diff options
Diffstat (limited to 'leapseconds.awk')
| -rw-r--r-- | leapseconds.awk | 249 |
1 files changed, 249 insertions, 0 deletions
diff --git a/leapseconds.awk b/leapseconds.awk new file mode 100644 index 0000000..15e8501 --- /dev/null +++ b/leapseconds.awk @@ -0,0 +1,249 @@ +# Generate zic format 'leapseconds' from NIST/IERS format 'leap-seconds.list'. + +# This file is in the public domain. + +# This program uses awk arithmetic. POSIX requires awk to support +# exact integer arithmetic only through 10**10, which means for NTP +# timestamps this program works only to the year 2216, which is the +# year 1900 plus 10**10 seconds. However, in practice +# POSIX-conforming awk implementations invariably use IEEE-754 double +# and so support exact integers through 2**53. By the year 2216, +# POSIX will almost surely require at least 2**53 for awk, so for NTP +# timestamps this program should be good until the year 285,428,681 +# (the year 1900 plus 2**53 seconds). By then leap seconds will be +# long obsolete, as the Earth will likely slow down so much that +# there will be more than 25 hours per day and so some other scheme +# will be needed. + +BEGIN { + print "# Allowance for leap seconds added to each time zone file." + print "" + print "# This file is in the public domain." + print "" + print "# This file is generated automatically from the data in the public-domain" + print "# NIST/IERS format leap-seconds.list file, which can be copied from" + print "# <https://hpiers.obspm.fr/iers/bul/bulc/ntp/leap-seconds.list>" + print "# or, in a variant with different comments, from" + print "# <ftp://ftp.boulder.nist.gov/pub/time/leap-seconds.list>." + print "# For more about leap-seconds.list, please see" + print "# The NTP Timescale and Leap Seconds" + print "# <https://www.eecis.udel.edu/~mills/leap.html>." + print "" + print "# The rules for leap seconds are specified in Annex 1 (Time scales) of:" + print "# Standard-frequency and time-signal emissions." + print "# International Telecommunication Union - Radiocommunication Sector" + print "# (ITU-R) Recommendation TF.460-6 (02/2002)" + print "# <https://www.itu.int/rec/R-REC-TF.460-6-200202-I/>." + print "# The International Earth Rotation and Reference Systems Service (IERS)" + print "# periodically uses leap seconds to keep UTC to within 0.9 s of UT1" + print "# (a proxy for Earth's angle in space as measured by astronomers)" + print "# and publishes leap second data in a copyrighted file" + print "# <https://hpiers.obspm.fr/iers/bul/bulc/Leap_Second.dat>." + print "# See: Levine J. Coordinated Universal Time and the leap second." + print "# URSI Radio Sci Bull. 2016;89(4):30-6. doi:10.23919/URSIRSB.2016.7909995" + print "# <https://ieeexplore.ieee.org/document/7909995>." + print "" + print "# There were no leap seconds before 1972, as no official mechanism" + print "# accounted for the discrepancy between atomic time (TAI) and the earth's" + print "# rotation. The first (\"1 Jan 1972\") data line in leap-seconds.list" + print "# does not denote a leap second; it denotes the start of the current definition" + print "# of UTC." + print "" + print "# All leap-seconds are Stationary (S) at the given UTC time." + print "# The correction (+ or -) is made at the given time, so in the unlikely" + print "# event of a negative leap second, a line would look like this:" + print "# Leap YEAR MON DAY 23:59:59 - S" + print "# Typical lines look like this:" + print "# Leap YEAR MON DAY 23:59:60 + S" + + monthabbr[ 1] = "Jan" + monthabbr[ 2] = "Feb" + monthabbr[ 3] = "Mar" + monthabbr[ 4] = "Apr" + monthabbr[ 5] = "May" + monthabbr[ 6] = "Jun" + monthabbr[ 7] = "Jul" + monthabbr[ 8] = "Aug" + monthabbr[ 9] = "Sep" + monthabbr[10] = "Oct" + monthabbr[11] = "Nov" + monthabbr[12] = "Dec" + + sstamp_init() +} + +# In case the input has CRLF form a la NIST. +{ sub(/\r$/, "") } + +/^#[ \t]*[Uu]pdated through/ || /^#[ \t]*[Ff]ile expires on/ { + last_lines = last_lines $0 "\n" +} + +/^#[$][ \t]/ { updated = $2 } +/^#[@][ \t]/ { expires = $2 } + +/^[ \t]*#/ { next } + +{ + NTP_timestamp = $1 + TAI_minus_UTC = $2 + if (old_TAI_minus_UTC) { + if (old_TAI_minus_UTC < TAI_minus_UTC) { + sign = "23:59:60\t+" + } else { + sign = "23:59:59\t-" + } + sstamp_to_ymdhMs(NTP_timestamp - 1, ss_NTP) + printf "Leap\t%d\t%s\t%d\t%s\tS\n", \ + ss_year, monthabbr[ss_month], ss_mday, sign + } + old_TAI_minus_UTC = TAI_minus_UTC +} + +END { + print "" + + if (expires) { + sstamp_to_ymdhMs(expires, ss_NTP) + + print "# UTC timestamp when this leap second list expires." + print "# Any additional leap seconds will come after this." + if (! EXPIRES_LINE) { + print "# This Expires line is commented out for now," + print "# so that pre-2020a zic implementations do not reject this file." + } + printf "%sExpires %.4d\t%s\t%.2d\t%.2d:%.2d:%.2d\n", \ + EXPIRES_LINE ? "" : "#", \ + ss_year, monthabbr[ss_month], ss_mday, ss_hour, ss_min, ss_sec + } else { + print "# (No Expires line, since the expires time is unknown.)" + } + + # The difference between the NTP and POSIX epochs is 70 years + # (including 17 leap days), each 24 hours of 60 minutes of 60 + # seconds each. + epoch_minus_NTP = ((1970 - 1900) * 365 + 17) * 24 * 60 * 60 + + print "" + print "# POSIX timestamps for the data in this file:" + if (updated) { + sstamp_to_ymdhMs(updated, ss_NTP) + printf "#updated %d (%.4d-%.2d-%.2d %.2d:%.2d:%.2d UTC)\n", \ + updated - epoch_minus_NTP, \ + ss_year, ss_month, ss_mday, ss_hour, ss_min, ss_sec + } else { + print "#(updated time unknown)" + } + if (expires) { + sstamp_to_ymdhMs(expires, ss_NTP) + printf "#expires %d (%.4d-%.2d-%.2d %.2d:%.2d:%.2d UTC)\n", \ + expires - epoch_minus_NTP, \ + ss_year, ss_month, ss_mday, ss_hour, ss_min, ss_sec + } else { + print "#(expires time unknown)" + } + printf "\n%s", last_lines +} + +# sstamp_to_ymdhMs - convert seconds timestamp to date and time +# +# Call as: +# +# sstamp_to_ymdhMs(sstamp, epoch_days) +# +# where: +# +# sstamp - is the seconds timestamp. +# epoch_days - is the timestamp epoch in Gregorian days since 1600-03-01. +# ss_NTP is appropriate for an NTP sstamp. +# +# Both arguments should be nonnegative integers. +# On return, the following variables are set based on sstamp: +# +# ss_year - Gregorian calendar year +# ss_month - month of the year (1-January to 12-December) +# ss_mday - day of the month (1-31) +# ss_hour - hour (0-23) +# ss_min - minute (0-59) +# ss_sec - second (0-59) +# ss_wday - day of week (0-Sunday to 6-Saturday) +# +# The function sstamp_init should be called prior to using sstamp_to_ymdhMs. + +function sstamp_init() +{ + # Days in month N, where March is month 0 and January month 10. + ss_mon_days[ 0] = 31 + ss_mon_days[ 1] = 30 + ss_mon_days[ 2] = 31 + ss_mon_days[ 3] = 30 + ss_mon_days[ 4] = 31 + ss_mon_days[ 5] = 31 + ss_mon_days[ 6] = 30 + ss_mon_days[ 7] = 31 + ss_mon_days[ 8] = 30 + ss_mon_days[ 9] = 31 + ss_mon_days[10] = 31 + + # Counts of days in a Gregorian year, quad-year, century, and quad-century. + ss_year_days = 365 + ss_quadyear_days = ss_year_days * 4 + 1 + ss_century_days = ss_quadyear_days * 25 - 1 + ss_quadcentury_days = ss_century_days * 4 + 1 + + # Standard day epochs, suitable for epoch_days. + # ss_MJD = 94493 + # ss_POSIX = 135080 + ss_NTP = 109513 +} + +function sstamp_to_ymdhMs(sstamp, epoch_days, \ + quadcentury, century, quadyear, year, month, day) +{ + ss_hour = int(sstamp / 3600) % 24 + ss_min = int(sstamp / 60) % 60 + ss_sec = sstamp % 60 + + # Start with a count of days since 1600-03-01 Gregorian. + day = epoch_days + int(sstamp / (24 * 60 * 60)) + + # Compute a year-month-day date with days of the month numbered + # 0-30, months (March-February) numbered 0-11, and years that start + # start March 1 and end after the last day of February. A quad-year + # starts on March 1 of a year evenly divisible by 4 and ends after + # the last day of February 4 years later. A century starts on and + # ends before March 1 in years evenly divisible by 100. + # A quad-century starts on and ends before March 1 in years divisible + # by 400. While the number of days in a quad-century is a constant, + # the number of days in each other time period can vary by 1. + # Any variation is in the last day of the time period (there might + # or might not be a February 29) where it is easy to deal with. + + quadcentury = int(day / ss_quadcentury_days) + day -= quadcentury * ss_quadcentury_days + ss_wday = (day + 3) % 7 + century = int(day / ss_century_days) + century -= century == 4 + day -= century * ss_century_days + quadyear = int(day / ss_quadyear_days) + day -= quadyear * ss_quadyear_days + year = int(day / ss_year_days) + year -= year == 4 + day -= year * ss_year_days + for (month = 0; month < 11; month++) { + if (day < ss_mon_days[month]) + break + day -= ss_mon_days[month] + } + + # Convert the date to a conventional day of month (1-31), + # month (1-12, January-December) and Gregorian year. + ss_mday = day + 1 + if (month <= 9) { + ss_month = month + 3 + } else { + ss_month = month - 9 + year++ + } + ss_year = 1600 + quadcentury * 400 + century * 100 + quadyear * 4 + year +} |