leapseconds.awk revision 360362
1352354Sphilip# Generate zic format 'leapseconds' from NIST format 'leap-seconds.list'. 2308265Sgjb 3308265Sgjb# This file is in the public domain. 4308265Sgjb 5352354Sphilip# This program uses awk arithmetic. POSIX requires awk to support 6352354Sphilip# exact integer arithmetic only through 10**10, which means for NTP 7352354Sphilip# timestamps this program works only to the year 2216, which is the 8352354Sphilip# year 1900 plus 10**10 seconds. However, in practice 9352354Sphilip# POSIX-conforming awk implementations invariably use IEEE-754 double 10352354Sphilip# and so support exact integers through 2**53. By the year 2216, 11352354Sphilip# POSIX will almost surely require at least 2**53 for awk, so for NTP 12352354Sphilip# timestamps this program should be good until the year 285,428,681 13352354Sphilip# (the year 1900 plus 2**53 seconds). By then leap seconds will be 14352354Sphilip# long obsolete, as the Earth will likely slow down so much that 15352354Sphilip# there will be more than 25 hours per day and so some other scheme 16352354Sphilip# will be needed. 17352354Sphilip 18308265SgjbBEGIN { 19308265Sgjb print "# Allowance for leap seconds added to each time zone file." 20308265Sgjb print "" 21308265Sgjb print "# This file is in the public domain." 22308265Sgjb print "" 23308265Sgjb print "# This file is generated automatically from the data in the public-domain" 24352354Sphilip print "# NIST format leap-seconds.list file, which can be copied from" 25339630Sphilip print "# <ftp://ftp.nist.gov/pub/time/leap-seconds.list>" 26352354Sphilip print "# or <ftp://ftp.boulder.nist.gov/pub/time/leap-seconds.list>." 27308265Sgjb print "# For more about leap-seconds.list, please see" 28308265Sgjb print "# The NTP Timescale and Leap Seconds" 29339630Sphilip print "# <https://www.eecis.udel.edu/~mills/leap.html>." 30308265Sgjb print "" 31352354Sphilip print "# The rules for leap seconds are specified in Annex 1 (Time scales) of:" 32352354Sphilip print "# Standard-frequency and time-signal emissions." 33352354Sphilip print "# International Telecommunication Union - Radiocommunication Sector" 34352354Sphilip print "# (ITU-R) Recommendation TF.460-6 (02/2002)" 35352354Sphilip print "# <https://www.itu.int/rec/R-REC-TF.460-6-200202-I/>." 36352354Sphilip print "# The International Earth Rotation and Reference Systems Service (IERS)" 37308265Sgjb print "# periodically uses leap seconds to keep UTC to within 0.9 s of UT1" 38352354Sphilip print "# (a proxy for Earth's angle in space as measured by astronomers)" 39339630Sphilip print "# and publishes leap second data in a copyrighted file" 40339630Sphilip print "# <https://hpiers.obspm.fr/iers/bul/bulc/Leap_Second.dat>." 41339630Sphilip print "# See: Levine J. Coordinated Universal Time and the leap second." 42325159Sphilip print "# URSI Radio Sci Bull. 2016;89(4):30-6. doi:10.23919/URSIRSB.2016.7909995" 43339630Sphilip print "# <https://ieeexplore.ieee.org/document/7909995>." 44342668Sphilip print "" 45352354Sphilip print "# There were no leap seconds before 1972, as no official mechanism" 46352354Sphilip print "# accounted for the discrepancy between atomic time (TAI) and the earth's" 47352354Sphilip print "# rotation. The first (\"1 Jan 1972\") data line in leap-seconds.list" 48342668Sphilip print "# does not denote a leap second; it denotes the start of the current definition" 49352354Sphilip print "# of UTC." 50308265Sgjb print "" 51352354Sphilip print "# All leap-seconds are Stationary (S) at the given UTC time." 52352354Sphilip print "# The correction (+ or -) is made at the given time, so in the unlikely" 53352354Sphilip print "# event of a negative leap second, a line would look like this:" 54352354Sphilip print "# Leap YEAR MON DAY 23:59:59 - S" 55352354Sphilip print "# Typical lines look like this:" 56352354Sphilip print "# Leap YEAR MON DAY 23:59:60 + S" 57339630Sphilip 58339630Sphilip monthabbr[ 