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/* $OpenBSD: pesach.c,v 1.2 2004/12/10 20:50:45 mickey Exp $ */
/*
* Copyright (c) 2004 Michael Shalayeff
* All rights reserved.
*
* Permission to use, copy, modify, and distribute this software for any
* purpose with or without fee is hereby granted, provided that the above
* copyright notice and this permission notice appear in all copies.
*
* THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
* WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
* MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
* ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
* WHATSOEVER RESULTING FROM LOSS OF MIND, USE, DATA OR PROFITS, WHETHER IN
* AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT
* OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
*/
#ifndef lint
static const char rcsid[] = "$OpenBSD: pesach.c,v 1.2 2004/12/10 20:50:45 mickey Exp $";
#endif /* not lint */
#include <stdio.h>
#include <tzfile.h>
#include "calendar.h"
/* Calculate the Julian date of Pesach using the Gauss formula */
#define T (33. + 14. / 24.)
#define L ((1. + 485. / 1080.) / 24. / 19.)
#define K ((29. + (12. + 793. / 1080.) / 24. ) / 19.)
int
pesach(int R)
{
int a, b, y, cumdays;
double d;
y = R + 3760;
a = (12 * y + 17) % 19;
b = y % 4;
d = (T - 10 * K + L + 14) + K * a + b / 4. - L * y;
cumdays = d;
/* the postponement */
switch ((int)(cumdays + 3 * y + 5 * b + 5) % 7) {
case 1:
if (a > 6 && d - cumdays >= (15. + 204. / 1080.) / 24.)
cumdays += 2;
break;
case 0:
if (a <= 11 || d - cumdays < (21. + 589. / 1080.) / 24.)
break;
/* FALLTHROUGH */
case 2:
case 4:
case 6:
cumdays++;
break;
}
if (R > 1582)
cumdays += R / 100 - R /400 - 2;
return (31 + 28 + cumdays + (isleap(R)? 1 : 0));
}
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