source: trunk/FACT++/erfa/src/dat.c@ 19594

Last change on this file since 19594 was 18921, checked in by tbretz, 8 years ago
Updated to ERFA 1.4.0
File size: 11.4 KB
Line 
1#include "erfa.h"
2
3int eraDat(int iy, int im, int id, double fd, double *deltat )
4/*
5** - - - - - - -
6** e r a D a t
7** - - - - - - -
8**
9** For a given UTC date, calculate delta(AT) = TAI-UTC.
10**
11** :------------------------------------------:
12** : :
13** : IMPORTANT :
14** : :
15** : A new version of this function must be :
16** : produced whenever a new leap second is :
17** : announced. There are four items to :
18** : change on each such occasion: :
19** : :
20** : 1) A new line must be added to the set :
21** : of statements that initialize the :
22** : array "changes". :
23** : :
24** : 2) The constant IYV must be set to the :
25** : current year. :
26** : :
27** : 3) The "Latest leap second" comment :
28** : below must be set to the new leap :
29** : second date. :
30** : :
31** : 4) The "This revision" comment, later, :
32** : must be set to the current date. :
33** : :
34** : Change (2) must also be carried out :
35** : whenever the function is re-issued, :
36** : even if no leap seconds have been :
37** : added. :
38** : :
39** : Latest leap second: 2016 December 31 :
40** : :
41** :__________________________________________:
42**
43** Given:
44** iy int UTC: year (Notes 1 and 2)
45** im int month (Note 2)
46** id int day (Notes 2 and 3)
47** fd double fraction of day (Note 4)
48**
49** Returned:
50** deltat double TAI minus UTC, seconds
51**
52** Returned (function value):
53** int status (Note 5):
54** 1 = dubious year (Note 1)
55** 0 = OK
56** -1 = bad year
57** -2 = bad month
58** -3 = bad day (Note 3)
59** -4 = bad fraction (Note 4)
60** -5 = internal error (Note 5)
61**
62** Notes:
63**
64** 1) UTC began at 1960 January 1.0 (JD 2436934.5) and it is improper
65** to call the function with an earlier date. If this is attempted,
66** zero is returned together with a warning status.
67**
68** Because leap seconds cannot, in principle, be predicted in
69** advance, a reliable check for dates beyond the valid range is
70** impossible. To guard against gross errors, a year five or more
71** after the release year of the present function (see the constant
72** IYV) is considered dubious. In this case a warning status is
73** returned but the result is computed in the normal way.
74**
75** For both too-early and too-late years, the warning status is +1.
76** This is distinct from the error status -1, which signifies a year
77** so early that JD could not be computed.
78**
79** 2) If the specified date is for a day which ends with a leap second,
80** the TAI-UTC value returned is for the period leading up to the
81** leap second. If the date is for a day which begins as a leap
82** second ends, the TAI-UTC returned is for the period following the
83** leap second.
84**
85** 3) The day number must be in the normal calendar range, for example
86** 1 through 30 for April. The "almanac" convention of allowing
87** such dates as January 0 and December 32 is not supported in this
88** function, in order to avoid confusion near leap seconds.
89**
90** 4) The fraction of day is used only for dates before the
91** introduction of leap seconds, the first of which occurred at the
92** end of 1971. It is tested for validity (0 to 1 is the valid
93** range) even if not used; if invalid, zero is used and status -4
94** is returned. For many applications, setting fd to zero is
95** acceptable; the resulting error is always less than 3 ms (and
96** occurs only pre-1972).
97**
98** 5) The status value returned in the case where there are multiple
99** errors refers to the first error detected. For example, if the
100** month and day are 13 and 32 respectively, status -2 (bad month)
101** will be returned. The "internal error" status refers to a
102** case that is impossible but causes some compilers to issue a
103** warning.
104**
105** 6) In cases where a valid result is not available, zero is returned.
106**
107** References:
108**
109** 1) For dates from 1961 January 1 onwards, the expressions from the
110** file ftp://maia.usno.navy.mil/ser7/tai-utc.dat are used.
111**
112** 2) The 5ms timestep at 1961 January 1 is taken from 2.58.1 (p87) of
113** the 1992 Explanatory Supplement.
114**
115** Called:
116** eraCal2jd Gregorian calendar to JD
117**
118** Copyright (C) 2013-2017, NumFOCUS Foundation.
119** Derived, with permission, from the SOFA library. See notes at end of file.
