CalendarWeek

From Axaptapedia

/// <summary>
/// Calculates the Calendar Week of a Date according to the German Standard
/// </summary>
/// <param name="inputDate">The Date</param>
/// <returns>Returns an Integer representing the Calendar Week</returns>
/// <remarks>
/// <para>
/// This Method is only relevant for the German Culture.
/// It is considerably faster than the Method
/// <see cref="GetInternationalCalendarWeek"/>.
/// </para>
/// <para>
/// The Calculation is based on the
/// C++-Algorithm from Ekkehard Hess out of an Article on
/// 29 July 1999 in the Newsgroup
/// borland.public.cppbuilder.language
///(released for general use)
/// </para>
/// </remarks>
 
static int calendarWeek_DE(Date inputDate)
{
    real    a           = trunc((14 - (mthOfYr(inputDate))) / 12);
    real    y           = year(inputDate) + 4800 - a;
    real    m           = (mthOfYr(inputDate)) + (12 * a) - 3;
    real    jd;
    real    d4;
    real    L;
    real    dl;
    int     calendarWeek;
    ;
 
    jd  = str2int(substr(date2str(inputDate, 123, 2, 2, 2, 2, 2), 1, 2)) +
            trunc(((153 * m) + 2) / 5) + (365 * y) + 
            trunc(y / 4) - trunc(y / 100) + trunc (y / 400) - 32045;
    d4  = (jd + 31741 - (jd mod 7)) mod 146097 mod 36524 mod 1461;
    L   = trunc(d4 / 1460);
    dl  = ((d4 - L) mod 365) + L;
 
    calendarWeek    = trunc(dl / 7) + 1;
 
    return calendarWeek;
}