70 lines
2.4 KiB
C
70 lines
2.4 KiB
C
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/*-
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* SPDX-License-Identifier: BSD-2-Clause-FreeBSD
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*
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* Copyright (c) 1996 Wolfram Schneider <wosch@FreeBSD.org>. Berlin.
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* All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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*
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* THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
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* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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* ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
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* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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* SUCH DAMAGE.
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*/
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#include <sys/cdefs.h>
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__FBSDID("$FreeBSD$");
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#include <stdio.h>
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#include <stdlib.h>
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#include <string.h>
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#include "calendar.h"
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/* return year day for Easter */
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/*
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* This code is based on the Calendar FAQ's code for how to calculate
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* easter is. This is the Gregorian calendar version. They refer to
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* the Algorithm of Oudin in the "Explanatory Supplement to the
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* Astronomical Almanac".
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*/
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int
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easter(int year) /* 0 ... abcd, NOT since 1900 */
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{
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int G, /* Golden number - 1 */
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C, /* Century */
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H, /* 23 - epact % 30 */
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I, /* days from 21 March to Paschal full moon */
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J, /* weekday of full moon */
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L; /* days from 21 March to Sunday on of before full moon */
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G = year % 19;
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C = year / 100;
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H = (C - C / 4 - (8 * C + 13) / 25 + 19 * G + 15) % 30;
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I = H - (H / 28) * (1 - (H / 28) * (29 / (H + 1)) * ((21 - G) / 11));
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J = (year + year / 4 + I + 2 - C + C / 4) % 7;
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L = I - J;
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if (isleap(year))
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return 31 + 29 + 21 + L + 7;
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else
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return 31 + 28 + 21 + L + 7;
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}
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