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#pike __REAL_VERSION__ 
 
//! This is the standard western calendar, which is a derivate 
//! of the Gregorian calendar, but with weeks that starts on 
//! Monday instead of Sunday. 
 
inherit Calendar.Gregorian:Gregorian; 
 
#include "constants.h" 
 
string calendar_name() { return "ISO"; } 
 
#define WEEK_MAJORITY 4 
 
private protected mixed __initstuff=lambda() 
{ 
   f_week_day_shortname_from_number="week_day_shortname_from_number"; 
   f_week_day_name_from_number="week_day_name_from_number"; 
   f_year_name_from_number="year_name_from_number"; 
   f_week_day_number_from_name="week_day_number_from_name"; 
}(); 
 
protected int compat_week_day(int n) 
{ 
   return n%7; 
} 
 
protected string year_name_from_number(int y) 
{ 
   if (y>0) return ""+y; 
   else return (1-y)+" BC"; 
} 
 
protected array(int) week_from_julian_day(int jd) 
{ 
// [week-year,week,day-of-week,ndays,week-julian-day] 
 
   [int y,int yjd]=year_from_julian_day(jd); 
   int yday=jd-yjd+1; 
   int wjd=jd-jd%7; 
 
#if 1 
   int k=WEEK_MAJORITY+(yjd-WEEK_MAJORITY)%7; 
   int w=(yday+k-1)/7; 
 
//     werror("wjd %d: %O %O %O, %O %O %O\n",jd,y,yjd,yday,k,w,wjd); 
 
   if (!w) 
   { 
// handle the case that the day is in the previous year; 
// years previous to years staring on saturday, 
//              ...  and leap years starting on sunday 
 
      y--; 
      w=52+( (k==WEEK_MAJORITY) || 
             ( (k==WEEK_MAJORITY+1) && year_leap_year(y) ) ); 
   } 
   else if (w==53 && k>=5-year_leap_year(y) && k<10-year_leap_year(y)) 
   { 
// handle the case that the week is in the next year 
      y++; 
      w=1; 
   } 
 
#else 
 
// Calendar FAQ algorithm (Stefan Potthast): 
// not used, does not calculate the week-year 
 
   int d4 = (jd+31741 - (jd %7))%146097 %36524 %1461; 
   int L  = d4/1460; 
   int d1 = ((d4-L) % 365) + L; 
 
   int w = d1/7 + 1; 
 
//     werror("wjd %d: %O %O %O, %O\n",jd,y,yjd,yday,wjd,w); 
 
 
 
#endif 
 
//     werror("wjd %d: = %d, %d, %d, %d, %d\n", 
//      jd,@({y,w,1+(yjd+yday-1)%7,7,wjd})); 
 
   return ({y,w,1+(yjd+yday-1)%7,7,wjd}); 
} 
 
protected array(int) week_from_week(int y,int w) 
{ 
// [week-year,week,1 (wd),ndays,week-julian-day] 
 
   int yjd=julian_day_from_year(y); 
   int wjd=-WEEK_MAJORITY+yjd-(yjd+WEEK_MAJORITY-1)%7; 
 
//     werror("bip %O %O: %O %O\n",y,w,yjd,wjd); 
 
   if (w<1 || w>52) // may or may not be out of this year 
      return week_from_julian_day(wjd+w*7); 
 
   return ({y,w,1,7,wjd+w*7}); 
//   fixme 
} 
 
class cYear 
{ 
   inherit Gregorian::cYear; 
   TimeRange place(TimeRange what,void|int force) 
   { 
      if (what->is_day) 
      { 
         int wyd=what->yd; 
         if (md==CALUNKNOWN) make_month(); 
         if (wyd>=55) 
         { 
            int l1=year_leap_year(what->y); 
            int l2=year_leap_year(y); 
            if (l1 != l2) 
            { 
               // (Apparently) the leap day was moved from February 24th to 
               // 29th on year 2000 in the ISO calendar. 
               // 
               // This code was overly clever and enforced that move by mapping 
               // the 24th in leap years before 2000 to 29th in 2000 and 
               // following leap years. That leads to nonlinear behavior, i.e. 
               // 
               //                 Day(y1,m1,d1) <= Day(y2,m2,d2) 
               //                              ===> 
               //      Day(y1,m1,d1) + n*Year() <= Day(y2,m2,d2) + n*Year() 
               // 
               // wasn't always true in the ISO calendar. That's bad when doing 
               // date arithmetic. 
               // 
               // That has now been fixed by simply mapping all days one-to-one 
               // between leap years, regardless whether they're before 2000 or 
               // not. 
               // 
               // The exact date for the leap day still has effect when 
               // converting between leap and non-leap years, though. 
               // 
               // /mast 
               if (l1) { 
                 int ld1=(what->y<2000)?55:60; // 24th or 29th february 
                 if (wyd>ld1) wyd--; 
                 else if (wyd==ld1) { 
                   if (force) wyd--; // Lossy case - prefer to keep the month. 
                   else return 0; 
                 } 
               } 
               else { 
                  int ld2=(y<2000)?55:60; // 24th or 29th february 
                  if (wyd>=ld2) wyd++; 
               } 
            } 
         } 
         if (!force && wyd>number_of_days()) return 0; 
 
         return Day("ymd_yd",rules,y,yjd,yjd+wyd-1,wyd,what->n); 
      } 
 
      return ::place(what, force); 
   } 
} 
 
class cMonth 
{ 
   inherit Gregorian::cMonth; 
 
   TimeRange place(TimeRange what,int|void force) 
   { 
      if (what->is_day) 
      { 
         int wmd=what->month_day(); 
         if (md==CALUNKNOWN) make_month(); 
         if (what->m==2 && m==2 && wmd>=24) 
         { 
            int l1=year_leap_year(what->y); 
            int l2=year_leap_year(y); 
            if (l1 != l2) 
            { 
               // See note above about leap day mapping. 
               if (l1) { 
                 int ld1=(what->y<2000)?24:29; // 24th or 29th february 
                 if (wmd>ld1) wmd--; 
                 else if (wmd==ld1) { 
                   if (force) wmd--; // Lossy case - prefer to keep the month. 
                   else return 0; 
                 } 
               } 
               else 
               { 
                  int ld2=(y<2000)?24:29; // 24th or 29th february 
                  if (wmd>=ld2) wmd++; 
               } 
            } 
         } 
         if (!force && wmd>number_of_days()) return 0; 
         return Day("ymd_yd",rules,y,yjd,jd+wmd-1,yd+wmd-1,what->n); 
      } 
 
      return ::place(what, force); 
   } 
}