1] = "Jan" 59339630Sphilip monthabbr[ 2] = "Feb" 60339630Sphilip monthabbr[ 3] = "Mar" 61339630Sphilip monthabbr[ 4] = "Apr" 62339630Sphilip monthabbr[ 5] = "May" 63339630Sphilip monthabbr[ 6] = "Jun" 64339630Sphilip monthabbr[ 7] = "Jul" 65339630Sphilip monthabbr[ 8] = "Aug" 66339630Sphilip monthabbr[ 9] = "Sep" 67339630Sphilip monthabbr[10] = "Oct" 68339630Sphilip monthabbr[11] = "Nov" 69339630Sphilip monthabbr[12] = "Dec" 70352354Sphilip 71352354Sphilip sstamp_init() 72308265Sgjb} 73308265Sgjb 74360362Sphilip# In case the input has CRLF form a la NIST. 75360362Sphilip{ sub(/\r$/, "") } 76360362Sphilip 77352354Sphilip/^#[ \t]*[Uu]pdated through/ || /^#[ \t]*[Ff]ile expires on/ { 78308265Sgjb last_lines = last_lines $0 "\n" 79308265Sgjb} 80308265Sgjb 81339630Sphilip/^#[$][ \t]/ { updated = $2 } 82339630Sphilip/^#[@][ \t]/ { expires = $2 } 83339630Sphilip 84352354Sphilip/^[ \t]*#/ { next } 85308265Sgjb 86308265Sgjb{ 87308265Sgjb NTP_timestamp = $1 88308265Sgjb TAI_minus_UTC = $2 89308265Sgjb if (old_TAI_minus_UTC) { 90308265Sgjb if (old_TAI_minus_UTC < TAI_minus_UTC) { 91308265Sgjb sign = "23:59:60\t+" 92308265Sgjb } else { 93308265Sgjb sign = "23:59:59\t-" 94308265Sgjb } 95352354Sphilip sstamp_to_ymdhMs(NTP_timestamp - 1, ss_NTP) 96352354Sphilip printf "Leap\t%d\t%s\t%d\t%s\tS\n", \ 97352354Sphilip ss_year, monthabbr[ss_month], ss_mday, sign 98308265Sgjb } 99308265Sgjb old_TAI_minus_UTC = TAI_minus_UTC 100308265Sgjb} 101308265Sgjb 102308265SgjbEND { 103360362Sphilip sstamp_to_ymdhMs(expires, ss_NTP) 104360362Sphilip 105360362Sphilip print "" 106360362Sphilip print "# UTC timestamp when this leap second list expires." 107360362Sphilip print "# Any additional leap seconds will come after this." 108360362Sphilip print "# This Expires line is commented out for now," 109360362Sphilip print "# so that pre-2020a zic implementations do not reject this file." 110360362Sphilip printf "%sExpires %.4d\t%s\t%.2d\t%.2d:%.2d:%.2d\n", \ 111360362Sphilip EXPIRES_LINE ? "" : "#", \ 112360362Sphilip ss_year, monthabbr[ss_month], ss_mday, ss_hour, ss_min, ss_sec 113360362Sphilip 114339630Sphilip # The difference between the NTP and POSIX epochs is 70 years 115339630Sphilip # (including 17 leap days), each 24 hours of 60 minutes of 60 116339630Sphilip # seconds each. 117339630Sphilip epoch_minus_NTP = ((1970 - 1900) * 365 + 17) * 24 * 60 * 60 118339630Sphilip 119339630Sphilip print "" 120339630Sphilip print "# POSIX timestamps for the data in this file:" 121352354Sphilip sstamp_to_ymdhMs(updated, ss_NTP) 122352354Sphilip printf "#updated %d (%.4d-%.2d-%.2d %.2d:%.2d:%.2d UTC)\n", \ 123352354Sphilip updated - epoch_minus_NTP, \ 124352354Sphilip ss_year, ss_month, ss_mday, ss_hour, ss_min, ss_sec 125352354Sphilip sstamp_to_ymdhMs(expires, ss_NTP) 126352354Sphilip printf "#expires %d (%.4d-%.2d-%.2d %.2d:%.2d:%.2d UTC)\n", \ 127352354Sphilip expires - epoch_minus_NTP, \ 128352354Sphilip ss_year, ss_month, ss_mday, ss_hour, ss_min, ss_sec 129352354Sphilip 130308265Sgjb printf "\n%s", last_lines 131308265Sgjb} 132352354Sphilip 133352354Sphilip# sstamp_to_ymdhMs - convert seconds timestamp to date and time 134352354Sphilip# 135352354Sphilip# Call as: 136352354Sphilip# 137352354Sphilip# sstamp_to_ymdhMs(sstamp, epoch_days) 138352354Sphilip# 139352354Sphilip# where: 140352354Sphilip# 141352354Sphilip# sstamp - is the seconds timestamp. 142352354Sphilip# epoch_days - is the timestamp epoch in Gregorian days since 1600-03-01. 143352354Sphilip# ss_NTP is appropriate for an NTP sstamp. 144352354Sphilip# 145352354Sphilip# Both arguments should be nonnegative integers. 146352354Sphilip# On return, the following variables are set based on sstamp: 147352354Sphilip# 148352354Sphilip# ss_year - Gregorian calendar year 149352354Sphilip# ss_month - month of the year (1-January to 12-December) 150352354Sphilip# ss_mday - day of the month (1-31) 151352354Sphilip# ss_hour - hour (0-23) 152352354Sphilip# ss_min - minute (0-59) 153352354Sphilip# ss_sec - second (0-59) 154352354Sphilip# ss_wday - day of week (0-Sunday to 6-Saturday) 155352354Sphilip# 156352354Sphilip# The function sstamp_init should be called prior to using sstamp_to_ymdhMs. 