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 27 #include <sys/cdefs.h> 28 __FBSDID("$FreeBSD$"); 29 30 #include <stdio.h> 31 #include <stdlib.h> 32 #include <string.h> 33 #include <time.h> 34 35 #include "calendar.h" 36 37 /* return year day for Easter */ 38 39 /* 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". 44 */ 45 46 int 47 easter(int year) /* 0 ... abcd, NOT since 1900 */ 48 { 49 int G, /* Golden number - 1 */ 50 C, /* Century */ 51 H, /* 23 - epact % 30 */ 52 I, /* days from 21 March to Paschal full moon */ 53 J, /* weekday of full moon */ 54 L; /* days from 21 March to Sunday on of before full moon */ 55 56 G = year % 19; 57 C = year / 100; 58 H = (C - C / 4 - (8 * C + 13) / 25 + 19 * G + 15) % 30; 59 I = H - (H / 28) * (1 - (H / 28) * (29 / (H + 1)) * ((21 - G) / 11)); 60 J = (year + year / 4 + I + 2 - C + C / 4) % 7; 61 62 L = I - J; 63 64 if (year % 400 == 0 || (year % 4 == 0 && year % 100 != 0)) 65 return 31 + 29 + 21 + L + 7; 66 else 67 return 31 + 28 + 21 + L + 7; 68 } 69 70 /* return year day for Easter or easter depending days 71 * Match: Easter([+-][0-9]+)? 72 * e.g: Easter-2 is Good Friday (2 days before Easter) 73 */ 74 75 int 76 geteaster(char *s, int year) 77 { 78 int offset = 0; 79 80 #define EASTER "easter" 81 #define EASTERNAMELEN (sizeof(EASTER) - 1) 82 83 if (strncasecmp(s, EASTER, EASTERNAMELEN) == 0) 84 s += EASTERNAMELEN; 85 else if (neaster.name != NULL 86 && strncasecmp(s, neaster.name, neaster.len) == 0) 87 s += neaster.len; 88 else 89 return (0); 90 91 #if DEBUG 92 printf("%s %d %d\n", s, year, EASTERNAMELEN); 93 #endif 94 95 /* Easter+1 or Easter-2 96 * ^ ^ */ 97 98 switch (*s) { 99 100 case '-': 101 case '+': 102 offset = atoi(s); 103 break; 104 105 default: 106 offset = 0; 107 } 108 109 return (easter(year) + offset); 110 } 111