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#include "sofa.h"
int iauDat(int iy, int im, int id, double fd, double *deltat)
/*
** - - - - - - -
** i a u D a t
** - - - - - - -
**
** For a given UTC date, calculate Delta(AT) = TAI-UTC.
**
** :------------------------------------------:
** : :
** : IMPORTANT :
** : :
** : A new version of this function must be :
** : produced whenever a new leap second is :
** : announced. There are four items to :
** : change on each such occasion: :
** : :
** : 1) A new line must be added to the set :
** : of statements that initialize the :
** : array "changes". :
** : :
** : 2) The constant IYV must be set to the :
** : current year. :
** : :
** : 3) The "Latest leap second" comment :
** : below must be set to the new leap :
** : second date. :
** : :
** : 4) The "This revision" comment, later, :
** : must be set to the current date. :
** : :
** : Change (2) must also be carried out :
** : whenever the function is re-issued, :
** : even if no leap seconds have been :
** : added. :
** : :
** : Latest leap second: 2016 December 31 :
** : :
** :__________________________________________:
**
** This function is part of the International Astronomical Union's
** SOFA (Standards Of Fundamental Astronomy) software collection.
**
** Status: user-replaceable support function.
**
** Given:
** iy int UTC: year (Notes 1 and 2)
** im int month (Note 2)
** id int day (Notes 2 and 3)
** fd double fraction of day (Note 4)
**
** Returned:
** deltat double TAI minus UTC, seconds
**
** Returned (function value):
** int status (Note 5):
** 1 = dubious year (Note 1)
** 0 = OK
** -1 = bad year
** -2 = bad month
** -3 = bad day (Note 3)
** -4 = bad fraction (Note 4)
** -5 = internal error (Note 5)
**
** Notes:
**
** 1) UTC began at 1960 January 1.0 (JD 2436934.5) and it is improper
** to call the function with an earlier date. If this is attempted,
** zero is returned together with a warning status.
**
** Because leap seconds cannot, in principle, be predicted in
** advance, a reliable check for dates beyond the valid range is
** impossible. To guard against gross errors, a year five or more
** after the release year of the present function (see the constant
** IYV) is considered dubious. In this case a warning status is
** returned but the result is computed in the normal way.
**
** For both too-early and too-late years, the warning status is +1.
** This is distinct from the error status -1, which signifies a year
** so early that JD could not be computed.
**
** 2) If the specified date is for a day which ends with a leap second,
** the TAI-UTC value returned is for the period leading up to the
** leap second. If the date is for a day which begins as a leap
** second ends, the TAI-UTC returned is for the period following the
** leap second.
**
** 3) The day number must be in the normal calendar range, for example
** 1 through 30 for April. The "almanac" convention of allowing
** such dates as January 0 and December 32 is not supported in this
** function, in order to avoid confusion near leap seconds.
**
** 4) The fraction of day is used only for dates before the
** introduction of leap seconds, the first of which occurred at the
** end of 1971. It is tested for validity (0 to 1 is the valid
** range) even if not used; if invalid, zero is used and status -4
** is returned. For many applications, setting fd to zero is
** acceptable; the resulting error is always less than 3 ms (and
** occurs only pre-1972).
