Calendar functions

[JMB]

The input syntax used for dates in these calendar functions that I have coded, is the same used by the HP Prime built-in functions: YYYY.MMDD.

The valid range of dates is also the range used by the HP Prime built-in functions: from 1582.1015 (Julian day 2299161) to 9999.1231 (Julian day 5373484).

Most functions have a very short coding, because they take avantatge of the HP Prime functions DAYOFWEEK, DDAYS and DATEADD.

Listing [Updated. I corrected a typo found by ggauny@live.fr]

PHP Code:

// Calendar functions
// JMB - April 2017
// Valid dates are from 1582.1015 (Julian day 2299161) to 9999.1231 (Julian day 5373484)

#pragma mode( separator(.,;) integer(h32) )

EXPORT Is_Date_Valid(d)
// d:date → 1=valid date, 0=invalid date
BEGIN
  IFTE(d<1582.1015 OR d>9999.1231 OR DAYOFWEEK(d)<0, 0, 1);
END;

EXPORT Is_Leap_Year(d)
// d:date or year → 1=leap year, 0=ordinary year
BEGIN
  DAYOFWEEK(IP(d)+0.0229) > 0;
END;

EXPORT Century(d)
// d:date or year → century
BEGIN
  IP((d-1)/100)+1;
END;

EXPORT Year(d)
// d:date → year
BEGIN
  IP(d);
END;

EXPORT Month(d)
// d:date → month
BEGIN
  IP(FP(d)*100);
END;

EXPORT Day(d)
// d:date → day
BEGIN
  FP(FP(d)*100)*100;
END;

EXPORT Date_to_Julian_Day(d)
// d:date → Julian day
BEGIN
  2299161+DDAYS(1582.1015,d);
END;

EXPORT Julian_Day_to_Date(jd)
// jd:Julian day → date
BEGIN
  DATEADD(1582.1015,jd-2299161);
END;

EXPORT Week_Number(d)
// d:date → week number (ISO 8601)
BEGIN
  LOCAL yr:=Year(d), mn:=Month(d), dy:=Day(d);
  LOCAL DoW_0101:=IFTE(yr==1582,1,DAYOFWEEK(yr+0.0101));  
  LOCAL DoW_Yp1_0101:=IFTE(yr==9999,6,DAYOFWEEK(yr+1.0101));
  LOCAL wn:=IP((IFTE(yr==1582,Date_to_Julian_Day(d)-2298884,DDAYS(yr+0.0101,d))+DoW_0101-1)/7);
  IF mn==12 AND DoW_Yp1_0101≤4 AND (32-dy)<DoW_Yp1_0101 THEN
    RETURN 1;
  ELSE
    IF DoW_0101≤4 THEN
      RETURN wn+1;
    ELSE
      IF mn==1 AND (9-dy)>DoW_0101 THEN
        RETURN Week_Number(yr-1+0.1231);
      ELSE
        RETURN wn;
      END;
    END;
  END;
END; 


Here are some examples:

Is_Date_Valid(2017.0401) → 1
Is_Date_Valid(2017.0229) → 0

Is_Leap_Year(2017.0401) → 0
Is_Leap_Year(2017) → 0
Is_Leap_Year(2016.0401) → 1
Is_Leap_Year(2016) → 1

Century(2017.0401) → 21
Century(2017) → 21

Year(2017.0401) → 2017

Month(2017.0401) → 4

Day(2017.0401) → 1

Date_to_Julian_Day(2017.0401) → 2457845

Julian_Day_to_Date(2457845) → 2017.0401

Week_Number(2017.0401) → 13