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Diffstat (limited to 'ast/erfa/taiutc.c')
| -rw-r--r-- | ast/erfa/taiutc.c | 168 |
1 files changed, 168 insertions, 0 deletions
diff --git a/ast/erfa/taiutc.c b/ast/erfa/taiutc.c new file mode 100644 index 0000000..c9f6958 --- /dev/null +++ b/ast/erfa/taiutc.c @@ -0,0 +1,168 @@ +#include "erfa.h" + +int eraTaiutc(double tai1, double tai2, double *utc1, double *utc2) +/* +** - - - - - - - - - - +** e r a T a i u t c +** - - - - - - - - - - +** +** Time scale transformation: International Atomic Time, TAI, to +** Coordinated Universal Time, UTC. +** +** 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 ERFA convention. +** +** 3) The function eraD2dtf 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 eraDat for further details. +** +** Called: +** eraUtctai 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) +** +** Copyright (C) 2013-2014, NumFOCUS Foundation. +** Derived, with permission, from the SOFA library. See notes at end of file. +*/ +{ + int big1; + int i, j; + double a1, a2, u1, u2, g1, g2; + + +/* Put the two parts of the TAI into big-first order. */ + big1 = ( tai1 >= 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 = eraUtctai(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) 2013-2014, 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. +** +*/ |