1 /*-
2 * SPDX-License-Identifier: BSD-2-Clause
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 <sys/cdefs.h>
30 #include <stdio.h>
31 #include <stdlib.h>
32 #include <string.h>
33
34 #include "calendar.h"
35
36 #define PASKHA "paskha"
37 #define PASKHALEN (sizeof(PASKHA) - 1)
38
39 /* return difference in days between Julian and Gregorian calendars */
40 int
j2g(int year)41 j2g(int year)
42 {
43 return (year < 1500) ?
44 0 :
45 10 + (year/100 - 16) - ((year/100 - 16) / 4);
46 }
47
48 /* return year day for Orthodox Easter using Gauss formula */
49 /* (new style result) */
50
51 int
paskha(int R)52 paskha(int R) /*year*/
53 {
54 int a, b, c, d, e;
55 static int x = 15;
56 static int y = 6;
57 int *cumday;
58
59 a = R % 19;
60 b = R % 4;
61 c = R % 7;
62 d = (19 * a + x) % 30;
63 e = (2 * b + 4 * c + 6 * d + y) % 7;
64 cumday = cumdaytab[isleap(R)];
65 return (((cumday[3] + 1) + 22) + (d + e) + j2g(R));
66 }
67