/*$Id: sum_2d_array.c,v 1.2 1999/10/22 17:20:11 ali Exp $
**	
**
** NAME:
**
** 	sum_2d_array.c
**
** PURPOSE:
**	This C function is used to demonstrate how to read a 2 dimensional
**      IDL array. It calculates the sum of a subsection of the input array.
**      The subsection is specified like this:
**
**  0,0--------------------------------------------x_size-1,0
**  |
**  |    x_start,y_start------------x_end,y_start
**  |    |                                    |
**  |    | this region will be summed         |
**  |    |                                    |
**  |    x_start,y_end--------------x_end,y_end
**  |
**  |
**  0,y_size-1
**
**      this is equivalent to the IDL statement:
**      IDL>r = TOTAL(arr[x_start:x_end,y_start:y_end],/DOUBLE)
**
** CATEGORY:
**	Dynamic Link
**
** CALLING SEQUENCE:
**	This function is called in IDL by using the following commands:
**
**      IDL>arr =  DINDGEN(20,20)
**      IDL>x_start = 5L
**      IDL>x_end = 10L
**      IDL>x_size = 20L
**      IDL>y_start = 5L
**      IDL>y_end = 10L
**      IDL>y_size = 20L
**      IDL>r = CALL_EXTERNAL('sum_2d_array.so','sum_2d_array',$
                              arr,x_start,x_end,x_size,$
                              y_start,y_end,y_size,/D_VALUE)
**
**      See sum_2d_array.pro for a more complete calling sequence.
**
** INPUTS:
**      arr - a 2 dimensional IDL array (type is double)
**      x_start - X index of the start of the subsection (type is long)
**      x_end   - X index of the end of the subsection   (type is long)
**      x_size  - size of the X dimension of arr         (type is long)
**      y_start - Y index of the start of the subsection (type is long)
**      y_end   - Y index of the end of the subsection   (type is long)
**      y_size  - size of the Y dimension of arr         (type is long)
**
** OUTPUTS:
**	The function returns the sum of all of the elements of the
**      subsection of the array.
**
** SIDE EFFECTS:
**	None.
**
** RESTRICTIONS:
**
**      None.
**
** MODIFICATION HISTORY:
**	Written May, 1998 JJG
**
*/

#include <stdio.h>
#include "export.h"

/* make sure that this routine is exported on the Macintosh */
#if defined(__POWERPC__)
__declspec(export) double sum_2d_array(int argc,void* argv[]);
#endif

double IDL_STDCALL sum_2d_array(int argc,void* argv[])
{
     /* since we didn't know the dimensions of the array
        at compile time, we must treat the input array
        as if it were a one dimensional vector. */
     double* arr;
     IDL_LONG x_start,x_end,x_size,y_start,y_end,y_size,x,y;

     double result = 0.0;

     if (argc != 7) return 0.0;

     arr = (double*)argv[0];
     x_start = *(int*)argv[1];
     x_end = *(int*)argv[2];
     x_size = *(int*)argv[3];
     y_start = *(int*)argv[4];
     y_end = *(int*)argv[5];
     y_size = *(int*)argv[6];

     /* make sure that we don't go outside the array.
        strictly speaking, this is redundant since identical
        checks are performed in the IDL wrapper routine.
	IDL_MIN() and IDL_MAX() are macros from export.h */
     x_start = IDL_MAX(x_start,0);
     y_start = IDL_MAX(y_start,0);
     x_end = IDL_MIN(x_end,x_size-1);
     y_end = IDL_MIN(y_end,y_size-1);

     /* loop through the subsection */
     for (y = y_start;y <= y_end;y++)
       for (x = x_start;x <= x_end;x++)
	 result += arr[x + y*x_size]; /* build the 2d index: arr[x,y] */

     return result;
}