//2024-1-12   姜青羊
//always的if-else语句，实现多路选择逻辑

module fn_sw (
                        a,
                        b,
                        sel,
                        y
                    );

input                   a,b;
input[1:0]              sel;

output                  y;
reg                     y;

always @(*)begin
    if(sel==00)
      y=a&b;
    else if(sel==01)
      y=a|b;
    else if(sel==10)
      y=a^b;
    else
      y=~(a^b);
end
   
endmodule


//----------------testbench------------

module tn_fn_sw ();

reg[3:0]                 selab;                     
wire                     yy;

initial begin
                         selab=0000;
                #200     $stop;    
end

always #10               selab=selab+1;

fn_sw u_fn_sw (
                        .a(selab[1]),
                        .b(selab[0]),
                        .sel(selab[3:2]),
                        .y(yy)
                    ); 

endmodule