paskha.c revision 181322 
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 <sys/cdefs.h>
28__FBSDID("$FreeBSD: head/usr.bin/calendar/paskha.c 181322 2008-08-05 08:11:54Z edwin $");
29
30#include <stdio.h>
31#include <stdlib.h>
32#include <string.h>
33#include <time.h>
34
35#include "calendar.h"
36
37#define	PASKHA		"paskha"
38#define	PASKHALEN	(sizeof(PASKHA) - 1)
39
40static int paskha(int);
41
42/* return year day for Orthodox Easter using Gauss formula */
43/* (old style result) */
44
45static int
46paskha(int R) /*year*/
47{
48	int a, b, c, d, e;
49	static int x = 15;
50	static int y = 6;
51
52	a = R % 19;
53	b = R % 4;
54	c = R % 7;
55	d = (19 * a + x) % 30;
56	e = (2 * b + 4 * c + 6 * d + y) % 7;
57	return (((cumdays[3] + 1) + 22) + (d + e));
58}
59
60/* return year day for Orthodox Easter depending days */
61
62int
63getpaskha(char *s, int year)
64{
65	int offset;
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		s += npaskha.len;
72	else
73		return 0;
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