usr.bin/calendar/paskha.c

   1 /*
   2  * Copyright (C) 1993-1996 by Andrey A. Chernov, Moscow, Russia.
   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 ``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 REGENTS 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: src/usr.bin/calendar/paskha.c,v 1.8 2007/05/07 11:18:30 dwmalone Exp $
  27  * $DragonFly: src/usr.bin/calendar/paskha.c,v 1.5 2007/09/24 20:31:44 pavalos Exp $
  28  */
  29
  30 #include <stdio.h>
  31 #include <stdlib.h>
  32 #include <string.h>
  33 #include <time.h>
  34
  35 #include "calendar.h"
  36
  37 #define PASKHA "paskha"
  38 #define PASKHALEN (sizeof(PASKHA) - 1)
  39
  40 static int paskha(int);
  41
  42 /* return year day for Orthodox Easter using Gauss formula */
  43 /* (old style result) */
  44
  45 /* R: year */
  46 static int
  47 paskha(int R)
  48 {
  49         int a, b, c, d, e;
  50         static int x = 15;
  51         static int y = 6;
  52
  53         a = R % 19;
  54         b = R % 4;
  55         c = R % 7;
  56         d = (19*a + x) % 30;
  57         e = (2*b + 4*c + 6*d + y) % 7;
  58         return(((cumdays[3] + 1) + 22) + (d + e));
  59 }
  60
  61 /* return year day for Orthodox Easter depending days */
  62
  63 int
  64 getpaskha(char *s, int year)
  65 {
  66         int offset;
  67
  68         if (strncasecmp(s, PASKHA, PASKHALEN) == 0)
  69             s += PASKHALEN;
  70         else if (npaskha.name != NULL
  71                  && strncasecmp(s, npaskha.name, npaskha.len) == 0
  72                 )
  73             s += npaskha.len;
  74         else
  75             return(0);
  76
  77
  78         /* Paskha+1  or Paskha-2
  79          *       ^            ^   */
  80
  81         switch(*s) {
  82         case '-':
  83         case '+':
  84             offset = atoi(s);
  85             break;
  86
  87         default:
  88             offset = 0;
  89             break;
  90         }
  91
  92         return(paskha(year) + offset + 13/* new style */);
  93 }