Annotation of src/usr.bin/calendar/pesach.c, Revision 1.4
1.4 ! millert 1: /* $OpenBSD: pesach.c,v 1.3 2009/10/27 23:59:36 deraadt Exp $ */
1.1 mickey 2:
3: /*
4: * Copyright (c) 2004 Michael Shalayeff
5: * All rights reserved.
6: *
7: * Permission to use, copy, modify, and distribute this software for any
8: * purpose with or without fee is hereby granted, provided that the above
9: * copyright notice and this permission notice appear in all copies.
10: *
11: * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
12: * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
13: * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
14: * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
15: * WHATSOEVER RESULTING FROM LOSS OF MIND, USE, DATA OR PROFITS, WHETHER IN
16: * AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT
17: * OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
18: */
19:
20: #include <stdio.h>
21:
22: #include "calendar.h"
23:
24: /* Calculate the Julian date of Pesach using the Gauss formula */
25:
26: #define T (33. + 14. / 24.)
27: #define L ((1. + 485. / 1080.) / 24. / 19.)
28: #define K ((29. + (12. + 793. / 1080.) / 24. ) / 19.)
29:
30: int
31: pesach(int R)
32: {
33: int a, b, y, cumdays;
34: double d;
35:
36: y = R + 3760;
37:
38: a = (12 * y + 17) % 19;
39: b = y % 4;
40: d = (T - 10 * K + L + 14) + K * a + b / 4. - L * y;
41: cumdays = d;
42:
43: /* the postponement */
44: switch ((int)(cumdays + 3 * y + 5 * b + 5) % 7) {
45: case 1:
46: if (a > 6 && d - cumdays >= (15. + 204. / 1080.) / 24.)
47: cumdays += 2;
48: break;
49:
50: case 0:
51: if (a <= 11 || d - cumdays < (21. + 589. / 1080.) / 24.)
52: break;
53: /* FALLTHROUGH */
54: case 2:
55: case 4:
56: case 6:
57: cumdays++;
58: break;
59: }
60:
61: if (R > 1582)
62: cumdays += R / 100 - R /400 - 2;
63:
64: return (31 + 28 + cumdays + (isleap(R)? 1 : 0));
65: }