/*-
* SPDX-License-Identifier: BSD-2-Clause
*
* Copyright (c) 1996 Wolfram Schneider <wosch@FreeBSD.org>. Berlin.
* 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 AND CONTRIBUTORS ``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 AUTHOR 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>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "calendar.h"
/* return year day for Easter */
/*
* This code is based on the Calendar FAQ's code for how to calculate
* easter is. This is the Gregorian calendar version. They refer to
* the Algorithm of Oudin in the "Explanatory Supplement to the
* Astronomical Almanac".
*/
int
easter(int year) /* 0 ... abcd, NOT since 1900 */
{
int G, /* Golden number - 1 */
C, /* Century */
H, /* 23 - epact % 30 */
I, /* days from 21 March to Paschal full moon */
J, /* weekday of full moon */
L; /* days from 21 March to Sunday on of before full moon */
G = year % 19;
C = year / 100;
H = (C - C / 4 - (8 * C + 13) / 25 + 19 * G + 15) % 30;
I = H - (H / 28) * (1 - (H / 28) * (29 / (H + 1)) * ((21 - G) / 11));
J = (year + year / 4 + I + 2 - C + C / 4) % 7;
L = I - J;
if (isleap(year))
return 31 + 29 + 21 + L + 7;
else
return 31 + 28 + 21 + L + 7;
}
plain