mirror of
https://github.com/adtools/clib2.git
synced 2025-12-08 14:59:05 +00:00
7f0f7929ba
- Replaced ISO Latin 1 code #160 with a plain blank space (ASCII code #32) where necessary git-svn-id: file:///Users/olsen/Code/migration-svn-zu-git/logical-line-staging/clib2/trunk@15305 87f5fb63-7c3d-0410-a384-fd976d0f7a62
87 lines
2.7 KiB
C
87 lines
2.7 KiB
C
/*
|
|
* $Id: time_weekday.c,v 1.2 2006-01-08 12:04:27 obarthel Exp $
|
|
*
|
|
* :ts=4
|
|
*
|
|
* Portable ISO 'C' (1994) runtime library for the Amiga computer
|
|
* Copyright (c) 2002-2015 by Olaf Barthel <obarthel (at) gmx.net>
|
|
* All rights reserved.
|
|
*
|
|
* Redistribution and use in source and binary forms, with or without
|
|
* modification, are permitted provided that the following conditions
|
|
* are met:
|
|
*
|
|
* - Redistributions of source code must retain the above copyright
|
|
* notice, this list of conditions and the following disclaimer.
|
|
*
|
|
* - Neither the name of Olaf Barthel nor the names of contributors
|
|
* may be used to endorse or promote products derived from this
|
|
* software without specific prior written permission.
|
|
*
|
|
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
|
|
* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
|
|
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
|
|
* ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
|
|
* LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
|
|
* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
|
|
* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
|
|
* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
|
|
* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
|
|
* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
|
|
* POSSIBILITY OF SUCH DAMAGE.
|
|
*/
|
|
|
|
/****************************************************************************/
|
|
|
|
#ifndef _TIME_HEADERS_H
|
|
#include "time_headers.h"
|
|
#endif /* _TIME_HEADERS_H */
|
|
|
|
/****************************************************************************/
|
|
|
|
int
|
|
__calculate_weekday(int year,int month,int day)
|
|
{
|
|
/* This algorithm comes from <http://klausler.com/new-dayofweek.html>. */
|
|
static const char month_skew[12] =
|
|
{
|
|
0,3,3,6,
|
|
1,4,6,2,
|
|
5,0,3,5
|
|
};
|
|
|
|
int sum;
|
|
|
|
/* Subtract 1900 from the year. */
|
|
sum = year - 1900;
|
|
|
|
/* To that number, add one fourth of itself, discarding
|
|
any remainder. This sum is the year's skew value. */
|
|
sum += sum / 4;
|
|
|
|
/* If the month in question is January or February in a leap
|
|
year, subtract 1 from the sum. */
|
|
if(month == 1 || month == 2)
|
|
{
|
|
int leap_year_adjust;
|
|
|
|
/* Figure out if the year is a leap year. */
|
|
if((year % 4) != 0)
|
|
leap_year_adjust = 0;
|
|
else if ((year % 400) == 0)
|
|
leap_year_adjust = 1;
|
|
else if ((year % 100) == 0)
|
|
leap_year_adjust = 0;
|
|
else
|
|
leap_year_adjust = 1;
|
|
|
|
sum -= leap_year_adjust;
|
|
}
|
|
|
|
/* Add the month's skew value from the table. */
|
|
sum += day + month_skew[month-1];
|
|
|
|
/* The sum is the number of days after Sunday on which the date falls. */
|
|
return(sum % 7);
|
|
}
|