Merge commit 'd26ed8388f100a12996c0b92a98040ef2ba7fa8e' as 'ast'

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diff --git a/ast/erfa/gmst82.c b/ast/erfa/gmst82.c
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+#include "erfa.h"
+
+double eraGmst82(double dj1, double dj2)
+/*
+**  - - - - - - - - - -
+**   e r a G m s t 8 2
+**  - - - - - - - - - -
+**
+**  Universal Time to Greenwich mean sidereal time (IAU 1982 model).
+**
+**  Given:
+**     dj1,dj2    double    UT1 Julian Date (see note)
+**
+**  Returned (function value):
+**                double    Greenwich mean sidereal time (radians)
+**
+**  Notes:
+**
+**  1) The UT1 date dj1+dj2 is a Julian Date, apportioned in any
+**     convenient way between the arguments dj1 and dj2.  For example,
+**     JD(UT1)=2450123.7 could be expressed in any of these ways,
+**     among others:
+**
+**             dj1            dj2
+**
+**         2450123.7          0          (JD method)
+**          2451545        -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.  The J2000 and MJD methods are good compromises
+**     between resolution and convenience.  The date & time method is
+**     best matched to the algorithm used:  maximum accuracy (or, at
+**     least, minimum noise) is delivered when the dj1 argument is for
+**     0hrs UT1 on the day in question and the dj2 argument lies in the
+**     range 0 to 1, or vice versa.
+**
+**  2) The algorithm is based on the IAU 1982 expression.  This is
+**     always described as giving the GMST at 0 hours UT1.  In fact, it
+**     gives the difference between the GMST and the UT, the steady
+**     4-minutes-per-day drawing-ahead of ST with respect to UT.  When
+**     whole days are ignored, the expression happens to equal the GMST
+**     at 0 hours UT1 each day.
+**
+**  3) In this function, the entire UT1 (the sum of the two arguments
+**     dj1 and dj2) is used directly as the argument for the standard
+**     formula, the constant term of which is adjusted by 12 hours to
+**     take account of the noon phasing of Julian Date.  The UT1 is then
+**     added, but omitting whole days to conserve accuracy.
+**
+**  Called:
+**     eraAnp       normalize angle into range 0 to 2pi
+**
+**  References:
+**
+**     Transactions of the International Astronomical Union,
+**     XVIII B, 67 (1983).
+**
+**     Aoki et al., Astron. Astrophys. 105, 359-361 (1982).
+**
+**  Copyright (C) 2013-2016, NumFOCUS Foundation.
+**  Derived, with permission, from the SOFA library.  See notes at end of file.
+*/
+{
+/* Coefficients of IAU 1982 GMST-UT1 model */
+   double A = 24110.54841  -  ERFA_DAYSEC / 2.0;
+   double B = 8640184.812866;
+   double C = 0.093104;
+   double D =  -6.2e-6;
+
+/* Note: the first constant, A, has to be adjusted by 12 hours */
+/* because the UT1 is supplied as a Julian date, which begins  */
+/* at noon.                                                    */
+
+   double d1, d2, t, f, gmst;
+
+
+/* Julian centuries since fundamental epoch. */
+   if (dj1 < dj2) {
+      d1 = dj1;
+      d2 = dj2;
+   } else {
+      d1 = dj2;
+      d2 = dj1;
+   }
+   t = (d1 + (d2 - ERFA_DJ00)) / ERFA_DJC;
+
+/* Fractional part of JD(UT1), in seconds. */
+   f = ERFA_DAYSEC * (fmod(d1, 1.0) + fmod(d2, 1.0));
+
+/* GMST at this UT1. */
+   gmst = eraAnp(ERFA_DS2R * ((A + (B + (C + D * t) * t) * t) + f));
+
+   return gmst;
+
+}
+/*----------------------------------------------------------------------
+**  
+**  
+**  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.
+**  
+*/