#include "sofa.h"
#include "sofam.h"

int iauCal2jd(int iy, int im, int id, double *djm0, double *djm)
/*
**  - - - - - - - - - -
**   i a u C a l 2 j d
**  - - - - - - - - - -
**
**  Gregorian Calendar to Julian Date.
**
**  This function is part of the International Astronomical Union's
**  SOFA (Standards of Fundamental Astronomy) software collection.
**
**  Status:  support function.
**
**  Given:
**     iy,im,id  int     year, month, day in Gregorian calendar (Note 1)
**
**  Returned:
**     djm0      double  MJD zero-point: always 2400000.5
**     djm       double  Modified Julian Date for 0 hrs
**
**  Returned (function value):
**               int     status:
**                           0 = OK
**                          -1 = bad year   (Note 3: JD not computed)
**                          -2 = bad month  (JD not computed)
**                          -3 = bad day    (JD computed)
**
**  Notes:
**
**  1) The algorithm used is valid from -4800 March 1, but this
**     implementation rejects dates before -4799 January 1.
**
**  2) The Julian Date is returned in two pieces, in the usual SOFA
**     manner, which is designed to preserve time resolution.  The
**     Julian Date is available as a single number by adding djm0 and
**     djm.
**
**  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).
**
**  This revision:  2021 May 11
**
**  SOFA release 2023-10-11
**
**  Copyright (C) 2023 IAU SOFA Board.  See notes at end.
*/
{
   int j, ly, my;
   long iypmy;

/* Earliest year allowed (4800BC) */
   const int IYMIN = -4799;

/* Month lengths in days */
   static const int mtab[]
                     = {31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};


/* Preset status. */
   j = 0;

/* Validate year and month. */
   if (iy < IYMIN) return -1;
   if (im < 1 || im > 12) return -2;

/* If February in a leap year, 1, otherwise 0. */
   ly = ((im == 2) && !(iy%4) && (iy%100 || !(iy%400)));

/* Validate day, taking into account leap years. */
   if ( (id < 1) || (id > (mtab[im-1] + ly))) j = -3;

/* Return result. */
   my = (im - 14) / 12;
   iypmy = (long) (iy + my);
   *djm0 = DJM0;
   *djm = (double)((1461L * (iypmy + 4800L)) / 4L
                 + (367L * (long) (im - 2 - 12 * my)) / 12L
                 - (3L * ((iypmy + 4900L) / 100L)) / 4L
                 + (long) id - 2432076L);

/* Return status. */
   return j;

/* Finished. */

/*----------------------------------------------------------------------
**
**  Copyright (C) 2023
**  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
**
**--------------------------------------------------------------------*/
}
