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 29 __FBSDID("$FreeBSD$"); 30 31 #include <stdio.h> 32 #include <stdlib.h> 33 #include <string.h> 34 #include <time.h> 35 36 #include "calendar.h" 37 38 /* return year day for Easter */ 39 40 /* 41 * This code is based on the Calendar FAQ's code for how to calculate 42 * easter is. This is the Gregorian calendar version. They refer to 43 * the Algorithm of Oudin in the "Explanatory Supplement to the 44 * Astronomical Almanac". 45 */ 46 47 int easter (year) 48 int year; /* 0 ... abcd, NOT since 1900 */ 49 { 50 int G, /* Golden number - 1 */ 51 C, /* Century */ 52 H, /* 23 - epact % 30 */ 53 I, /* days from 21 March to Paschal full moon */ 54 J, /* weekday of full moon */ 55 L; /* days from 21 March to Sunday on of before full moon */ 56 57 G = year % 19; 58 C = year / 100; 59 H = (C - C/4 - (8*C+13)/25 + 19*G + 15) % 30; 60 I = H - (H/28)*(1 - (H/28)*(29/(H + 1))*((21 - G)/11)); 61 J = (year + year/4 + I + 2 - C + C/4) % 7; 62 63 L = I - J; 64 65 if (year % 400 == 0 || (year % 4 == 0 && year % 100 != 0)) 66 return 31 + 29 + 21 + L + 7; 67 else 68 return 31 + 28 + 21 + L + 7; 69 } 70 71 /* return year day for Easter or easter depending days 72 * Match: Easter([+-][0-9]+)? 73 * e.g: Easter-2 is Good Friday (2 days before Easter) 74 */ 75 76 int 77 geteaster(s, year) 78 char *s; 79 int year; 80 { 81 int offset = 0; 82 extern struct fixs neaster; 83 84 #define EASTER "easter" 85 #define EASTERNAMELEN (sizeof(EASTER) - 1) 86 87 if (strncasecmp(s, EASTER, EASTERNAMELEN) == 0) 88 s += EASTERNAMELEN; 89 else if ( neaster.name != NULL 90 && strncasecmp(s, neaster.name, neaster.len) == 0 91 ) 92 s += neaster.len; 93 else 94 return(0); 95 96 #if DEBUG 97 printf("%s %d %d\n", s, year, EASTERNAMELEN); 98 #endif 99 100 /* Easter+1 or Easter-2 101 * ^ ^ */ 102 103 switch(*s) { 104 105 case '-': 106 case '+': 107 offset = atoi(s); 108 break; 109 110 default: 111 offset = 0; 112 } 113 114 return (easter(year) + offset); 115 } 116