choose_volume(struct archive_read *a, struct iso9660 *iso9660)
{
	struct file_info *file;
	int64_t skipsize;
	struct vd *vd;
	const void *block;
	char seenJoliet;

	vd = &(iso9660->primary);
	if (!iso9660->opt_support_joliet)
		iso9660->seenJoliet = 0;
	if (iso9660->seenJoliet &&
		vd->location > iso9660->joliet.location)
 		/* This condition is unlikely; by way of caution. */
 		vd = &(iso9660->joliet);
 
	skipsize = LOGICAL_BLOCK_SIZE * vd->location;
 	skipsize = __archive_read_consume(a, skipsize);
 	if (skipsize < 0)
 		return ((int)skipsize);
	iso9660->current_position = skipsize;

	block = __archive_read_ahead(a, vd->size, NULL);
	if (block == NULL) {
		archive_set_error(&a->archive, ARCHIVE_ERRNO_MISC,
		    "Failed to read full block when scanning "
		    "ISO9660 directory list");
		return (ARCHIVE_FATAL);
	}

	/*
	 * While reading Root Directory, flag seenJoliet must be zero to
	 * avoid converting special name 0x00(Current Directory) and
	 * next byte to UCS2.
	 */
	seenJoliet = iso9660->seenJoliet;/* Save flag. */
	iso9660->seenJoliet = 0;
	file = parse_file_info(a, NULL, block);
	if (file == NULL)
		return (ARCHIVE_FATAL);
	iso9660->seenJoliet = seenJoliet;

	/*
	 * If the iso image has both RockRidge and Joliet, we preferentially
	 * use RockRidge Extensions rather than Joliet ones.
	 */
	if (vd == &(iso9660->primary) && iso9660->seenRockridge
	    && iso9660->seenJoliet)
		iso9660->seenJoliet = 0;

	if (vd == &(iso9660->primary) && !iso9660->seenRockridge
 	    && iso9660->seenJoliet) {
 		/* Switch reading data from primary to joliet. */
 		vd = &(iso9660->joliet);
		skipsize = LOGICAL_BLOCK_SIZE * vd->location;
 		skipsize -= iso9660->current_position;
 		skipsize = __archive_read_consume(a, skipsize);
 		if (skipsize < 0)
			return ((int)skipsize);
		iso9660->current_position += skipsize;

		block = __archive_read_ahead(a, vd->size, NULL);
		if (block == NULL) {
			archive_set_error(&a->archive, ARCHIVE_ERRNO_MISC,
			    "Failed to read full block when scanning "
			    "ISO9660 directory list");
			return (ARCHIVE_FATAL);
		}
		iso9660->seenJoliet = 0;
		file = parse_file_info(a, NULL, block);
		if (file == NULL)
			return (ARCHIVE_FATAL);
		iso9660->seenJoliet = seenJoliet;
	}

	/* Store the root directory in the pending list. */
	if (add_entry(a, iso9660, file) != ARCHIVE_OK)
		return (ARCHIVE_FATAL);
	if (iso9660->seenRockridge) {
		a->archive.archive_format = ARCHIVE_FORMAT_ISO9660_ROCKRIDGE;
		a->archive.archive_format_name =
		    "ISO9660 with Rockridge extensions";
	}

	return (ARCHIVE_OK);
}

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.