1 #include "erfa.h"
2
eraTtut1(double tt1,double tt2,double dt,double * ut11,double * ut12)3 int eraTtut1(double tt1, double tt2, double dt,
4 double *ut11, double *ut12)
5 /*
6 ** - - - - - - - - -
7 ** e r a T t u t 1
8 ** - - - - - - - - -
9 **
10 ** Time scale transformation: Terrestrial Time, TT, to Universal Time,
11 ** UT1.
12 **
13 ** Given:
14 ** tt1,tt2 double TT as a 2-part Julian Date
15 ** dt double TT-UT1 in seconds
16 **
17 ** Returned:
18 ** ut11,ut12 double UT1 as a 2-part Julian Date
19 **
20 ** Returned (function value):
21 ** int status: 0 = OK
22 **
23 ** Notes:
24 **
25 ** 1) tt1+tt2 is Julian Date, apportioned in any convenient way between
26 ** the two arguments, for example where tt1 is the Julian Day Number
27 ** and tt2 is the fraction of a day. The returned ut11,ut12 follow
28 ** suit.
29 **
30 ** 2) The argument dt is classical Delta T.
31 **
32 ** Reference:
33 **
34 ** Explanatory Supplement to the Astronomical Almanac,
35 ** P. Kenneth Seidelmann (ed), University Science Books (1992)
36 **
37 ** Copyright (C) 2013-2014, NumFOCUS Foundation.
38 ** Derived, with permission, from the SOFA library. See notes at end of file.
39 */
40 {
41 double dtd;
42
43
44 /* Result, safeguarding precision. */
45 dtd = dt / ERFA_DAYSEC;
46 if ( tt1 > tt2 ) {
47 *ut11 = tt1;
48 *ut12 = tt2 - dtd;
49 } else {
50 *ut11 = tt1 - dtd;
51 *ut12 = tt2;
52 }
53
54 /* Status (always OK). */
55 return 0;
56
57 }
58 /*----------------------------------------------------------------------
59 **
60 **
61 ** Copyright (C) 2013-2014, NumFOCUS Foundation.
62 ** All rights reserved.
63 **
64 ** This library is derived, with permission, from the International
65 ** Astronomical Union's "Standards of Fundamental Astronomy" library,
66 ** available from http://www.iausofa.org.
67 **
68 ** The ERFA version is intended to retain identical functionality to
69 ** the SOFA library, but made distinct through different function and
70 ** file names, as set out in the SOFA license conditions. The SOFA
71 ** original has a role as a reference standard for the IAU and IERS,
72 ** and consequently redistribution is permitted only in its unaltered
73 ** state. The ERFA version is not subject to this restriction and
74 ** therefore can be included in distributions which do not support the
75 ** concept of "read only" software.
76 **
77 ** Although the intent is to replicate the SOFA API (other than
78 ** replacement of prefix names) and results (with the exception of
79 ** bugs; any that are discovered will be fixed), SOFA is not
80 ** responsible for any errors found in this version of the library.
81 **
82 ** If you wish to acknowledge the SOFA heritage, please acknowledge
83 ** that you are using a library derived from SOFA, rather than SOFA
84 ** itself.
85 **
86 **
87 ** TERMS AND CONDITIONS
88 **
89 ** Redistribution and use in source and binary forms, with or without
90 ** modification, are permitted provided that the following conditions
91 ** are met:
92 **
93 ** 1 Redistributions of source code must retain the above copyright
94 ** notice, this list of conditions and the following disclaimer.
95 **
96 ** 2 Redistributions in binary form must reproduce the above copyright
97 ** notice, this list of conditions and the following disclaimer in
98 ** the documentation and/or other materials provided with the
99 ** distribution.
100 **
101 ** 3 Neither the name of the Standards Of Fundamental Astronomy Board,
102 ** the International Astronomical Union nor the names of its
103 ** contributors may be used to endorse or promote products derived
104 ** from this software without specific prior written permission.
105 **
106 ** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
107 ** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
108 ** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
109 ** FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
110 ** COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
111 ** INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
112 ** BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
113 ** LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
114 ** CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
115 ** LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
116 ** ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
117 ** POSSIBILITY OF SUCH DAMAGE.
118 **
119 */
120