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- Plugged in a different algorithm for calculating the day of the week in

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strftime() and asctime_r(). This one isn't sensitive to the effects of
  adding/subtracting the local time zone.


git-svn-id: file:///Users/olsen/Code/migration-svn-zu-git/logical-line-staging/clib2/trunk@14813 87f5fb63-7c3d-0410-a384-fd976d0f7a62
This commit is contained in:
Olaf Barthel
2005-01-26 18:41:39 +00:00
parent 987316e638
commit 0b1d21471d
8 changed files with 113 additions and 34 deletions
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86
library/time_weekday.c Normal file
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/*
* $Id: time_weekday.c,v 1.1 2005-01-26 18:41:39 obarthel Exp $
*
* :ts=4
*
* Portable ISO 'C' (1994) runtime library for the Amiga computer
* Copyright (c) 2002-2005 by Olaf Barthel <olsen@sourcery.han.de>
* 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);
}