题目：
A “population count” circuit counts the number of '1’s in an input vector. Build a population count circuit for a 255-bit input vector.

解题：

module top_module( input [254:0] in,output [7:0] out );int i;always@(*)beginout=8'b0;for(i=0;i<255;i++)if(in[i]==1)out=out+1'b1;elseout=out;end
endmodule

结果正确：