xref: /freebsd-9.3-release/usr.bin/calendar/paskha.c

/*
 * Copyright (C) 1993-1996 by Andrey A. Chernov, Moscow, Russia.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

#include <sys/cdefs.h>
__FBSDID("$FreeBSD: head/usr.bin/calendar/paskha.c 200420 2009-12-11 23:35:38Z delphij $");

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#include "calendar.h"

#define	PASKHA		"paskha"
#define	PASKHALEN	(sizeof(PASKHA) - 1)

static int paskha(int);

/* return year day for Orthodox Easter using Gauss formula */
/* (old style result) */

static int
paskha(int R) /*year*/
{
	int a, b, c, d, e;
	static int x = 15;
	static int y = 6;

	a = R % 19;
	b = R % 4;
	c = R % 7;
	d = (19 * a + x) % 30;
	e = (2 * b + 4 * c + 6 * d + y) % 7;
	return (((cumdays[3] + 1) + 22) + (d + e));
}

/* return year day for Orthodox Easter depending days */

int
getpaskha(char *s, int year)
{
	int offset;

	if (strncasecmp(s, PASKHA, PASKHALEN) == 0)
		s += PASKHALEN;
	else if (npaskha.name != NULL
	    && strncasecmp(s, npaskha.name, npaskha.len) == 0)
		s += npaskha.len;
	else
		return 0;

	/* Paskha+1  or Paskha-2
	 *       ^            ^   */

	switch (*s) {

	case '-':
	case '+':
		offset = atoi(s);
		break;

	default:
		offset = 0;
		break;
	}

	return (paskha(year) + offset + 13 /* new style */);
}