ostern.c revision 15714 
1/*
2 * Copyright (c) 1995 Wolfram Schneider. Public domain.
3 *
4 * $Id: ostern.c,v 1.1 1996/02/02 06:02:40 wosch Exp $
5*/
6
7#include <string.h>
8#include <stdlib.h>
9
10/* return year day for Easter */
11
12int easter (year)
13    int year;            /* 0 ... abcd, NOT since 1900 */
14{
15
16    int e_a, e_b, e_c, e_d, e_e,e_f, e_g, e_h, e_i, e_k,
17        e_l, e_m, e_n, e_p, e_q;
18
19    /* silly, but it works */
20    e_a = year % 19;
21    e_b = year / 100;
22    e_c = year % 100;
23
24    e_d = e_b / 4;
25    e_e = e_b % 4;
26    e_f = (e_b + 8) / 25;
27    e_g = (e_b + 1 - e_f) / 3;
28    e_h = ((19 * e_a) + 15 + e_b - (e_d + e_g)) % 30;
29    e_i = e_c / 4;
30    e_k = e_c % 4;
31    e_l = (32 + 2 * e_e + 2 * e_i - (e_h + e_k)) % 7;
32    e_m = (e_a + 11 * e_h + 22 * e_l) / 451;
33    e_n = (e_h + e_l + 114 - (7 * e_m)) / 31;
34    e_p = (e_h + e_l + 114 - (7 * e_m)) % 31;
35    e_p = e_p + 1;
36
37    e_q = 31 + 28;
38
39    if (e_k == 0 && e_c != 0)
40	e_q += 1;
41
42    if (e_n == 4)
43	e_q += 31;
44
45    e_q += e_p;
46
47#if DEBUG
48    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);
49#endif
50
51    return (e_q);
52}
53
54/* return year day for  Easter or easter depending days
55 * Match: Easter([+-][0-9]+)?
56 * e.g: Easter-2 is  Good Friday (2 days before Easter)
57 */
58
59int
60geteaster(s, year)
61	char *s;
62        int year;
63{
64	register int offset = 0;
65
66#define EASTER "easter"
67#define EASTERNAMELEN (sizeof(EASTER) - 1)
68
69	/* no easter */
70	if (strncasecmp(s, EASTER, EASTERNAMELEN))
71	    return(0);
72
73#if DEBUG
74	printf("%s %d %d\n", s, year, EASTERNAMELEN);
75#endif
76
77	/* Easter+1  or Easter-2
78	 *       ^            ^   */
79
80	switch(*(s + EASTERNAMELEN)) {
81
82	case '-':
83	    offset = -(atoi(s + EASTERNAMELEN + 1));
84	    break;
85
86	case '+':
87	    offset = atoi(s + EASTERNAMELEN + 1);
88	    break;
89
90	default:
91	    offset = 0;
92	}
93
94	return (easter(year) + offset);
95}
96