FACT++  1.0
ut1utc.c
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1 #include "erfa.h"
2 
3 int eraUt1utc(double ut11, double ut12, double dut1,
4  double *utc1, double *utc2)
5 /*
6 ** - - - - - - - - - -
7 ** e r a U t 1 u t c
8 ** - - - - - - - - - -
9 **
10 ** Time scale transformation: Universal Time, UT1, to Coordinated
11 ** Universal Time, UTC.
12 **
13 ** Given:
14 ** ut11,ut12 double UT1 as a 2-part Julian Date (Note 1)
15 ** dut1 double Delta UT1: UT1-UTC in seconds (Note 2)
16 **
17 ** Returned:
18 ** utc1,utc2 double UTC as a 2-part quasi Julian Date (Notes 3,4)
19 **
20 ** Returned (function value):
21 ** int status: +1 = dubious year (Note 5)
22 ** 0 = OK
23 ** -1 = unacceptable date
24 **
25 ** Notes:
26 **
27 ** 1) ut11+ut12 is Julian Date, apportioned in any convenient way
28 ** between the two arguments, for example where ut11 is the Julian
29 ** Day Number and ut12 is the fraction of a day. The returned utc1
30 ** and utc2 form an analogous pair, except that a special convention
31 ** is used, to deal with the problem of leap seconds - see Note 3.
32 **
33 ** 2) Delta UT1 can be obtained from tabulations provided by the
34 ** International Earth Rotation and Reference Systems Service. The
35 ** value changes abruptly by 1s at a leap second; however, close to
36 ** a leap second the algorithm used here is tolerant of the "wrong"
37 ** choice of value being made.
38 **
39 ** 3) JD cannot unambiguously represent UTC during a leap second unless
40 ** special measures are taken. The convention in the present
41 ** function is that the returned quasi JD day UTC1+UTC2 represents
42 ** UTC days whether the length is 86399, 86400 or 86401 SI seconds.
43 **
44 ** 4) The function eraD2dtf can be used to transform the UTC quasi-JD
45 ** into calendar date and clock time, including UTC leap second
46 ** handling.
47 **
48 ** 5) The warning status "dubious year" flags UTCs that predate the
49 ** introduction of the time scale or that are too far in the future
50 ** to be trusted. See eraDat for further details.
51 **
52 ** Called:
53 ** eraJd2cal JD to Gregorian calendar
54 ** eraDat delta(AT) = TAI-UTC
55 ** eraCal2jd Gregorian calendar to JD
56 **
57 ** References:
58 **
59 ** McCarthy, D. D., Petit, G. (eds.), IERS Conventions (2003),
60 ** IERS Technical Note No. 32, BKG (2004)
61 **
62 ** Explanatory Supplement to the Astronomical Almanac,
63 ** P. Kenneth Seidelmann (ed), University Science Books (1992)
64 **
65 ** Copyright (C) 2013-2015, NumFOCUS Foundation.
66 ** Derived, with permission, from the SOFA library. See notes at end of file.
