src/tools/tz/leap-seconds.list
#
# In the following text, the symbol '#' introduces
# a comment, which continues from that symbol until
# the end of the line. A plain comment line has a
# whitespace character following the comment indicator.
# There are also special comment lines defined below.
# A special comment will always have a non-whitespace
# character in column 2.
#
# A blank line should be ignored.
#
# The following table shows the corrections that must
# be applied to compute International Atomic Time (TAI)
# from the Coordinated Universal Time (UTC) values that
# are transmitted by almost all time services.
#
# The first column shows an epoch as a number of seconds
# since 1 January 1900, 00:00:00 (1900.0 is also used to
# indicate the same epoch.) Both of these time stamp formats
# ignore the complexities of the time scales that were
# used before the current definition of UTC at the start
# of 1972. (See note 3 below.)
# The second column shows the number of seconds that
# must be added to UTC to compute TAI for any timestamp
# at or after that epoch. The value on each line is
# valid from the indicated initial instant until the
# epoch given on the next one or indefinitely into the
# future if there is no next line.
# (The comment on each line shows the representation of
# the corresponding initial epoch in the usual
# day-month-year format. The epoch always begins at
# 00:00:00 UTC on the indicated day. See Note 5 below.)
#
# Important notes:
#
# 1. Coordinated Universal Time (UTC) is often referred to
# as Greenwich Mean Time (GMT). The GMT time scale is no
# longer used, and the use of GMT to designate UTC is
# discouraged.
#
# 2. The UTC time scale is realized by many national
# laboratories and timing centers. Each laboratory
# identifies its realization with its name: Thus
# UTC(NIST), UTC(USNO), etc. The differences among
# these different realizations are typically on the
# order of a few nanoseconds (i.e., 0.000 000 00x s)
# and can be ignored for many purposes. These differences
# are tabulated in Circular T, which is published monthly
# by the International Bureau of Weights and Measures
# (BIPM). See www.bipm.org for more information.
#
# 3. The current definition of the relationship between UTC
# and TAI dates from 1 January 1972. A number of different
# time scales were in use before that epoch, and it can be
# quite difficult to compute precise timestamps and time
# intervals in those "prehistoric" days. For more information,
# consult:
#
# The Explanatory Supplement to the Astronomical
# Ephemeris.
# or
# Terry Quinn, "The BIPM and the Accurate Measurement
# of Time," Proc. of the IEEE, Vol. 79, pp. 894-905,
# July, 1991. <http://dx.doi.org/10.1109/5.84965>
# reprinted in:
# Christine Hackman and Donald B Sullivan (eds.)
# Time and Frequency Measurement
# American Association of Physics Teachers (1996)
# <http://tf.nist.gov/general/pdf/1168.pdf>, pp. 75-86
#
# 4. The decision to insert a leap second into UTC is currently
# the responsibility of the International Earth Rotation and
# Reference Systems Service. (The name was changed from the
# International Earth Rotation Service, but the acronym IERS
# is still used.)
#
# Leap seconds are announced by the IERS in its Bulletin C.
#
# See www.iers.org for more details.
#
# Every national laboratory and timing center uses the
# data from the BIPM and the IERS to construct UTC(lab),
# their local realization of UTC.
#
# Although the definition also includes the possibility
# of dropping seconds ("negative" leap seconds), this has
# never been done and is unlikely to be necessary in the
# foreseeable future.
#
# 5. If your system keeps time as the number of seconds since
# some epoch (e.g., NTP timestamps), then the algorithm for
# assigning a UTC time stamp to an event that happens during a positive
# leap second is not well defined. The official name of that leap
# second is 23:59:60, but there is no way of representing that time
# in these systems.
# Many systems of this type effectively stop the system clock for
# one second during the leap second and use a time that is equivalent
# to 23:59:59 UTC twice. For these systems, the corresponding TAI
# timestamp would be obtained by advancing to the next entry in the
# following table when the time equivalent to 23:59:59 UTC
# is used for the second time. Thus the leap second which
# occurred on 30 June 1972 at 23:59:59 UTC would have TAI
# timestamps computed as follows:
#
# ...
# 30 June 1972 23:59:59 (2287785599, first time): TAI= UTC + 10 seconds
# 30 June 1972 23:59:60 (2287785599,second time): TAI= UTC + 11 seconds
# 1 July 1972 00:00:00 (2287785600) TAI= UTC + 11 seconds
# ...
#
# If your system realizes the leap second by repeating 00:00:00 UTC twice
# (this is possible but not usual), then the advance to the next entry
# in the table must occur the second time that a time equivalent to
# 00:00:00 UTC is used. Thus, using the same example as above:
#
# ...
# 30 June 1972 23:59:59 (2287785599): TAI= UTC + 10 seconds
# 30 June 1972 23:59:60 (2287785600, first time): TAI= UTC + 10 seconds
# 1 July 1972 00:00:00 (2287785600,second time): TAI= UTC + 11 seconds
# ...
