SUBROUTINE iau_D2DTF ( SCALE, NDP, D1, D2, IY, IM, ID, IHMSF, J )
*+
*  - - - - - - - - - -
*   i a u _ D 2 D T F
*  - - - - - - - - - -
*
*  Format for output a 2-part Julian Date (or in the case of UTC a
*  quasi-JD form that includes special provision for leap seconds).
*
*  This routine is part of the International Astronomical Union's
*  SOFA (Standards of Fundamental Astronomy) software collection.
*
*  Status:  support routine.
*
*  Given:
*     SCALE      c*(*)  time scale ID (Note 1)
*     NDP        i      resolution (Note 2)
*     D1,D2      d      time as a 2-part Julian Date (Notes 3,4)
*
*  Returned:
*     IY,IM,ID   i      year, month, day in Gregorian calendar (Note 5)
*     IHMSF      i(4)   hours, minutes, seconds, fraction (Note 1)
*     J          i      status: +1 = dubious year (Note 5)
*                                0 = OK
*                               -1 = unacceptable date (Note 6)
*
*  Notes:
*
*  1) SCALE identifies the time scale.  Only the value 'UTC' (in upper
*     case) is significant, and enables handling of leap seconds (see
*     Note 4).
*
*  2) NDP is the number of decimal places in the seconds field, and can
*     have negative as well as positive values, such as:
*
*     NDP         resolution
*     -4            1 00 00
*     -3            0 10 00
*     -2            0 01 00
*     -1            0 00 10
*      0            0 00 01
*      1            0 00 00.1
*      2            0 00 00.01
*      3            0 00 00.001
*
*     The limits are platform dependent, but a safe range is -5 to +9.
*
*  3) D1+D2 is Julian Date, apportioned in any convenient way between
*     the two arguments, for example where D1 is the Julian Day Number
*     and D2 is the fraction of a day.  In the case of UTC, where the
*     use of JD is problematical, special conventions apply:  see the
*     next note.
*
*  4) JD cannot unambiguously represent UTC during a leap second unless
*     special measures are taken.  The SOFA internal convention is that
*     the quasi-JD day represents UTC days whether the length is 86399,
*     86400 or 86401 SI seconds.  In the 1960-1972 era there were
*     smaller jumps (in either direction) each time the linear UTC(TAI)
*     expression was changed, and these "mini-leaps" are also included
*     in the SOFA convention.
*
*  5) The warning status "dubious year" flags UTCs that predate the
*     introduction of the time scale or that are too far in the future
*     to be trusted.  See iau_DAT for further details.
*
*  6) For calendar conventions and limitations, see iau_CAL2JD.
*
*  Called:
*     iau_JD2CAL   JD to Gregorian calendar
*     iau_D2TF     decompose days to hms
*     iau_DAT      delta(AT) = TAI-UTC
*
*  This revision:  2014 February 15
*
*  SOFA release 2016-05-03
*
*  Copyright (C) 2016 IAU SOFA Board.  See notes at end.
*
*-----------------------------------------------------------------------

      IMPLICIT NONE
      CHARACTER*(*) SCALE
      INTEGER NDP
      DOUBLE PRECISION D1, D2
      INTEGER IY, IM, ID, IHMSF(4), J

*  Days to seconds
      DOUBLE PRECISION D2S
      PARAMETER ( D2S = 86400D0 )

      LOGICAL LEAP
      CHARACTER S
      INTEGER IY1, IM1, ID1, JS, IY2, IM2, ID2, IHMSF1(4), I
      DOUBLE PRECISION A1, B1, FD, DAT0, DAT12, W, DAT24, DLEAP

* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

*  The two-part JD.
      A1 = D1
      B1 = D2

*  Provisional calendar date.
      CALL iau_JD2CAL ( A1, B1, IY1, IM1, ID1, FD, JS )
      IF ( JS.NE.0 ) GO TO 9

*  Is this a leap second day?
      LEAP = .FALSE.
      IF ( SCALE.EQ.'UTC' ) THEN

*     TAI-UTC at 0h today.
         CALL iau_DAT ( IY1, IM1, ID1, 0D0, DAT0, JS )
         IF ( JS.LT.0 ) GO TO 9

*     TAI-UTC at 12h today (to detect drift).
         CALL iau_DAT ( IY1, IM1, ID1, 0.5D0, DAT12, JS )
         IF ( JS.LT.0 ) GO TO 9

*     TAI-UTC at 0h tomorrow (to detect jumps).
         CALL iau_JD2CAL ( A1+1.5D0, B1-FD, IY2, IM2, ID2, W, JS )
         IF ( JS.NE.0 ) GO TO 9
         CALL iau_DAT ( IY2, IM2, ID2, 0D0, DAT24, JS )
         IF ( JS.LT.0 ) GO TO 9

*     Any sudden change in TAI-UTC (seconds).
         DLEAP = DAT24 - ( 2D0 * DAT12 - DAT0 )

*     If leap second day, scale the fraction of a day into SI.
         LEAP = DLEAP.NE.0D0
         IF ( LEAP ) FD = FD + FD*DLEAP/D2S

      END IF

*  Provisional time of day.
      CALL iau_D2TF ( NDP, FD, S, IHMSF1 )

*  Has the (rounded) time gone past 24h?
      IF ( IHMSF1(1).GT.23 ) THEN

*     Yes.  We probably need tomorrow's calendar date.
         CALL iau_JD2CAL ( A1+1.5D0, B1-FD, IY2, IM2, ID2, W, JS )
         IF ( JS.LT.0 ) GO TO 9

*     Is today a leap second day?
         IF ( .NOT. LEAP ) THEN

*        No.  Use 0h tomorrow.
            IY1 = IY2
            IM1 = IM2
            ID1 = ID2
            IHMSF1(1) = 0
            IHMSF1(2) = 0
            IHMSF1(3) = 0

         ELSE

*        Yes.  Are we past the leap second itself?
            IF ( IHMSF1(3).GT.0 ) THEN

*           Yes.  Use tomorrow but allow for the leap second.
               IY1 = IY2
               IM1 = IM2
               ID1 = ID2
               IHMSF1(1) = 0
               IHMSF1(2) = 0
               IHMSF1(3) = 0

            ELSE

*           No.  Use 23 59 60... today.
               IHMSF1(1) = 23
               IHMSF1(2) = 59
               IHMSF1(3) = 60
            END IF

*        If rounding to 10s or coarser always go up to new day.
            IF ( NDP.LT.0 .AND. IHMSF1(3).EQ.60 ) THEN
               IY1 = IY2
               IM1 = IM2
               ID1 = ID2
               IHMSF1(1) = 0
               IHMSF1(2) = 0
               IHMSF1(3) = 0
            END IF
         END IF
      END IF

*  Results.
      IY = IY1
      IM = IM1
      ID = ID1
      DO 2 I=1,4
         IHMSF(I) = IHMSF1(I)
 2    CONTINUE

*  Status.
 9    CONTINUE
      J = JS

*  Finished.

*+----------------------------------------------------------------------
*
*  Copyright (C) 2016
*  Standards Of Fundamental Astronomy Board
*  of the International Astronomical Union.
*
*  =====================
*  SOFA Software License
*  =====================
*
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*
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*  CONDITIONS WHICH APPLY TO ITS USE.
*
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*-----------------------------------------------------------------------

      END