paskha.c revision 205821 
1219019Sgabor/*-
2219019Sgabor * Copyright (C) 1993-1996 by Andrey A. Chernov, Moscow, Russia.
3219019Sgabor * All rights reserved.
4219019Sgabor *
5219019Sgabor * Redistribution and use in source and binary forms, with or without
6219019Sgabor * modification, are permitted provided that the following conditions
7219019Sgabor * are met:
8219019Sgabor * 1. Redistributions of source code must retain the above copyright
9219019Sgabor *    notice, this list of conditions and the following disclaimer.
10219019Sgabor * 2. Redistributions in binary form must reproduce the above copyright
11219019Sgabor *    notice, this list of conditions and the following disclaimer in the
12219019Sgabor *    documentation and/or other materials provided with the distribution.
13219019Sgabor *
14219019Sgabor * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND
15219019Sgabor * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
16219019Sgabor * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
17219019Sgabor * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
18219019Sgabor * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
19219019Sgabor * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
20219019Sgabor * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
21219019Sgabor * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
22219019Sgabor * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
23219019Sgabor * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
24219019Sgabor * SUCH DAMAGE.
25219019Sgabor */
26219019Sgabor
27219019Sgabor#include <sys/cdefs.h>
28219019Sgabor__FBSDID("$FreeBSD: head/usr.bin/calendar/paskha.c 205821 2010-03-29 06:49:20Z edwin $");
29219019Sgabor
30219019Sgabor#include <stdio.h>
31219019Sgabor#include <stdlib.h>
32219019Sgabor#include <string.h>
33219019Sgabor
34219019Sgabor#include "calendar.h"
35219019Sgabor
36219019Sgabor#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
42int
43paskha(int R) /*year*/
44{
45	int a, b, c, d, e;
46	static int x = 15;
47	static int y = 6;
48	int *cumday;
49
50	a = R % 19;
51	b = R % 4;
52	c = R % 7;
53	d = (19 * a + x) % 30;
54	e = (2 * b + 4 * c + 6 * d + y) % 7;
55	cumday = cumdaytab[isleap(R)];
56	return (((cumday[3] + 1) + 22) + (d + e));
57}
58