#
# in both cases the use of timestamps based on TAI produces a smooth
# time scale with no discontinuity in the time interval. However,
# although the long-term behavior of the time scale is correct in both
# methods, the second method is technically not correct because it adds
# the extra second to the wrong day.
#
# This complexity would not be needed for negative leap seconds (if they
# are ever used). The UTC time would skip 23:59:59 and advance from
# 23:59:58 to 00:00:00 in that case. The TAI offset would decrease by
# 1 second at the same instant. This is a much easier situation to deal
# with, since the difficulty of unambiguously representing the epoch
# during the leap second does not arise.
#
# Some systems implement leap seconds by amortizing the leap second
# over the last few minutes of the day. The frequency of the local
# clock is decreased (or increased) to realize the positive (or
# negative) leap second. This method removes the time step described
# above. Although the long-term behavior of the time scale is correct
# in this case, this method introduces an error during the adjustment
# period both in time and in frequency with respect to the official
# definition of UTC.
#
# Questions or comments to:
# Judah Levine
# Time and Frequency Division
# NIST
# Boulder, Colorado
# Judah.Levine@nist.gov
#
# Last Update of leap second values: 8 July 2016
#
# The following line shows this last update date in NTP timestamp
# format. This is the date on which the most recent change to
# the leap second data was added to the file. This line can
# be identified by the unique pair of characters in the first two
# columns as shown below.
#
#$ 3676924800
#
# The NTP timestamps are in units of seconds since the NTP epoch,
# which is 1 January 1900, 00:00:00. The Modified Julian Day number
# corresponding to the NTP time stamp, X, can be computed as
#
# X/86400 + 15020
#
# where the first term converts seconds to days and the second
# term adds the MJD corresponding to the time origin defined above.
# The integer portion of the result is the integer MJD for that
# day, and any remainder is the time of day, expressed as the
# fraction of the day since 0 hours UTC. The conversion from day
# fraction to seconds or to hours, minutes, and seconds may involve
# rounding or truncation, depending on the method used in the
# computation.
#
# The data in this file will be updated periodically as new leap
# seconds are announced. In addition to being entered on the line
# above, the update time (in NTP format) will be added to the basic
# file name leap-seconds to form the name leap-seconds.<NTP TIME>.
# In addition, the generic name leap-seconds.list will always point to
# the most recent version of the file.
#
# This update procedure will be performed only when a new leap second
# is announced.
#
# The following entry specifies the expiration date of the data
# in this file in units of seconds since the origin at the instant
# 1 January 1900, 00:00:00. This expiration date will be changed
# at least twice per year whether or not a new leap second is
# announced. These semi-annual changes will be made no later
# than 1 June and 1 December of each year to indicate what
# action (if any) is to be taken on 30 June and 31 December,
# respectively. (These are the customary effective dates for new
# leap seconds.) This expiration date will be identified by a
# unique pair of characters in columns 1 and 2 as shown below.
# In the unlikely event that a leap second is announced with an
# effective date other than 30 June or 31 December, then this
# file will be edited to include that leap second as soon as it is
# announced or at least one month before the effective date
# (whichever is later).
# If an announcement by the IERS specifies that no leap second is
# scheduled, then only the expiration date of the file will
# be advanced to show that the information in the file is still
# current -- the update time stamp, the data and the name of the file
# will not change.
#
# Updated through IERS Bulletin C58
# File expires on: 28 June 2020
#
#@ 3802291200
#
2272060800 10 # 1 Jan 1972
2287785600 11 # 1 Jul 1972
2303683200 12 # 1 Jan 1973
2335219200 13 # 1 Jan 1974
2366755200 14 # 1 Jan 1975
2398291200 15 # 1 Jan 1976
2429913600 16 # 1 Jan 1977
2461449600 17 # 1 Jan 1978
2492985600 18 # 1 Jan 1979
2524521600 19 # 1 Jan 1980
2571782400 20 # 1 Jul 1981
2603318400 21 # 1 Jul 1982
2634854400 22 # 1 Jul 1983
2698012800 23 # 1 Jul 1985
2776982400 24 # 1 Jan 1988
2840140800 25 # 1 Jan 1990
2871676800 26 # 1 Jan 1991
2918937600 27 # 1 Jul 1992
2950473600 28 # 1 Jul 1993
2982009600 29 # 1 Jul 1994
3029443200 30 # 1 Jan 1996
3076704000 31 # 1 Jul 1997
3124137600 32 # 1 Jan 1999
3345062400 33 # 1 Jan 2006
3439756800 34 # 1 Jan 2009
3550089600 35 # 1 Jul 2012
3644697600 36 # 1 Jul 2015
3692217600 37 # 1 Jan 2017
#
# the following special comment contains the
# hash value of the data in this file computed
# use the secure hash algorithm as specified
# by FIPS 180-1. See the files in ~/pub/sha for
# the details of how this hash value is
# computed. Note that the hash computation
# ignores comments and whitespace characters
# in data lines. It includes the NTP values
# of both the last modification time and the
# expiration time of the file, but not the
# white space on those lines.
# the hash line is also ignored in the
# computation.
#
#h f28827d2 f263b6c3 ec0f19eb a3e0dbf0 97f3fa30