1 # Generate zic format 'leapseconds' from NIST format 'leap-seconds.list'.
3 # This file is in the public domain.
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
19 print "# Allowance for leap seconds added to each time zone file."
21 print "# This file is in the public domain."
23 print "# This file is generated automatically from the data in the public-domain"
24 print "# NIST format leap-seconds.list file, which can be copied from"
25 print "# <ftp://ftp.nist.gov/pub/time/leap-seconds.list>"
26 print "# or <ftp://ftp.boulder.nist.gov/pub/time/leap-seconds.list>."
27 print "# The NIST file is used instead of its IERS upstream counterpart"
28 print "# <https://hpiers.obspm.fr/iers/bul/bulc/ntp/leap-seconds.list>"
29 print "# because under US law the NIST file is public domain"
30 print "# whereas the IERS file's copyright and license status is unclear."
31 print "# For more about leap-seconds.list, please see"
32 print "# The NTP Timescale and Leap Seconds"
33 print "# <https://www.eecis.udel.edu/~mills/leap.html>."
35 print "# The rules for leap seconds are specified in Annex 1 (Time scales) of:"
36 print "# Standard-frequency and time-signal emissions."
37 print "# International Telecommunication Union - Radiocommunication Sector"
38 print "# (ITU-R) Recommendation TF.460-6 (02/2002)"
39 print "# <https://www.itu.int/rec/R-REC-TF.460-6-200202-I/>."
40 print "# The International Earth Rotation and Reference Systems Service (IERS)"
41 print "# periodically uses leap seconds to keep UTC to within 0.9 s of UT1"
42 print "# (a proxy for Earth's angle in space as measured by astronomers)"
43 print "# and publishes leap second data in a copyrighted file"
44 print "# <https://hpiers.obspm.fr/iers/bul/bulc/Leap_Second.dat>."
45 print "# See: Levine J. Coordinated Universal Time and the leap second."
46 print "# URSI Radio Sci Bull. 2016;89(4):30-6. doi:10.23919/URSIRSB.2016.7909995"
47 print "# <https://ieeexplore.ieee.org/document/7909995>."
49 print "# There were no leap seconds before 1972, as no official mechanism"
50 print "# accounted for the discrepancy between atomic time (TAI) and the earth's"
51 print "# rotation. The first (\"1 Jan 1972\") data line in leap-seconds.list"
52 print "# does not denote a leap second; it denotes the start of the current definition"
55 print "# All leap-seconds are Stationary (S) at the given UTC time."
56 print "# The correction (+ or -) is made at the given time, so in the unlikely"
57 print "# event of a negative leap second, a line would look like this:"
58 print "# Leap YEAR MON DAY 23:59:59 - S"
59 print "# Typical lines look like this:"
60 print "# Leap YEAR MON DAY 23:59:60 + S"
78 # In case the input has CRLF form a la NIST.
81 /^#[ \t]*[Uu]pdated through/ || /^#[ \t]*[Ff]ile expires on/ {
82 last_lines = last_lines $0 "\n"
85 /^#[$][ \t]/ { updated = $2 }
86 /^#[@][ \t]/ { expires = $2 }
93 if (old_TAI_minus_UTC) {
94 if (old_TAI_minus_UTC < TAI_minus_UTC) {
99 sstamp_to_ymdhMs(NTP_timestamp - 1, ss_NTP)
100 printf "Leap\t%d\t%s\t%d\t%s\tS\n", \
101 ss_year, monthabbr[ss_month], ss_mday, sign
103 old_TAI_minus_UTC = TAI_minus_UTC
107 sstamp_to_ymdhMs(expires, ss_NTP)
110 print "# UTC timestamp when this leap second list expires."
111 print "# Any additional leap seconds will come after this."
112 if (! EXPIRES_LINE) {
113 print "# This Expires line is commented out for now,"
114 print "# so that pre-2020a zic implementations do not reject this file."
