#include "erfa.h"

int eraTdbtt(double tdb1, double tdb2, double dtr,
             double *tt1, double *tt2 )
/*
**  - - - - - - - - -
**   e r a T d b t t
**  - - - - - - - - -
**
**  Time scale transformation:  Barycentric Dynamical Time, TDB, to
**  Terrestrial Time, TT.
**
**  Given:
**     tdb1,tdb2  double    TDB as a 2-part Julian Date
**     dtr        double    TDB-TT in seconds
**
**  Returned:
**     tt1,tt2    double    TT as a 2-part Julian Date
**
**  Returned (function value):
**                int       status:  0 = OK
**
**  Notes:
**
**  1) tdb1+tdb2 is Julian Date, apportioned in any convenient way
**     between the two arguments, for example where tdb1 is the Julian
**     Day Number and tdb2 is the fraction of a day.  The returned
**     tt1,tt2 follow suit.
**
**  2) The argument dtr represents the quasi-periodic component of the
**     GR transformation between TT and TCB.  It is dependent upon the
**     adopted solar-system ephemeris, and can be obtained by numerical
**     integration, by interrogating a precomputed time ephemeris or by
**     evaluating a model such as that implemented in the ERFA function
**     eraDtdb.   The quantity is dominated by an annual term of 1.7 ms
**     amplitude.
**
**  3) TDB is essentially the same as Teph, the time argument for the
**     JPL solar system ephemerides.
**
**  References:
**
**     McCarthy, D. D., Petit, G. (eds.), IERS Conventions (2003),
**     IERS Technical Note No. 32, BKG (2004)
**
**     IAU 2006 Resolution 3
**
**  Copyright (C) 2013-2017, NumFOCUS Foundation.
**  Derived, with permission, from the SOFA library.  See notes at end of file.
*/
{
   double dtrd;


/* Result, safeguarding precision. */
   dtrd = dtr / ERFA_DAYSEC;
   if ( tdb1 > tdb2 ) {
      *tt1 = tdb1;
      *tt2 = tdb2 - dtrd;
   } else {
      *tt1 = tdb1 - dtrd;
      *tt2 = tdb2;
   }

/* Status (always OK). */
   return 0;

}
/*----------------------------------------------------------------------
**  
**  
**  Copyright (C) 2013-2017, NumFOCUS Foundation.
**  All rights reserved.
**  
**  This library is derived, with permission, from the International
**  Astronomical Union's "Standards of Fundamental Astronomy" library,
**  available from http://www.iausofa.org.
**  
**  The ERFA version is intended to retain identical functionality to
**  the SOFA library, but made distinct through different function and
**  file names, as set out in the SOFA license conditions.  The SOFA
**  original has a role as a reference standard for the IAU and IERS,
**  and consequently redistribution is permitted only in its unaltered
**  state.  The ERFA version is not subject to this restriction and
**  therefore can be included in distributions which do not support the
**  concept of "read only" software.
**  
**  Although the intent is to replicate the SOFA API (other than
**  replacement of prefix names) and results (with the exception of
**  bugs;  any that are discovered will be fixed), SOFA is not
**  responsible for any errors found in this version of the library.
**  
**  If you wish to acknowledge the SOFA heritage, please acknowledge
**  that you are using a library derived from SOFA, rather than SOFA
**  itself.
**  
**  
**  TERMS AND CONDITIONS
**  
**  Redistribution and use in source and binary forms, with or without
**  modification, are permitted provided that the following conditions
**  are met:
**  
**  1 Redistributions of source code must retain the above copyright
**    notice, this list of conditions and the following disclaimer.
**  
**  2 Redistributions in binary form must reproduce the above copyright
**    notice, this list of conditions and the following disclaimer in
**    the documentation and/or other materials provided with the
**    distribution.
**  
**  3 Neither the name of the Standards Of Fundamental Astronomy Board,
**    the International Astronomical Union nor the names of its
**    contributors may be used to endorse or promote products derived
**    from this software without specific prior written permission.
**  
**  THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
**  "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
**  LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
**  FOR A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE
**  COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
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**  
*/