Annotation of src/share/zoneinfo/leapseconds.awk, Revision 1.1
1.1 ! millert 1: # Generate zic format 'leapseconds' from NIST 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:
! 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"
! 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>."
! 34: print ""
! 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>."
! 48: print ""
! 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"
! 53: print "# of UTC."
! 54: print ""
! 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"
! 61:
! 62: monthabbr[ 1] = "Jan"
! 63: monthabbr[ 2] = "Feb"
! 64: monthabbr[ 3] = "Mar"
! 65: monthabbr[ 4] = "Apr"
! 66: monthabbr[ 5] = "May"
! 67: monthabbr[ 6] = "Jun"
! 68: monthabbr[ 7] = "Jul"
! 69: monthabbr[ 8] = "Aug"
! 70: monthabbr[ 9] = "Sep"
! 71: monthabbr[10] = "Oct"
! 72: monthabbr[11] = "Nov"
! 73: monthabbr[12] = "Dec"
! 74:
! 75: sstamp_init()
! 76: }
! 77:
! 78: # In case the input has CRLF form a la NIST.
! 79: { sub(/\r$/, "") }
! 80:
! 81: /^#[ \t]*[Uu]pdated through/ || /^#[ \t]*[Ff]ile expires on/ {
! 82: last_lines = last_lines $0 "\n"
! 83: }
! 84:
! 85: /^#[$][ \t]/ { updated = $2 }
! 86: /^#[@][ \t]/ { expires = $2 }
! 87:
! 88: /^[ \t]*#/ { next }
! 89:
! 90: {
! 91: NTP_timestamp = $1
! 92: TAI_minus_UTC = $2
! 93: if (old_TAI_minus_UTC) {
! 94: if (old_TAI_minus_UTC < TAI_minus_UTC) {
! 95: sign = "23:59:60\t+"
! 96: } else {
! 97: sign = "23:59:59\t-"
! 98: }
! 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
! 102: }
! 103: old_TAI_minus_UTC = TAI_minus_UTC
! 104: }
! 105:
! 106: END {
! 107: print ""
! 108:
! 109: if (expires) {
! 110: sstamp_to_ymdhMs(expires, ss_NTP)
! 111:
! 112: print "# UTC timestamp when this leap second list expires."
! 113: print "# Any additional leap seconds will come after this."
! 114: if (! EXPIRES_LINE) {
! 115: print "# This Expires line is commented out for now,"
! 116: print "# so that pre-2020a zic implementations do not reject this file."
! 117: }
! 118: printf "%sExpires %.4d\t%s\t%.2d\t%.2d:%.2d:%.2d\n", \
! 119: EXPIRES_LINE ? "" : "#", \
! 120: ss_year, monthabbr[ss_month], ss_mday, ss_hour, ss_min, ss_sec
! 121: } else {
! 122: print "# (No Expires line, since the expires time is unknown.)"
! 123: }
! 124:
! 125: # The difference between the NTP and POSIX epochs is 70 years
! 126: # (including 17 leap days), each 24 hours of 60 minutes of 60
! 127: # seconds each.
! 128: epoch_minus_NTP = ((1970 - 1900) * 365 + 17) * 24 * 60 * 60
! 129:
! 130: print ""
! 131: print "# POSIX timestamps for the data in this file:"
! 132: if (updated) {
! 133: sstamp_to_ymdhMs(updated, ss_NTP)
! 134: printf "#updated %d (%.4d-%.2d-%.2d %.2d:%.2d:%.2d UTC)\n", \
! 135: updated - epoch_minus_NTP, \
! 136: ss_year, ss_month, ss_mday, ss_hour, ss_min, ss_sec
! 137: } else {
! 138: print "#(updated time unknown)"
! 139: }
! 140: if (expires) {
! 141: sstamp_to_ymdhMs(expires, ss_NTP)
! 142: printf "#expires %d (%.4d-%.2d-%.2d %.2d:%.2d:%.2d UTC)\n", \
! 143: expires - epoch_minus_NTP, \
! 144: ss_year, ss_month, ss_mday, ss_hour, ss_min, ss_sec
! 145: } else {
! 146: print "#(expires time unknown)"
! 147: }
! 148: printf "\n%s", last_lines
! 149: }
! 150:
! 151: # sstamp_to_ymdhMs - convert seconds timestamp to date and time
! 152: #
! 153: # Call as:
! 154: #
! 155: # sstamp_to_ymdhMs(sstamp, epoch_days)
! 156: #
! 157: # where:
! 158: #
! 159: # sstamp - is the seconds timestamp.
