44. Bus Error Checker

How do you plan to solve it?

module error_checker_xz (input [7:0] bus, output all_known, output has_unknown, output [7:0] bus_if_known);
wire any_xz = (^(bus ^ bus)) === 1'bx;
assign has_unknown = any_xz;
assign all_known = ~any_xz;
assign bus_if_known = {8{all_known}} & bus;  
endmodule