Here's the main bit of code; the two documents from which I derived it
are over the 40k limit. One is the calendar FAQ text version. The other
is a file easter_date.txt that is a thread from:
Newsgroups: soc.religion.christian
From: [EMAIL PROTECTED] (Mike Siemon)
Subject: Easter algorithms I
Organization: ATT Bell Laboratories
Approved: [EMAIL PROTECTED]
Does anyone want such files?
Anyway, the implemented formulas are below. The header files are just
for keeping track of Palm-specific variables for different modules.
/*
*
* Created with Falch.net DeveloperStudio
* http://www.falch.net/
*
* Created : 4/11/01 12:18:42 AM
* Creator : (Unknown)
*
/
#include Pilot.h
#include Easter.h
#include Easter_res.h
extern Boolean England;
extern UInt16 YearAD;
Char Orthodox_Julian[20], Orthodox_Gregorian[20], Western[20];
typedef enum {Julian,Gregorian} calendar;
/* The Golden Number is the order of the year in the 19-year lunar
cycle.
* It is the same in Julian or Gregorian calendars, and is listed in the
* output of this program under the heading GN.
*/
int GoldenNumber(int year)
{
return ((year % 19) + 1);
}
/* All dates in this program are referred to March 1st; so 32 means
* April 1 and 0 means February 28th or 29th. Leap years are needed
* for printing February dates (and for dominical letters).
*/
int Leap(int year, calendar style)
{
if (year % 4)
return 0;
else switch(style) {
case Julian:return 1;
case Gregorian: return (year % 100 || year % 400 == 0);
}
}
#define century (year/100)
/* Gregorian solar correction -- this is the number of days difference
* between Julian and Gregorian civil dates, in effect the number of
* excess leap years in the Julian calendar since the time of Nicea.
* This correction derives from the Gregorian introduction of non-leap
* century years, giving mean tropical year = 365.2425 days.
*/
int Solar(int year)
{
return (century - century/4 - 2);
}
/* Gregorian lunar correction -- this is only used for the computation
of
* the paschal new moon (via epact), but might as well be pulled out on
* its own. I give the pedantically correct version.
* This correction derives from the mean lunar month being 29.53059 days
* instead of the 6939.75/235 assumed in the Julian calendar. It is one
* days in (roughly) 312.5 years, or 8 days in 2500 years.
*/
int Lunar(int year)
{
return ((century - 15 - (century-17)/25)/3);
}
/* Epact is the age of the moon on March 1st (same as January 1st);
* It (may have) derived from Greek methods of calculating the extra
* (epagomenal) months intercalated into the regular 12 at 7 points
* of the 19-year Metonic cycle. However, it is not used in Julian
* easter calculations and is provided here only for Gregorian NewMoon.
*/
int Epact(int year)
{
int epact;
epact = (11*GoldenNumber(year) - Solar(year) + Lunar(year)) % 30;
if (epact 0)
epact += 30;
return epact;
}
/* Here's the hard one. Keep in mind that there are several artificial
* conventions -- the equinox is ALWAYS March 21; new moon is ALWAYS the
* date on which a fictitious average moon is one day old, and the
full
* moon is 13 days later, on the 14th of the month. In the Julian
version
* (and MOSTLY in the Gregorian) the pre-paschal month has 30 days. All
* of this works out keeping fairly close to astronomical reality in the
* Gregorian case, but it is not necessarily exact.
*/
int NewMoon(int year, calendar style)
{
int new_moon, epact;
switch (style) {
case Julian:
new_moon = (4 - 11*GoldenNumber(year)) % 30;
while (new_moon 8)
new_moon += 30;
return new_moon;
case Gregorian:
epact = Epact(year);
new_moon = 31-epact;
if (new_moon 8) {
new_moon += 30;
if (epact == 24 || epact == 25 year%19 10)
new_moon--;
}
return new_moon;
}
}
int WeekDay(int date, int year, calendar style)
{
int d;
d = date + year + year/4;
if (style == Gregorian)
d -= Solar(year);
return (d % 7);
}
/* Given the Paschal full moon, we just step to the next Sunday ...
*/
int Easter(int year, calendar style)
{
int paschal_moon;
