1 /* $OpenBSD: ostern.c,v 1.5 2004/12/10 15:31:01 mickey Exp $ */
2
3 /*
4 * Copyright (c) 1996 Wolfram Schneider <wosch@FreeBSD.org>. Berlin.
5 * All rights reserved.
6 *
7 * Redistribution and use in source and binary forms, with or without
8 * modification, are permitted provided that the following conditions
9 * are met:
10 * 1. Redistributions of source code must retain the above copyright
11 * notice, this list of conditions and the following disclaimer.
12 * 2. Redistributions in binary form must reproduce the above copyright
13 * notice, this list of conditions and the following disclaimer in the
14 * documentation and/or other materials provided with the distribution.
15 *
16 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
17 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
18 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
19 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
20 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
21 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
22 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
23 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
24 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
25 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
26 * SUCH DAMAGE.
27 *
28 * $Id: ostern.c,v 1.5 2004/12/10 15:31:01 mickey Exp $
29 */
30
31 #ifndef lint
32 static const char rcsid[] = "$OpenBSD: ostern.c,v 1.5 2004/12/10 15:31:01 mickey Exp $";
33 #endif /* not lint */
34
35 #include <stdio.h>
36 #include <time.h>
37 #include <tzfile.h>
38
39 #include "calendar.h"
40
41 /* return year day for Easter */
42
easter(year)43 int easter (year)
44 int year; /* 0 ... abcd, NOT since 1900 */
45 {
46
47 int e_a, e_b, e_c, e_d, e_e,e_f, e_g, e_h, e_i, e_k,
48 e_l, e_m, e_n, e_p, e_q;
49
50 /* silly, but it works */
51 e_a = year % 19;
52 e_b = year / 100;
53 e_c = year % 100;
54
55 e_d = e_b / 4;
56 e_e = e_b % 4;
57 e_f = (e_b + 8) / 25;
58 e_g = (e_b + 1 - e_f) / 3;
59 e_h = ((19 * e_a) + 15 + e_b - (e_d + e_g)) % 30;
60 e_i = e_c / 4;
61 e_k = e_c % 4;
62 e_l = (32 + 2 * e_e + 2 * e_i - (e_h + e_k)) % 7;
63 e_m = (e_a + 11 * e_h + 22 * e_l) / 451;
64 e_n = (e_h + e_l + 114 - (7 * e_m)) / 31;
65 e_p = (e_h + e_l + 114 - (7 * e_m)) % 31;
66 e_p = e_p + 1;
67
68 e_q = 31 + 28 + e_p;
69 if (isleap(year))
70 e_q++;
71
72 if (e_n == 4)
73 e_q += 31;
74
75 #if DEBUG
76 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);
77 #endif
78
79 return (e_q);
80 }
81