ostern.c revision 15737 
1/*
2 * Copyright (c) 1995 Wolfram Schneider. Public domain.
3 *
4 * $Id: ostern.c,v 1.3 1996/05/10 17:32:05 ache Exp $
5*/
6
7#include <stdio.h>
8#include <stdlib.h>
9#include <string.h>
10#include <time.h>
11
12#include "calendar.h"
13
14/* return year day for Easter */
15
16int easter (year)
17    int year;            /* 0 ... abcd, NOT since 1900 */
18{
19
20    int e_a, e_b, e_c, e_d, e_e,e_f, e_g, e_h, e_i, e_k,
21        e_l, e_m, e_n, e_p, e_q;
22
23    /* silly, but it works */
24    e_a = year % 19;
25    e_b = year / 100;
26    e_c = year % 100;
27
28    e_d = e_b / 4;
29    e_e = e_b % 4;
30    e_f = (e_b + 8) / 25;
31    e_g = (e_b + 1 - e_f) / 3;
32    e_h = ((19 * e_a) + 15 + e_b - (e_d + e_g)) % 30;
33    e_i = e_c / 4;
34    e_k = e_c % 4;
35    e_l = (32 + 2 * e_e + 2 * e_i - (e_h + e_k)) % 7;
36    e_m = (e_a + 11 * e_h + 22 * e_l) / 451;
37    e_n = (e_h + e_l + 114 - (7 * e_m)) / 31;
38    e_p = (e_h + e_l + 114 - (7 * e_m)) % 31;
39    e_p = e_p + 1;
40
41    e_q = 31 + 28;
42
43    if (e_k == 0 && e_c != 0)
44	e_q += 1;
45
46    if (e_n == 4)
47	e_q += 31;
48
49    e_q += e_p;
50
51#if DEBUG
52    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);
53#endif
54
55    return (e_q);
56}
57
58/* return year day for  Easter or easter depending days
59 * Match: Easter([+-][0-9]+)?
60 * e.g: Easter-2 is  Good Friday (2 days before Easter)
61 */
62
63int
64geteaster(s, year)
65	char *s;
66        int year;
67{
68	register int offset = 0;
69	extern struct fixs neaster;
70
71#define EASTER "easter"
72#define EASTERNAMELEN (sizeof(EASTER) - 1)
73
74	if (strncasecmp(s, EASTER, EASTERNAMELEN) == 0)
75	    s += EASTERNAMELEN;
76	else if (   neaster.name != NULL
77		 && strncasecmp(s, neaster.name, neaster.len) == 0
78		)
79	    s += neaster.len;
80	else
81	    return(0);
82
83#if DEBUG
84	printf("%s %d %d\n", s, year, EASTERNAMELEN);
85#endif
86
87	/* Easter+1  or Easter-2
88	 *       ^            ^   */
89
90	switch(*s) {
91
92	case '-':
93	case '+':
94	    offset = atoi(s);
95	    break;
96
97	default:
98	    offset = 0;
99	}
100
101	return (easter(year) + offset);
102}
103