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