1 /* $OpenBSD: paskha.c,v 1.7 2015/03/15 00:41:28 millert Exp $ */
2
3 /*
4 * Copyright (C) 1993-1996 by Andrey A. Chernov, Moscow, Russia.
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 ``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 REGENTS 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
29 #include <stdio.h>
30
31 #include "calendar.h"
32
33 /* return year day for Orthodox Easter using Gauss formula */
34 /* (new style result); subtract 13 for old style */
35
36 int
paskha(int R)37 paskha(int R) /*year*/
38 {
39 int a, b, c, d, e;
40 static int x = 15;
41 static int y = 6;
42 int cumdays;
43
44 a = R % 19;
45 b = R % 4;
46 c = R % 7;
47 d = (19*a + x) % 30;
48 e = (2*b + 4*c + 6*d + y) % 7;
49 cumdays = 31 + 28;
50 if (isleap(R))
51 cumdays++;
52 return ((cumdays + 22) + (d + e) + 13);
53 }
54