wsutil/epochs.h

   1 /** @file
   2  *
   3  * Definitions of epoch values for various absolute time types.
   4  *
   5  * Wireshark - Network traffic analyzer
   6  * By Gerald Combs <gerald@wireshark.org>
   7  * Copyright 2006 Gerald Combs
   8  *
   9  * SPDX-License-Identifier: GPL-2.0-or-later
  10  */
  11
  12 #ifndef __EPOCHS_H__
  13 #define __EPOCHS_H__
  14
  15 #include <glib.h>
  16
  17 /*
  18  * Deltas between the epochs for various non-UN*X time stamp formats and
  19  * the January 1, 1970, 00:00:00 (proleptic?) UTC epoch for the UN*X time
  20  * stamp format.
  21  */
  22
  23 /*
  24  * 1900-01-01 00:00:00 (proleptic?) UTC.
  25  * Used by a number of time formats.
  26  */
  27 #define EPOCH_DELTA_1900_01_01_00_00_00_UTC 2208988800U
  28
  29 /*
  30  * 1904-01-01 00:00:00 (proleptic?) UTC.
  31  * Used in the classic Mac OS, and by formats, such as MPEG-4 Part 14 (MP4),
  32  * which is based on Apple's QuickTime format.
  33  */
  34 #define EPOCH_DELTA_1904_01_01_00_00_00_UTC  2082844800U
  35
  36 /*
  37  * 1601-01-01 (proleptic Gregorian) 00:00:00 (proleptic?) UTC.
  38  * The Windows NT epoch, used in a number of places, as it is
  39  * the start of a 400 year Gregorian cycle.
  40  *
  41  * This is
  42  *
  43  *     369*365.25*24*60*60-(3*24*60*60+6*60*60)
  44  *
  45  * or equivalently,
  46  *
  47  *     (89*4*365.25+(3*4+1)*365)*24*60*60
  48  *
  49  * 1970-1601 is 369; 365.25 is the average length of a year in days,
  50  * including leap years.
  51  *
  52  * 369 = 4*92 + 1, so there are 92 groups of 4 consecutive years plus
  53  * one leftover year, 1969, with 365 days.
  54  *
  55  * All but three of the groups of 4 consecutive years average 365.25 days
  56  * per year, as they have one leap year in the group. However, 1700, 1800,
  57  * and 1900 were not leap years, as, while they're all evenly divisible by 4,
  58  * they're also evenly divisible by 100, but not evenly divisible by 400.
  59  *
  60  * So we have 89 groups of 4 consecutive years that average 365.25
  61  * days per year, 3 groups of 4 consecutive years that average 365 days
  62  * (as they lack a leap year), and one leftover year, 1969, that is
  63  * 365 days long.
  64  */
  65 #define EPOCH_DELTA_1601_01_01_00_00_00_UTC UINT64_C(11644473600)
  66
  67 /*
  68  * 2000-01-01 00:00:00 UTC.
  69  * Used by the Zigbee Zigbee Cluster Library protocol.
  70  */
  71 #define EPOCH_DELTA_2000_01_01_00_00_00_UTC ((unsigned)(((3*365 + 366)*7 + 2*365)*24*3600))
  72
  73 #endif /* __EPOCHS_H__ */