Global sxbp_direction_t: This should be changed to an enum.
Global sxbp_dump_spiral (sxbp_spiral_t spiral, sxbp_buffer_t *buffer): The return type of this function could be changed to sxbp_status_t, as none of the serialisation-specific error codes can ever be returned by it.
Global sxbp_plot_spiral (sxbp_spiral_t *spiral, sxbp_length_t perfection_threshold, uint32_t max_line, void(*progress_callback)(sxbp_spiral_t *spiral, uint32_t latest_line, uint32_t target_line, void *progress_callback_user_data), void *progress_callback_user_data): Improve the efficiency of this function so that it runs much faster.
Global sxbp_rotation_t: This might need to be changed to an enum.
Global sxbp_spiral_points (sxbp_spiral_t spiral, sxbp_co_ord_array_t *output, sxbp_co_ord_t start_point, size_t start, size_t end): Might also need to add an assertion to check that end is never less than start.
Global sxbp_sum_lines (sxbp_spiral_t spiral, size_t start, size_t end): Might also need to add an assertion to check that end is never less than start.