[tz] Proposal regarding tz DB and leap second updates
Arthur David Olson
arthurdavidolson at gmail.com
Tue Aug 13 12:26:01 UTC 2013
> I took the liberty of removing the copy of the IERS announcement
> from the generated 'leapseconds' since its copyright status was unclear.
I've sent a suggestion to the IERS to include copyright status information
in their notices;
we'll see what happens. (If anyone on the list believes it's worthwhile and
has weight with them...)
--ado
On Tue, Aug 13, 2013 at 3:07 AM, Paul Eggert <eggert at cs.ucla.edu> wrote:
> Bradley White privately sent a Perl script to generate
> 'leapseconds' from the NIST leap-seconds.list file.
> Since we use POSIX Awk for the other processing
> it's probably better to use Awk here, too, so here's a proposed
> patch with all the Makefile bells and whistles, which I pushed
> to the experimental github repository. The patch removes the
> file 'leapseconds' from the repository because it's now generated
> automatically. I took the liberty of removing the copy of the
> IERS announcement from the generated 'leapseconds' since its copyright
> status was unclear. The NIST leap-seconds.list file is public domain,
> so it's OK for us to redistribute it.
>
> From 459b72d3edec98488e5132d4473c4678b4ed5a73 Mon Sep 17 00:00:00 2001
> From: Paul Eggert <eggert at cs.ucla.edu>
> Date: Mon, 12 Aug 2013 23:58:29 -0700
> Subject: [PATCH] Generate the 'leapseconds' file automatically from
> leap-seconds.list.
>
> * leap-seconds.list: New file, copied from the NIST.
> * leapseconds: Remove from git; it's now generated.
> * leapseconds.awk: New file.
> * Makefile (DATA): Add leap-seconds.list. Remove leapseconds.
> (MISC): Add leapseconds.awk.
> (leapseconds): New rule.
> (right_posix, posix_right): Depend on leapseconds.
> (clean_misc): Remove leapseconds.
> ---
> Makefile | 14 ++--
> leap-seconds.list | 231
> ++++++++++++++++++++++++++++++++++++++++++++++++++++++
> leapseconds | 100 -----------------------
> leapseconds.awk | 68 ++++++++++++++++
> 4 files changed, 308 insertions(+), 105 deletions(-)
> create mode 100644 leap-seconds.list
> delete mode 100644 leapseconds
> create mode 100644 leapseconds.awk
>
> diff --git a/Makefile b/Makefile
> index db7f56e..68d7132 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -318,10 +318,11 @@ NDATA= systemv factory
> SDATA= solar87 solar88 solar89
> TDATA= $(YDATA) $(NDATA) $(SDATA)
> TABDATA= iso3166.tab zone.tab
> -DATA= $(YDATA) $(NDATA) $(SDATA) $(TABDATA) leapseconds
> yearistype.sh
> +DATA= $(YDATA) $(NDATA) $(SDATA) $(TABDATA) \
> + leap-seconds.list yearistype.sh
> WEB_PAGES= tz-art.htm tz-link.htm
> MISC= usno1988 usno1989 usno1989a usno1995 usno1997 usno1998 \
> - $(WEB_PAGES) checktab.awk workman.sh \
> + $(WEB_PAGES) checktab.awk leapseconds.awk
> workman.sh \
> zoneinfo2tdf.pl
> ENCHILADA= $(COMMON) $(DOCS) $(SOURCES) $(DATA) $(MISC)
>
> @@ -375,6 +376,9 @@ yearistype: yearistype.sh
> cp yearistype.sh yearistype
> chmod +x yearistype
>
> +leapseconds: leapseconds.awk leap-seconds.list
> + $(AWK) -f leapseconds.awk leap-seconds.list >$@
> +
> posix_only: zic $(TDATA)
> $(ZIC) -y $(YEARISTYPE) -d $(TZDIR) -L /dev/null $(TDATA)
>
> @@ -390,14 +394,14 @@ right_only: zic leapseconds $(TDATA)
> # Therefore, the other two directories are now siblings of $(TZDIR).
> # You must replace all of $(TZDIR) to switch from not using leap seconds
> # to using them, or vice versa.
> -right_posix: right_only
> +right_posix: right_only leapseconds
> rm -fr $(TZDIR)-leaps
> ln -s $(TZDIR_BASENAME) $(TZDIR)-leaps || \
> $(ZIC) -y $(YEARISTYPE) \
> -d $(TZDIR)-leaps -L leapseconds $(TDATA)
> $(ZIC) -y $(YEARISTYPE) -d $(TZDIR)-posix -L /dev/null
> $(TDATA)
>
> -posix_right: posix_only
> +posix_right: posix_only leapseconds
> rm -fr $(TZDIR)-posix
> ln -s $(TZDIR_BASENAME) $(TZDIR)-posix || \
> $(ZIC) -y $(YEARISTYPE) \
> @@ -440,7 +444,7 @@ check_web: $(WEB_PAGES)
>
> clean_misc:
> rm -f core *.o *.out \
> - date tzselect version.h zdump zic yearistype
> + date leapseconds tzselect version.h zdump zic yearistype
> clean: clean_misc
> rm -f -r tzpublic
>
> diff --git a/leap-seconds.list b/leap-seconds.list
> new file mode 100644
> index 0000000..7df3de6
> --- /dev/null
> +++ b/leap-seconds.list
> @@ -0,0 +1,231 @@
> +#
> +# 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 1900.0 and 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.fr for more information.