67 */
68 {
69  int big1;
70  int i, iy, im, id, js;
71  double duts, u1, u2, d1, dats1, d2, fd, dats2, ddats, us1, us2, du;
72 
73 /* UT1-UTC in seconds. */
74  duts = dut1;
75 
76 /* Put the two parts of the UT1 into big-first order. */
77  big1 = ( ut11 >= ut12 );
78  if ( big1 ) {
79  u1 = ut11;
80  u2 = ut12;
81  } else {
82  u1 = ut12;
83  u2 = ut11;
84  }
85 
86 /* See if the UT1 can possibly be in a leap-second day. */
87  d1 = u1;
88  dats1 = 0;
89  for ( i = -1; i <= 3; i++ ) {
90  d2 = u2 + (double) i;
91  if ( eraJd2cal(d1, d2, &iy, &im, &id, &fd) ) return -1;
92  js = eraDat(iy, im, id, 0.0, &dats2);
93  if ( js < 0 ) return -1;
94  if ( i == - 1 ) dats1 = dats2;
95  ddats = dats2 - dats1;
96  if ( fabs(ddats) >= 0.5 ) {
97 
98  /* Yes, leap second nearby: ensure UT1-UTC is "before" value. */
99  if ( ddats * duts >= 0 ) duts -= ddats;
100 
101  /* UT1 for the start of the UTC day that ends in a leap. */
102  if ( eraCal2jd(iy, im, id, &d1, &d2) ) return -1;
103  us1 = d1;
104  us2 = d2 - 1.0 + duts/ERFA_DAYSEC;
105 
106  /* Is the UT1 after this point? */
107  du = u1 - us1;
108  du += u2 - us2;
109  if ( du > 0 ) {
110 
111  /* Yes: fraction of the current UTC day that has elapsed. */
112  fd = du * ERFA_DAYSEC / ( ERFA_DAYSEC + ddats );
113 
114  /* Ramp UT1-UTC to bring about ERFA's JD(UTC) convention. */
115  duts += ddats * ( fd <= 1.0 ? fd : 1.0 );
116  }
117 
118  /* Done. */
119  break;
120  }
121  dats1 = dats2;
122  }
123 
124 /* Subtract the (possibly adjusted) UT1-UTC from UT1 to give UTC. */
125  u2 -= duts / ERFA_DAYSEC;
126 
127 /* Result, safeguarding precision. */
128  if ( big1 ) {
129  *utc1 = u1;
130  *utc2 = u2;
131  } else {
132  *utc1 = u2;
133  *utc2 = u1;
134  }
135 
136 /* Status. */
137  return js;
138 
139 }
140 /*----------------------------------------------------------------------
141 **
142 **
143 ** Copyright (C) 2013-2015, NumFOCUS Foundation.
144 ** All rights reserved.
145 **
146 ** This library is derived, with permission, from the International
147 ** Astronomical Union's "Standards of Fundamental Astronomy" library,
148 ** available from http://www.iausofa.org.
149 **
150 ** The ERFA version is intended to retain identical functionality to
151 ** the SOFA library, but made distinct through different function and
152 ** file names, as set out in the SOFA license conditions. The SOFA
153 ** original has a role as a reference standard for the IAU and IERS,
154 ** and consequently redistribution is permitted only in its unaltered
155 ** state. The ERFA version is not subject to this restriction and
156 ** therefore can be included in distributions which do not support the
157 ** concept of "read only" software.
158 **
159 ** Although the intent is to replicate the SOFA API (other than
160 ** replacement of prefix names) and results (with the exception of
161 ** bugs; any that are discovered will be fixed), SOFA is not
162 ** responsible for any errors found in this version of the library.
163 **
164 ** If you wish to acknowledge the SOFA heritage, please acknowledge
165 ** that you are using a library derived from SOFA, rather than SOFA
166 ** itself.
167 **
168 **
169 ** TERMS AND CONDITIONS
170 **
171 ** Redistribution and use in source and binary forms, with or without
172 ** modification, are permitted provided that the following conditions
173 ** are met:
174 **
175 ** 1 Redistributions of source code must retain the above copyright
176 ** notice, this list of conditions and the following disclaimer.
177 **
178 ** 2 Redistributions in binary form must reproduce the above copyright
179 ** notice, this list of conditions and the following disclaimer in
180 ** the documentation and/or other materials provided with the
181 ** distribution.
182 **
183 ** 3 Neither the name of the Standards Of Fundamental Astronomy Board,
184 ** the International Astronomical Union nor the names of its
185 ** contributors may be used to endorse or promote products derived
186 ** from this software without specific prior written permission.
187 **
188 ** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
189 ** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
190 ** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
191 ** FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
192 ** COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
193 ** INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
194 ** BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
195 ** LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
196 ** CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
197 ** LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
198 ** ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
199 ** POSSIBILITY OF SUCH DAMAGE.
200 **
201 */
int i
Definition: db_dim_client.c:21
char id[4]
Definition: FITS.h:71
#define ERFA_DAYSEC
Definition: erfam.h:75
int eraJd2cal(double dj1, double dj2, int *iy, int *im, int *id, double *fd)
Definition: jd2cal.c:3
int eraDat(int iy, int im, int id, double fd, double *deltat)
Definition: dat.c:3
int eraUt1utc(double ut11, double ut12, double dut1, double *utc1, double *utc2)
Definition: ut1utc.c:3
int eraCal2jd(int iy, int im, int id, double *djm0, double *djm)
Definition: cal2jd.c:3