1# Generate zic format 'leapseconds' from NIST/IERS format 'leap-seconds.list'. 2 3# This file is in the public domain. 4 5# This program uses awk arithmetic. POSIX requires awk to support 6# exact integer arithmetic only through 10**10, which means for NTP 7# timestamps this program works only to the year 2216, which is the 8# year 1900 plus 10**10 seconds. However, in practice 9# POSIX-conforming awk implementations invariably use IEEE-754 double 10# and so support exact integers through 2**53. By the year 2216, 11# POSIX will almost surely require at least 2**53 for awk, so for NTP 12# timestamps this program should be good until the year 285,428,681 13# (the year 1900 plus 2**53 seconds). By then leap seconds will be 14# long obsolete, as the Earth will likely slow down so much that 15# there will be more than 25 hours per day and so some other scheme 16# will be needed. 17 18BEGIN { 19 print "# Allowance for leap seconds added to each time zone file." 20 print "" 21 print "# This file is in the public domain." 22 print "" 23 print "# This file is generated automatically from the data in the public-domain" 24 print "# NIST/IERS format leap-seconds.list file, which can be copied from" 25 print "# <https://hpiers.obspm.fr/iers/bul/bulc/ntp/leap-seconds.list>" 26 print "# or, in a variant with different comments, from" 27 print "# <ftp://ftp.boulder.nist.gov/pub/time/leap-seconds.list>." 28 print "# For more about leap-seconds.list, please see" 29 print "# The NTP Timescale and Leap Seconds" 30 print "# <https://www.eecis.udel.edu/~mills/leap.html>." 31 print "" 32 print "# The rules for leap seconds are specified in Annex 1 (Time scales) of:" 33 print "# Standard-frequency and time-signal emissions." 34 print "# International Telecommunication Union - Radiocommunication Sector" 35 print "# (ITU-R) Recommendation TF.460-6 (02/2002)" 36 print "# <https://www.itu.int/rec/R-REC-TF.460-6-200202-I/>." 37 print "# The International Earth Rotation and Reference Systems Service (IERS)" 38 print "# periodically uses leap seconds to keep UTC to within 0.9 s of UT1" 39 print "# (a proxy for Earth's angle in space as measured by astronomers)" 40 print "# and publishes leap second data in a copyrighted file" 41 print "# <https://hpiers.obspm.fr/iers/bul/bulc/Leap_Second.dat>." 42 print "# See: Levine J. Coordinated Universal Time and the leap second." 43 print "# URSI Radio Sci Bull. 2016;89(4):30-6. doi:10.23919/URSIRSB.2016.7909995" 44 print "# <https://ieeexplore.ieee.org/document/7909995>." 45 print "" 46 print "# There were no leap seconds before 1972, as no official mechanism" 47 print "# accounted for the discrepancy between atomic time (TAI) and the earth's" 48 print "# rotation. The first (\"1 Jan 1972\") data line in leap-seconds.list" 49 print "# does not denote a leap second; it denotes the start of the current definition" 50 print "# of UTC." 51 print "" 52 print "# All leap-seconds are Stationary (S) at the given UTC time." 53 print "# The correction (+ or -) is made at the given time, so in the unlikely" 54 print "# event of a negative leap second, a line would look like this:" 55 print "# Leap YEAR MON DAY 23:59:59 - S" 56 print "# Typical lines look like this:" 57 print "# Leap YEAR MON DAY 23:59:60 + S" 58 59 monthabbr[ 1] = "Jan" 60 monthabbr[ 2] = "Feb" 61 monthabbr[ 3] = "Mar" 62 monthabbr[ 4] = "Apr" 63 monthabbr[ 5] = "May" 64 monthabbr[ 6] = "Jun" 65 monthabbr[ 7] = "Jul" 66 monthabbr[ 8] = "Aug" 67 monthabbr[ 9] = "Sep" 68 monthabbr[10] = "Oct" 69 monthabbr[11] = "Nov" 70 monthabbr[12] = "Dec" 71 72 sstamp_init() 73} 74 75# In case the input has CRLF form a la NIST. 76{ sub(/\r$/, "") } 77 78/^#[ \t]*[Uu]pdated through/ || /^#[ \t]*[Ff]ile expires on/ { 79 last_lines = last_lines $0 "\n" 80} 81 82/^#[$][ \t]/ { updated = $2 } 83/^#[@][ \t]/ { expires = $2 } 84 85/^[ \t]*#/ { next } 86 87{ 88 NTP_timestamp = $1 89 TAI_minus_UTC = $2 90 if (old_TAI_minus_UTC) { 91 if (old_TAI_minus_UTC < TAI_minus_UTC) { 92 sign = "23:59:60\t+" 93 } else { 94 sign = "23:59:59\t-" 95 } 96 sstamp_to_ymdhMs(NTP_timestamp - 1, ss_NTP) 97 printf "Leap\t%d\t%s\t%d\t%s\tS\n", \ 98 ss_year, monthabbr[ss_month], ss_mday, sign 99 } 100 old_TAI_minus_UTC = TAI_minus_UTC 101} 102 103END { 104 print "" 105 106 if (expires) { 107 sstamp_to_ymdhMs(expires, ss_NTP) 108 109 print "# UTC timestamp when this leap second list expires." 