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/****************************************************************************
* sched/clock_dow.c
*
* Copyright (C) 2012 Gregory Nutt. All rights reserved.
* Author: Gregory Nutt <gnutt@nuttx.org>
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
*
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in
* the documentation and/or other materials provided with the
* distribution.
* 3. Neither the name NuttX nor the names of its 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.
*
****************************************************************************/
/****************************************************************************
* Included Files
****************************************************************************/
#include <nuttx/config.h>
#include <stdint.h>
#include <nuttx/clock.h>
#include "clock_internal.h"
/****************************************************************************
* Pre-processor Definitions
****************************************************************************/
/****************************************************************************
* Private Data
****************************************************************************/
/* 23 * (month + 1) / 9, month = 0..11 */
static const uint8_t g_lookup[12] = {2, 5, 7, 10, 12, 15, 17, 20, 23, 25, 28, 30};
/****************************************************************************
* Public Functions
****************************************************************************/
/****************************************************************************
* Name: clock_dow
*
* Description:
* Calculate the day of week (DOW) from they year month and day. Based on
* an algorithm pubished in 1990 by Michael Keith and Tom Craver with some
* tweaks to handle months in the range 0-11.
*
* Parameters:
* year - year (e.g., 1988)
* month - 0 through 11
* day - 1 through 31
*
* Return Value:
* The day of the week as days since Sunday: 0 = Sunday, 1 = Monday, etc.
*
* Assumptions:
*
****************************************************************************/
int clock_dow(int year, int month, int day)
{
day += month < 2 ? year-- : year - 2;
return ((int)g_lookup[month] + day + 4 + year/4 - year/100 + year/400) % 7;
}
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