paskha.c revision 59945 
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 * $FreeBSD: head/usr.bin/calendar/paskha.c 59945 2000-05-04 11:28:55Z phantom $
27 */
28
29#include <stdio.h>
30#include <stdlib.h>
31#include <string.h>
32#include <time.h>
33
34#include "calendar.h"
35
36#define PASKHA "paskha"
37#define PASKHALEN (sizeof(PASKHA) - 1)
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	extern int *cumdays;
50
51	a = R % 19;
52	b = R % 4;
53	c = R % 7;
54	d = (19*a + x) % 30;
55	e = (2*b + 4*c + 6*d + y) % 7;
56	return (((cumdays[3] + 1) + 22) + (d + e));
57}
58
59/* return year day for Orthodox Easter depending days */
60
61int
62getpaskha(s, year)
63	char *s;
64        int year;
65{
66	int offset;
67	extern struct fixs npaskha;
68
69	if (strncasecmp(s, PASKHA, PASKHALEN) == 0)
70	    s += PASKHALEN;
71	else if (   npaskha.name != NULL
72		 && strncasecmp(s, npaskha.name, npaskha.len) == 0
73		)
74	    s += npaskha.len;
75	else
76	    return 0;
77
78
79	/* Paskha+1  or Paskha-2
80	 *       ^            ^   */
81
82	switch(*s) {
83
84	case '-':
85	case '+':
86	    offset = atoi(s);
87	    break;
88
89	default:
90	    offset = 0;
91	    break;
92	}
93
94	return (paskha(year) + offset + 13/* new style */);
95}
96