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253 lines
8.9 KiB
Awk
253 lines
8.9 KiB
Awk
# Generate zic format 'leapseconds' from NIST format 'leap-seconds.list'.
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# This file is in the public domain.
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# This program uses awk arithmetic. POSIX requires awk to support
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# exact integer arithmetic only through 10**10, which means for NTP
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# timestamps this program works only to the year 2216, which is the
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# year 1900 plus 10**10 seconds. However, in practice
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# POSIX-conforming awk implementations invariably use IEEE-754 double
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# and so support exact integers through 2**53. By the year 2216,
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# POSIX will almost surely require at least 2**53 for awk, so for NTP
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# timestamps this program should be good until the year 285,428,681
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# (the year 1900 plus 2**53 seconds). By then leap seconds will be
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# long obsolete, as the Earth will likely slow down so much that
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# there will be more than 25 hours per day and so some other scheme
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# will be needed.
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BEGIN {
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print "# Allowance for leap seconds added to each time zone file."
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print ""
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print "# This file is in the public domain."
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print ""
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print "# This file is generated automatically from the data in the public-domain"
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print "# NIST format leap-seconds.list file, which can be copied from"
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print "# <ftp://ftp.nist.gov/pub/time/leap-seconds.list>"
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print "# or <ftp://ftp.boulder.nist.gov/pub/time/leap-seconds.list>."
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print "# The NIST file is used instead of its IERS upstream counterpart"
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print "# <https://hpiers.obspm.fr/iers/bul/bulc/ntp/leap-seconds.list>"
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print "# because under US law the NIST file is public domain"
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print "# whereas the IERS file's copyright and license status is unclear."
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print "# For more about leap-seconds.list, please see"
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print "# The NTP Timescale and Leap Seconds"
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print "# <https://www.eecis.udel.edu/~mills/leap.html>."
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print ""
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print "# The rules for leap seconds are specified in Annex 1 (Time scales) of:"
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print "# Standard-frequency and time-signal emissions."
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print "# International Telecommunication Union - Radiocommunication Sector"
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print "# (ITU-R) Recommendation TF.460-6 (02/2002)"
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print "# <https://www.itu.int/rec/R-REC-TF.460-6-200202-I/>."
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print "# The International Earth Rotation and Reference Systems Service (IERS)"
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print "# periodically uses leap seconds to keep UTC to within 0.9 s of UT1"
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print "# (a proxy for Earth's angle in space as measured by astronomers)"
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print "# and publishes leap second data in a copyrighted file"
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print "# <https://hpiers.obspm.fr/iers/bul/bulc/Leap_Second.dat>."
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print "# See: Levine J. Coordinated Universal Time and the leap second."
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print "# URSI Radio Sci Bull. 2016;89(4):30-6. doi:10.23919/URSIRSB.2016.7909995"
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print "# <https://ieeexplore.ieee.org/document/7909995>."
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print ""
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print "# There were no leap seconds before 1972, as no official mechanism"
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print "# accounted for the discrepancy between atomic time (TAI) and the earth's"
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print "# rotation. The first (\"1 Jan 1972\") data line in leap-seconds.list"
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print "# does not denote a leap second; it denotes the start of the current definition"
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print "# of UTC."
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print ""
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print "# All leap-seconds are Stationary (S) at the given UTC time."
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print "# The correction (+ or -) is made at the given time, so in the unlikely"
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print "# event of a negative leap second, a line would look like this:"
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print "# Leap YEAR MON DAY 23:59:59 - S"
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print "# Typical lines look like this:"
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print "# Leap YEAR MON DAY 23:59:60 + S"
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monthabbr[ 1] = "Jan"
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monthabbr[ 2] = "Feb"
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monthabbr[ 3] = "Mar"
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monthabbr[ 4] = "Apr"
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monthabbr[ 5] = "May"
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monthabbr[ 6] = "Jun"
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monthabbr[ 7] = "Jul"
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monthabbr[ 8] = "Aug"
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monthabbr[ 9] = "Sep"
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monthabbr[10] = "Oct"
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monthabbr[11] = "Nov"
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monthabbr[12] = "Dec"
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sstamp_init()
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}
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# In case the input has CRLF form a la NIST.
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{ sub(/\r$/, "") }
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/^#[ \t]*[Uu]pdated through/ || /^#[ \t]*[Ff]ile expires on/ {
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last_lines = last_lines $0 "\n"
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}
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/^#[$][ \t]/ { updated = $2 }
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/^#[@][ \t]/ { expires = $2 }
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/^[ \t]*#/ { next }
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{
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NTP_timestamp = $1
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TAI_minus_UTC = $2
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if (old_TAI_minus_UTC) {
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if (old_TAI_minus_UTC < TAI_minus_UTC) {
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sign = "23:59:60\t+"
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} else {
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sign = "23:59:59\t-"
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}
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sstamp_to_ymdhMs(NTP_timestamp - 1, ss_NTP)
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printf "Leap\t%d\t%s\t%d\t%s\tS\n", \
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ss_year, monthabbr[ss_month], ss_mday, sign
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}
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old_TAI_minus_UTC = TAI_minus_UTC
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}
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END {
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print ""
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if (expires) {
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sstamp_to_ymdhMs(expires, ss_NTP)
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print "# UTC timestamp when this leap second list expires."
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print "# Any additional leap seconds will come after this."
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if (! EXPIRES_LINE) {
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print "# This Expires line is commented out for now,"
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print "# so that pre-2020a zic implementations do not reject this file."
