case (in)
      8'b00000000: out = 2'dx;
      8'b00000001: out = 2'dx;
      8'b00000010: out = 2'dx;
      8'b00000011: out = 2'dx;
[...]
      8'b00110000: out = 2'dx;
      8'b00110001: out = 2'b01;
      8'b00110010: out = 2'dx;
[...]

      8'b10101011: out = 2'dx;
      8'b10101100: out = 2'b10;
      8'b10101101: out = 2'dx;
[...]
      8'b11110100: out = 2'dx;
      8'b11110101: out = 2'b11;
      8'b11110110: out = 2'dx;
[...]
      8'b11111110: out = 2'dx;
      8'b11111111: out = 2'dx;
      endcase