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# Generate the 'leapseconds' file from 'leap-seconds.list'. 
 
# This file is in the public domain. 
 
BEGIN { 
  print "# Allowance for leap seconds added to each time zone file." 
  print "" 
  print "# This file is in the public domain." 
  print "" 
  print "# This file is generated automatically from the data in the public-domain" 
  print "# leap-seconds.list file, which can be copied from" 
  print "# <ftp://ftp.nist.gov/pub/time/leap-seconds.list>" 
  print "# or <ftp://ftp.boulder.nist.gov/pub/time/leap-seconds.list>" 
  print "# or <ftp://tycho.usno.navy.mil/pub/ntp/leap-seconds.list>." 
  print "# For more about leap-seconds.list, please see" 
  print "# The NTP Timescale and Leap Seconds" 
  print "# <https://www.eecis.udel.edu/~mills/leap.html>." 
  print "" 
  print "# The International Earth Rotation and Reference Systems Service" 
  print "# periodically uses leap seconds to keep UTC to within 0.9 s of UT1" 
  print "# (which measures the true angular orientation of the earth in space)" 
  print "# and publishes leap second data in a copyrighted file" 
  print "# <https://hpiers.obspm.fr/iers/bul/bulc/Leap_Second.dat>." 
  print "# See: Levine J. Coordinated Universal Time and the leap second." 
  print "# URSI Radio Sci Bull. 2016;89(4):30-6. doi:10.23919/URSIRSB.2016.7909995" 
  print "# <https://ieeexplore.ieee.org/document/7909995>." 
  print "" 
  print "# There were no leap seconds before 1972, because the official mechanism" 
  print "# accounting for the discrepancy between atomic time and the earth's rotation" 
  print "# did not exist.  The first (\"1 Jan 1972\") data line in leap-seconds.list" 
  print "# does not denote a leap second; it denotes the start of the current definition" 
  print"# of UTC." 
  print "" 
  print "# The correction (+ or -) is made at the given time, so lines" 
  print "# will typically look like:" 
  print "#      Leap    YEAR    MON     DAY     23:59:60        +       R/S" 
  print "# or" 
  print "#      Leap    YEAR    MON     DAY     23:59:59        -       R/S" 
  print "" 
  print "# If the leap second is Rolling (R) the given time is local time (unused here)." 
 
  monthabbr[ 1] = "Jan" 
  monthabbr[ 2] = "Feb" 
  monthabbr[ 3] = "Mar" 
  monthabbr[ 4] = "Apr" 
  monthabbr[ 5] = "May" 
  monthabbr[ 6] = "Jun" 
  monthabbr[ 7] = "Jul" 
  monthabbr[ 8] = "Aug" 
  monthabbr[ 9] = "Sep" 
  monthabbr[10] = "Oct" 
  monthabbr[11] = "Nov" 
  monthabbr[12] = "Dec" 
  for (i in monthabbr) { 
      monthnum[monthabbr[i]] = i 
      monthlen[i] = 31 
  } 
  monthlen[2] = 28 
  monthlen[4] = monthlen[6] = monthlen[9] = monthlen[11] = 30 
} 
 
/^#\tUpdated through/ || /^#\tFile expires on:/ { 
    last_lines = last_lines $0 "\n" 
} 
 
/^#[$][ \t]/ { updated = $2 } 
/^#[@][ \t]/ { expires = $2 } 
 
/^#/ { next } 
 
{ 
    NTP_timestamp = $1 
    TAI_minus_UTC = $2 
    hash_mark = $3 
    one = $4 
    month = $5 
    year = $6 
    if (old_TAI_minus_UTC) { 
        if (old_TAI_minus_UTC < TAI_minus_UTC) { 
            sign = "23:59:60\t+" 
        } else { 
            sign = "23:59:59\t-" 
        } 
        m = monthnum[month] - 1 
        if (m == 0) { 
            year--; 
            m = 12 
        } 
        month = monthabbr[m] 
        day = monthlen[m] 
        day += m == 2 && year % 4 == 0 && (year % 100 != 0 || year % 400 == 0) 
        printf "Leap\t%s\t%s\t%s\t%s\tS\n", year, month, day, sign 
    } 
    old_TAI_minus_UTC = TAI_minus_UTC 
} 
 
END { 
    # The difference between the NTP and POSIX epochs is 70 years 
    # (including 17 leap days), each 24 hours of 60 minutes of 60 
    # seconds each. 
    epoch_minus_NTP = ((1970 - 1900) * 365 + 17) * 24 * 60 * 60 
 
    print "" 
    print "# POSIX timestamps for the data in this file:" 
    printf "#updated %s\n", updated - epoch_minus_NTP 
    printf "#expires %s\n", expires - epoch_minus_NTP 
    printf "\n%s", last_lines 
}