pike.git / lib / modules / Calendar.pmod / tzdata / leap-seconds.list

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pike.git/lib/modules/Calendar.pmod/tzdata/leap-seconds.list:1: -  + # + # 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 C55 + # File expires on: 28 December 2018 + # + #@ 3754944000 + # + 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 44dcf58c e28d25aa b36612c8 f3d3e8b5 a8fdf478   Newline at end of file added.