source: trunk/MagicSoft/slalib/cldj.c@ 14342

#include "slalib.h"
#include "slamac.h"
void slaCldj ( int iy, int im, int id, double *djm, int *j )
/*
**  - - - - - - - -
**   s l a C l d j
**  - - - - - - - -
**
**  Gregorian calendar to Modified Julian Date.
**
**  Given:
**     iy,im,id     int    year, month, day in Gregorian calendar
**
**  Returned:
**     *djm         double Modified Julian Date (JD-2400000.5) for 0 hrs
**     *j           int    status:
**                           0 = OK
**                           1 = bad year   (MJD not computed)
**                           2 = bad month  (MJD not computed)
**                           3 = bad day    (MJD computed)
**
**  The year must be -4699 (i.e. 4700BC) or later.
**
**  The algorithm is derived from that of Hatcher 1984 (QJRAS 25, 53-55).
**
**  Last revision:   29 August 1994
**
**  Copyright P.T.Wallace.  All rights reserved.
*/
{
   long iyL, imL;

/* Month lengths in days */
   static int mtab[12] = { 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 };



/* Validate year */
   if ( iy < -4699 ) { *j = 1; return; }

/* Validate month */
   if ( ( im < 1 ) || ( im > 12 ) ) { *j = 2; return; }

/* Allow for leap year */
   mtab[1] = ( ( ( iy % 4 ) == 0 ) &&
             ( ( ( iy % 100 ) != 0 ) || ( ( iy % 400 ) == 0 ) ) ) ?
             29 : 28;

/* Validate day */
   *j = ( id < 1 || id > mtab[im-1] ) ? 3 : 0;

/* Lengthen year and month numbers to avoid overflow */
   iyL = (long) iy;
   imL = (long) im;

/* Perform the conversion */
   *djm = (double)
        ( ( 1461L * ( iyL - ( 12L - imL ) / 10L + 4712L ) ) / 4L
        + ( 306L * ( ( imL + 9L ) % 12L ) + 5L ) / 10L
        - ( 3L * ( ( iyL - ( 12L - imL ) / 10L + 4900L ) / 100L ) ) / 4L
        + (long) id - 2399904L );
}