48 lines
1.1 KiB
C
48 lines
1.1 KiB
C
// SPDX-License-Identifier: GPL-2.0+
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#include <common.h>
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#include <command.h>
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#include <errno.h>
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#include <rtc.h>
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#include <linux/time.h>
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static int month_offset[] = {
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0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334
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};
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/*
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* This only works for the Gregorian calendar - i.e. after 1752 (in the UK)
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*/
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int rtc_calc_weekday(struct rtc_time *tm)
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{
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int leaps_to_date;
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int last_year;
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int day;
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if (tm->tm_year < 1753)
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return -1;
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last_year = tm->tm_year - 1;
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/* Number of leap corrections to apply up to end of last year */
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leaps_to_date = last_year / 4 - last_year / 100 + last_year / 400;
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/*
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* This year is a leap year if it is divisible by 4 except when it is
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* divisible by 100 unless it is divisible by 400
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*
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* e.g. 1904 was a leap year, 1900 was not, 1996 is, and 2000 is.
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*/
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if (tm->tm_year % 4 == 0 &&
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((tm->tm_year % 100 != 0) || (tm->tm_year % 400 == 0)) &&
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tm->tm_mon > 2) {
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/* We are past Feb. 29 in a leap year */
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day = 1;
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} else {
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day = 0;
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}
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day += last_year * 365 + leaps_to_date + month_offset[tm->tm_mon - 1] +
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tm->tm_mday;
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tm->tm_wday = day % 7;
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return 0;
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} |