ostern.c revision 50477 
1/*
2 * Copyright (c) 1996 Wolfram Schneider <wosch@FreeBSD.org>. Berlin.
3 * All rights reserved.
4 *
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions
7 * are met:
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.
13 *
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
24 * SUCH DAMAGE.
25 *
26 * $FreeBSD: head/usr.bin/calendar/ostern.c 50477 1999-08-28 01:08:13Z peter $
27 */
28
29#include <stdio.h>
30#include <stdlib.h>
31#include <string.h>
32#include <time.h>
33
34#include "calendar.h"
35
36/* return year day for Easter */
37
38int easter (year)
39    int year;            /* 0 ... abcd, NOT since 1900 */
40{
41
42    int e_a, e_b, e_c, e_d, e_e,e_f, e_g, e_h, e_i, e_k,
43        e_l, e_m, e_n, e_p, e_q;
44
45    /* silly, but it works */
46    e_a = year % 19;
47    e_b = year / 100;
48    e_c = year % 100;
49
50    e_d = e_b / 4;
51    e_e = e_b % 4;
52    e_f = (e_b + 8) / 25;
53    e_g = (e_b + 1 - e_f) / 3;
54    e_h = ((19 * e_a) + 15 + e_b - (e_d + e_g)) % 30;
55    e_i = e_c / 4;
56    e_k = e_c % 4;
57    e_l = (32 + 2 * e_e + 2 * e_i - (e_h + e_k)) % 7;
58    e_m = (e_a + 11 * e_h + 22 * e_l) / 451;
59    e_n = (e_h + e_l + 114 - (7 * e_m)) / 31;
60    e_p = (e_h + e_l + 114 - (7 * e_m)) % 31;
61    e_p = e_p + 1;
62
63    e_q = 31 + 28;
64
65    if (e_k == 0 && e_c != 0)
66	e_q += 1;
67
68    if (e_n == 4)
69	e_q += 31;
70
71    e_q += e_p;
72
73#if DEBUG
74    printf("%d %d %d %d %d %d %d %d %d %d %d %d %d %d %d\n", e_a , e_b , e_c , e_d , e_e , e_f , e_g , e_h , e_i , e_k , e_l , e_m , e_n  , e_p , e_q);
75#endif
76
77    return (e_q);
78}
79
80/* return year day for  Easter or easter depending days
81 * Match: Easter([+-][0-9]+)?
82 * e.g: Easter-2 is  Good Friday (2 days before Easter)
83 */
84
85int
86geteaster(s, year)
87	char *s;
88        int year;
89{
90	register int offset = 0;
91	extern struct fixs neaster;
92
93#define EASTER "easter"
94#define EASTERNAMELEN (sizeof(EASTER) - 1)
95
96	if (strncasecmp(s, EASTER, EASTERNAMELEN) == 0)
97	    s += EASTERNAMELEN;
98	else if (   neaster.name != NULL
99		 && strncasecmp(s, neaster.name, neaster.len) == 0
100		)
101	    s += neaster.len;
102	else
103	    return(0);
104
105#if DEBUG
106	printf("%s %d %d\n", s, year, EASTERNAMELEN);
107#endif
108
109	/* Easter+1  or Easter-2
110	 *       ^            ^   */
111
112	switch(*s) {
113
114	case '-':
115	case '+':
116	    offset = atoi(s);
117	    break;
118
119	default:
120	    offset = 0;
121	}
122
123	return (easter(year) + offset);
124}
125