**
** 5) The status value returned in the case where there are multiple
** errors refers to the first error detected. For example, if the
** month and day are 13 and 32 respectively, status -2 (bad month)
** will be returned. The "internal error" status refers to a
** case that is impossible but causes some compilers to issue a
** warning.
**
** 6) In cases where a valid result is not available, zero is returned.
**
** References:
**
** 1) For dates from 1961 January 1 onwards, the expressions from the
** file ftp://maia.usno.navy.mil/ser7/tai-utc.dat are used.
**
** 2) The 5ms timestep at 1961 January 1 is taken from 2.58.1 (p87) of
** the 1992 Explanatory Supplement.
**
** Called:
** iauCal2jd Gregorian calendar to JD
**
** This revision: 2020 May 31
**
** SOFA release 2020-07-21
**
** Copyright (C) 2020 IAU SOFA Board. See notes at end.
*/
{
/* Release year for this version of iauDat */
enum { IYV = 2020};
/* Reference dates (MJD) and drift rates (s/day), pre leap seconds */
static const double drift[][2] = {
{ 37300.0, 0.0012960 },
{ 37300.0, 0.0012960 },
{ 37300.0, 0.0012960 },
{ 37665.0, 0.0011232 },
{ 37665.0, 0.0011232 },
{ 38761.0, 0.0012960 },
{ 38761.0, 0.0012960 },
{ 38761.0, 0.0012960 },
{ 38761.0, 0.0012960 },
{ 38761.0, 0.0012960 },
{ 38761.0, 0.0012960 },
{ 38761.0, 0.0012960 },
{ 39126.0, 0.0025920 },
{ 39126.0, 0.0025920 }
};
/* Number of Delta(AT) expressions before leap seconds were introduced */
enum { NERA1 = (int) (sizeof drift / sizeof (double) / 2) };
/* Dates and Delta(AT)s */
static const struct {
int iyear, month;
double delat;
} changes[] = {
{ 1960, 1, 1.4178180 },
{ 1961, 1, 1.4228180 },
{ 1961, 8, 1.3728180 },
{ 1962, 1, 1.8458580 },
{ 1963, 11, 1.9458580 },
{ 1964, 1, 3.2401300 },
{ 1964, 4, 3.3401300 },
{ 1964, 9, 3.4401300 },
{ 1965, 1, 3.5401300 },
{ 1965, 3, 3.6401300 },
{ 1965, 7, 3.7401300 },
{ 1965, 9, 3.8401300 },
{ 1966, 1, 4.3131700 },
{ 1968, 2, 4.2131700 },
{ 1972, 1, 10.0 },
{ 1972, 7, 11.0 },
{ 1973, 1, 12.0 },
{ 1974, 1, 13.0 },
{ 1975, 1, 14.0 },
{ 1976, 1, 15.0 },
{ 1977, 1, 16.0 },
{ 1978, 1, 17.0 },
{ 1979, 1, 18.0 },
{ 1980, 1, 19.0 },
{ 1981, 7, 20.0 },
{ 1982, 7, 21.0 },
{ 1983, 7, 22.0 },
{ 1985, 7, 23.0 },
{ 1988, 1, 24.0 },
{ 1990, 1, 25.0 },
{ 1991, 1, 26.0 },
{ 1992, 7, 27.0 },
{ 1993, 7, 28.0 },
{ 1994, 7, 29.0 },
{ 1996, 1, 30.0 },
{ 1997, 7, 31.0 },
{ 1999, 1, 32.0 },
{ 2006, 1, 33.0 },
{ 2009, 1, 34.0 },
{ 2012, 7, 35.0 },
{ 2015, 7, 36.0 },
{ 2017, 1, 37.0 }
};
/* Number of Delta(AT) changes */
enum { NDAT = (int) (sizeof changes / sizeof changes[0]) };
/* Miscellaneous local variables */
int j, i, m;
double da, djm0, djm;
/* Initialize the result to zero. */
*deltat = da = 0.0;
/* If invalid fraction of a day, set error status and give up. */
if (fd < 0.0 || fd > 1.0) return -4;
/* Convert the date into an MJD. */
j = iauCal2jd(iy, im, id, &djm0, &djm);
/* If invalid year, month, or day, give up. */
if (j < 0) return j;
/* If pre-UTC year, set warning status and give up. */
if (iy < changes[0].iyear) return 1;
/* If suspiciously late year, set warning status but proceed. */
if (iy > IYV + 5) j = 1;
/* Combine year and month to form a date-ordered integer... */
m = 12*iy + im;
/* ...and use it to find the preceding table entry. */
for (i = NDAT-1; i >=0; i--) {
if (m >= (12 * changes[i].iyear + changes[i].month)) break;
}
/* Prevent underflow warnings. */
if (i < 0) return -5;
/* Get the Delta(AT). */
da = changes[i].delat;
/* If pre-1972, adjust for drift. */
if (i < NERA1) da += (djm + fd - drift[i][0]) * drift[i][1];
/* Return the Delta(AT) value. */
*deltat = da;
/* Return the status. */
return j;
