paskha.c revision 15737 
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 <stdio.h>
28#include <stdlib.h>
29#include <string.h>
30#include <time.h>
31
32#include "calendar.h"
33
34#define PASKHA "paskha"
35#define PASKHALEN (sizeof(PASKHA) - 1)
36
37/* return year day for Orthodox Easter using Gauss formula */
38/* (old style result) */
39
40static int
41paskha (R)
42int R;  /*year*/
43{
44	int a, b, c, d, e;
45	static int x = 15;
46	static int y = 6;
47	extern int *cumdays;
48
49	a = R % 19;
50	b = R % 4;
51	c = R % 7;
52	d = (19*a + x) % 30;
53	e = (2*b + 4*c + 6*d + y) % 7;
54	return (((cumdays[3] + 1) + 22) + (d + e));
55}
56
57/* return year day for Orthodox Easter depending days */
58
59int
60getpaskha(s, year)
61	char *s;
62        int year;
63{
64	int offset;
65	extern struct fixs npaskha;
66
67	if (strncasecmp(s, PASKHA, PASKHALEN) == 0)
68	    s += PASKHALEN;
69	else if (   npaskha.name != NULL
70		 && strncasecmp(s, npaskha.name, npaskha.len) == 0
71		)
72	    s += npaskha.len;
73	else
74	    return 0;
75
76
77	/* Paskha+1  or Paskha-2
78	 *       ^            ^   */
79
80	switch(*s) {
81
82	case '-':
83	case '+':
84	    offset = atoi(s);
85	    break;
86
87	default:
88	    offset = 0;
89	    break;
90	}
91
92	return (paskha(year) + offset + 13/* new style */);
93}
94