source: branches/FACT++_lidctrl_usb/erfa/src/utctai.c@ 19875

Last change on this file since 19875 was 18711, checked in by tbretz, 10 years ago
Updated to ERFA 1.3.0 (no relevant code change except the leap second at the beginning of 2017)
File size: 6.7 KB
Line 
1#include "erfa.h"
2
3int eraUtctai(double utc1, double utc2, double *tai1, double *tai2)
4/*
5** - - - - - - - - - -
6** e r a U t c t a i
7** - - - - - - - - - -
8**
9** Time scale transformation: Coordinated Universal Time, UTC, to
10** International Atomic Time, TAI.
11**
12** Given:
13** utc1,utc2 double UTC as a 2-part quasi Julian Date (Notes 1-4)
14**
15** Returned:
16** tai1,tai2 double TAI as a 2-part Julian Date (Note 5)
17**
18** Returned (function value):
19** int status: +1 = dubious year (Note 3)
20** 0 = OK
21** -1 = unacceptable date
22**
23** Notes:
24**
25** 1) utc1+utc2 is quasi Julian Date (see Note 2), apportioned in any
26** convenient way between the two arguments, for example where utc1
27** is the Julian Day Number and utc2 is the fraction of a day.
28**
29** 2) JD cannot unambiguously represent UTC during a leap second unless
30** special measures are taken. The convention in the present
31** function is that the JD day represents UTC days whether the
32** length is 86399, 86400 or 86401 SI seconds. In the 1960-1972 era
33** there were smaller jumps (in either direction) each time the
34** linear UTC(TAI) expression was changed, and these "mini-leaps"
35** are also included in the ERFA convention.
36**
37** 3) The warning status "dubious year" flags UTCs that predate the
38** introduction of the time scale or that are too far in the future
39** to be trusted. See eraDat for further details.
40**
41** 4) The function eraDtf2d converts from calendar date and time of day
42** into 2-part Julian Date, and in the case of UTC implements the
43** leap-second-ambiguity convention described above.
44**
45** 5) The returned TAI1,TAI2 are such that their sum is the TAI Julian
46** Date.
47**
48** Called:
49** eraJd2cal JD to Gregorian calendar
50** eraDat delta(AT) = TAI-UTC
51** eraCal2jd Gregorian calendar to JD
52**
53** References:
54**
55** McCarthy, D. D., Petit, G. (eds.), IERS Conventions (2003),
56** IERS Technical Note No. 32, BKG (2004)
57**
58** Explanatory Supplement to the Astronomical Almanac,
59** P. Kenneth Seidelmann (ed), University Science Books (1992)
60**
61** Copyright (C) 2013-2016, NumFOCUS Foundation.
62** Derived, with permission, from the SOFA library. See notes at end of file.
63*/
64{
65 int big1;
66 int iy, im, id, j, iyt, imt, idt;
67 double u1, u2, fd, dat0, dat12, w, dat24, dlod, dleap, z1, z2, a2;
68
69
70/* Put the two parts of the UTC into big-first order. */
71 big1 = ( utc1 >= utc2 );
72 if ( big1 ) {
73 u1 = utc1;
74 u2 = utc2;
75 } else {
76 u1 = utc2;
77 u2 = utc1;
78 }
79
80/* Get TAI-UTC at 0h today. */
81 j = eraJd2cal(u1, u2, &iy, &im, &id, &fd);
82 if ( j ) return j;
83 j = eraDat(iy, im, id, 0.0, &dat0);
84 if ( j < 0 ) return j;
85
86/* Get TAI-UTC at 12h today (to detect drift). */
87 j = eraDat(iy, im, id, 0.5, &dat12);
88 if ( j < 0 ) return j;
89
90/* Get TAI-UTC at 0h tomorrow (to detect jumps). */
91 j = eraJd2cal(u1+1.5, u2-fd, &iyt, &imt, &idt, &w);
92 if ( j ) return j;
93 j = eraDat(iyt, imt, idt, 0.0, &dat24);
94 if ( j < 0 ) return j;
95
96/* Separate TAI-UTC change into per-day (DLOD) and any jump (DLEAP). */
97 dlod = 2.0 * (dat12 - dat0);
98 dleap = dat24 - (dat0 + dlod);
99
100/* Remove any scaling applied to spread leap into preceding day. */
101 fd *= (ERFA_DAYSEC+dleap)/ERFA_DAYSEC;
102
103/* Scale from (pre-1972) UTC seconds to SI seconds. */
104 fd *= (ERFA_DAYSEC+dlod)/ERFA_DAYSEC;
105
106/* Today's calendar date to 2-part JD. */
107 if ( eraCal2jd(iy, im, id, &z1, &z2) ) return -1;
108
109/* Assemble the TAI result, preserving the UTC split and order. */
110 a2 = z1 - u1;
111 a2 += z2;
112 a2 += fd + dat0/ERFA_DAYSEC;
113 if ( big1 ) {
114 *tai1 = u1;
115 *tai2 = a2;
116 } else {
117 *tai1 = a2;
118 *tai2 = u1;
119 }
120
121/* Status. */
122 return j;
123
124}
125/*----------------------------------------------------------------------
126**
127**
128** Copyright (C) 2013-2016, NumFOCUS Foundation.
129** All rights reserved.
130**
131** This library is derived, with permission, from the International
132** Astronomical Union's "Standards of Fundamental Astronomy" library,
133** available from http://www.iausofa.org.
134**
135** The ERFA version is intended to retain identical functionality to
136** the SOFA library, but made distinct through different function and
137** file names, as set out in the SOFA license conditions. The SOFA
138** original has a role as a reference standard for the IAU and IERS,
139** and consequently redistribution is permitted only in its unaltered
140** state. The ERFA version is not subject to this restriction and
141** therefore can be included in distributions which do not support the
142** concept of "read only" software.
143**
144** Although the intent is to replicate the SOFA API (other than
145** replacement of prefix names) and results (with the exception of
146** bugs; any that are discovered will be fixed), SOFA is not
147** responsible for any errors found in this version of the library.
148**
149** If you wish to acknowledge the SOFA heritage, please acknowledge
150** that you are using a library derived from SOFA, rather than SOFA
151** itself.
152**
153**
154** TERMS AND CONDITIONS
155**
156** Redistribution and use in source and binary forms, with or without
157** modification, are permitted provided that the following conditions
158** are met:
159**
160** 1 Redistributions of source code must retain the above copyright
161** notice, this list of conditions and the following disclaimer.
162**
163** 2 Redistributions in binary form must reproduce the above copyright
164** notice, this list of conditions and the following disclaimer in
165** the documentation and/or other materials provided with the
166** distribution.
167**
168** 3 Neither the name of the Standards Of Fundamental Astronomy Board,
169** the International Astronomical Union nor the names of its
170** contributors may be used to endorse or promote products derived
171** from this software without specific prior written permission.
172**
173** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
174** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
175** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
176** FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
177** COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
178** INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
179** BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
180** LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
181** CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
182** LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
183** ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
184** POSSIBILITY OF SUCH DAMAGE.
185**
186*/
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