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}
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printf "%sExpires %.4d\t%s\t%.2d\t%.2d:%.2d:%.2d\n", \
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EXPIRES_LINE ? "" : "#", \
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ss_year, monthabbr[ss_month], ss_mday, ss_hour, ss_min, ss_sec
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} else {
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print "# (No Expires line, since the expires time is unknown.)"
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}
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# The difference between the NTP and POSIX epochs is 70 years
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# (including 17 leap days), each 24 hours of 60 minutes of 60
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# seconds each.
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epoch_minus_NTP = ((1970 - 1900) * 365 + 17) * 24 * 60 * 60
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print ""
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print "# POSIX timestamps for the data in this file:"
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if (updated) {
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sstamp_to_ymdhMs(updated, ss_NTP)
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printf "#updated %d (%.4d-%.2d-%.2d %.2d:%.2d:%.2d UTC)\n", \
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updated - epoch_minus_NTP, \
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ss_year, ss_month, ss_mday, ss_hour, ss_min, ss_sec
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} else {
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print "#(updated time unknown)"
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}
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if (expires) {
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sstamp_to_ymdhMs(expires, ss_NTP)
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printf "#expires %d (%.4d-%.2d-%.2d %.2d:%.2d:%.2d UTC)\n", \
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expires - epoch_minus_NTP, \
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ss_year, ss_month, ss_mday, ss_hour, ss_min, ss_sec
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} else {
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print "#(expires time unknown)"
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}
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printf "\n%s", last_lines
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}
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# sstamp_to_ymdhMs - convert seconds timestamp to date and time
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#
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# Call as:
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#
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# sstamp_to_ymdhMs(sstamp, epoch_days)
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#
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# where:
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#
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# sstamp - is the seconds timestamp.
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# epoch_days - is the timestamp epoch in Gregorian days since 1600-03-01.
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# ss_NTP is appropriate for an NTP sstamp.
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#
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# Both arguments should be nonnegative integers.
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# On return, the following variables are set based on sstamp:
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#
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# ss_year - Gregorian calendar year
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# ss_month - month of the year (1-January to 12-December)
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# ss_mday - day of the month (1-31)
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# ss_hour - hour (0-23)
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# ss_min - minute (0-59)
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# ss_sec - second (0-59)
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# ss_wday - day of week (0-Sunday to 6-Saturday)
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#
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# The function sstamp_init should be called prior to using sstamp_to_ymdhMs.
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function sstamp_init()
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{
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# Days in month N, where March is month 0 and January month 10.
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ss_mon_days[ 0] = 31
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ss_mon_days[ 1] = 30
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ss_mon_days[ 2] = 31
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ss_mon_days[ 3] = 30
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ss_mon_days[ 4] = 31
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ss_mon_days[ 5] = 31
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ss_mon_days[ 6] = 30
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ss_mon_days[ 7] = 31
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ss_mon_days[ 8] = 30
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ss_mon_days[ 9] = 31
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ss_mon_days[10] = 31
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# Counts of days in a Gregorian year, quad-year, century, and quad-century.
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ss_year_days = 365
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ss_quadyear_days = ss_year_days * 4 + 1
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ss_century_days = ss_quadyear_days * 25 - 1
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ss_quadcentury_days = ss_century_days * 4 + 1
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# Standard day epochs, suitable for epoch_days.
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# ss_MJD = 94493
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# ss_POSIX = 135080
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ss_NTP = 109513
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}
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function sstamp_to_ymdhMs(sstamp, epoch_days, \
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quadcentury, century, quadyear, year, month, day)
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{
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ss_hour = int(sstamp / 3600) % 24
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ss_min = int(sstamp / 60) % 60
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ss_sec = sstamp % 60
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# Start with a count of days since 1600-03-01 Gregorian.
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day = epoch_days + int(sstamp / (24 * 60 * 60))
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# Compute a year-month-day date with days of the month numbered
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# 0-30, months (March-February) numbered 0-11, and years that start
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# start March 1 and end after the last day of February. A quad-year
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# starts on March 1 of a year evenly divisible by 4 and ends after
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# the last day of February 4 years later. A century starts on and
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# ends before March 1 in years evenly divisible by 100.
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# A quad-century starts on and ends before March 1 in years divisible
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# by 400. While the number of days in a quad-century is a constant,
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# the number of days in each other time period can vary by 1.
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# Any variation is in the last day of the time period (there might
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# or might not be a February 29) where it is easy to deal with.
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quadcentury = int(day / ss_quadcentury_days)
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day -= quadcentury * ss_quadcentury_days
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ss_wday = (day + 3) % 7
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century = int(day / ss_century_days)
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century -= century == 4
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day -= century * ss_century_days
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quadyear = int(day / ss_quadyear_days)
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day -= quadyear * ss_quadyear_days
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year = int(day / ss_year_days)
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year -= year == 4
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day -= year * ss_year_days
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for (month = 0; month < 11; month++) {
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if (day < ss_mon_days[month])
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break
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day -= ss_mon_days[month]
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}
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# Convert the date to a conventional day of month (1-31),
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# month (1-12, January-December) and Gregorian year.
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ss_mday = day + 1
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if (month <= 9) {
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ss_month = month + 3
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} else {
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ss_month = month - 9
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year++
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}
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ss_year = 1600 + quadcentury * 400 + century * 100 + quadyear * 4 + year
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}
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