text: #include "erfa.h"
  
  double eraGmst06(double uta, double utb, double tta, double ttb)
  /*
  **  - - - - - - - - - -
  **   e r a G m s t 0 6
  **  - - - - - - - - - -
  **
  **  Greenwich mean sidereal time (consistent with IAU 2006 precession).
  **
  **  Given:
  **     uta,utb    double    UT1 as a 2-part Julian Date (Notes 1,2)
  **     tta,ttb    double    TT as a 2-part Julian Date (Notes 1,2)
  **
  **  Returned (function value):
  **                double    Greenwich mean sidereal time (radians)
  **
  **  Notes:
  **
  **  1) The UT1 and TT dates uta+utb and tta+ttb respectively, are both
  **     Julian Dates, apportioned in any convenient way between the
  **     argument pairs.  For example, JD=2450123.7 could be expressed in
  **     any of these ways, among others:
  **
  **            Part A        Part B
  **
  **         2450123.7           0.0       (JD method)
  **         2451545.0       -1421.3       (J2000 method)
  **         2400000.5       50123.2       (MJD method)
  **         2450123.5           0.2       (date & time method)
  **
  **     The JD method is the most natural and convenient to use in
  **     cases where the loss of several decimal digits of resolution
  **     is acceptable (in the case of UT;  the TT is not at all critical
  **     in this respect).  The J2000 and MJD methods are good compromises
  **     between resolution and convenience.  For UT, the date & time
  **     method is best matched to the algorithm that is used by the Earth
  **     rotation angle function, called internally:  maximum precision is
  **     delivered when the uta argument is for 0hrs UT1 on the day in
  **     question and the utb argument lies in the range 0 to 1, or vice
  **     versa.
  **
  **  2) Both UT1 and TT are required, UT1 to predict the Earth rotation
  **     and TT to predict the effects of precession.  If UT1 is used for
  **     both purposes, errors of order 100 microarcseconds result.
  **
  **  3) This GMST is compatible with the IAU 2006 precession and must not
  **     be used with other precession models.
  **
  **  4) The result is returned in the range 0 to 2pi.
  **
  **  Called:
  **     eraEra00     Earth rotation angle, IAU 2000
  **     eraAnp       normalize angle into range 0 to 2pi
  **
  **  Reference:
  **
  **     Capitaine, N., Wallace, P.T. & Chapront, J., 2005,
  **     Astron.Astrophys. 432, 355
  **
  **  Copyright (C) 2013-2019, NumFOCUS Foundation.
  **  Derived, with permission, from the SOFA library.  See notes at end of file.
  */
  {
     double t, gmst;
  
  
  /* TT Julian centuries since J2000.0. */
     t = ((tta - ERFA_DJ00) + ttb) / ERFA_DJC;
  
  /* Greenwich mean sidereal time, IAU 2006. */
     gmst = eraAnp(eraEra00(uta, utb) +
                    (    0.014506     +
                    (  4612.156534    +
                    (     1.3915817   +
                    (    -0.00000044  +
                    (    -0.000029956 +
                    (    -0.0000000368 )
            * t) * t) * t) * t) * t) * ERFA_DAS2R);
  
     return gmst;
  
  }
  /*----------------------------------------------------------------------
  **  
  **  
  **  Copyright (C) 2013-2019, 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.
  **  
  */
  