tcgtt.c

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#include "erfa.h"

int eraTcgtt(double tcg1, double tcg2, double *tt1, double *tt2)
/*
**  - - - - - - - - -
**   e r a T c g t t
**  - - - - - - - - -
**
**  Time scale transformation:  Geocentric Coordinate Time, TCG, to
**  Terrestrial Time, TT.
**
**  Given:
**     tcg1,tcg2  double    TCG as a 2-part Julian Date
**
**  Returned:
**     tt1,tt2    double    TT as a 2-part Julian Date
**
**  Returned (function value):
**                int       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 tcg22 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
**
**  Copyright (C) 2013-2015, NumFOCUS Foundation.
**  Derived, with permission, from the SOFA library.  See notes at end of file.
*/
{

/* 1977 Jan 1 00:00:32.184 TT, as MJD */
   static const double t77t = ERFA_DJM77 + ERFA_TTMTAI/ERFA_DAYSEC;

/* Result, safeguarding precision. */
   if ( tcg1 > tcg2 ) {
      *tt1 = tcg1;
      *tt2 = tcg2 - ( ( tcg1 - ERFA_DJM0 ) + ( tcg2 - t77t ) ) * ERFA_ELG;
   } else {
      *tt1 = tcg1 - ( ( tcg2 - ERFA_DJM0 ) + ( tcg1 - t77t ) ) * ERFA_ELG;
      *tt2 = tcg2;
   }

/* OK status. */
   return 0;

}
/*----------------------------------------------------------------------
**  
**  
**  Copyright (C) 2013-2015, 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:
**  
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**    notice, this list of conditions and the following disclaimer.
**  
**  2 Redistributions in binary form must reproduce the above copyright
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**  
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*/