116 printf "%sExpires %.4d\t%s\t%.2d\t%.2d:%.2d:%.2d\n", \
117 EXPIRES_LINE ? "" : "#", \
118 ss_year, monthabbr[ss_month], ss_mday, ss_hour, ss_min, ss_sec
120 # The difference between the NTP and POSIX epochs is 70 years
121 # (including 17 leap days), each 24 hours of 60 minutes of 60
123 epoch_minus_NTP = ((1970 - 1900) * 365 + 17) * 24 * 60 * 60
126 print "# POSIX timestamps for the data in this file:"
127 sstamp_to_ymdhMs(updated, ss_NTP)
128 printf "#updated %d (%.4d-%.2d-%.2d %.2d:%.2d:%.2d UTC)\n", \
129 updated - epoch_minus_NTP, \
130 ss_year, ss_month, ss_mday, ss_hour, ss_min, ss_sec
131 sstamp_to_ymdhMs(expires, ss_NTP)
132 printf "#expires %d (%.4d-%.2d-%.2d %.2d:%.2d:%.2d UTC)\n", \
133 expires - epoch_minus_NTP, \
134 ss_year, ss_month, ss_mday, ss_hour, ss_min, ss_sec
136 printf "\n%s", last_lines
139 # sstamp_to_ymdhMs - convert seconds timestamp to date and time
143 # sstamp_to_ymdhMs(sstamp, epoch_days)
147 # sstamp - is the seconds timestamp.
148 # epoch_days - is the timestamp epoch in Gregorian days since 1600-03-01.
149 # ss_NTP is appropriate for an NTP sstamp.
151 # Both arguments should be nonnegative integers.
152 # On return, the following variables are set based on sstamp:
154 # ss_year - Gregorian calendar year
155 # ss_month - month of the year (1-January to 12-December)
156 # ss_mday - day of the month (1-31)
157 # ss_hour - hour (0-23)
158 # ss_min - minute (0-59)
159 # ss_sec - second (0-59)
160 # ss_wday - day of week (0-Sunday to 6-Saturday)
162 # The function sstamp_init should be called prior to using sstamp_to_ymdhMs.
164 function sstamp_init()
166 # Days in month N, where March is month 0 and January month 10.
179 # Counts of days in a Gregorian year, quad-year, century, and quad-century.
181 ss_quadyear_days = ss_year_days * 4 + 1
182 ss_century_days = ss_quadyear_days * 25 - 1
183 ss_quadcentury_days = ss_century_days * 4 + 1
185 # Standard day epochs, suitable for epoch_days.
191 function sstamp_to_ymdhMs(sstamp, epoch_days, \
192 quadcentury, century, quadyear, year, month, day)
194 ss_hour = int(sstamp / 3600) % 24
195 ss_min = int(sstamp / 60) % 60
198 # Start with a count of days since 1600-03-01 Gregorian.
199 day = epoch_days + int(sstamp / (24 * 60 * 60))
201 # Compute a year-month-day date with days of the month numbered
202 # 0-30, months (March-February) numbered 0-11, and years that start
203 # start March 1 and end after the last day of February. A quad-year
204 # starts on March 1 of a year evenly divisible by 4 and ends after
205 # the last day of February 4 years later. A century starts on and
206 # ends before March 1 in years evenly divisible by 100.
207 # A quad-century starts on and ends before March 1 in years divisible
208 # by 400. While the number of days in a quad-century is a constant,
209 # the number of days in each other time period can vary by 1.
210 # Any variation is in the last day of the time period (there might
211 # or might not be a February 29) where it is easy to deal with.
213 quadcentury = int(day / ss_quadcentury_days)
214 day -= quadcentury * ss_quadcentury_days
215 ss_wday = (day + 3) % 7
216 century = int(day / ss_century_days)
217 century -= century == 4
218 day -= century * ss_century_days
219 quadyear = int(day / ss_quadyear_days)
220 day -= quadyear * ss_quadyear_days
221 year = int(day / ss_year_days)
223 day -= year * ss_year_days
224 for (month = 0; month < 11; month++) {
225 if (day < ss_mon_days[month])
227 day -= ss_mon_days[month]
230 # Convert the date to a conventional day of month (1-31),
231 # month (1-12, January-December) and Gregorian year.
239 ss_year = 1600 + quadcentury * 400 + century * 100 + quadyear * 4 + year