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sys: timeutil: add module

Add a generic API to provide the inverse operation for gmtime and as a
home for future generic time-related functions that are not in POSIX.

Signed-off-by: Peter A. Bigot <pab@pabigot.com>
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pabigot authored and carlescufi committed Jul 1, 2019
1 parent 3e8df8b commit 9d25b671bcd499a00ccc98d20789c3691ee07197
Showing with 103 additions and 0 deletions.
  1. +41 −0 include/sys/timeutil.h
  2. +1 −0 lib/os/CMakeLists.txt
  3. +61 −0 lib/os/timeutil.c
@@ -0,0 +1,41 @@
/*
* Copyright (c) 2019 Peter Bigot Consulting, LLC
*
* SPDX-License-Identifier: Apache-2.0
*/

/**
* @file
* @brief Utilities supporting operation on time data structures.
*
* POSIX defines gmtime() to convert from time_t to struct tm, but all
* inverse transformations are non-standard or require access to time
* zone information. timeutil_timegm() implements the functionality
* of the GNU extension timegm() function.
*/

#ifndef ZEPHYR_INCLUDE_SYS_TIMEUTIL_H_
#define ZEPHYR_INCLUDE_SYS_TIMEUTIL_H_

#include <time.h>

#ifdef __cplusplus
extern "C" {
#endif

/**
* @brief Convert broken-down time to a POSIX epoch offset in seconds.
*
* @param tm pointer to broken down time.
*
* @return the corresponding time in the POSIX epoch time scale.
*
* @see http://man7.org/linux/man-pages/man3/timegm.3.html
*/
time_t timeutil_timegm(struct tm *tm);

#ifdef __cplusplus
}
#endif

#endif /* ZEPHYR_INCLUDE_SYS_TIMEUTIL_H_ */
@@ -12,6 +12,7 @@ zephyr_sources(
mempool.c
rb.c
thread_entry.c
timeutil.c
work_q.c
)

@@ -0,0 +1,61 @@
/*
* Copyright (c) 2019 Peter Bigot Consulting, LLC
*
* SPDX-License-Identifier: Apache-2.0
*/

/*
* The time_days_from_civil function is derived directly from public
* domain content written by Howard Hinnant and available at:
* http://howardhinnant.github.io/date_algorithms.html#days_from_civil
*/

#include <zephyr/types.h>
#include <sys/timeutil.h>

/** Convert a civil (proleptic Gregorian) date to days relative to
* 1970-01-01.
*
* @param y the calendar year
* @param m the calendar month, in the range [1, 12]
* @param d the day of the month, in the range [1, last_day_of_month(y, m)]
*
* @return the signed number of days between the specified day and
* 1970-01-01
*
* @see http://howardhinnant.github.io/date_algorithms.html#days_from_civil
*/
static s64_t time_days_from_civil(s64_t y,
unsigned int m,
unsigned int d)
{
y -= m <= 2;

s64_t era = (y >= 0 ? y : y - 399) / 400;
unsigned int yoe = y - era * 400;
unsigned int doy = (153U * (m + (m > 2 ? -3 : 9)) + 2U) / 5U + d;
unsigned int doe = yoe * 365U + yoe / 4U - yoe / 100U + doy;

return era * 146097 + (time_t)doe - 719468;
}

/** Convert civil time to UNIX time.
*
* @param tvp pointer to a civil time structure. `tm_year`, `tm_mon`,
* `tm_mday`, `tm_hour`, `tm_min`, and `tm_sec` must be valid. All
* other fields are ignored.
*
* @return the signed number of seconds between 1970-01-01T00:00:00
* and the specified time ignoring leap seconds and DST offsets.
*/
time_t timeutil_timegm(struct tm *tm)
{
s64_t y = 1900 + (s64_t)tm->tm_year;
unsigned int m = tm->tm_mon + 1;
unsigned int d = tm->tm_mday - 1;
s64_t ndays = time_days_from_civil(y, m, d);

return (time_t)tm->tm_sec
+ 60 * (tm->tm_min + 60 * tm->tm_hour)
+ 86400 * ndays;
}

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