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diff --git a/wsutil/epochs.h b/wsutil/epochs.h
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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__ */