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+#include "erfa.h"
+
+int eraTttcg(double tt1, double tt2, double *tcg1, double *tcg2)
+/*
+** - - - - - - - - -
+** e r a T t t c g
+** - - - - - - - - -
+**
+** Time scale transformation: Terrestrial Time, TT, to Geocentric
+** Coordinate Time, TCG.
+**
+** Given:
+** tt1,tt2 double TT as a 2-part Julian Date
+**
+** Returned:
+** tcg1,tcg2 double TCG as a 2-part Julian Date
+**
+** Returned (function value):
+** int status: 0 = OK
+**
+** Note:
+**
+** tt1+tt2 is Julian Date, apportioned in any convenient way between
+** the two arguments, for example where tt1 is the Julian Day Number
+** and tt2 is the fraction of a day. The returned tcg1,tcg2 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) 2013-2016, 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;
+
+/* TT to TCG rate */
+ static const double elgg = ERFA_ELG/(1.0-ERFA_ELG);
+
+
+/* Result, safeguarding precision. */
+ if ( tt1 > tt2 ) {
+ *tcg1 = tt1;
+ *tcg2 = tt2 + ( ( tt1 - ERFA_DJM0 ) + ( tt2 - t77t ) ) * elgg;
+ } else {
+ *tcg1 = tt1 + ( ( tt2 - ERFA_DJM0 ) + ( tt1 - t77t ) ) * elgg;
+ *tcg2 = tt2;
+ }
+
+/* Status (always OK). */
+ return 0;
+
+}
+/*----------------------------------------------------------------------
+**
+**
+** Copyright (C) 2013-2016, 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,
+** INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+** BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+** LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+** CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+** LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
+** ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+** POSSIBILITY OF SUCH DAMAGE.
+**
+*/