ostern.c revision 70598
117849Swosch/* 217849Swosch * Copyright (c) 1996 Wolfram Schneider <wosch@FreeBSD.org>. Berlin. 317849Swosch * All rights reserved. 413840Swosch * 517849Swosch * Redistribution and use in source and binary forms, with or without 617849Swosch * modification, are permitted provided that the following conditions 717849Swosch * are met: 817849Swosch * 1. Redistributions of source code must retain the above copyright 917849Swosch * notice, this list of conditions and the following disclaimer. 1017849Swosch * 2. Redistributions in binary form must reproduce the above copyright 1117849Swosch * notice, this list of conditions and the following disclaimer in the 1217849Swosch * documentation and/or other materials provided with the distribution. 1317849Swosch * 1417849Swosch * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND 1517849Swosch * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 1617849Swosch * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 1717849Swosch * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE 1817849Swosch * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 1917849Swosch * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 2017849Swosch * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 2117849Swosch * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 2217849Swosch * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 2317849Swosch * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 2417849Swosch * SUCH DAMAGE. 2517849Swosch * 2650477Speter * $FreeBSD: head/usr.bin/calendar/ostern.c 70598 2001-01-02 11:35:57Z dwmalone $ 2717849Swosch */ 2813840Swosch 2915737Sache#include <stdio.h> 3015737Sache#include <stdlib.h> 3113840Swosch#include <string.h> 3215737Sache#include <time.h> 3313840Swosch 3415720Sache#include "calendar.h" 3515720Sache 3613840Swosch/* return year day for Easter */ 3713840Swosch 3870598Sdwmalone/* 3970598Sdwmalone * This code is based on the Calendar FAQ's code for how to calculate 4070598Sdwmalone * easter is. This is the Gregorian calendar version. They refer to 4170598Sdwmalone * the Algorithm of Oudin in the "Explanatory Supplement to the 4270598Sdwmalone * Astronomical Almanac". 4370598Sdwmalone */ 4470598Sdwmalone 4513840Swoschint easter (year) 4613840Swosch int year; /* 0 ... abcd, NOT since 1900 */ 4713840Swosch{ 4870598Sdwmalone int G, /* Golden number - 1 */ 4970598Sdwmalone C, /* Century */ 5070598Sdwmalone H, /* 23 - epact % 30 */ 5170598Sdwmalone I, /* days from 21 March to Paschal full moon */ 5270598Sdwmalone J, /* weekday of full moon */ 5370598Sdwmalone L; /* days from 21 March to Sunday on of before full moon */ 5413840Swosch 5570598Sdwmalone G = year % 19; 5670598Sdwmalone C = year / 100; 5770598Sdwmalone H = (C - C/4 - (8*C+13)/25 + 19*G + 15) % 30; 5870598Sdwmalone I = H - (H/28)*(1 - (H/28)*(29/(H + 1))*((21 - G)/11)); 5970598Sdwmalone J = (year + year/4 + I + 2 - C + C/4) % 7; 6013840Swosch 6170598Sdwmalone L = I - J; 6213840Swosch 6370598Sdwmalone if (year % 400 == 0 || (year % 4 == 0 && year % 100 != 0)) 6470598Sdwmalone return 31 + 29 + 21 + L + 7; 6570598Sdwmalone else 6670598Sdwmalone return 31 + 28 + 21 + L + 7; 6713840Swosch} 6813840Swosch 6913840Swosch/* return year day for Easter or easter depending days 7013840Swosch * Match: Easter([+-][0-9]+)? 7113840Swosch * e.g: Easter-2 is Good Friday (2 days before Easter) 7213840Swosch */ 7313840Swosch 7413840Swoschint 7513840Swoschgeteaster(s, year) 7613840Swosch char *s; 7713840Swosch int year; 7813840Swosch{ 7913840Swosch register int offset = 0; 8015720Sache extern struct fixs neaster; 8113840Swosch 8213840Swosch#define EASTER "easter" 8313840Swosch#define EASTERNAMELEN (sizeof(EASTER) - 1) 8413840Swosch 8515720Sache if (strncasecmp(s, EASTER, EASTERNAMELEN) == 0) 8615720Sache s += EASTERNAMELEN; 8715720Sache else if ( neaster.name != NULL 8815720Sache && strncasecmp(s, neaster.name, neaster.len) == 0 8915720Sache ) 9015720Sache s += neaster.len; 9115720Sache else 9213840Swosch return(0); 9313840Swosch 9413840Swosch#if DEBUG 9513840Swosch printf("%s %d %d\n", s, year, EASTERNAMELEN); 9613840Swosch#endif 9713840Swosch 9813840Swosch /* Easter+1 or Easter-2 9913840Swosch * ^ ^ */ 10013840Swosch 10115720Sache switch(*s) { 10213840Swosch 10313840Swosch case '-': 10413840Swosch case '+': 10515720Sache offset = atoi(s); 10613840Swosch break; 10713840Swosch 10813840Swosch default: 10913840Swosch offset = 0; 11013840Swosch } 11113840Swosch 11213840Swosch return (easter(year) + offset); 11313840Swosch} 114