paskha.c revision 15723 
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#include <stdio.h>
30
31#include "calendar.h"
32
33#define PASKHA "paskha"
34#define PASKHALEN (sizeof(PASKHA) - 1)
35
36/* return year day for Orthodox Easter using Gauss formula */
37/* (old style result) */
38
39static int
40paskha (R)
41int R;  /*year*/
42{
43	int a, b, c, d, e;
44	static int x = 15;
45	static int y = 6;
46	extern int *cumdays;
47
48	a = R % 19;
49	b = R % 4;
50	c = R % 7;
51	d = (19*a + x) % 30;
52	e = (2*b + 4*c + 6*d + y) % 7;
53	return (((cumdays[3] + 1) + 22) + (d + e));
54}
55
56/* return year day for Orthodox Easter depending days */
57
58int
59getpaskha(s, year)
60	char *s;
61        int year;
62{
63	int offset;
64	extern struct fixs npaskha;
65
66	if (strncasecmp(s, PASKHA, PASKHALEN) == 0)
67	    s += PASKHALEN;
68	else if (   npaskha.name != NULL
69		 && strncasecmp(s, npaskha.name, npaskha.len) == 0
70		)
71	    s += npaskha.len;
72	else
73	    return 0;
74
75
76	/* Paskha+1  or Paskha-2
77	 *       ^            ^   */
78
79	switch(*s) {
80
81	case '-':
82	case '+':
83	    offset = atoi(s);
84	    break;
85
86	default:
87	    offset = 0;
88	    break;
89	}
90
91	return (paskha(year) + offset + 13/* new style */);
92}
93