62 lines
1.7 KiB
C
62 lines
1.7 KiB
C
/*
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* Copyright (c) 2019 Peter Bigot Consulting, LLC
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*
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* SPDX-License-Identifier: Apache-2.0
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*/
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/*
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* The time_days_from_civil function is derived directly from public
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* domain content written by Howard Hinnant and available at:
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* http://howardhinnant.github.io/date_algorithms.html#days_from_civil
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*/
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#include <zephyr/types.h>
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#include <sys/timeutil.h>
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/** Convert a civil (proleptic Gregorian) date to days relative to
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* 1970-01-01.
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*
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* @param y the calendar year
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* @param m the calendar month, in the range [1, 12]
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* @param d the day of the month, in the range [1, last_day_of_month(y, m)]
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*
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* @return the signed number of days between the specified day and
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* 1970-01-01
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*
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* @see http://howardhinnant.github.io/date_algorithms.html#days_from_civil
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*/
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static s64_t time_days_from_civil(s64_t y,
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unsigned int m,
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unsigned int d)
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{
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y -= m <= 2;
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s64_t era = (y >= 0 ? y : y - 399) / 400;
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unsigned int yoe = y - era * 400;
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unsigned int doy = (153U * (m + (m > 2 ? -3 : 9)) + 2U) / 5U + d;
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unsigned int doe = yoe * 365U + yoe / 4U - yoe / 100U + doy;
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return era * 146097 + (time_t)doe - 719468;
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}
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/** Convert civil time to UNIX time.
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*
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* @param tvp pointer to a civil time structure. `tm_year`, `tm_mon`,
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* `tm_mday`, `tm_hour`, `tm_min`, and `tm_sec` must be valid. All
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* other fields are ignored.
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*
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* @return the signed number of seconds between 1970-01-01T00:00:00
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* and the specified time ignoring leap seconds and DST offsets.
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*/
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time_t timeutil_timegm(struct tm *tm)
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{
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s64_t y = 1900 + (s64_t)tm->tm_year;
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unsigned int m = tm->tm_mon + 1;
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unsigned int d = tm->tm_mday - 1;
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s64_t ndays = time_days_from_civil(y, m, d);
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return (time_t)tm->tm_sec
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+ 60 * (tm->tm_min + 60 * tm->tm_hour)
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+ 86400 * ndays;
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}
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