#include "sofa.h" #include "sofam.h" #include int iauJd2cal(double dj1, double dj2, int *iy, int *im, int *id, double *fd) /* ** - - - - - - - - - - ** i a u J d 2 c a l ** - - - - - - - - - - ** ** Julian Date to Gregorian year, month, day, and fraction of a day. ** ** This function is part of the International Astronomical Union's ** SOFA (Standards Of Fundamental Astronomy) software collection. ** ** Status: support function. ** ** 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 1) ** ** 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) ** ** Separating integer and fraction uses the "compensated summation" ** algorithm of Kahan-Neumaier to preserve as much precision as ** possible irrespective of the jd1+jd2 apportionment. ** ** 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. ** ** References: ** ** Explanatory Supplement to the Astronomical Almanac, ** P. Kenneth Seidelmann (ed), University Science Books (1992), ** Section 12.92 (p604). ** ** Klein, A., A Generalized Kahan-Babuska-Summation-Algorithm. ** Computing, 76, 279-293 (2006), Section 3. ** ** This revision: 2021 May 11 ** ** SOFA release 2021-05-12 ** ** Copyright (C) 2021 IAU SOFA Board. See notes at end. */ { /* Minimum and maximum allowed JD */ const double DJMIN = -68569.5; const double DJMAX = 1e9; long jd, i, l, n, k; double dj, f1, f2, d, s, cs, v[2], x, t, f; /* Verify date is acceptable. */ dj = dj1 + dj2; if (dj < DJMIN || dj > DJMAX) return -1; /* Separate day and fraction (where -0.5 <= fraction < 0.5). */ d = dnint(dj1); f1 = dj1 - d; jd = (long) d; d = dnint(dj2); f2 = dj2 - d; jd += (long) d; /* Compute f1+f2+0.5 using compensated summation (Klein 2006). */ s = 0.5; cs = 0.0; v[0] = f1; v[1] = f2; for ( i = 0; i < 2; i++ ) { x = v[i]; t = s + x; cs += fabs(s) >= fabs(x) ? (s-t) + x : (x-t) + s; s = t; if ( s >= 1.0 ) { jd++; s -= 1.0; } } f = s + cs; cs = f - s; /* Deal with negative f. */ if ( f < 0.0 ) { /* Compensated summation: assume that |s| <= 1.0. */ f = s + 1.0; cs += (1.0-f) + s; s = f; f = s + cs; cs = f - s; jd--; } /* Deal with f that is 1.0 or more (when rounded to double). */ if ( (f-1.0) >= -DBL_EPSILON/4.0 ) { /* Compensated summation: assume that |s| <= 1.0. */ t = s - 1.0; cs += (s-t) - 1.0; s = t; f = s + cs; if ( -DBL_EPSILON/2.0 < f ) { jd++; f = gmax(f, 0.0); } } /* 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; /* Success. */ return 0; /* Finished. */ /*---------------------------------------------------------------------- ** ** 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 ** **--------------------------------------------------------------------*/ }