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+      DOUBLE PRECISION FUNCTION sla_DAT (UTC)
+*+
+*     - - - -
+*      D A T
+*     - - - -
+*
+*  Increment to be applied to Coordinated Universal Time UTC to give
+*  International Atomic Time TAI (double precision)
+*
+*  Given:
+*     UTC      d      UTC date as a modified JD (JD-2400000.5)
+*
+*  Result:  TAI-UTC in seconds
+*
+*  Notes:
+*
+*  1  The UTC is specified to be a date rather than a time to indicate
+*     that care needs to be taken not to specify an instant which lies
+*     within a leap second.  Though in most cases UTC can include the
+*     fractional part, correct behaviour on the day of a leap second
+*     can only be guaranteed up to the end of the second 23:59:59.
+*
+*  2  For epochs from 1961 January 1 onwards, the expressions from the
+*     file ftp://maia.usno.navy.mil/ser7/tai-utc.dat are used.
+*
+*  3  The 5ms timestep at 1961 January 1 is taken from 2.58.1 (p87) of
+*     the 1992 Explanatory Supplement.
+*
+*  4  UTC began at 1960 January 1.0 (JD 2436934.5) and it is improper
+*     to call the routine with an earlier epoch.  However, if this
+*     is attempted, the TAI-UTC expression for the year 1960 is used.
+*
+*
+*     :-----------------------------------------:
+*     :                                         :
+*     :                IMPORTANT                :
+*     :                                         :
+*     :  This routine must be updated on each   :
+*     :     occasion that a leap second is      :
+*     :                announced                :
+*     :                                         :
+*     :  Latest leap second:  1999 January 1    :
+*     :                                         :
+*     :-----------------------------------------:
+*
+*  P.T.Wallace   Starlink   31 May 1999
+*
+*  Copyright (C) 1999 Rutherford Appleton Laboratory
+*-
+
+      IMPLICIT NONE
+
+      DOUBLE PRECISION UTC
+
+      DOUBLE PRECISION DT
+
+
+
+      IF (.FALSE.) THEN
+
+* - - - - - - - - - - - - - - - - - - - - - - *
+*  Add new code here on each occasion that a  *
+*  leap second is announced, and update the   *
+*  preamble comments appropriately.           *
+* - - - - - - - - - - - - - - - - - - - - - - *
+
+*     1999 January 1
+      ELSE IF (UTC.GE.51179D0) THEN
+         DT=32D0
+
+*     1997 July 1
+      ELSE IF (UTC.GE.50630D0) THEN
+         DT=31D0
+
+*     1996 January 1
+      ELSE IF (UTC.GE.50083D0) THEN
+         DT=30D0
+
+*     1994 July 1
+      ELSE IF (UTC.GE.49534D0) THEN
+         DT=29D0
+
+*     1993 July 1
+      ELSE IF (UTC.GE.49169D0) THEN
+         DT=28D0
+
+*     1992 July 1
+      ELSE IF (UTC.GE.48804D0) THEN
+         DT=27D0
+
+*     1991 January 1
+      ELSE IF (UTC.GE.48257D0) THEN
+         DT=26D0
+
+*     1990 January 1
+      ELSE IF (UTC.GE.47892D0) THEN
+         DT=25D0
+
+*     1988 January 1
+      ELSE IF (UTC.GE.47161D0) THEN
+         DT=24D0
+
+*     1985 July 1
+      ELSE IF (UTC.GE.46247D0) THEN
+         DT=23D0
+
+*     1983 July 1
+      ELSE IF (UTC.GE.45516D0) THEN
+         DT=22D0
+
+*     1982 July 1
+      ELSE IF (UTC.GE.45151D0) THEN
+         DT=21D0
+
+*     1981 July 1
+      ELSE IF (UTC.GE.44786D0) THEN
+         DT=20D0
+
+*     1980 January 1
+      ELSE IF (UTC.GE.44239D0) THEN
+         DT=19D0
+
+*     1979 January 1
+      ELSE IF (UTC.GE.43874D0) THEN
+         DT=18D0
+
+*     1978 January 1
+      ELSE IF (UTC.GE.43509D0) THEN
+         DT=17D0
+
+*     1977 January 1
+      ELSE IF (UTC.GE.43144D0) THEN
+         DT=16D0
+
+*     1976 January 1
+      ELSE IF (UTC.GE.42778D0) THEN
+         DT=15D0
+
+*     1975 January 1
+      ELSE IF (UTC.GE.42413D0) THEN
+         DT=14D0
+
+*     1974 January 1
+      ELSE IF (UTC.GE.42048D0) THEN
+         DT=13D0
+
+*     1973 January 1
+      ELSE IF (UTC.GE.41683D0) THEN
+         DT=12D0
+
+*     1972 July 1
+      ELSE IF (UTC.GE.41499D0) THEN
+         DT=11D0
+
+*     1972 January 1
+      ELSE IF (UTC.GE.41317D0) THEN
+         DT=10D0
+
+*     1968 February 1
+      ELSE IF (UTC.GE.39887D0) THEN
+         DT=4.2131700D0+(UTC-39126D0)*0.002592D0
+
+*     1966 January 1
+      ELSE IF (UTC.GE.39126D0) THEN
+         DT=4.3131700D0+(UTC-39126D0)*0.002592D0
+
+*     1965 September 1
+      ELSE IF (UTC.GE.39004D0) THEN
+         DT=3.8401300D0+(UTC-38761D0)*0.001296D0
+
+*     1965 July 1
+      ELSE IF (UTC.GE.38942D0) THEN
+         DT=3.7401300D0+(UTC-38761D0)*0.001296D0
+
+*     1965 March 1
+      ELSE IF (UTC.GE.38820D0) THEN
+         DT=3.6401300D0+(UTC-38761D0)*0.001296D0
+
+*     1965 January 1
+      ELSE IF (UTC.GE.38761D0) THEN
+         DT=3.5401300D0+(UTC-38761D0)*0.001296D0
+
+*     1964 September 1
+      ELSE IF (UTC.GE.38639D0) THEN
+         DT=3.4401300D0+(UTC-38761D0)*0.001296D0
+
+*     1964 April 1
+      ELSE IF (UTC.GE.38486D0) THEN
+         DT=3.3401300D0+(UTC-38761D0)*0.001296D0
+
+*     1964 January 1
+      ELSE IF (UTC.GE.38395D0) THEN
+         DT=3.2401300D0+(UTC-38761D0)*0.001296D0
+
+*     1963 November 1
+      ELSE IF (UTC.GE.38334D0) THEN
+         DT=1.9458580D0+(UTC-37665D0)*0.0011232D0
+
+*     1962 January 1
+      ELSE IF (UTC.GE.37665D0) THEN
+         DT=1.8458580D0+(UTC-37665D0)*0.0011232D0
+
+*     1961 August 1
+      ELSE IF (UTC.GE.37512D0) THEN
+         DT=1.3728180D0+(UTC-37300D0)*0.001296D0
+
+*     1961 January 1
+      ELSE IF (UTC.GE.37300D0) THEN
+         DT=1.4228180D0+(UTC-37300D0)*0.001296D0
+
+*     Before that
+      ELSE
+         DT=1.4178180D0+(UTC-37300D0)*0.001296D0
+
+      END IF
+
+      sla_DAT=DT
+
+      END