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/*
Anacron - run commands periodically
Copyright (C) 1998 Itai Tzur <itzur@actcom.co.il>
Copyright (C) 1999 Sean 'Shaleh' Perry <shaleh@debian.org>
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
The GNU General Public License can also be found in the file
`COPYING' that comes with the Anacron source distribution.
*/
#include <limits.h>
#include "gregor.h"
const static int
days_in_month[] = {
31, /* Jan */
28, /* Feb (non-leap) */
31, /* Mar */
30, /* Apr */
31, /* May */
30, /* Jun */
31, /* Jul */
31, /* Aug */
30, /* Sep */
31, /* Oct */
30, /* Nov */
31 /* Dec */
};
static int leap(int year);
int
day_num(int year, int month, int day)
/* Return the "day number" of the date year-month-day according to the
* "proleptic Gregorian calendar".
* If the given date is invalid, return -1.
*
* Here, "day number" is defined as the number of days since December 31,
* 1 B.C. (Gregorian). (January 1, 1 A.D. is day number 1 etc...)
*
* The Gregorian calendar was instituted by Pope Gregory XIII in 1582,
* and has gradually spread to become the international standard calendar.
* The proleptic Gregorian calendar is formed by projecting the date system
* of the Gregorian calendar to dates before its adoption.
*
* For more details, see:
* http://astro.nmsu.edu/~lhuber/leaphist.html
* http://www.magnet.ch/serendipity/hermetic/cal_stud/cal_art.htm
* and your local library.
*/
{
int dn;
int i;
const int isleap; /* save three calls to leap() */
/* Some validity checks */
/* we don't deal with B.C. years here */
if (year < 1) return - 1;
/* conservative overflow estimate */
if (year > (INT_MAX / 366)) return - 1;
if (month > 12 || month < 1) return - 1;
if (day < 1) return - 1;
isleap = leap(year);
if (month != 2) {
if(day > days_in_month[month - 1]) return - 1;
}
else if ((isleap && day > 29) || (!isleap && day > 28))
return - 1;
/* First calculate the day number of December 31 last year */
/* save us from doing (year - 1) over and over */
i = year - 1;
/* 365 days in a "regular" year + number of leap days */
dn = (i * 365) + ((i / 4) - (i / 100) + (i / 400));
/* Now, day number of the last day of the previous month */
for (i = month - 1; i > 0; --i)
dn += days_in_month[i - 1];
/* Add 29 February ? */
if (month > 2 && isleap) ++dn;
/* How many days into month are we */
dn += day;
return dn;
}
static int
leap(int year)
/* Is this a leap year ? */
{
/* every year exactly divisible by 4 is "leap" */
/* unless it is exactly divisible by 100 */
/* but not by 400 */
return (year % 4 == 0 && (year % 100 != 0 || year % 400 == 0));
}
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