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#include "erfa.h"
int eraTcbtdb(double tcb1, double tcb2, double *tdb1, double *tdb2)
/*
** - - - - - - - - - -
** e r a T c b t d b
** - - - - - - - - - -
**
** Time scale transformation: Barycentric Coordinate Time, TCB, to
** Barycentric Dynamical Time, TDB.
**
** Given:
** tcb1,tcb2 double TCB as a 2-part Julian Date
**
** Returned:
** tdb1,tdb2 double TDB as a 2-part Julian Date
**
** Returned (function value):
** int status: 0 = OK
**
** Notes:
**
** 1) tcb1+tcb2 is Julian Date, apportioned in any convenient way
** between the two arguments, for example where tcb1 is the Julian
** Day Number and tcb2 is the fraction of a day. The returned
** tdb1,tdb2 follow suit.
**
** 2) The 2006 IAU General Assembly introduced a conventional linear
** transformation between TDB and TCB. This transformation
** compensates for the drift between TCB and terrestrial time TT,
** and keeps TDB approximately centered on TT. Because the
** relationship between TT and TCB depends on the adopted solar
** system ephemeris, the degree of alignment between TDB and TT over
** long intervals will vary according to which ephemeris is used.
** Former definitions of TDB attempted to avoid this problem by
** stipulating that TDB and TT should differ only by periodic
** effects. This is a good description of the nature of the
** relationship but eluded precise mathematical formulation. The
** conventional linear relationship adopted in 2006 sidestepped
** these difficulties whilst delivering a TDB that in practice was
** consistent with values before that date.
**
** 3) TDB is essentially the same as Teph, the time argument for the
** JPL solar system ephemerides.
**
** Reference:
**
** IAU 2006 Resolution B3
**
** Copyright (C) 2013-2016, NumFOCUS Foundation.
** Derived, with permission, from the SOFA library. See notes at end of file.
*/
{
/* 1977 Jan 1 00:00:32.184 TT, as two-part JD */
static const double t77td = ERFA_DJM0 + ERFA_DJM77;
static const double t77tf = ERFA_TTMTAI/ERFA_DAYSEC;
/* TDB (days) at TAI 1977 Jan 1.0 */
static const double tdb0 = ERFA_TDB0/ERFA_DAYSEC;
double d;
/* Result, safeguarding precision. */
if ( tcb1 > tcb2 ) {
d = tcb1 - t77td;
*tdb1 = tcb1;
*tdb2 = tcb2 + tdb0 - ( d + ( tcb2 - t77tf ) ) * ERFA_ELB;
} else {
d = tcb2 - t77td;
*tdb1 = tcb1 + tdb0 - ( d + ( tcb1 - t77tf ) ) * ERFA_ELB;
*tdb2 = tcb2;
}
/* Status (always OK). */
return 0;
}
/*----------------------------------------------------------------------
**
**
** 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.
**
*/
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