2 * Copyright (c) 1996 Wolfram Schneider <wosch@FreeBSD.org>. Berlin.
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions
8 * 1. Redistributions of source code must retain the above copyright
9 * notice, this list of conditions and the following disclaimer.
10 * 2. Redistributions in binary form must reproduce the above copyright
11 * notice, this list of conditions and the following disclaimer in the
12 * documentation and/or other materials provided with the distribution.
14 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
15 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
16 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
17 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
18 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
19 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
20 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
21 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
22 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
23 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
26 * $FreeBSD: src/usr.bin/calendar/ostern.c,v 1.8.2.2 2002/05/27 12:14:46 dwmalone Exp $
27 * $DragonFly: src/usr.bin/calendar/ostern.c,v 1.3 2003/10/02 17:42:26 hmp Exp $
37 /* return year day for Easter */
40 * This code is based on the Calendar FAQ's code for how to calculate
41 * easter is. This is the Gregorian calendar version. They refer to
42 * the Algorithm of Oudin in the "Explanatory Supplement to the
43 * Astronomical Almanac".
48 int G, /* Golden number - 1 */
50 H, /* 23 - epact % 30 */
51 I, /* days from 21 March to Paschal full moon */
52 J, /* weekday of full moon */
53 L; /* days from 21 March to Sunday on of before full moon */
57 H = (C - C/4 - (8*C+13)/25 + 19*G + 15) % 30;
58 I = H - (H/28)*(1 - (H/28)*(29/(H + 1))*((21 - G)/11));
59 J = (year + year/4 + I + 2 - C + C/4) % 7;
63 if (year % 400 == 0 || (year % 4 == 0 && year % 100 != 0))
64 return 31 + 29 + 21 + L + 7;
66 return 31 + 28 + 21 + L + 7;
69 /* return year day for Easter or easter depending days
70 * Match: Easter([+-][0-9]+)?
71 * e.g: Easter-2 is Good Friday (2 days before Easter)
75 geteaster(char *s, int year)
78 extern struct fixs neaster;
80 #define EASTER "easter"
81 #define EASTERNAMELEN (sizeof(EASTER) - 1)
83 if (strncasecmp(s, EASTER, EASTERNAMELEN) == 0)
85 else if ( neaster.name != NULL
86 && strncasecmp(s, neaster.name, neaster.len) == 0
93 printf("%s %d %d\n", s, year, EASTERNAMELEN);
96 /* Easter+1 or Easter-2
110 return (easter(year) + offset);