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dat.c
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dat.c
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#include "erfa.h"
#include "erfadatextra.h"
int eraDat(int iy, int im, int id, double fd, double *deltat)
/*
** - - - - - - -
** e r a 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 :
** : :
** :__________________________________________:
**
** 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:
** eraCal2jd Gregorian calendar to JD
**
** This revision: 2023 January 17
**
** Copyright (C) 2013-2023, NumFOCUS Foundation.
** Derived, with permission, from the SOFA library. See notes at end of file.
*/
{
/* Release year for this version of eraDat */
enum { IYV = 2023};
/* 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 eraLEAPSECOND _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]) };
/* Get/initialise leap-second if needed */
int NDAT;
eraLEAPSECOND *changes;
NDAT = eraDatini(_changes, _NDAT, &changes);
/* 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 = eraCal2jd(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;
/* Finished. */
}
/*----------------------------------------------------------------------
**
**
** Copyright (C) 2013-2023, NumFOCUS Foundation.
** All rights reserved.
**
** This library is derived, with permission, from the International
** Astronomical Union's "Standards of Fundamental Astronomy" library,
** available from http://www.iausofa.org.
**
** The ERFA version is intended to retain identical functionality to
** the SOFA library, but made distinct through different function and
** file names, as set out in the SOFA license conditions. The SOFA
** original has a role as a reference standard for the IAU and IERS,
** and consequently redistribution is permitted only in its unaltered
** state. The ERFA version is not subject to this restriction and
** therefore can be included in distributions which do not support the
** concept of "read only" software.
**
** Although the intent is to replicate the SOFA API (other than
** replacement of prefix names) and results (with the exception of
** bugs; any that are discovered will be fixed), SOFA is not
** responsible for any errors found in this version of the library.
**
** If you wish to acknowledge the SOFA heritage, please acknowledge
** that you are using a library derived from SOFA, rather than SOFA
** itself.
**
**
** TERMS AND CONDITIONS
**
** Redistribution and use in source and binary forms, with or without
** modification, are permitted provided that the following conditions
** are met:
**
** 1 Redistributions of source code must retain the above copyright
** notice, this list of conditions and the following disclaimer.
**
** 2 Redistributions in binary form must reproduce the above copyright
** notice, this list of conditions and the following disclaimer in
** the documentation and/or other materials provided with the
** distribution.
**
** 3 Neither the name of the Standards Of Fundamental Astronomy Board,
** the International Astronomical Union nor the names of its
** contributors may be used to endorse or promote products derived
** from this software without specific prior written permission.
**
** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
** FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
** COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
** INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
** BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
** LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
** CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
** LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
** ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
** POSSIBILITY OF SUCH DAMAGE.
**
*/