tzdata: update to 2018g

[unleashed.git] / contrib / tzdata / 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 C56
#       File expires on:  28 June 2019
#
#@      3770668800
#
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      62ca19f6 96a4ae0a 3708451c 9f8693f4 016604eb