89 lines
3.4 KiB
C
89 lines
3.4 KiB
C
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/****************************************************************************
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* sched/clock_dow.c
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*
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* Copyright (C) 2012 Gregory Nutt. All rights reserved.
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* Author: Gregory Nutt <gnutt@nuttx.org>
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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*
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in
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* the documentation and/or other materials provided with the
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* distribution.
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* 3. Neither the name NuttX nor the names of its contributors may be
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* used to endorse or promote products derived from this software
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* without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
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* FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
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* COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
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* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
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* BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
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* OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
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* AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
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* ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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* POSSIBILITY OF SUCH DAMAGE.
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*
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****************************************************************************/
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/****************************************************************************
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* Included Files
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****************************************************************************/
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#include <nuttx/config.h>
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#include <stdint.h>
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#include <nuttx/clock.h>
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#include "clock_internal.h"
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/****************************************************************************
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* Pre-processor Definitions
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****************************************************************************/
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/****************************************************************************
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* Private Data
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****************************************************************************/
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/* 23 * (month + 1) / 9, month = 0..11 */
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static const uint8_t g_lookup[12] = {2, 5, 7, 10, 12, 15, 17, 20, 23, 25, 28, 30};
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/****************************************************************************
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* Public Functions
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****************************************************************************/
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/****************************************************************************
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* Name: clock_dow
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*
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* Description:
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* Calculate the day of week (DOW) from they year month and day. Based on
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* an algorithm pubished in 1990 by Michael Keith and Tom Craver with some
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* tweaks to handle months in the range 0-11.
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*
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* Parameters:
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* year - year (e.g., 1988)
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* month - 0 through 11
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* day - 1 through 31
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*
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* Return Value:
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* The day of the week as days since Sunday: 0 = Sunday, 1 = Monday, etc.
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*
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* Assumptions:
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*
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****************************************************************************/
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int clock_dow(int year, int month, int day)
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{
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day += month < 2 ? year-- : year - 2;
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return ((int)g_lookup[month] + day + 4 + year/4 - year/100 + year/400) % 7;
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}
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