#include "sofa.h"

double iauGmst00(double uta, double utb, double tta, double ttb)
/*
**  - - - - - - - - - -
**   i a u G m s t 0 0
**  - - - - - - - - - -
**
**  Greenwich mean sidereal time (model consistent with IAU 2000
**  resolutions).
**
**  This function is part of the International Astronomical Union's
**  SOFA (Standards Of Fundamental Astronomy) software collection.
**
**  Status:  canonical model.
**
**  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 2000 resolutions and must be
**     used only in conjunction with other IAU 2000 compatible
**     components such as precession-nutation and equation of the
**     equinoxes.
**
**  4) The result is returned in the range 0 to 2pi.
**
**  5) The algorithm is from Capitaine et al. (2003) and IERS
**     Conventions 2003.
**
**  Called:
**     iauEra00     Earth rotation angle, IAU 2000
**     iauAnp       normalize angle into range 0 to 2pi
**
**  References:
**
**     Capitaine, N., Wallace, P.T. and McCarthy, D.D., "Expressions to
**     implement the IAU 2000 definition of UT1", Astronomy &
**     Astrophysics, 406, 1135-1149 (2003)
**
**     McCarthy, D. D., Petit, G. (eds.), IERS Conventions (2003),
**     IERS Technical Note No. 32, BKG (2004)
**
**  This revision:  2013 June 18
**
**  SOFA release 2013-12-02
**
**  Copyright (C) 2013 IAU SOFA Board.  See notes at end.
*/
{
   double t, gmst;


/* TT Julian centuries since J2000.0. */
   t = ((tta - DJ00) + ttb) / DJC;

/* Greenwich Mean Sidereal Time, IAU 2000. */
   gmst = iauAnp(iauEra00(uta, utb) +
                   (     0.014506   +
                   (  4612.15739966 +
                   (     1.39667721 +
                   (    -0.00009344 +
                   (     0.00001882 )
          * t) * t) * t) * t) * DAS2R);

   return gmst;

/*----------------------------------------------------------------------
**
**  Copyright (C) 2013
**  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,
**     and use and adapt its code and algorithms in your own software,
**     on a world-wide, royalty-free basis.  That portion of your
**     distribution that does not consist of intact and unchanged copies
**     of SOFA source code files is a "derived work" that must comply
**     with the following requirements:
**
**     a) Your work shall be marked or carry a statement that it
**        (i) uses routines and computations derived by you from
**        software provided by SOFA under license to you; and
**        (ii) does not itself constitute software provided by and/or
**        endorsed by SOFA.
**
**     b) The source code of your derived work must contain descriptions
**        of how the derived work is based upon, contains and/or differs
**        from the original SOFA software.
**
**     c) The names of all routines in your derived work shall not
**        include the prefix "iau" or "sofa" or trivial modifications
**        thereof such as changes of case.
**
**     d) The origin of the SOFA components of your derived work must
**        not be misrepresented;  you must not claim that you wrote the
**        original software, nor file a patent application for SOFA
**        software or algorithms embedded in the SOFA software.
**
**     e) These requirements must be reproduced intact in any source
**        distribution and shall apply to anyone to whom you have
**        granted a further right to modify the source code of your
**        derived work.
**
**     Note that, as originally distributed, the SOFA software is
**     intended to be a definitive implementation of the IAU standards,
**     and consequently third-party modifications are discouraged.  All
**     variations, no matter how minor, must be explicitly marked as
**     such, as explained above.
**
**  4. You shall not cause the SOFA software to be brought into
**     disrepute, either by misuse, or use for inappropriate tasks, or
**     by inappropriate modification.
**
**  5. The SOFA software is provided "as is" and SOFA makes no warranty
**     as to its use or performance.   SOFA does not and cannot warrant
**     the performance or results which the user may obtain by using the
**     SOFA software.  SOFA makes no warranties, express or implied, as
**     to non-infringement of third party rights, merchantability, or
**     fitness for any particular purpose.  In no event will SOFA be
**     liable to the user for any consequential, incidental, or special
**     damages, including any lost profits or lost savings, even if a
**     SOFA representative has been advised of such damages, or for any
**     claim by any third party.
**
**  6. The provision of any version of the SOFA software under the terms
**     and conditions specified herein does not imply that future
**     versions will also be made available under the same terms and
**     conditions.
*
**  In any published work or commercial product which uses the SOFA
**  software directly, acknowledgement (see www.iausofa.org) is
**  appreciated.
**
**  Correspondence concerning SOFA software should be addressed as
**  follows:
**
**      By email:  sofa@ukho.gov.uk
**      By post:   IAU SOFA Center
**                 HM Nautical Almanac Office
**                 UK Hydrographic Office
**                 Admiralty Way, Taunton
**                 Somerset, TA1 2DN
**                 United Kingdom
**
**--------------------------------------------------------------------*/
}