! 160: # epoch_days - is the timestamp epoch in Gregorian days since 1600-03-01.
! 161: # ss_NTP is appropriate for an NTP sstamp.
! 162: #
! 163: # Both arguments should be nonnegative integers.
! 164: # On return, the following variables are set based on sstamp:
! 165: #
! 166: # ss_year - Gregorian calendar year
! 167: # ss_month - month of the year (1-January to 12-December)
! 168: # ss_mday - day of the month (1-31)
! 169: # ss_hour - hour (0-23)
! 170: # ss_min - minute (0-59)
! 171: # ss_sec - second (0-59)
! 172: # ss_wday - day of week (0-Sunday to 6-Saturday)
! 173: #
! 174: # The function sstamp_init should be called prior to using sstamp_to_ymdhMs.
! 175:
! 176: function sstamp_init()
! 177: {
! 178: # Days in month N, where March is month 0 and January month 10.
! 179: ss_mon_days[ 0] = 31
! 180: ss_mon_days[ 1] = 30
! 181: ss_mon_days[ 2] = 31
! 182: ss_mon_days[ 3] = 30
! 183: ss_mon_days[ 4] = 31
! 184: ss_mon_days[ 5] = 31
! 185: ss_mon_days[ 6] = 30
! 186: ss_mon_days[ 7] = 31
! 187: ss_mon_days[ 8] = 30
! 188: ss_mon_days[ 9] = 31
! 189: ss_mon_days[10] = 31
! 190:
! 191: # Counts of days in a Gregorian year, quad-year, century, and quad-century.
! 192: ss_year_days = 365
! 193: ss_quadyear_days = ss_year_days * 4 + 1
! 194: ss_century_days = ss_quadyear_days * 25 - 1
! 195: ss_quadcentury_days = ss_century_days * 4 + 1
! 196:
! 197: # Standard day epochs, suitable for epoch_days.
! 198: # ss_MJD = 94493
! 199: # ss_POSIX = 135080
! 200: ss_NTP = 109513
! 201: }
! 202:
! 203: function sstamp_to_ymdhMs(sstamp, epoch_days, \
! 204: quadcentury, century, quadyear, year, month, day)
! 205: {
! 206: ss_hour = int(sstamp / 3600) % 24
! 207: ss_min = int(sstamp / 60) % 60
! 208: ss_sec = sstamp % 60
! 209:
! 210: # Start with a count of days since 1600-03-01 Gregorian.
! 211: day = epoch_days + int(sstamp / (24 * 60 * 60))
! 212:
! 213: # Compute a year-month-day date with days of the month numbered
! 214: # 0-30, months (March-February) numbered 0-11, and years that start
! 215: # start March 1 and end after the last day of February. A quad-year
! 216: # starts on March 1 of a year evenly divisible by 4 and ends after
! 217: # the last day of February 4 years later. A century starts on and
! 218: # ends before March 1 in years evenly divisible by 100.
! 219: # A quad-century starts on and ends before March 1 in years divisible
! 220: # by 400. While the number of days in a quad-century is a constant,
! 221: # the number of days in each other time period can vary by 1.
! 222: # Any variation is in the last day of the time period (there might
! 223: # or might not be a February 29) where it is easy to deal with.
! 224:
! 225: quadcentury = int(day / ss_quadcentury_days)
! 226: day -= quadcentury * ss_quadcentury_days
! 227: ss_wday = (day + 3) % 7
! 228: century = int(day / ss_century_days)
! 229: century -= century == 4
! 230: day -= century * ss_century_days
! 231: quadyear = int(day / ss_quadyear_days)
! 232: day -= quadyear * ss_quadyear_days
! 233: year = int(day / ss_year_days)
! 234: year -= year == 4
! 235: day -= year * ss_year_days
! 236: for (month = 0; month < 11; month++) {
! 237: if (day < ss_mon_days[month])
! 238: break
! 239: day -= ss_mon_days[month]
! 240: }
! 241:
! 242: # Convert the date to a conventional day of month (1-31),
! 243: # month (1-12, January-December) and Gregorian year.
! 244: ss_mday = day + 1
! 245: if (month <= 9) {
! 246: ss_month = month + 3
! 247: } else {
! 248: ss_month = month - 9
! 249: year++
! 250: }
! 251: ss_year = 1600 + quadcentury * 400 + century * 100 + quadyear * 4 + year
! 252: }
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