/* img_diff.c diff two imgfiles.
img_diff file1 file2 > diff.out
23 Feb 2009 WHFS
Updates old "diff" to be independent on file size.
*/

#include "img_predict.h"

int main (int argc, char **argv) {

	short int *x, y;
	int	i, nx, ny, n;
	FILE *fp;
	
	if (argc != 3) {
		fprintf (stderr, "usage: img_diff file1.img file2.img > diffout.img\n");
		exit (-1);
	}
	
	if (check_imgfile_size (argv[1], &nx, &ny) ) {
		fprintf (stderr, "img_diff:  FATAL ERROR.  Cannot understand size of %s\n", argv[1]);
		exit (EXIT_FAILURE);
	}
	
	n = nx * ny;
	if ( (x = (short int *) malloc ( (size_t) (2 * n) ) ) == NULL) {
		fprintf (stderr, "img_diff:  FATAL ERROR.  Cannot malloc %d bytes\n", 2*n);
		exit (EXIT_FAILURE);
	}

	if ( (fp = fopen(argv[1], "r") ) == NULL) {
		fprintf (stderr, "img_diff:  FATAL ERROR.  Cannot open r %s\n", argv[1]);
		exit (-1);
	}
	if ( (fread ( (void *)x, (size_t)2, (size_t)n, fp) ) != n) {
		fprintf (stderr, "img_diff:  FATAL ERROR reading %s\n", argv[1]);
		exit (-1);
	}
	fclose (fp);
	
	if ( (fp = fopen(argv[2], "r") ) == NULL) {
		fprintf (stderr, "img_diff:  FATAL ERROR.  Cannot open r %s\n", argv[2]);
		exit (-1);
	}
	for (i = 0; i < n; i++) {
		if ( (fread ( (void *)&y, (size_t)2, (size_t)1, fp) ) != 1) {
			fprintf (stderr, "img_diff:  FATAL ERROR reading i = %d from %s\n", i, argv[2]);
			exit (-1);
		}
		x[i] -= y;
	}
	fclose (fp);
	
	if ( (fwrite( (void *)x, (size_t)2, (size_t)n, stdout) ) != n) {
		fprintf (stderr, "img_diff:  FATAL ERROR writing diff to stdout\n");
		exit (-1);
	}
	fclose (fp);
	
	free ((void *)x);

	exit (EXIT_SUCCESS);
}