Easter Day Calculation

[kfmason]

All,
If (like me) you've always wondered how 'they' decided
when easter is and have written diary apps where you've
scratched your head when it came to allowing for
national/bank holidays; you will find this useful.
I've written it in C, assembler, sql and VB (as well
as the COBOL version below) if anyone is 'that'
interested.

Cheers All
(email: kfmason@tinyonline.co.uk).

------------------------------------------------------

******************************************************
*Easter falls on the First Sunday following the first*
*Full moon that occurs on or after 21 March. This    *
*algorithm, attributed to Guass, will return for a   *
*given year, >=1583, a value for Easter Sunday in the*
*format MMDD. It returns the date in the same field  *
*as the request year. The input year variable is     *
*v-year, the output is v-easterday(mmdd).            *
******************************************************

WORKING-STORAGE SECTION.

01 V-YEAR       PIC S9(04) VALUE ZERO.
01 V-DAY        PIC S9(02) VALUE ZERO.
01 V-EASTERDAY  PIC S9(04) VALUE ZERO.
01 V-CENTURY    PIC S9(02) VALUE ZERO.
01 V-GOLDEN     PIC S9(04) VALUE ZERO.
01 V-GREGORIAN  PIC S9(04) VALUE ZERO.
01 V-CLAVIAN    PIC S9(04) VALUE ZERO.
01 V-FACTOR     PIC S9(06) VALUE ZERO.
01 V-EPACT      PIC S9(06) VALUE ZERO.

PROCEDURE DIVISION

XX-CALCULATE EASTERDAY.
 *******************************************************
 * Step 1 Century   - Century of requested year.       *
 * Step 2 Golden    - Number of the year in the Metonic*
 *                    Cycle and used to determine the  *
 *                    position of the calendar moon.   *
 * Step 3 Gregorian - Years in which a leap year did   *
 *                    notoccur.                        *
 * Step 4 Clavian   - Correction for the Metonic Cycle *
 *                    (about 8 days every 2,500 years. *
 * Step 5 Factor    - Variable for storing intermediate*
 *                    value.                           *
 * Step 6 Epact     - Age of the moon on 1 January,    *
 *                    used to calc when the full moon  *
 *                    occurs.                          *
 *******************************************************

 * Step 1
   COMPUTE V-CENTURY = (V-YEAR / 100) + 1

 * Step 2
   COMPUTE V-GOLDEN= FUNCTION MOD(V-YEAR, 19) + 1

 * Step 3
   COMPUTE V-GREGORIAN = (V-CENTURY * 3) / 4 - 12

 * Step 4
   COMPUTE V-CLAVIAN
        = (V-CENTURY * 8 + 5) / 25 - 5 - V-GREGORIAN
 * Step 5
   COMPUTE V-FACTOR
        = (V-YEAR * 5) / 4 - V-GREGORIAN - 10
 * Step 6
   COMPUTE V-EPACT
   = FUNCTION MOD((V-GOLDEN * 11 + 20 + V-CLAVIAN), 30) 

   IF V-EPACT = 24
      ADD 1 TO V-EPACT
   ELSE
      IF V-EPACT = 25
         IF V-GOLDEN > 11
            ADD 1 TO V-EPACT
         END-IF
      END-IF
   END-IF

  COMPUTE V-DAY = 44 - V-EPACT
  
  IF V-DAY < 21
     ADD 30 TO V-DAY
  END-IF
  
  COMPUTE V-DAY
  = V-DAY + 7 - (FUNCTION MOD((V-DAY + V-FACTOR), 7)) 

  IF V-DAY <= 31
     ADD 300 TO V-DAY GIVING V-EASTERDAY
  ELSE
     SUBTRACT 31 FROM V-DAY
     ADD 400 TO V-DAY GIVING V-EASTERDAY
  END-IF
  .
XX-EXIT.
   EXIT.

 

[Crox]

I like these kind of messages a lot!

Thanks! [sig][/sig]