/*----------------------------------------------------------------------
**
** Copyright (C) 2018
** Standards Of Fundamental Astronomy Board
** of the International Astronomical Union.
**
** =====================
** SOFA Software License
** =====================
**
** NOTICE TO USER:
**
** BY USING THIS SOFTWARE YOU ACCEPT THE FOLLOWING SIX TERMS AND
** CONDITIONS WHICH APPLY TO ITS USE.
**
** 1. The Software is owned by the IAU SOFA Board ("SOFA").
**
** 2. Permission is granted to anyone to use the SOFA software for any
** purpose, including commercial applications, free of charge and
** without payment of royalties, subject to the conditions and
** restrictions listed below.
**
** 3. You (the user) may copy and distribute SOFA source code to others,
** and use and adapt its code and algorithms in your own software,
** on a world-wide, royalty-free basis. That portion of your
** distribution that does not consist of intact and unchanged copies
** of SOFA source code files is a "derived work" that must comply
** with the following requirements:
**
** a) Your work shall be marked or carry a statement that it
** (i) uses routines and computations derived by you from
** software provided by SOFA under license to you; and
** (ii) does not itself constitute software provided by and/or
** endorsed by SOFA.
**
** b) The source code of your derived work must contain descriptions
** of how the derived work is based upon, contains and/or differs
** from the original SOFA software.
**
** c) UNLIKE OTHER SOFA SOFTWARE, WHICH IS STRICTLY "READ ONLY",
** USERS ARE PERMITTED TO REPLACE THIS FUNCTION WITH ONE USING
** THE SAME NAME BUT DIFFERENT CODE. This is to allow use of
** locally supported mechanisms for keeping track of leap
** seconds, perhaps file or network based. It avoids the need
** for applications to be relinked periodically in order to pick
** up SOFA updates.
**
** d) The origin of the SOFA components of your derived work must
** not be misrepresented; you must not claim that you wrote the
** original software, nor file a patent application for SOFA
** software or algorithms embedded in the SOFA software.
**
** e) These requirements must be reproduced intact in any source
** distribution and shall apply to anyone to whom you have
** granted a further right to modify the source code of your
** derived work.
**
** Note that, as originally distributed, the SOFA software is
** intended to be a definitive implementation of the IAU standards,
** and consequently third-party modifications are discouraged. All
** variations, no matter how minor, must be explicitly marked as
** such, as explained above.
**
** 4. You shall not cause the SOFA software to be brought into
** disrepute, either by misuse, or use for inappropriate tasks, or
** by inappropriate modification.
**
** 5. The SOFA software is provided "as is" and SOFA makes no warranty
** as to its use or performance. SOFA does not and cannot warrant
** the performance or results which the user may obtain by using the
** SOFA software. SOFA makes no warranties, express or implied, as
** to non-infringement of third party rights, merchantability, or
** fitness for any particular purpose. In no event will SOFA be
** liable to the user for any consequential, incidental, or special
** damages, including any lost profits or lost savings, even if a
** SOFA representative has been advised of such damages, or for any
** claim by any third party.
**
** 6. The provision of any version of the SOFA software under the terms
** and conditions specified herein does not imply that future
** versions will also be made available under the same terms and
** conditions.
*
** In any published work or commercial product which uses the SOFA
** software directly, acknowledgement (see www.iausofa.org) is
** appreciated.
**
** Correspondence concerning SOFA software should be addressed as
** follows:
**
** By email: sofa@ukho.gov.uk
** By post: IAU SOFA Center
** HM Nautical Almanac Office
** UK Hydrographic Office
** Admiralty Way, Taunton
** Somerset, TA1 2DN
** United Kingdom
**
**--------------------------------------------------------------------*/
}