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#include "sofa.h"
int iauTaiutc(double tai1, double tai2, double *utc1, double *utc2)
/*
** - - - - - - - - - -
** i a u T a i u t c
** - - - - - - - - - -
**
** Time scale transformation: International Atomic Time, TAI, to
** Coordinated Universal Time, UTC.
**
** This function is part of the International Astronomical Union's
** SOFA (Standards of Fundamental Astronomy) software collection.
**
** Status: canonical.
**
** Given:
** tai1,tai2 double TAI as a 2-part Julian Date (Note 1)
**
** Returned:
** utc1,utc2 double UTC as a 2-part quasi Julian Date (Notes 1-3)
**
** Returned (function value):
** int status: +1 = dubious year (Note 4)
** 0 = OK
** -1 = unacceptable date
**
** Notes:
**
** 1) tai1+tai2 is Julian Date, apportioned in any convenient way
** between the two arguments, for example where tai1 is the Julian
** Day Number and tai2 is the fraction of a day. The returned utc1
** and utc2 form an analogous pair, except that a special convention
** is used, to deal with the problem of leap seconds - see the next
** note.
**
** 2) JD cannot unambiguously represent UTC during a leap second unless
** special measures are taken. The convention in the present
** function is that the JD day represents UTC days whether the
** length is 86399, 86400 or 86401 SI seconds. In the 1960-1972 era
** there were smaller jumps (in either direction) each time the
** linear UTC(TAI) expression was changed, and these "mini-leaps"
** are also included in the SOFA convention.
**
** 3) The function iauD2dtf can be used to transform the UTC quasi-JD
** into calendar date and clock time, including UTC leap second
** handling.
**
** 4) The warning status "dubious year" flags UTCs that predate the
** introduction of the time scale or that are too far in the future
** to be trusted. See iauDat for further details.
**
** Called:
** iauUtctai UTC to TAI
**
** References:
**
** McCarthy, D. D., Petit, G. (eds.), IERS Conventions (2003),
** IERS Technical Note No. 32, BKG (2004)
**
** Explanatory Supplement to the Astronomical Almanac,
** P. Kenneth Seidelmann (ed), University Science Books (1992)
**
** This revision: 2019 June 20
**
** SOFA release 2020-07-21
**
** Copyright (C) 2020 IAU SOFA Board. See notes at end.
*/
{
int big1;
int i, j;
double a1, a2, u1, u2, g1, g2;
/* Put the two parts of the TAI into big-first order. */
big1 = ( fabs(tai1) >= fabs(tai2) );
if ( big1 ) {
a1 = tai1;
a2 = tai2;
} else {
a1 = tai2;
a2 = tai1;
}
/* Initial guess for UTC. */
u1 = a1;
u2 = a2;
/* Iterate (though in most cases just once is enough). */
for ( i = 0; i < 3; i++ ) {
/* Guessed UTC to TAI. */
j = iauUtctai(u1, u2, &g1, &g2);
if ( j < 0 ) return j;
/* Adjust guessed UTC. */
u2 += a1 - g1;
u2 += a2 - g2;
}
/* Return the UTC result, preserving the TAI order. */
if ( big1 ) {
*utc1 = u1;
*utc2 = u2;
} else {
*utc1 = u2;
*utc2 = u1;
}
/* Status. */
return j;
/*----------------------------------------------------------------------
**
** Copyright (C) 2020
** 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) The names of all routines in your derived work shall not
** include the prefix "iau" or "sofa" or trivial modifications
** thereof such as changes of case.
**
** 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
**
**--------------------------------------------------------------------*/
}