contrib/tzdata/leapseconds.awk

   1 # Generate the 'leapseconds' file from 'leap-seconds.list'.
   2
   3 # This file is in the public domain.
   4
   5 BEGIN {
   6   print "# Allowance for leap seconds added to each time zone file."
   7   print ""
   8   print "# This file is in the public domain."
   9   print ""
  10   print "# This file is generated automatically from the data in the public-domain"
  11   print "# leap-seconds.list file, which can be copied from"
  12   print "# <ftp://ftp.nist.gov/pub/time/leap-seconds.list>"
  13   print "# or <ftp://ftp.boulder.nist.gov/pub/time/leap-seconds.list>"
  14   print "# or <ftp://tycho.usno.navy.mil/pub/ntp/leap-seconds.list>."
  15   print "# For more about leap-seconds.list, please see"
  16   print "# The NTP Timescale and Leap Seconds"
  17   print "# <https://www.eecis.udel.edu/~mills/leap.html>."
  18   print ""
  19   print "# The International Earth Rotation and Reference Systems Service"
  20   print "# periodically uses leap seconds to keep UTC to within 0.9 s of UT1"
  21   print "# (which measures the true angular orientation of the earth in space)"
  22   print "# and publishes leap second data in a copyrighted file"
  23   print "# <https://hpiers.obspm.fr/iers/bul/bulc/Leap_Second.dat>."
  24   print "# See: Levine J. Coordinated Universal Time and the leap second."
  25   print "# URSI Radio Sci Bull. 2016;89(4):30-6. doi:10.23919/URSIRSB.2016.7909995"
  26   print "# <https://ieeexplore.ieee.org/document/7909995>."
  27   print "# There were no leap seconds before 1972, because the official mechanism"
  28   print "# accounting for the discrepancy between atomic time and the earth's rotation"
  29   print "# did not exist."
  30   print ""
  31   print "# The correction (+ or -) is made at the given time, so lines"
  32   print "# will typically look like:"
  33   print "#      Leap    YEAR    MON     DAY     23:59:60        +       R/S"
  34   print "# or"
  35   print "#      Leap    YEAR    MON     DAY     23:59:59        -       R/S"
  36   print ""
  37   print "# If the leap second is Rolling (R) the given time is local time (unused here)."
  38
  39   monthabbr[ 1] = "Jan"
  40   monthabbr[ 2] = "Feb"
  41   monthabbr[ 3] = "Mar"
  42   monthabbr[ 4] = "Apr"
  43   monthabbr[ 5] = "May"
  44   monthabbr[ 6] = "Jun"
  45   monthabbr[ 7] = "Jul"
  46   monthabbr[ 8] = "Aug"
  47   monthabbr[ 9] = "Sep"
  48   monthabbr[10] = "Oct"
  49   monthabbr[11] = "Nov"
  50   monthabbr[12] = "Dec"
  51   for (i in monthabbr) {
  52       monthnum[monthabbr[i]] = i
  53       monthlen[i] = 31
  54   }
  55   monthlen[2] = 28
  56   monthlen[4] = monthlen[6] = monthlen[9] = monthlen[11] = 30
  57 }
  58
  59 /^#\tUpdated through/ || /^#\tFile expires on:/ {
  60     last_lines = last_lines $0 "\n"
  61 }
  62
  63 /^#[$][ \t]/ { updated = $2 }
  64 /^#[@][ \t]/ { expires = $2 }
  65
  66 /^#/ { next }
  67
  68 {
  69     NTP_timestamp = $1
  70     TAI_minus_UTC = $2
  71     hash_mark = $3
  72     one = $4
  73     month = $5
  74     year = $6
  75     if (old_TAI_minus_UTC) {
  76         if (old_TAI_minus_UTC < TAI_minus_UTC) {
  77             sign = "23:59:60\t+"
  78         } else {
  79             sign = "23:59:59\t-"
  80         }
  81         m = monthnum[month] - 1
  82         if (m == 0) {
  83             year--;
  84             m = 12
  85         }
  86         month = monthabbr[m]
  87         day = monthlen[m]
  88         day += m == 2 && year % 4 == 0 && (year % 100 != 0 || year % 400 == 0)
  89         printf "Leap\t%s\t%s\t%s\t%s\tS\n", year, month, day, sign
  90     }
  91     old_TAI_minus_UTC = TAI_minus_UTC
  92 }
  93
  94 END {
  95     # The difference between the NTP and POSIX epochs is 70 years
  96     # (including 17 leap days), each 24 hours of 60 minutes of 60
  97     # seconds each.
  98     epoch_minus_NTP = ((1970 - 1900) * 365 + 17) * 24 * 60 * 60
  99
 100     print ""
 101     print "# POSIX timestamps for the data in this file:"
 102     printf "#updated %s\n", updated - epoch_minus_NTP
 103     printf "#expires %s\n", expires - epoch_minus_NTP
 104     printf "\n%s", last_lines
 105 }