74 lines
2.5 KiB
C
74 lines
2.5 KiB
C
/****************************************************************************
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* sched/clock/clock_dow.c
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*
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* Licensed to the Apache Software Foundation (ASF) under one or more
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* contributor license agreements. See the NOTICE file distributed with
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* this work for additional information regarding copyright ownership. The
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* ASF licenses this file to you under the Apache License, Version 2.0 (the
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* "License"); you may not use this file except in compliance with the
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* License. You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
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* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
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* License for the specific language governing permissions and limitations
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* under the License.
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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/clock.h"
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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] =
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{
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2, 5, 7, 10, 12, 15, 17, 20, 23, 25, 28, 30
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};
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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 published 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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* Input 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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* Returned 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 -
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year / 100 + year / 400) % 7;
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}
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