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