priority encoder

A priority encoder is a combinational circuit that, when given an input bit vector, outputs the position of the first 1 bit in the vector. For example, a 8-bit priority encoder given the input 8'b10010000 would output 3'd4, because bit[4] is first bit that is high.

Build a 4-bit priority encoder. For this problem, if none of the input bits are high (i.e., input is zero), output zero. Note that a 4-bit number has 16 possible combinations.

Always case2 - HDLBits (01xz.net)

完成一个优先编码器，只不过这个优先编码器是倒着来从小位开始的，比如第0位出现了1，则编码结果为0；第0位为0，第1位出现了1，则编码结果为1；第0位为0，第1位为0，第2位为1，则编码结果为2，依此类推

所以这样下来这道题就容易理解了，编写代码即可

// synthesis verilog_input_version verilog_2001
module top_module (
    input [3:0] in,
    output reg [1:0] pos  );
 always @(*)begin 
        if(in[0])begin
            pos<=2'd0;
        end
        else if(in[1])begin
            pos<=2'd1;
        end
        else if(in[2])begin
            pos<=2'd2;
        end
        else if(in[3])begin
            pos<=2'd3;
        end
        else begin
            pos<=2'd0;
        end
    end   

endmodule