157352354Sphilip 158352354Sphilipfunction sstamp_init() 159352354Sphilip{ 160352354Sphilip # Days in month N, where March is month 0 and January month 10. 161352354Sphilip ss_mon_days[ 0] = 31 162352354Sphilip ss_mon_days[ 1] = 30 163352354Sphilip ss_mon_days[ 2] = 31 164352354Sphilip ss_mon_days[ 3] = 30 165352354Sphilip ss_mon_days[ 4] = 31 166352354Sphilip ss_mon_days[ 5] = 31 167352354Sphilip ss_mon_days[ 6] = 30 168352354Sphilip ss_mon_days[ 7] = 31 169352354Sphilip ss_mon_days[ 8] = 30 170352354Sphilip ss_mon_days[ 9] = 31 171352354Sphilip ss_mon_days[10] = 31 172352354Sphilip 173352354Sphilip # Counts of days in a Gregorian year, quad-year, century, and quad-century. 174352354Sphilip ss_year_days = 365 175352354Sphilip ss_quadyear_days = ss_year_days * 4 + 1 176352354Sphilip ss_century_days = ss_quadyear_days * 25 - 1 177352354Sphilip ss_quadcentury_days = ss_century_days * 4 + 1 178352354Sphilip 179352354Sphilip # Standard day epochs, suitable for epoch_days. 180352354Sphilip # ss_MJD = 94493 181352354Sphilip # ss_POSIX = 135080 182352354Sphilip ss_NTP = 109513 183352354Sphilip} 184352354Sphilip 185352354Sphilipfunction sstamp_to_ymdhMs(sstamp, epoch_days, \ 186352354Sphilip quadcentury, century, quadyear, year, month, day) 187352354Sphilip{ 188352354Sphilip ss_hour = int(sstamp / 3600) % 24 189352354Sphilip ss_min = int(sstamp / 60) % 60 190352354Sphilip ss_sec = sstamp % 60 191352354Sphilip 192352354Sphilip # Start with a count of days since 1600-03-01 Gregorian. 193352354Sphilip day = epoch_days + int(sstamp / (24 * 60 * 60)) 194352354Sphilip 195352354Sphilip # Compute a year-month-day date with days of the month numbered 196352354Sphilip # 0-30, months (March-February) numbered 0-11, and years that start 197352354Sphilip # start March 1 and end after the last day of February. A quad-year 198352354Sphilip # starts on March 1 of a year evenly divisible by 4 and ends after 199352354Sphilip # the last day of February 4 years later. A century starts on and 200352354Sphilip # ends before March 1 in years evenly divisible by 100. 201352354Sphilip # A quad-century starts on and ends before March 1 in years divisible 202352354Sphilip # by 400. While the number of days in a quad-century is a constant, 203352354Sphilip # the number of days in each other time period can vary by 1. 204352354Sphilip # Any variation is in the last day of the time period (there might 205352354Sphilip # or might not be a February 29) where it is easy to deal with. 206352354Sphilip 207352354Sphilip quadcentury = int(day / ss_quadcentury_days) 208352354Sphilip day -= quadcentury * ss_quadcentury_days 209352354Sphilip ss_wday = (day + 3) % 7 210352354Sphilip century = int(day / ss_century_days) 211352354Sphilip century -= century == 4 212352354Sphilip day -= century * ss_century_days 213352354Sphilip quadyear = int(day / ss_quadyear_days) 214352354Sphilip day -= quadyear * ss_quadyear_days 215352354Sphilip year = int(day / ss_year_days) 216352354Sphilip year -= year == 4 217352354Sphilip day -= year * ss_year_days 218352354Sphilip for (month = 0; month < 11; month++) { 219352354Sphilip if (day < ss_mon_days[month]) 220352354Sphilip break 221352354Sphilip day -= ss_mon_days[month] 222352354Sphilip } 223352354Sphilip 224352354Sphilip # Convert the date to a conventional day of month (1-31), 225352354Sphilip # month (1-12, January-December) and Gregorian year. 226352354Sphilip ss_mday = day + 1 227352354Sphilip if (month <= 9) { 228352354Sphilip ss_month = month + 3 229352354Sphilip } else { 230352354Sphilip ss_month = month - 9 231352354Sphilip year++ 232352354Sphilip } 233352354Sphilip ss_year = 1600 + quadcentury * 400 + century * 100 + quadyear * 4 + year 234352354Sphilip} 235