view release on metacpan or  search on metacpan

erfasrc/src/cal2jd.c  view on Meta::CPAN

#include "erfa.h"

int eraCal2jd(int iy, int im, int id, double *djm0, double *djm)
/*
**  - - - - - - - - - -
**   e r a C a l 2 j d
**  - - - - - - - - - -
**
**  Gregorian Calendar to Julian Date.
**
**  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 ERFA
**     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).
**
**  Copyright (C) 2013-2020, NumFOCUS Foundation.
**  Derived, with permission, from the SOFA library.  See notes at end of file.
*/
{
   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;