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/** @file
*
* Definitions of epoch values for various absolute time types.
*
* Wireshark - Network traffic analyzer
* By Gerald Combs <gerald@wireshark.org>
* Copyright 2006 Gerald Combs
*
* SPDX-License-Identifier: GPL-2.0-or-later
*/
#ifndef __EPOCHS_H__
#define __EPOCHS_H__
#include <glib.h>
/*
* Deltas between the epochs for various non-UN*X time stamp formats and
* the January 1, 1970, 00:00:00 (proleptic?) UTC epoch for the UN*X time
* stamp format.
*/
/*
* 1900-01-01 00:00:00 (proleptic?) UTC.
* Used by a number of time formats.
*/
#define EPOCH_DELTA_1900_01_01_00_00_00_UTC 2208988800U
/*
* 1904-01-01 00:00:00 (proleptic?) UTC.
* Used in the classic Mac OS, and by formats, such as MPEG-4 Part 14 (MP4),
* which is based on Apple's QuickTime format.
*/
#define EPOCH_DELTA_1904_01_01_00_00_00_UTC 2082844800U
/*
* 1601-01-01 (proleptic Gregorian) 00:00:00 (proleptic?) UTC.
* The Windows NT epoch, used in a number of places, as it is
* the start of a 400 year Gregorian cycle.
*
* This is
*
* 369*365.25*24*60*60-(3*24*60*60+6*60*60)
*
* or equivalently,
*
* (89*4*365.25+(3*4+1)*365)*24*60*60
*
* 1970-1601 is 369; 365.25 is the average length of a year in days,
* including leap years.
*
* 369 = 4*92 + 1, so there are 92 groups of 4 consecutive years plus
* one leftover year, 1969, with 365 days.
*
* All but three of the groups of 4 consecutive years average 365.25 days
* per year, as they have one leap year in the group. However, 1700, 1800,
* and 1900 were not leap years, as, while they're all evenly divisible by 4,
* they're also evenly divisible by 100, but not evenly divisible by 400.
*
* So we have 89 groups of 4 consecutive years that average 365.25
* days per year, 3 groups of 4 consecutive years that average 365 days
* (as they lack a leap year), and one leftover year, 1969, that is
* 365 days long.
*/
#define EPOCH_DELTA_1601_01_01_00_00_00_UTC G_GUINT64_CONSTANT(11644473600)
#endif /* __EPOCHS_H__ */
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