_gd2GetHeader (gdIOCtxPtr in, int *sx, int *sy,
               int *cs, int *vers, int *fmt, int *ncx, int *ncy,
               t_chunk_info ** chunkIdx)
{
	int i;
	int ch;
	char id[5];
	t_chunk_info *cidx;
	int sidx;
	int nc;

	GD2_DBG (printf ("Reading gd2 header info\n"));

	for (i = 0; i < 4; i++) {
		ch = gdGetC (in);
		if (ch == EOF) {
			goto fail1;
		};
		id[i] = ch;
	};
	id[4] = 0;

	GD2_DBG (printf ("Got file code: %s\n", id));

	/* Equiv. of 'magick'.  */
	if (strcmp (id, GD2_ID) != 0) {
		GD2_DBG (printf ("Not a valid gd2 file\n"));
		goto fail1;
	};

	/* Version */
	if (gdGetWord (vers, in) != 1) {
		goto fail1;
	};
	GD2_DBG (printf ("Version: %d\n", *vers));

	if ((*vers != 1) && (*vers != 2)) {
		GD2_DBG (printf ("Bad version: %d\n", *vers));
		goto fail1;
	};

	/* Image Size */
	if (!gdGetWord (sx, in)) {
		GD2_DBG (printf ("Could not get x-size\n"));
		goto fail1;
	}
	if (!gdGetWord (sy, in)) {
		GD2_DBG (printf ("Could not get y-size\n"));
		goto fail1;
	}
	GD2_DBG (printf ("Image is %dx%d\n", *sx, *sy));

	/* Chunk Size (pixels, not bytes!) */
	if (gdGetWord (cs, in) != 1) {
		goto fail1;
	};
	GD2_DBG (printf ("ChunkSize: %d\n", *cs));

	if ((*cs < GD2_CHUNKSIZE_MIN) || (*cs > GD2_CHUNKSIZE_MAX)) {
		GD2_DBG (printf ("Bad chunk size: %d\n", *cs));
		goto fail1;
	};

	/* Data Format */
	if (gdGetWord (fmt, in) != 1) {
		goto fail1;
	};
	GD2_DBG (printf ("Format: %d\n", *fmt));

	if ((*fmt != GD2_FMT_RAW) && (*fmt != GD2_FMT_COMPRESSED) &&
	        (*fmt != GD2_FMT_TRUECOLOR_RAW) &&
	        (*fmt != GD2_FMT_TRUECOLOR_COMPRESSED)) {
		GD2_DBG (printf ("Bad data format: %d\n", *fmt));
		goto fail1;
	};


	/* # of chunks wide */
	if (gdGetWord (ncx, in) != 1) {
		goto fail1;
	};
	GD2_DBG (printf ("%d Chunks Wide\n", *ncx));

	/* # of chunks high */
	if (gdGetWord (ncy, in) != 1) {
		goto fail1;
	};
 	GD2_DBG (printf ("%d Chunks vertically\n", *ncy));
 
 	if (gd2_compressed (*fmt)) {
 		nc = (*ncx) * (*ncy);
 
 		GD2_DBG (printf ("Reading %d chunk index entries\n", nc));
		if (overflow2(sizeof(t_chunk_info), nc)) {
			goto fail1;
		}
		sidx = sizeof (t_chunk_info) * nc;
		if (sidx <= 0) {
			goto fail1;
		}

		cidx = gdCalloc (sidx, 1);
		if (cidx == NULL) {
			goto fail1;
		}
		for (i = 0; i < nc; i++) {
			if (gdGetInt (&cidx[i].offset, in) != 1) {
				goto fail2;
			};
			if (gdGetInt (&cidx[i].size, in) != 1) {
				goto fail2;
			};
			if (cidx[i].offset < 0 || cidx[i].size < 0)
				goto fail2;
		};
		*chunkIdx = cidx;
	};

	GD2_DBG (printf ("gd2 header complete\n"));

	return 1;
fail2:
	gdFree(cidx);
fail1:
	return 0;
}

The product performs a calculation that can produce an integer overflow or wraparound when the logic assumes that the resulting value will always be larger than the original value. This occurs when an integer value is incremented to a value that is too large to store in the associated representation. When this occurs, the value may become a very small or negative number.