casez(sel[31:0])
32'b??????????????????????????????1: a = 0;
32'b?????????????????????????????10: a = 1;
32'b????????????????????????????100: a = 0;
32'b???????????????????????????1000: a = 1;
32'b??????????????????????????10000: a = 0;
......省略..................
32'b100000000000000000000000000: a = 1;
default: a =0;
encase
Warning (10762): Verilog HDL Case Statement warning at **: can't check case statement for completeness because the case expression has too many possible states