paskha.c revision 15714 
1/*
2 * Copyright (C) 1993-1996 by Andrey A. Chernov, Moscow, Russia.
3 * All rights reserved.
4 *
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions
7 * are met:
8 * 1. Redistributions of source code must retain the above copyright
9 *    notice, this list of conditions and the following disclaimer.
10 * 2. Redistributions in binary form must reproduce the above copyright
11 *    notice, this list of conditions and the following disclaimer in the
12 *    documentation and/or other materials provided with the distribution.
13 *
14 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND
15 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
16 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
17 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
18 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
19 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
20 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
21 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
22 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
23 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
24 * SUCH DAMAGE.
25 */
26
27#include <stdlib.h>
28#include <string.h>
29
30#define PASKHA "paskha"
31#define PASKHALEN (sizeof(PASKHA) - 1)
32
33/* KOI8-R encoding, needed to fully handle Russian case */
34#define PASKHA1 "�����"
35#define PASKHALEN1 (sizeof(PASKHA1) - 1)
36
37extern int *cumdays;
38
39/* return year day for Orthodox Easter using Gauss formula */
40/* (old style result) */
41
42static int
43paskha (R)
44int R;  /*year*/
45{
46	int a, b, c, d, e;
47	static int x = 15;
48	static int y = 6;
49
50	a = R % 19;
51	b = R % 4;
52	c = R % 7;
53	d = (19*a + x) % 30;
54	e = (2*b + 4*c + 6*d + y) % 7;
55	return ((cumdays[2/*feb*/] + 22/*mar*/) + (d + e));
56}
57
58/* return year day for Orthodox Easter depending days */
59
60int
61getpaskha(s, year)
62	char *s;
63        int year;
64{
65	int offset;
66
67	if (strncasecmp(s, PASKHA, PASKHALEN) == 0)
68	    s += PASKHALEN;
69	else if (strncasecmp(s, PASKHA1, PASKHALEN1) == 0)
70	    s += PASKHALEN1;
71	else
72	    return 0;
73
74
75	/* Paskha+1  or Paskha-2
76	 *       ^            ^   */
77
78	switch(*s) {
79
80	case '-':
81	case '+':
82	    offset = atoi(s);
83	    break;
84
85	default:
86	    offset = 0;
87	    break;
88	}
89
90	return (paskha(year) + offset + 13/* new style */);
91}
92