> +#
> +# 3. The current defintion of the relationship between UTC
> +# and TAI dates from 1 January 1972. A number of different
> +# time scales were in use before than 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.
> +#
> +# 4. The insertion of leap seconds into UTC is currently the
> +# responsibility of the International Earth Rotation Service,
> +# which is located at the Paris Observatory:
> +#
> +# Central Bureau of IERS
> +# 61, Avenue de l'Observatoire
> +# 75014 Paris, France.
> +#
> +# Leap seconds are announced by the IERS in its Bulletin C
> +#
> +# See hpiers.obspm.fr or www.iers.org for more details.
> +#
> +# All national laboratories and timing centers use the
> +# data from the BIPM and the IERS to construct their
> +# local realizations 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 equivlent 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.
> +#
> +# 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.
> +#
> +# Questions or comments to:
> +# Judah Levine
> +# Time and Frequency Division
> +# NIST
> +# Boulder, Colorado
> +# jlevine at boulder.nist.gov
> +#
> +# Last Update of leap second values: 11 January 2012
> +#
> +# 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.
> +#
> +#$ 3535228800
> +#
> +# The NTP timestamps are in units of seconds since the NTP epoch,
> +# which is 1900.0. 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 1900.0. 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 1900.0. 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 C46
> +# File expires on: 28 June 2014
> +#
> +#@ 3612902400
> +#
> +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
> +#
> +# 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 1151a8f e85a5069 9000fcdb 3d5e5365 1d505b37
> diff --git a/leapseconds b/leapseconds
> deleted file mode 100644
> index 5b5c70e..0000000
> --- a/leapseconds
> +++ /dev/null
> @@ -1,100 +0,0 @@
> -# <pre>
> -# This file is in the public domain, so clarified as of
> -# 2009-05-17 by Arthur David Olson.
> -
> -# Allowance for leapseconds added to each timezone file.
> -
> -# The International Earth Rotation Service periodically uses leap seconds
> -# to keep UTC to within 0.9 s of UT1
> -# (which measures the true angular orientation of the earth in space); see
> -# Terry J Quinn, The BIPM and the accurate measure of time,
> -# Proc IEEE 79, 7 (July 1991), 894-905.
> -# There were no leap seconds before 1972, because the official mechanism
> -# accounting for the discrepancy between atomic time and the earth's
> rotation
> -# did not exist until the early 1970s.
> -
> -# The correction (+ or -) is made at the given time, so lines
> -# will typically look like:
> -# Leap YEAR MON DAY 23:59:60 + R/S
> -# or
> -# Leap YEAR MON DAY 23:59:59 - R/S
> -
> -# If the leapsecond is Rolling (R) the given time is local time
> -# If the leapsecond is Stationary (S) the given time is UTC
> -
> -# Leap YEAR MONTH DAY HH:MM:SS CORR R/S
> -Leap 1972 Jun 30 23:59:60 + S
> -Leap 1972 Dec 31 23:59:60 + S
> -Leap 1973 Dec 31 23:59:60 + S
> -Leap 1974 Dec 31 23:59:60 + S
> -Leap 1975 Dec 31 23:59:60 + S
> -Leap 1976 Dec 31 23:59:60 + S
> -Leap 1977 Dec 31 23:59:60 + S
> -Leap 1978 Dec 31 23:59:60 + S
> -Leap 1979 Dec 31 23:59:60 + S
> -Leap 1981 Jun 30 23:59:60 + S
> -Leap 1982 Jun 30 23:59:60 + S
> -Leap 1983 Jun 30 23:59:60 + S
> -Leap 1985 Jun 30 23:59:60 + S
> -Leap 1987 Dec 31 23:59:60 + S
> -Leap 1989 Dec 31 23:59:60 + S
> -Leap 1990 Dec 31 23:59:60 + S
> -Leap 1992 Jun 30 23:59:60 + S
> -Leap 1993 Jun 30 23:59:60 + S
> -Leap 1994 Jun 30 23:59:60 + S
> -Leap 1995 Dec 31 23:59:60 + S
> -Leap 1997 Jun 30 23:59:60 + S
> -Leap 1998 Dec 31 23:59:60 + S
> -Leap 2005 Dec 31 23:59:60 + S
> -Leap 2008 Dec 31 23:59:60 + S
> -Leap 2012 Jun 30 23:59:60 + S
> -
> -# INTERNATIONAL EARTH ROTATION AND REFERENCE SYSTEMS SERVICE (IERS)
> -#
> -# SERVICE INTERNATIONAL DE LA ROTATION TERRESTRE ET DES SYSTEMES DE
> REFERENCE
> -#
> -#
> -# SERVICE DE LA ROTATION TERRESTRE
> -# OBSERVATOIRE DE PARIS
> -# 61, Av. de l'Observatoire 75014 PARIS (France)
> -# Tel. : 33 (0) 1 40 51 22 26
> -# FAX : 33 (0) 1 40 51 22 91
> -# e-mail : (E-Mail Removed)
> -# http://hpiers.obspm.fr/eop-pc
> -#
> -# Paris, 5 January 2012
> -#
> -#
> -# Bulletin C 43
> -#
> -# To authorities responsible
> -# for the measurement and
> -# distribution of time
> -#
> -#
> -# UTC TIME STEP
> -# on the 1st of July 2012
> -#
> -#
> -# A positive leap second will be introduced at the end of June 2012.
