
// Assuming the first valid positive date in a proleptic Gregorian calendar is
// 0001-01-01, this resulted in an end date of 9957-06-26.
// Hence we documented that years up to and including 9956 are handled.
/* XXX: it is unclear history why this value was chosen, the representable
 * 9999-12-31 would be 3652060 days from 0001-01-01. Even 9998-12-31 to
 * distinguish from a maximum possible date would be 3651695.
 * There is connectivity/source/commontools/dbconversion.cxx that still has the
 * same value to calculate with css::util::Date */
/* XXX can that dbconversion cope with years > 9999 or negative years at all?
 * Database fields may be limited to positive 4 digits. */
 
constexpr sal_Int32 MIN_DAYS = -11968265; // -32768-01-01
constexpr sal_Int32 MAX_DAYS = 11967900; //  32767-12-31
 
constexpr sal_Int16 kYearMax = SAL_MAX_INT16;
constexpr sal_Int16 kYearMin = SAL_MIN_INT16;
 
constexpr sal_Int32 nNullDateDays = convertDateToDays(30, 12, 1899);
static_assert(nNullDateDays == 693594);
 
sal_Int32 convertDateToDaysNormalizing(sal_uInt16 nDay, sal_uInt16 nMonth, sal_Int16 nYear)
{
    // Speed-up the common null-date 1899-12-30.
    if (nYear == 1899 && nMonth == 12 && nDay == 30)
        return nNullDateDays;
 
    normalize(nDay, nMonth, nYear);
    return convertDateToDays(nDay, nMonth, nYear);
}
 
bool isValidDate(sal_uInt16 nDay, sal_uInt16 nMonth, sal_Int16 nYear)
{
    if (nYear == 0)
        return false;
    if (nMonth < 1 || 12 < nMonth)
        return false;
    if (nDay < 1 || (nDay > comphelper::date::getDaysInMonth(nMonth, nYear)))
        return false;
    return true;
}
 
void convertDaysToDate(sal_Int32 nDays, sal_uInt16& rDay, sal_uInt16& rMonth, sal_Int16& rYear)
{
    if (nDays <= MIN_DAYS)
    {
        rDay = 1;
        rMonth = 1;
        rYear = kYearMin;
        return;
    }
    if (nDays >= MAX_DAYS)
    {
        rDay = 31;
        rMonth = 12;
        rYear = kYearMax;
        return;
    }
 
    // Day 0 is -0001-12-31, day 1 is 0001-01-01
    const sal_Int16 nSign = (nDays <= 0 ? -1 : 1);
    sal_Int32 nTempDays;
    sal_Int32 i = 0;
    bool bCalc;
 
    do
    {
        rYear = static_cast<sal_Int16>((nDays / 365) - (i * nSign));
        if (rYear == 0)
            rYear = nSign;
        nTempDays = nDays - YearToDays(rYear);
        bCalc = false;
        if (nTempDays < 1)
        {
            i += nSign;
            bCalc = true;
        }
        else
        {
            if (nTempDays > 365)
            {
                if ((nTempDays != 366) || !isLeapYear(rYear))
                {
                    i -= nSign;
                    bCalc = true;
                }
            }
        }
    } while (bCalc);
 
    rMonth = 1;
    while (nTempDays > getDaysInMonth(rMonth, rYear))
    {
        nTempDays -= getDaysInMonth(rMonth, rYear);
        ++rMonth;
    }
 
    rDay = static_cast<sal_uInt16>(nTempDays);
}
 
bool normalize(sal_uInt16& rDay, sal_uInt16& rMonth, sal_Int16& rYear)
{
    if (isValidDate(rDay, rMonth, rYear))
        return false;
 
    if (rDay == 0 && rMonth == 0 && rYear == 0)
        return false; // empty date
 
    if (rDay == 0)
    {
        if (rMonth == 0)
            ; // nothing, handled below
        else
            --rMonth;
        // Last day of month is determined at the end.
    }
 
    if (rMonth > 12)
    {
        rYear += rMonth / 12;
        rMonth = rMonth % 12;
        if (rYear == 0)
            rYear = 1;
    }
    if (rMonth == 0)
    {
        --rYear;
        if (rYear == 0)
            rYear = -1;
        rMonth = 12;
    }
 
    if (rYear < 0)
    {
        sal_uInt16 nDays;
        while (rDay > (nDays = getDaysInMonth(rMonth, rYear)))
        {
            rDay -= nDays;
            if (rMonth > 1)
                --rMonth;
            else
            {
                if (rYear == kYearMin)
                {
                    rDay = 1;
                    rMonth = 1;
                    return true;
                }
                --rYear;
                rMonth = 12;
            }
        }
    }
    else
    {
        sal_uInt16 nDays;
        while (rDay > (nDays = getDaysInMonth(rMonth, rYear)))
        {
            rDay -= nDays;
            if (rMonth < 12)
                ++rMonth;
            else
            {
                if (rYear == kYearMax)
                {
                    rDay = 31;
                    rMonth = 12;
                    return true;
                }
                ++rYear;
                rMonth = 1;
            }
        }
    }
 
    if (rDay == 0)
        rDay = getDaysInMonth(rMonth, rYear);
 
    return true;
}
 
} // namespace comphelper::date
 
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