1 /* $OpenBSD: pesach.c,v 1.2 2004/12/10 20:50:45 mickey Exp $ */ 2 3 /* 4 * Copyright (c) 2004 Michael Shalayeff 5 * All rights reserved. 6 * 7 * Permission to use, copy, modify, and distribute this software for any 8 * purpose with or without fee is hereby granted, provided that the above 9 * copyright notice and this permission notice appear in all copies. 10 * 11 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES 12 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF 13 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR 14 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES 15 * WHATSOEVER RESULTING FROM LOSS OF MIND, USE, DATA OR PROFITS, WHETHER IN 16 * AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT 17 * OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. 18 */ 19 20 #ifndef lint 21 static const char rcsid[] = "$OpenBSD: pesach.c,v 1.2 2004/12/10 20:50:45 mickey Exp $"; 22 #endif /* not lint */ 23 24 #include <stdio.h> 25 #include <tzfile.h> 26 27 #include "calendar.h" 28 29 /* Calculate the Julian date of Pesach using the Gauss formula */ 30 31 #define T (33. + 14. / 24.) 32 #define L ((1. + 485. / 1080.) / 24. / 19.) 33 #define K ((29. + (12. + 793. / 1080.) / 24. ) / 19.) 34 35 int 36 pesach(int R) 37 { 38 int a, b, y, cumdays; 39 double d; 40 41 y = R + 3760; 42 43 a = (12 * y + 17) % 19; 44 b = y % 4; 45 d = (T - 10 * K + L + 14) + K * a + b / 4. - L * y; 46 cumdays = d; 47 48 /* the postponement */ 49 switch ((int)(cumdays + 3 * y + 5 * b + 5) % 7) { 50 case 1: 51 if (a > 6 && d - cumdays >= (15. + 204. / 1080.) / 24.) 52 cumdays += 2; 53 break; 54 55 case 0: 56 if (a <= 11 || d - cumdays < (21. + 589. / 1080.) / 24.) 57 break; 58 /* FALLTHROUGH */ 59 case 2: 60 case 4: 61 case 6: 62 cumdays++; 63 break; 64 } 65 66 if (R > 1582) 67 cumdays += R / 100 - R /400 - 2; 68 69 return (31 + 28 + cumdays + (isleap(R)? 1 : 0)); 70 } 71