ostern.c revision 13840
1/* 2 * Copyright (c) 1995 Wolfram Schneider. Public domain. 3 * 4 * $Id: ostern.c,v 1.2 1996/02/01 13:05:12 wosch Exp $ 5*/ 6 7#include <string.h> 8 9/* return year day for Easter */ 10 11int easter (year) 12 int year; /* 0 ... abcd, NOT since 1900 */ 13{ 14 15 int e_a, e_b, e_c, e_d, e_e,e_f, e_g, e_h, e_i, e_k, 16 e_l, e_m, e_n, e_p, e_q; 17 18 /* silly, but it works */ 19 e_a = year % 19; 20 e_b = year / 100; 21 e_c = year % 100; 22 23 e_d = e_b / 4; 24 e_e = e_b % 4; 25 e_f = (e_b + 8) / 25; 26 e_g = (e_b + 1 - e_f) / 3; 27 e_h = ((19 * e_a) + 15 + e_b - (e_d + e_g)) % 30; 28 e_i = e_c / 4; 29 e_k = e_c % 4; 30 e_l = (32 + 2 * e_e + 2 * e_i - (e_h + e_k)) % 7; 31 e_m = (e_a + 11 * e_h + 22 * e_l) / 451; 32 e_n = (e_h + e_l + 114 - (7 * e_m)) / 31; 33 e_p = (e_h + e_l + 114 - (7 * e_m)) % 31; 34 e_p = e_p + 1; 35 36 e_q = 31 + 28; 37 38 if (e_k == 0 && e_c != 0) 39 e_q += 1; 40 41 if (e_n == 4) 42 e_q += 31; 43 44 e_q += e_p; 45 46#if DEBUG 47 printf("%d %d %d %d %d %d %d %d %d %d %d %d %d %d %d\n", e_a , e_b , e_c , e_d , e_e , e_f , e_g , e_h , e_i , e_k , e_l , e_m , e_n , e_p , e_q); 48#endif 49 50 return (e_q); 51} 52 53/* return year day for Easter or easter depending days 54 * Match: Easter([+-][0-9]+)? 55 * e.g: Easter-2 is Good Friday (2 days before Easter) 56 */ 57 58int 59geteaster(s, year) 60 char *s; 61 int year; 62{ 63 register int offset = 0; 64 65#define EASTER "easter" 66#define EASTERNAMELEN (sizeof(EASTER) - 1) 67 68 /* no easter */ 69 if (strncasecmp(s, EASTER, EASTERNAMELEN)) 70 return(0); 71 72#if DEBUG 73 printf("%s %d %d\n", s, year, EASTERNAMELEN); 74#endif 75 76 /* Easter+1 or Easter-2 77 * ^ ^ */ 78 79 switch(*(s + EASTERNAMELEN)) { 80 81 case '-': 82 offset = -(atoi(s + EASTERNAMELEN + 1)); 83 break; 84 85 case '+': 86 offset = atoi(s + EASTERNAMELEN + 1); 87 break; 88 89 default: 90 offset = 0; 91 } 92 93 return (easter(year) + offset); 94} 95