ostern.c revision 169343
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 */ 2613840Swosch 2787235Smarkm#include <sys/cdefs.h> 2887235Smarkm__FBSDID("$FreeBSD: head/usr.bin/calendar/ostern.c 169343 2007-05-07 11:18:30Z dwmalone $"); 2987235Smarkm 3015737Sache#include <stdio.h> 3115737Sache#include <stdlib.h> 3213840Swosch#include <string.h> 3315737Sache#include <time.h> 3413840Swosch 3515720Sache#include "calendar.h" 3615720Sache 3713840Swosch/* return year day for Easter */ 3813840Swosch 3970598Sdwmalone/* 4070598Sdwmalone * This code is based on the Calendar FAQ's code for how to calculate 4170598Sdwmalone * easter is. This is the Gregorian calendar version. They refer to 4270598Sdwmalone * the Algorithm of Oudin in the "Explanatory Supplement to the 4370598Sdwmalone * Astronomical Almanac". 4470598Sdwmalone */ 4570598Sdwmalone 46169343Sdwmaloneint 47169343Sdwmaloneeaster(int year) /* 0 ... abcd, NOT since 1900 */ 4813840Swosch{ 4970598Sdwmalone int G, /* Golden number - 1 */ 5070598Sdwmalone C, /* Century */ 5170598Sdwmalone H, /* 23 - epact % 30 */ 5270598Sdwmalone I, /* days from 21 March to Paschal full moon */ 5370598Sdwmalone J, /* weekday of full moon */ 5470598Sdwmalone L; /* days from 21 March to Sunday on of before full moon */ 5513840Swosch 5670598Sdwmalone G = year % 19; 5770598Sdwmalone C = year / 100; 5870598Sdwmalone H = (C - C/4 - (8*C+13)/25 + 19*G + 15) % 30; 5970598Sdwmalone I = H - (H/28)*(1 - (H/28)*(29/(H + 1))*((21 - G)/11)); 6070598Sdwmalone J = (year + year/4 + I + 2 - C + C/4) % 7; 6113840Swosch 6270598Sdwmalone L = I - J; 6313840Swosch 6470598Sdwmalone if (year % 400 == 0 || (year % 4 == 0 && year % 100 != 0)) 6570598Sdwmalone return 31 + 29 + 21 + L + 7; 6670598Sdwmalone else 6770598Sdwmalone return 31 + 28 + 21 + L + 7; 6813840Swosch} 6913840Swosch 7013840Swosch/* return year day for Easter or easter depending days 7113840Swosch * Match: Easter([+-][0-9]+)? 7213840Swosch * e.g: Easter-2 is Good Friday (2 days before Easter) 7313840Swosch */ 7413840Swosch 7513840Swoschint 76169343Sdwmalonegeteaster(char *s, int year) 7713840Swosch{ 7887235Smarkm int offset = 0; 7913840Swosch 8013840Swosch#define EASTER "easter" 8113840Swosch#define EASTERNAMELEN (sizeof(EASTER) - 1) 8213840Swosch 8315720Sache if (strncasecmp(s, EASTER, EASTERNAMELEN) == 0) 8415720Sache s += EASTERNAMELEN; 8515720Sache else if ( neaster.name != NULL 8615720Sache && strncasecmp(s, neaster.name, neaster.len) == 0 8715720Sache ) 8815720Sache s += neaster.len; 8915720Sache else 9013840Swosch return(0); 9113840Swosch 9213840Swosch#if DEBUG 9313840Swosch printf("%s %d %d\n", s, year, EASTERNAMELEN); 9413840Swosch#endif 9513840Swosch 9613840Swosch /* Easter+1 or Easter-2 9713840Swosch * ^ ^ */ 9813840Swosch 9915720Sache switch(*s) { 10013840Swosch 10113840Swosch case '-': 10213840Swosch case '+': 10315720Sache offset = atoi(s); 10413840Swosch break; 10513840Swosch 10613840Swosch default: 10713840Swosch offset = 0; 10813840Swosch } 10913840Swosch 11013840Swosch return (easter(year) + offset); 11113840Swosch} 112