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Diffstat (limited to 'ast/erfa/jd2cal.c')
| -rw-r--r-- | ast/erfa/jd2cal.c | 164 |
1 files changed, 164 insertions, 0 deletions
diff --git a/ast/erfa/jd2cal.c b/ast/erfa/jd2cal.c new file mode 100644 index 0000000..abe2b8f --- /dev/null +++ b/ast/erfa/jd2cal.c @@ -0,0 +1,164 @@ +#include "erfa.h" + +int eraJd2cal(double dj1, double dj2, + int *iy, int *im, int *id, double *fd) +/* +** - - - - - - - - - - +** e r a J d 2 c a l +** - - - - - - - - - - +** +** Julian Date to Gregorian year, month, day, and fraction of a day. +** +** Given: +** dj1,dj2 double Julian Date (Notes 1, 2) +** +** Returned (arguments): +** iy int year +** im int month +** id int day +** fd double fraction of day +** +** Returned (function value): +** int status: +** 0 = OK +** -1 = unacceptable date (Note 3) +** +** Notes: +** +** 1) The earliest valid date is -68569.5 (-4900 March 1). The +** largest value accepted is 1e9. +** +** 2) The Julian Date is apportioned in any convenient way between +** the arguments dj1 and dj2. For example, JD=2450123.7 could +** be expressed in any of these ways, among others: +** +** dj1 dj2 +** +** 2450123.7 0.0 (JD method) +** 2451545.0 -1421.3 (J2000 method) +** 2400000.5 50123.2 (MJD method) +** 2450123.5 0.2 (date & time method) +** +** 3) In early eras the conversion is from the "proleptic Gregorian +** calendar"; no account is taken of the date(s) of adoption of +** the Gregorian calendar, nor is the AD/BC numbering convention +** observed. +** +** Reference: +** +** Explanatory Supplement to the Astronomical Almanac, +** P. Kenneth Seidelmann (ed), University Science Books (1992), +** Section 12.92 (p604). +** +** Copyright (C) 2013-2016, NumFOCUS Foundation. +** Derived, with permission, from the SOFA library. See notes at end of file. +*/ +{ +/* Minimum and maximum allowed JD */ + const double DJMIN = -68569.5; + const double DJMAX = 1e9; + + long jd, l, n, i, k; + double dj, d1, d2, f1, f2, f, d; + + +/* Verify date is acceptable. */ + dj = dj1 + dj2; + if (dj < DJMIN || dj > DJMAX) return -1; + +/* Copy the date, big then small, and re-align to midnight. */ + if (dj1 >= dj2) { + d1 = dj1; + d2 = dj2; + } else { + d1 = dj2; + d2 = dj1; + } + d2 -= 0.5; + +/* Separate day and fraction. */ + f1 = fmod(d1, 1.0); + f2 = fmod(d2, 1.0); + f = fmod(f1 + f2, 1.0); + if (f < 0.0) f += 1.0; + d = floor(d1 - f1) + floor(d2 - f2) + floor(f1 + f2 - f); + jd = (long) floor(d) + 1L; + +/* Express day in Gregorian calendar. */ + l = jd + 68569L; + n = (4L * l) / 146097L; + l -= (146097L * n + 3L) / 4L; + i = (4000L * (l + 1L)) / 1461001L; + l -= (1461L * i) / 4L - 31L; + k = (80L * l) / 2447L; + *id = (int) (l - (2447L * k) / 80L); + l = k / 11L; + *im = (int) (k + 2L - 12L * l); + *iy = (int) (100L * (n - 49L) + i + l); + *fd = f; + + 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. +** +*/ |