1 #include "erfa.h"
2
eraTaiutc(double tai1,double tai2,double * utc1,double * utc2)3 int eraTaiutc(double tai1, double tai2, double *utc1, double *utc2)
4 /*
5 ** - - - - - - - - - -
6 ** e r a T a i u t c
7 ** - - - - - - - - - -
8 **
9 ** Time scale transformation: International Atomic Time, TAI, to
10 ** Coordinated Universal Time, UTC.
11 **
12 ** Given:
13 ** tai1,tai2 double TAI as a 2-part Julian Date (Note 1)
14 **
15 ** Returned:
16 ** utc1,utc2 double UTC as a 2-part quasi Julian Date (Notes 1-3)
17 **
18 ** Returned (function value):
19 ** int status: +1 = dubious year (Note 4)
20 ** 0 = OK
21 ** -1 = unacceptable date
22 **
23 ** Notes:
24 **
25 ** 1) tai1+tai2 is Julian Date, apportioned in any convenient way
26 ** between the two arguments, for example where tai1 is the Julian
27 ** Day Number and tai2 is the fraction of a day. The returned utc1
28 ** and utc2 form an analogous pair, except that a special convention
29 ** is used, to deal with the problem of leap seconds - see the next
30 ** note.
31 **
32 ** 2) JD cannot unambiguously represent UTC during a leap second unless
33 ** special measures are taken. The convention in the present
34 ** function is that the JD day represents UTC days whether the
35 ** length is 86399, 86400 or 86401 SI seconds. In the 1960-1972 era
36 ** there were smaller jumps (in either direction) each time the
37 ** linear UTC(TAI) expression was changed, and these "mini-leaps"
38 ** are also included in the ERFA convention.
39 **
40 ** 3) The function eraD2dtf can be used to transform the UTC quasi-JD
41 ** into calendar date and clock time, including UTC leap second
42 ** handling.
43 **
44 ** 4) The warning status "dubious year" flags UTCs that predate the
45 ** introduction of the time scale or that are too far in the future
46 ** to be trusted. See eraDat for further details.
47 **
48 ** Called:
49 ** eraUtctai UTC to TAI
50 **
51 ** References:
52 **
53 ** McCarthy, D. D., Petit, G. (eds.), IERS Conventions (2003),
54 ** IERS Technical Note No. 32, BKG (2004)
55 **
56 ** Explanatory Supplement to the Astronomical Almanac,
57 ** P. Kenneth Seidelmann (ed), University Science Books (1992)
58 **
59 ** Copyright (C) 2013-2014, NumFOCUS Foundation.
60 ** Derived, with permission, from the SOFA library. See notes at end of file.
61 */
62 {
63 int big1;
64 int i, j;
65 double a1, a2, u1, u2, g1, g2;
66
67
68 /* Put the two parts of the TAI into big-first order. */
69 big1 = ( tai1 >= tai2 );
70 if ( big1 ) {
71 a1 = tai1;
72 a2 = tai2;
73 } else {
74 a1 = tai2;
75 a2 = tai1;
76 }
77
78 /* Initial guess for UTC. */
79 u1 = a1;
80 u2 = a2;
81
82 /* Iterate (though in most cases just once is enough). */
83 for ( i = 0; i < 3; i++ ) {
84
85 /* Guessed UTC to TAI. */
86 j = eraUtctai(u1, u2, &g1, &g2);
87 if ( j < 0 ) return j;
88
89 /* Adjust guessed UTC. */
90 u2 += a1 - g1;
91 u2 += a2 - g2;
92 }
93
94 /* Return the UTC result, preserving the TAI order. */
95 if ( big1 ) {
96 *utc1 = u1;
97 *utc2 = u2;
98 } else {
99 *utc1 = u2;
100 *utc2 = u1;
101 }
102
103 /* Status. */
104 return j;
105
106 }
107 /*----------------------------------------------------------------------
108 **
109 **
110 ** Copyright (C) 2013-2014, NumFOCUS Foundation.
111 ** All rights reserved.
112 **
113 ** This library is derived, with permission, from the International
114 ** Astronomical Union's "Standards of Fundamental Astronomy" library,
115 ** available from http://www.iausofa.org.
116 **
117 ** The ERFA version is intended to retain identical functionality to
118 ** the SOFA library, but made distinct through different function and
119 ** file names, as set out in the SOFA license conditions. The SOFA
120 ** original has a role as a reference standard for the IAU and IERS,
121 ** and consequently redistribution is permitted only in its unaltered
122 ** state. The ERFA version is not subject to this restriction and
123 ** therefore can be included in distributions which do not support the
124 ** concept of "read only" software.
125 **
126 ** Although the intent is to replicate the SOFA API (other than
127 ** replacement of prefix names) and results (with the exception of
128 ** bugs; any that are discovered will be fixed), SOFA is not
129 ** responsible for any errors found in this version of the library.
130 **
131 ** If you wish to acknowledge the SOFA heritage, please acknowledge
132 ** that you are using a library derived from SOFA, rather than SOFA
133 ** itself.
134 **
135 **
136 ** TERMS AND CONDITIONS
137 **
138 ** Redistribution and use in source and binary forms, with or without
139 ** modification, are permitted provided that the following conditions
140 ** are met:
141 **
142 ** 1 Redistributions of source code must retain the above copyright
143 ** notice, this list of conditions and the following disclaimer.
144 **
145 ** 2 Redistributions in binary form must reproduce the above copyright
146 ** notice, this list of conditions and the following disclaimer in
147 ** the documentation and/or other materials provided with the
148 ** distribution.
149 **
150 ** 3 Neither the name of the Standards Of Fundamental Astronomy Board,
151 ** the International Astronomical Union nor the names of its
152 ** contributors may be used to endorse or promote products derived
153 ** from this software without specific prior written permission.
154 **
155 ** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
156 ** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
157 ** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
158 ** FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
159 ** COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
160 ** INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
161 ** BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
162 ** LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
163 ** CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
164 ** LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
165 ** ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
166 ** POSSIBILITY OF SUCH DAMAGE.
167 **
168 */
169