120*/
121{
122/* Release year for this version of eraDat */
123 enum { IYV = 2016};
124
125/* Reference dates (MJD) and drift rates (s/day), pre leap seconds */
126 static const double drift[][2] = {
127 { 37300.0, 0.0012960 },
128 { 37300.0, 0.0012960 },
129 { 37300.0, 0.0012960 },
130 { 37665.0, 0.0011232 },
131 { 37665.0, 0.0011232 },
132 { 38761.0, 0.0012960 },
133 { 38761.0, 0.0012960 },
134 { 38761.0, 0.0012960 },
135 { 38761.0, 0.0012960 },
136 { 38761.0, 0.0012960 },
137 { 38761.0, 0.0012960 },
138 { 38761.0, 0.0012960 },
139 { 39126.0, 0.0025920 },
140 { 39126.0, 0.0025920 }
141 };
142
143/* Number of Delta(AT) expressions before leap seconds were introduced */
144 enum { NERA1 = (int) (sizeof drift / sizeof (double) / 2) };
145
146/* Dates and Delta(AT)s */
147 static const struct {
148 int iyear, month;
149 double delat;
150 } changes[] = {
151 { 1960, 1, 1.4178180 },
152 { 1961, 1, 1.4228180 },
153 { 1961, 8, 1.3728180 },
154 { 1962, 1, 1.8458580 },
155 { 1963, 11, 1.9458580 },
156 { 1964, 1, 3.2401300 },
157 { 1964, 4, 3.3401300 },
158 { 1964, 9, 3.4401300 },
159 { 1965, 1, 3.5401300 },
160 { 1965, 3, 3.6401300 },
161 { 1965, 7, 3.7401300 },
162 { 1965, 9, 3.8401300 },
163 { 1966, 1, 4.3131700 },
164 { 1968, 2, 4.2131700 },
165 { 1972, 1, 10.0 },
166 { 1972, 7, 11.0 },
167 { 1973, 1, 12.0 },
168 { 1974, 1, 13.0 },
169 { 1975, 1, 14.0 },
170 { 1976, 1, 15.0 },
171 { 1977, 1, 16.0 },
172 { 1978, 1, 17.0 },
173 { 1979, 1, 18.0 },
174 { 1980, 1, 19.0 },
175 { 1981, 7, 20.0 },
176 { 1982, 7, 21.0 },
177 { 1983, 7, 22.0 },
178 { 1985, 7, 23.0 },
179 { 1988, 1, 24.0 },
180 { 1990, 1, 25.0 },
181 { 1991, 1, 26.0 },
182 { 1992, 7, 27.0 },
183 { 1993, 7, 28.0 },
184 { 1994, 7, 29.0 },
185 { 1996, 1, 30.0 },
186 { 1997, 7, 31.0 },
187 { 1999, 1, 32.0 },
188 { 2006, 1, 33.0 },
189 { 2009, 1, 34.0 },
190 { 2012, 7, 35.0 },
191 { 2015, 7, 36.0 },
192 { 2017, 1, 37.0 }
193 };
194
195/* Number of Delta(AT) changes */
196 enum { NDAT = (int) (sizeof changes / sizeof changes[0]) };
197
198/* Miscellaneous local variables */
199 int j, i, m;
200 double da, djm0, djm;
201
202
203/* Initialize the result to zero. */
204 *deltat = da = 0.0;
205
206/* If invalid fraction of a day, set error status and give up. */
207 if (fd < 0.0 || fd > 1.0) return -4;
208
209/* Convert the date into an MJD. */
210 j = eraCal2jd(iy, im, id, &djm0, &djm);
211
212/* If invalid year, month, or day, give up. */
213 if (j < 0) return j;
214
215/* If pre-UTC year, set warning status and give up. */
216 if (iy < changes[0].iyear) return 1;
217
218/* If suspiciously late year, set warning status but proceed. */
219 if (iy > IYV + 5) j = 1;
220
221/* Combine year and month to form a date-ordered integer... */
222 m = 12*iy + im;
223
224/* ...and use it to find the preceding table entry. */
225 for (i = NDAT-1; i >=0; i--) {
226 if (m >= (12 * changes[i].iyear + changes[i].month)) break;
227 }
228
229/* Prevent underflow warnings. */
230 if (i < 0) return -5;
231
232/* Get the Delta(AT). */
233 da = changes[i].delat;
234
235/* If pre-1972, adjust for drift. */
236 if (i < NERA1) da += (djm + fd - drift[i][0]) * drift[i][1];
237
238/* Return the Delta(AT) value. */
239 *deltat = da;
240
241/* Return the status. */
242 return j;
243
244}
245/*----------------------------------------------------------------------
246**
247**
248** Copyright (C) 2013-2017, NumFOCUS Foundation.
249** All rights reserved.
250**
251** This library is derived, with permission, from the International
252** Astronomical Union's "Standards of Fundamental Astronomy" library,
253** available from http://www.iausofa.org.
254**
255** The ERFA version is intended to retain identical functionality to
256** the SOFA library, but made distinct through different function and
257** file names, as set out in the SOFA license conditions. The SOFA
258** original has a role as a reference standard for the IAU and IERS,
259** and consequently redistribution is permitted only in its unaltered
260** state. The ERFA version is not subject to this restriction and
261** therefore can be included in distributions which do not support the
262** concept of "read only" software.
263**
264** Although the intent is to replicate the SOFA API (other than
265** replacement of prefix names) and results (with the exception of
266** bugs; any that are discovered will be fixed), SOFA is not
267** responsible for any errors found in this version of the library.
268**
269** If you wish to acknowledge the SOFA heritage, please acknowledge
270** that you are using a library derived from SOFA, rather than SOFA
271** itself.
272**
273**
274** TERMS AND CONDITIONS
275**
276** Redistribution and use in source and binary forms, with or without
277** modification, are permitted provided that the following conditions
278** are met:
279**
280** 1 Redistributions of source code must retain the above copyright
281** notice, this list of conditions and the following disclaimer.
282**
283** 2 Redistributions in binary form must reproduce the above copyright
284** notice, this list of conditions and the following disclaimer in
285** the documentation and/or other materials provided with the
286** distribution.
287**
288** 3 Neither the name of the Standards Of Fundamental Astronomy Board,
289** the International Astronomical Union nor the names of its
290** contributors may be used to endorse or promote products derived
291** from this software without specific prior written permission.
292**
293** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
294** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
295** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
296** FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
297** COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
298** INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
299** BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
300** LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
301** CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
302** LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
303** ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
304** POSSIBILITY OF SUCH DAMAGE.
305**
306*/
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