mirror of
https://git.FreeBSD.org/src.git
synced 2024-12-20 11:11:24 +00:00
101 lines
2.8 KiB
C
101 lines
2.8 KiB
C
/*-
|
|
* Copyright (c) 1997 Wolfgang Helbig
|
|
* 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.
|
|
*
|
|
* $FreeBSD$
|
|
*/
|
|
|
|
#include "calendar.h"
|
|
|
|
typedef struct date date;
|
|
|
|
static int easterodn(int y);
|
|
|
|
/* Compute Easter Sunday in Gregorian Calendar */
|
|
date *
|
|
easterg(int y, date *dt)
|
|
{
|
|
int c, i, j, k, l, n;
|
|
|
|
n = y % 19;
|
|
c = y / 100;
|
|
k = (c - 17) / 25;
|
|
i = (c - c/4 -(c-k)/3 + 19 * n + 15) % 30;
|
|
i = i -(i/28) * (1 - (i/28) * (29/(i + 1)) * ((21 - n)/11));
|
|
j = (y + y/4 + i + 2 - c + c/4) % 7;
|
|
l = i - j;
|
|
dt->m = 3 + (l + 40) / 44;
|
|
dt->d = l + 28 - 31*(dt->m / 4);
|
|
dt->y = y;
|
|
return (dt);
|
|
}
|
|
|
|
/* Compute the Gregorian date of Easter Sunday in Julian Calendar */
|
|
date *
|
|
easterog(int y, date *dt)
|
|
{
|
|
|
|
return (gdate(easterodn(y), dt));
|
|
}
|
|
|
|
/* Compute the Julian date of Easter Sunday in Julian Calendar */
|
|
date *
|
|
easteroj(int y, date * dt)
|
|
{
|
|
|
|
return (jdate(easterodn(y), dt));
|
|
}
|
|
|
|
/* Compute the day number of Easter Sunday in Julian Calendar */
|
|
static int
|
|
easterodn(int y)
|
|
{
|
|
/*
|
|
* Table for the easter limits in one metonic (19-year) cycle. 21
|
|
* to 31 is in March, 1 through 18 in April. Easter is the first
|
|
* sunday after the easter limit.
|
|
*/
|
|
int mc[] = {5, 25, 13, 2, 22, 10, 30, 18, 7, 27, 15, 4,
|
|
24, 12, 1, 21, 9, 29, 17};
|
|
|
|
/* Offset from a weekday to next sunday */
|
|
int ns[] = {6, 5, 4, 3, 2, 1, 7};
|
|
date dt;
|
|
int dn;
|
|
|
|
/* Assign the easter limit of y to dt */
|
|
dt.d = mc[y % 19];
|
|
|
|
if (dt.d < 21)
|
|
dt.m = 4;
|
|
else
|
|
dt.m = 3;
|
|
|
|
dt.y = y;
|
|
|
|
/* Return the next sunday after the easter limit */
|
|
dn = ndaysj(&dt);
|
|
return (dn + ns[weekday(dn)]);
|
|
}
|