110 print "# Any additional leap seconds will come after this." 111 if (! EXPIRES_LINE) { 112 print "# This Expires line is commented out for now," 113 print "# so that pre-2020a zic implementations do not reject this file." 114 } 115 printf "%sExpires %.4d\t%s\t%.2d\t%.2d:%.2d:%.2d\n", \ 116 EXPIRES_LINE ? "" : "#", \ 117 ss_year, monthabbr[ss_month], ss_mday, ss_hour, ss_min, ss_sec 118 } else { 119 print "# (No Expires line, since the expires time is unknown.)" 120 } 121 122 # The difference between the NTP and POSIX epochs is 70 years 123 # (including 17 leap days), each 24 hours of 60 minutes of 60 124 # seconds each. 125 epoch_minus_NTP = ((1970 - 1900) * 365 + 17) * 24 * 60 * 60 126 127 print "" 128 print "# POSIX timestamps for the data in this file:" 129 if (updated) { 130 sstamp_to_ymdhMs(updated, ss_NTP) 131 printf "#updated %d (%.4d-%.2d-%.2d %.2d:%.2d:%.2d UTC)\n", \ 132 updated - epoch_minus_NTP, \ 133 ss_year, ss_month, ss_mday, ss_hour, ss_min, ss_sec 134 } else { 135 print "#(updated time unknown)" 136 } 137 if (expires) { 138 sstamp_to_ymdhMs(expires, ss_NTP) 139 printf "#expires %d (%.4d-%.2d-%.2d %.2d:%.2d:%.2d UTC)\n", \ 140 expires - epoch_minus_NTP, \ 141 ss_year, ss_month, ss_mday, ss_hour, ss_min, ss_sec 142 } else { 143 print "#(expires time unknown)" 144 } 145 printf "\n%s", last_lines 146} 147 148# sstamp_to_ymdhMs - convert seconds timestamp to date and time 149# 150# Call as: 151# 152# sstamp_to_ymdhMs(sstamp, epoch_days) 153# 154# where: 155# 156# sstamp - is the seconds timestamp. 157# epoch_days - is the timestamp epoch in Gregorian days since 1600-03-01. 158# ss_NTP is appropriate for an NTP sstamp. 159# 160# Both arguments should be nonnegative integers. 161# On return, the following variables are set based on sstamp: 162# 163# ss_year - Gregorian calendar year 164# ss_month - month of the year (1-January to 12-December) 165# ss_mday - day of the month (1-31) 166# ss_hour - hour (0-23) 167# ss_min - minute (0-59) 168# ss_sec - second (0-59) 169# ss_wday - day of week (0-Sunday to 6-Saturday) 170# 171# The function sstamp_init should be called prior to using sstamp_to_ymdhMs. 172 173function sstamp_init() 174{ 175 # Days in month N, where March is month 0 and January month 10. 176 ss_mon_days[ 0] = 31 177 ss_mon_days[ 1] = 30 178 ss_mon_days[ 2] = 31 179 ss_mon_days[ 3] = 30 180 ss_mon_days[ 4] = 31 181 ss_mon_days[ 5] = 31 182 ss_mon_days[ 6] = 30 183 ss_mon_days[ 7] = 31 184 ss_mon_days[ 8] = 30 185 ss_mon_days[ 9] = 31 186 ss_mon_days[10] = 31 187 188 # Counts of days in a Gregorian year, quad-year, century, and quad-century. 189 ss_year_days = 365 190 ss_quadyear_days = ss_year_days * 4 + 1 191 ss_century_days = ss_quadyear_days * 25 - 1 192 ss_quadcentury_days = ss_century_days * 4 + 1 193 194 # Standard day epochs, suitable for epoch_days. 195 # ss_MJD = 94493 196 # ss_POSIX = 135080 197 ss_NTP = 109513 198} 199 200function sstamp_to_ymdhMs(sstamp, epoch_days, \ 201 quadcentury, century, quadyear, year, month, day) 202{ 203 ss_hour = int(sstamp / 3600) % 24 204 ss_min = int(sstamp / 60) % 60 205 ss_sec = sstamp % 60 206 207 # Start with a count of days since 1600-03-01 Gregorian. 208 day = epoch_days + int(sstamp / (24 * 60 * 60)) 209 210 # Compute a year-month-day date with days of the month numbered 211 # 0-30, months (March-February) numbered 0-11, and years that start 212 # start March 1 and end after the last day of February. A quad-year 213 # starts on March 1 of a year evenly divisible by 4 and ends after 214 # the last day of February 4 years later. A century starts on and 215 # ends before March 1 in years evenly divisible by 100. 216 # A quad-century starts on and ends before March 1 in years divisible 217 # by 400. While the number of days in a quad-century is a constant, 218 # the number of days in each other time period can vary by 1. 219 # Any variation is in the last day of the time period (there might 220 # or might not be a February 29) where it is easy to deal with. 221 222 quadcentury = int(day / ss_quadcentury_days) 223 day -= quadcentury * ss_quadcentury_days 224 ss_wday = (day + 3) % 7 225 century = int(day / ss_century_days) 226 century -= century == 4 227 day -= century * ss_century_days 228 quadyear = int(day / ss_quadyear_days) 229 day -= quadyear * ss_quadyear_days 230 year = int(day / ss_year_days) 231 year -= year == 4 232 day -= year * ss_year_days 233 for (month = 0; month < 11; month++) { 234 if (day < ss_mon_days[month]) 235 break 236 day -= ss_mon_days[month] 237 } 238 239 # Convert the date to a conventional day of month (1-31), 240 # month (1-12, January-December) and Gregorian year. 241 ss_mday = day + 1 242 if (month <= 9) { 243 ss_month = month + 3 244 } else { 245 ss_month = month - 9 246 year++ 247 } 248 ss_year = 1600 + quadcentury * 400 + century * 100 + quadyear * 4 + year 249} 250