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Diffstat (limited to 'ast/erfa/ut1utc.c')
-rw-r--r-- | ast/erfa/ut1utc.c | 202 |
1 files changed, 202 insertions, 0 deletions
diff --git a/ast/erfa/ut1utc.c b/ast/erfa/ut1utc.c new file mode 100644 index 0000000..6ec1b44 --- /dev/null +++ b/ast/erfa/ut1utc.c @@ -0,0 +1,202 @@ +#include "erfa.h" + +int eraUt1utc(double ut11, double ut12, double dut1, + double *utc1, double *utc2) +/* +** - - - - - - - - - - +** e r a U t 1 u t c +** - - - - - - - - - - +** +** Time scale transformation: Universal Time, UT1, to Coordinated +** Universal Time, UTC. +** +** Given: +** ut11,ut12 double UT1 as a 2-part Julian Date (Note 1) +** dut1 double Delta UT1: UT1-UTC in seconds (Note 2) +** +** Returned: +** utc1,utc2 double UTC as a 2-part quasi Julian Date (Notes 3,4) +** +** Returned (function value): +** int status: +1 = dubious year (Note 5) +** 0 = OK +** -1 = unacceptable date +** +** Notes: +** +** 1) ut11+ut12 is Julian Date, apportioned in any convenient way +** between the two arguments, for example where ut11 is the Julian +** Day Number and ut12 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 Note 3. +** +** 2) Delta UT1 can be obtained from tabulations provided by the +** International Earth Rotation and Reference Systems Service. The +** value changes abruptly by 1s at a leap second; however, close to +** a leap second the algorithm used here is tolerant of the "wrong" +** choice of value being made. +** +** 3) JD cannot unambiguously represent UTC during a leap second unless +** special measures are taken. The convention in the present +** function is that the returned quasi JD day UTC1+UTC2 represents +** UTC days whether the length is 86399, 86400 or 86401 SI seconds. +** +** 4) The function eraD2dtf can be used to transform the UTC quasi-JD +** into calendar date and clock time, including UTC leap second +** handling. +** +** 5) 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: +** eraJd2cal JD to Gregorian calendar +** eraDat delta(AT) = TAI-UTC +** eraCal2jd Gregorian calendar to JD +** +** 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) 2013-2016, NumFOCUS Foundation. +** Derived, with permission, from the SOFA library. See notes at end of file. +*/ +{ + int big1; + int i, iy, im, id, js; + double duts, u1, u2, d1, dats1, d2, fd, dats2, ddats, us1, us2, du; + + +/* UT1-UTC in seconds. */ + duts = dut1; + +/* Put the two parts of the UT1 into big-first order. */ + big1 = ( ut11 >= ut12 ); + if ( big1 ) { + u1 = ut11; + u2 = ut12; + } else { + u1 = ut12; + u2 = ut11; + } + +/* See if the UT1 can possibly be in a leap-second day. */ + d1 = u1; + dats1 = 0; + for ( i = -1; i <= 3; i++ ) { + d2 = u2 + (double) i; + if ( eraJd2cal(d1, d2, &iy, &im, &id, &fd) ) return -1; + js = eraDat(iy, im, id, 0.0, &dats2); + if ( js < 0 ) return -1; + if ( i == - 1 ) dats1 = dats2; + ddats = dats2 - dats1; + if ( fabs(ddats) >= 0.5 ) { + + /* Yes, leap second nearby: ensure UT1-UTC is "before" value. */ + if ( ddats * duts >= 0 ) duts -= ddats; + + /* UT1 for the start of the UTC day that ends in a leap. */ + if ( eraCal2jd(iy, im, id, &d1, &d2) ) return -1; + us1 = d1; + us2 = d2 - 1.0 + duts/ERFA_DAYSEC; + + /* Is the UT1 after this point? */ + du = u1 - us1; + du += u2 - us2; + if ( du > 0 ) { + + /* Yes: fraction of the current UTC day that has elapsed. */ + fd = du * ERFA_DAYSEC / ( ERFA_DAYSEC + ddats ); + + /* Ramp UT1-UTC to bring about ERFA's JD(UTC) convention. */ + duts += ddats * ( fd <= 1.0 ? fd : 1.0 ); + } + + /* Done. */ + break; + } + dats1 = dats2; + } + +/* Subtract the (possibly adjusted) UT1-UTC from UT1 to give UTC. */ + u2 -= duts / ERFA_DAYSEC; + +/* Result, safeguarding precision. */ + if ( big1 ) { + *utc1 = u1; + *utc2 = u2; + } else { + *utc1 = u2; + *utc2 = u1; + } + +/* Status. */ + return js; + +} +/*---------------------------------------------------------------------- +** +** +** Copyright (C) 2013-2016, 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. +** +*/ |