/* see page 59 */

#ifdef ASTROALGO
   #include <math.h>
   #include <stdio.h>
   #include "AstroAlgo.h"

   __declspec(dllexport) short __stdcall
#else
   short
#endif

ShJulianDay(double *pdoJD, double doY, double doM, double doD, short shCalendar)
            /* shCalendar JULIAN for julian, GREGORIAN for gregorian */
   {
   short  shReturnValue      = (short) 0;
   short  shIsLeap           = (short) 0;
   double adoDaysInMonth[12] = {31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};

   if (pdoJD != NULL)
      {
      *pdoJD = (double) 0;
      }

   if (pdoJD == NULL)
      {
      shReturnValue = (short) 1;
      }

   else if ((doM < 1) || (doM > 12))
      {
      shReturnValue = (short) 3;
      }

   else if ((doD < 1) || (doD > adoDaysInMonth[(int) doM - 1]))
      {
      shReturnValue = (short) 4;
      }

   else if (   (shCalendar != (short) JULIAN)
            && (shCalendar != (short) GREGORIAN)
          )
      {
      shReturnValue = (short) 5;
      }

   /* leap year validation */
   else if (ShIsLeapYear(&shIsLeap, (short) doY, shCalendar) != 0)
      {
      shReturnValue = (short) 901;
      }

   else if ((doM == 2) && (doD == 29) && (shIsLeap != 1))
      {
      shReturnValue = (short) 101;
      }

   else
      {
      double doA = (double) 0;
      double doB = (double) 0;

      if (doM <= 2)
         {
         doY -= (double)  1;
         doM += (double) 12;
         }

      doA = floor(doY / (double) 100);
      if (shCalendar == GREGORIAN)
         {
         doB = ((double) 2 - doA) + floor(doA / (double) 4);
         }

      #if 0
      (void) fprintf(stdout, "doA = %f, doB = %f\n", doA, doB);
      #endif

      *pdoJD =   floor((double) 365.25   * (doY + (double) 4716))
              + floor((double)  30.6001 * (doM + (double)    1))
              + doD + doB - (double) 1524.5;
      }

   return shReturnValue;
   }