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 "# For more about leap-seconds.list, please see"
28 print "# The NTP Timescale and Leap Seconds"
29 print "# <https://www.eecis.udel.edu/~mills/leap.html>."
31 print "# The rules for leap seconds are specified in Annex 1 (Time scales) of:"
32 print "# Standard-frequency and time-signal emissions."
33 print "# International Telecommunication Union - Radiocommunication Sector"
34 print "# (ITU-R) Recommendation TF.460-6 (02/2002)"
35 print "# <https://www.itu.int/rec/R-REC-TF.460-6-200202-I/>."
36 print "# The International Earth Rotation and Reference Systems Service (IERS)"
37 print "# periodically uses leap seconds to keep UTC to within 0.9 s of UT1"
38 print "# (a proxy for Earth's angle in space as measured by astronomers)"
39 print "# and publishes leap second data in a copyrighted file"
40 print "# <https://hpiers.obspm.fr/iers/bul/bulc/Leap_Second.dat>."
41 print "# See: Levine J. Coordinated Universal Time and the leap second."
42 print "# URSI Radio Sci Bull. 2016;89(4):30-6. doi:10.23919/URSIRSB.2016.7909995"
43 print "# <https://ieeexplore.ieee.org/document/7909995>."
45 print "# There were no leap seconds before 1972, as no official mechanism"
46 print "# accounted for the discrepancy between atomic time (TAI) and the earth's"
47 print "# rotation. The first (\"1 Jan 1972\") data line in leap-seconds.list"
48 print "# does not denote a leap second; it denotes the start of the current definition"
51 print "# All leap-seconds are Stationary (S) at the given UTC time."
52 print "# The correction (+ or -) is made at the given time, so in the unlikely"
53 print "# event of a negative leap second, a line would look like this:"
54 print "# Leap YEAR MON DAY 23:59:59 - S"
55 print "# Typical lines look like this:"
56 print "# Leap YEAR MON DAY 23:59:60 + S"
71 # Strip trailing CR, in case the input has CRLF form a la NIST.
77 /^#[ \t]*[Uu]pdated through/ || /^#[ \t]*[Ff]ile expires on/ {
78 last_lines = last_lines $0 "\n"
81 /^#[$][ \t]/ { updated = $2 }
82 /^#[@][ \t]/ { expires = $2 }
89 if (old_TAI_minus_UTC) {
90 if (old_TAI_minus_UTC < TAI_minus_UTC) {
95 sstamp_to_ymdhMs(NTP_timestamp - 1, ss_NTP)
96 printf "Leap\t%d\t%s\t%d\t%s\tS\n", \
97 ss_year, monthabbr[ss_month], ss_mday, sign
99 old_TAI_minus_UTC = TAI_minus_UTC
103 # The difference between the NTP and POSIX epochs is 70 years
104 # (including 17 leap days), each 24 hours of 60 minutes of 60
106 epoch_minus_NTP = ((1970 - 1900) * 365 + 17) * 24 * 60 * 60
109 print "# POSIX timestamps for the data in this file:"
110 sstamp_to_ymdhMs(updated, ss_NTP)
111 printf "#updated %d (%.4d-%.2d-%.2d %.2d:%.2d:%.2d UTC)\n", \
112 updated - epoch_minus_NTP, \
113 ss_year, ss_month, ss_mday, ss_hour, ss_min, ss_sec
114 sstamp_to_ymdhMs(expires, ss_NTP)
115 printf "#expires %d (%.4d-%.2d-%.2d %.2d:%.2d:%.2d UTC)\n", \
116 expires - epoch_minus_NTP, \
117 ss_year, ss_month, ss_mday, ss_hour, ss_min, ss_sec
119 printf "\n%s", last_lines
122 # sstamp_to_ymdhMs - convert seconds timestamp to date and time
126 # sstamp_to_ymdhMs(sstamp, epoch_days)
130 # sstamp - is the seconds timestamp.
131 # epoch_days - is the timestamp epoch in Gregorian days since 1600-03-01.
132 # ss_NTP is appropriate for an NTP sstamp.
134 # Both arguments should be nonnegative integers.
135 # On return, the following variables are set based on sstamp:
137 # ss_year - Gregorian calendar year
138 # ss_month - month of the year (1-January to 12-December)
139 # ss_mday - day of the month (1-31)
140 # ss_hour - hour (0-23)
141 # ss_min - minute (0-59)
142 # ss_sec - second (0-59)
143 # ss_wday - day of week (0-Sunday to 6-Saturday)
145 # The function sstamp_init should be called prior to using sstamp_to_ymdhMs.
147 function sstamp_init()
149 # Days in month N, where March is month 0 and January month 10.
162 # Counts of days in a Gregorian year, quad-year, century, and quad-century.
164 ss_quadyear_days = ss_year_days * 4 + 1
165 ss_century_days = ss_quadyear_days * 25 - 1
166 ss_quadcentury_days = ss_century_days * 4 + 1
168 # Standard day epochs, suitable for epoch_days.
174 function sstamp_to_ymdhMs(sstamp, epoch_days, \
175 quadcentury, century, quadyear, year, month, day)
177 ss_hour = int(sstamp / 3600) % 24
178 ss_min = int(sstamp / 60) % 60
181 # Start with a count of days since 1600-03-01 Gregorian.
182 day = epoch_days + int(sstamp / (24 * 60 * 60))
184 # Compute a year-month-day date with days of the month numbered
185 # 0-30, months (March-February) numbered 0-11, and years that start
186 # start March 1 and end after the last day of February. A quad-year
187 # starts on March 1 of a year evenly divisible by 4 and ends after
188 # the last day of February 4 years later. A century starts on and
189 # ends before March 1 in years evenly divisible by 100.
190 # A quad-century starts on and ends before March 1 in years divisible
191 # by 400. While the number of days in a quad-century is a constant,
192 # the number of days in each other time period can vary by 1.
193 # Any variation is in the last day of the time period (there might
194 # or might not be a February 29) where it is easy to deal with.
196 quadcentury = int(day / ss_quadcentury_days)
197 day -= quadcentury * ss_quadcentury_days
198 ss_wday = (day + 3) % 7
199 century = int(day / ss_century_days)
200 century -= century == 4
201 day -= century * ss_century_days
202 quadyear = int(day / ss_quadyear_days)
203 day -= quadyear * ss_quadyear_days
204 year = int(day / ss_year_days)
206 day -= year * ss_year_days
207 for (month = 0; month < 11; month++) {
208 if (day < ss_mon_days[month])
210 day -= ss_mon_days[month]
213 # Convert the date to a conventional day of month (1-31),
214 # month (1-12, January-December) and Gregorian year.
222 ss_year = 1600 + quadcentury * 400 + century * 100 + quadyear * 4 + year