#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 2021-01-25 ** ** Copyright (C) 2021 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) 2021 ** 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 ** **--------------------------------------------------------------------*/ }