paskha.c revision 200470 
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 200470 2009-12-13 04:50:11Z delphij $");
29
30#include <stdio.h>
31#include <stdlib.h>
32#include <string.h>
33
34#include "calendar.h"
35
36#define	PASKHA		"paskha"
37#define	PASKHALEN	(sizeof(PASKHA) - 1)
38
39static int paskha(int);
40
41/* return year day for Orthodox Easter using Gauss formula */
42/* (old style result) */
43
44static int
45paskha(int R) /*year*/
46{
47	int a, b, c, d, e;
48	static int x = 15;
49	static int y = 6;
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(char *s, int year)
63{
64	int offset;
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		s += npaskha.len;
71	else
72		return 0;
73
74	/* Paskha+1  or Paskha-2
75	 *       ^            ^   */
76
77	switch (*s) {
78
79	case '-':
80	case '+':
81		offset = atoi(s);
82		break;
83
84	default:
85		offset = 0;
86		break;
87	}
88
89	return (paskha(year) + offset + 13 /* new style */);
90}
91