Annotation of src/share/zoneinfo/leapseconds.awk, Revision 1.2
1.2 ! millert 1: # Generate zic format 'leapseconds' from NIST/IERS format 'leap-seconds.list'.
1.1 millert 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:
18: BEGIN {
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"
1.2 ! millert 24: print "# NIST/IERS format leap-seconds.list file, which can be copied from"
1.1 millert 25: print "# <https://hpiers.obspm.fr/iers/bul/bulc/ntp/leap-seconds.list>"
1.2 ! millert 26: print "# or, in a variant with different comments, from"
! 27: print "# <ftp://ftp.boulder.nist.gov/pub/time/leap-seconds.list>."
1.1 millert 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:
103: END {
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:
173: function 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:
200: function 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: }
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