SUBROUTINE iau_TCGTT ( TCG1, TCG2, TT1, TT2, J )
*+
*  - - - - - - - - - -
*   i a u _ T C G T T
*  - - - - - - - - - -
*
*  Time scale transformation:  Geocentric Coordinate Time, TCG, to
*  Terrestrial Time, TT.
*
*  This routine is part of the International Astronomical Union's
*  SOFA (Standards of Fundamental Astronomy) software collection.
*
*  Status:  canonical.
*
*  Given:
*     TCG1,TCG2    d      TCG as a 2-part Julian Date
*
*  Returned:
*     TT1,TT2      d      TT as a 2-part Julian Date
*     J            i      status:  0 = OK
*
*  Note:
*
*     TCG1+TCG2 is Julian Date, apportioned in any convenient way
*     between the two arguments, for example where TCG1 is the Julian
*     Day Number and TCG2 is the fraction of a day.  The returned
*     TT1,TT2 follow suit.
*
*  References:
*
*     McCarthy, D. D., Petit, G. (eds.), IERS Conventions (2003),
*     IERS Technical Note No. 32, BKG (2004)
*
*     IAU 2000 Resolution B1.9
*
*  This revision:  2020 October 23
*
*  SOFA release 2023-10-11
*
*  Copyright (C) 2023 IAU SOFA Board.  See notes at end.
*
*-----------------------------------------------------------------------

      IMPLICIT NONE
      DOUBLE PRECISION TCG1, TCG2, TT1, TT2
      INTEGER J

*  JD for MJD 0
      DOUBLE PRECISION DJM0
      PARAMETER (DJM0 = 2400000.5D0 )

*  1977 Jan 1 00:00:32.184 TT, as MJD
      DOUBLE PRECISION T77T
      PARAMETER ( T77T = 43144.0003725D0 )

*  L_G = 1 - dTT/dTCG
      DOUBLE PRECISION ELG
      PARAMETER ( ELG = 6.969290134D-10 )

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

*  Result, safeguarding precision.
      IF ( ABS(TCG1).GT.ABS(TCG2) ) THEN
         TT1 = TCG1
         TT2 = TCG2 - ( ( TCG1-DJM0 ) + ( TCG2-T77T ) ) * ELG
      ELSE
         TT1 = TCG1 - ( ( TCG2-DJM0 ) + ( TCG1-T77T ) ) * ELG
         TT2 = TCG2
      END IF

*  Status (always OK).
      J = 0

*  Finished.

*+----------------------------------------------------------------------
*
*  Copyright (C) 2023
*  Standards of Fundamental Astronomy Board
*  of the International Astronomical Union.
*
*  =====================
*  SOFA Software License
*  =====================
*
*  NOTICE TO USER:
*
*  BY USING THIS SOFTWARE YOU ACCEPT THE FOLLOWING SIX TERMS AND
*  CONDITIONS WHICH APPLY TO ITS USE.
*
*  1. The Software is owned by the IAU SOFA Board ("SOFA").
*
*  2. Permission is granted to anyone to use the SOFA software for any
*     purpose, including commercial applications, free of charge and
*     without payment of royalties, subject to the conditions and
*     restrictions listed below.
*
*  3. You (the user) may copy and distribute SOFA source code to others,
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*     distribution that does not consist of intact and unchanged copies
*     of SOFA source code files is a "derived work" that must comply
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*
*     a) Your work shall be marked or carry a statement that it
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*        endorsed by SOFA.
*
*     b) The source code of your derived work must contain descriptions
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*
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*        include the prefix "iau" or "sofa" or trivial modifications
*        thereof such as changes of case.
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*
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*
*  In any published work or commercial product which uses the SOFA
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*
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*      By post:   IAU SOFA Center
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*
*-----------------------------------------------------------------------

      END