ostern.c revision 15720 
1/*
2 * Copyright (c) 1995 Wolfram Schneider. Public domain.
3 *
4 * $Id: ostern.c,v 1.2 1996/05/10 16:29:42 ache Exp $
5*/
6
7#include <string.h>
8#include <stdlib.h>
9#include <stdio.h>
10
11#include "calendar.h"
12
13/* return year day for Easter */
14
15int easter (year)
16    int year;            /* 0 ... abcd, NOT since 1900 */
17{
18
19    int e_a, e_b, e_c, e_d, e_e,e_f, e_g, e_h, e_i, e_k,
20        e_l, e_m, e_n, e_p, e_q;
21
22    /* silly, but it works */
23    e_a = year % 19;
24    e_b = year / 100;
25    e_c = year % 100;
26
27    e_d = e_b / 4;
28    e_e = e_b % 4;
29    e_f = (e_b + 8) / 25;
30    e_g = (e_b + 1 - e_f) / 3;
31    e_h = ((19 * e_a) + 15 + e_b - (e_d + e_g)) % 30;
32    e_i = e_c / 4;
33    e_k = e_c % 4;
34    e_l = (32 + 2 * e_e + 2 * e_i - (e_h + e_k)) % 7;
35    e_m = (e_a + 11 * e_h + 22 * e_l) / 451;
36    e_n = (e_h + e_l + 114 - (7 * e_m)) / 31;
37    e_p = (e_h + e_l + 114 - (7 * e_m)) % 31;
38    e_p = e_p + 1;
39
40    e_q = 31 + 28;
41
42    if (e_k == 0 && e_c != 0)
43	e_q += 1;
44
45    if (e_n == 4)
46	e_q += 31;
47
48    e_q += e_p;
49
50#if DEBUG
51    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);
52#endif
53
54    return (e_q);
55}
56
57/* return year day for  Easter or easter depending days
58 * Match: Easter([+-][0-9]+)?
59 * e.g: Easter-2 is  Good Friday (2 days before Easter)
60 */
61
62int
63geteaster(s, year)
64	char *s;
65        int year;
66{
67	register int offset = 0;
68	extern struct fixs neaster;
69
70#define EASTER "easter"
71#define EASTERNAMELEN (sizeof(EASTER) - 1)
72
73	if (strncasecmp(s, EASTER, EASTERNAMELEN) == 0)
74	    s += EASTERNAMELEN;
75	else if (   neaster.name != NULL
76		 && strncasecmp(s, neaster.name, neaster.len) == 0
77		)
78	    s += neaster.len;
79	else
80	    return(0);
81
82#if DEBUG
83	printf("%s %d %d\n", s, year, EASTERNAMELEN);
84#endif
85
86	/* Easter+1  or Easter-2
87	 *       ^            ^   */
88
89	switch(*s) {
90
91	case '-':
92	case '+':
93	    offset = atoi(s);
94	    break;
95
96	default:
97	    offset = 0;
98	}
99
100	return (easter(year) + offset);
101}
102