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: AT&T 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; paschal_moon = NewMoon(year, style) + 13; return (paschal_moon + 7 - WeekDay(paschal_moon, year, style)); } /* The rest of the code turns numbers into human-readable output */ static Boolean frmDates_fldOrthodoxJulian_OnSelect(EventPtr event) { // Insert code for fldOrthodoxJulian FormPtr form; FieldPtr field; form = FrmGetActiveForm(); field = FrmGetObjectPtr(form,FrmGetObjectIndex(form,fldOrthodoxJulian)); FldCopy(field); return true; } static Boolean frmDates_fldOrthodoxGregorian_OnSelect(EventPtr event) { // Insert code for fldOrthodoxGregorian FormPtr form; FieldPtr field; form = FrmGetActiveForm(); field = FrmGetObjectPtr(form,FrmGetObjectIndex(form,fldOrthodoxGregorian)); FldCopy(field); return true; } static Boolean frmDates_fldWesternGregorian_OnSelect(EventPtr event) { // Insert code for fldWesternGregorian FormPtr form; FieldPtr field; form = FrmGetActiveForm(); field = FrmGetObjectPtr(form,FrmGetObjectIndex(form,fldWesternGregorian)); FldCopy(field); return true; } static Boolean frmDates_cmdNewYear_OnSelect(EventPtr event) { // Insert code for cmdNewYear FrmGotoForm(frmMain); return true; } Boolean frmDates_HandleEvent(EventPtr event) { FormPtr form; FieldPtr J1, J2, G; Boolean handled = false; int year, easterJ1, easterJ2, easterG; switch (event->eType) { case ctlSelectEvent: switch (event->data.ctlSelect.controlID) { // fldOrthodoxJulian receives an event case fldOrthodoxJulian: handled = frmDates_fldOrthodoxJulian_OnSelect(event); break; // fldOrthodoxGregorian receives an event case fldOrthodoxGregorian: handled = frmDates_fldOrthodoxGregorian_OnSelect(event); break; // fldWesternGregorian receives an event case fldWesternGregorian: handled = frmDates_fldWesternGregorian_OnSelect(event); break; // cmdNewYear receives an event case cmdNewYear: handled = frmDates_cmdNewYear_OnSelect(event); break; } break; case frmOpenEvent: form = FrmGetActiveForm(); J1 = FrmGetObjectPtr(form,FrmGetObjectIndex(form,fldOrthodoxJulian)); J2 = FrmGetObjectPtr(form,FrmGetObjectIndex(form,fldOrthodoxGregorian)); G = FrmGetObjectPtr(form,FrmGetObjectIndex(form,fldWesternGregorian)); // Calculate the necessary dates year = (int) YearAD; easterJ1 = Easter(year, Julian); easterJ2 = easterJ1 + Solar(year); easterG = Easter(year, Gregorian); if (easterJ1 > 31) StrPrintF(Orthodox_Julian, "%2d April AD %d", easterJ1-31, year); else StrPrintF(Orthodox_Julian, "%2d March AD %d", easterJ1, year); if (easterJ2 > 92) StrPrintF(Orthodox_Gregorian, "%2d June AD %d", easterJ2-92, year); else if (easterJ2 > 61) StrPrintF(Orthodox_Gregorian, "%2d May AD %d", easterJ2-61, year); else if (easterJ2 > 31) StrPrintF(Orthodox_Gregorian, "%2d April AD %d", easterJ2-31, year); else StrPrintF(Orthodox_Gregorian, "%2d March AD %d", easterJ2, year); if (easterG > 31) StrPrintF(Western, "%2d April AD %d", easterG-31, year); else StrPrintF(Western, "%2d March AD %d", easterG, year); if (year < 1583) { FldSetTextPtr(J1,Orthodox_Julian); FldSetTextPtr(J2,""); FldSetTextPtr(G,""); } else if (year < 1753 && England) { FldSetTextPtr(J1,Orthodox_Julian); FldSetTextPtr(J2,Orthodox_Gregorian); FldSetTextPtr(G,""); } else { FldSetTextPtr(J1,Orthodox_Julian); FldSetTextPtr(J2,Orthodox_Gregorian); FldSetTextPtr(G,Western); } // Repaint form on open FrmDrawForm(form); handled = true; break; } return handled; } On Sun, 2008-06-22 at 19:38 +0200, Hans Hagen wrote: > Charles P. Schaum wrote: > > Some calendar links, FYI: > > > > http://astro.nmsu.edu/~lhuber/leaphist.html > > http://www.smart.net/~mmontes/ec-cal.html > > http://www.tondering.dk/claus/calendar.html > > http://tycho.usno.navy.mil/vphase.html > > > > I would be happy to make available the C code for an Easter date > > calculator that I implemented on the Palm III. I used the complex > > algorithm that figures the "age" of the moon at New Year's. It > > originally came from Bell Labs, I think. > > well, we can make a nice l-calendar.lua module together > > just provide me the calculations (i can implement to lua code but i have > no time to figure out all the logic) > > > Hans > > ----------------------------------------------------------------- > Hans Hagen | PRAGMA ADE > Ridderstraat 27 | 8061 GH Hasselt | The Netherlands > tel: 038 477 53 69 | fax: 038 477 53 74 | www.pragma-ade.com > | www.pragma-pod.nl > ----------------------------------------------------------------- > ___________________________________________________________________________________ > If your question is of interest to others as well, please add an entry to the > Wiki! > > maillist : ntg-context@ntg.nl / http://www.ntg.nl/mailman/listinfo/ntg-context > webpage : http://www.pragma-ade.nl / http://tex.aanhet.net > archive : https://foundry.supelec.fr/projects/contextrev/ > wiki : http://contextgarden.net > ___________________________________________________________________________________ ___________________________________________________________________________________ If your question is of interest to others as well, please add an entry to the Wiki! maillist : ntg-context@ntg.nl / http://www.ntg.nl/mailman/listinfo/ntg-context webpage : http://www.pragma-ade.nl / http://tex.aanhet.net archive : https://foundry.supelec.fr/projects/contextrev/ wiki : http://contextgarden.net ___________________________________________________________________________________