> -# The sequence of dates of the UTC second markers will be:
> -#
> -# 2012 June 30, 23h 59m 59s
> -# 2012 June 30, 23h 59m 60s
> -# 2012 July 1, 0h 0m 0s
> -#
> -# The difference between UTC and the International Atomic Time TAI is:
> -#
> -# from 2009 January 1, 0h UTC, to 2012 July 1 0h UTC : UTC-TAI = - 34s
> -# from 2012 July 1, 0h UTC, until further notice : UTC-TAI = - 35s
> -#
> -# Leap seconds can be introduced in UTC at the end of the months of
> December
> -# or June, depending on the evolution of UT1-TAI. Bulletin C is mailed
> every
> -# six months, either to announce a time step in UTC or to confirm that
> there
> -# will be no time step at the next possible date.
> -#
> -#
> -# Daniel GAMBIS
> -# Head
> -# Earth Orientation Center of IERS
> -# Observatoire de Paris, France
> diff --git a/leapseconds.awk b/leapseconds.awk
> new file mode 100644
> index 0000000..732db99
> --- /dev/null
> +++ b/leapseconds.awk
> @@ -0,0 +1,68 @@
> +# Generate the 'leapseconds' file from 'leap-seconds.list'.
> +
> +# This file is in the public domain.
> +
> +BEGIN {
> + printf "%s", "\
> +# Allowance for leapseconds added to each timezone file.\n\
> +\n\
> +# This file is in the public domain.\n\
> +\n\
> +# This file is generated automatically from the data in the
> public-domain\n\
> +# leap-seconds.list file available from most NIST time servers.\n\
> +# If the URL <ftp://time.nist.gov/pub/leap-seconds.list> does not
> work,\n\
> +# you should be able to pick up leap-seconds.list from a secondary NIST
> server.\n\
> +# For more about leap-seconds.list, please see\n\
> +# The NTP Timescale and Leap Seconds\n\
> +# <http://www.eecis.udel.edu/~mills/leap.html>.\n\
> +\n\
> +# The International Earth Rotation Service periodically uses leap
> seconds\n\
> +# to keep UTC to within 0.9 s of UT1\n\
> +# (which measures the true angular orientation of the earth in space);
> see\n\
> +# Terry J Quinn, The BIPM and the accurate measure of time,\n\
> +# Proc IEEE 79, 7 (July 1991), 894-905 <http://dx.doi.org/10.1109/5.84965
> >.\n\
> +# There were no leap seconds before 1972, because the official
> mechanism\n\
> +# accounting for the discrepancy between atomic time and the earth's
> rotation\n\
> +# did not exist until the early 1970s.\n\
> +\n\
> +# The correction (+ or -) is made at the given time, so lines\n\
> +# will typically look like:\n\
> +# Leap YEAR MON DAY 23:59:60 + R/S\n\
> +# or\n\
> +# Leap YEAR MON DAY 23:59:59 - R/S\n\
> +\n\
> +# If the leapsecond is Rolling (R) the given time is local time.\n\
> +# If the leapsecond is Stationary (S) the given time is UTC.\n\
> +\n\
> +# Leap YEAR MONTH DAY HH:MM:SS CORR R/S\n\
> +"
> +}
> +
> +/^ *$/ { next }
> +/^#/ { next }
> +
> +{
> + NTP_timestamp = $1
> + TAI_minus_UTC = $2
> + hash_mark = $3
> + one = $4
> + month = $5
> + year = $6
> + if (old_TAI_minus_UTC) {
> + if (old_TAI_minus_UTC < TAI_minus_UTC) {
> + sign = "23:59:60\t+"
> + } else {
> + sign = "23:59:59\t-"
> + }
> + if (month == "Jan") {
> + year--;
> + month = "Dec";
> + day = 31
> + } else if (month == "Jul") {
> + month = "Jun";
> + day = 30
> + }
> + printf "Leap\t%s\t%s\t%s\t%s\tS\n", year, month, day, sign
> + }
> + old_TAI_minus_UTC = TAI_minus_UTC
> +}
> --
> 1.8.1.2
>
>
>
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