对255取余数

`timescale 1ns / 1ps
//对255取余数
//网上的那个用LUT
//至于说逼近法，我就不考虑了
module div_255(                          
 input dividend,              
 input clk,                           
 input rst_n,  
 output [7:0] remainder               
    );
 parameter dividor = 8'hff;
 reg [7:0] shifter;
 reg [2:0] count;
 reg flag;
 always @(posedge clk or negedge rst_n)
 begin
 if(!rst_n)
 begin
 shifter <= 8'h00;
 count <= 3'b000;
 flag <= 1'b0;
 end
 else 
 begin
 if(count==3'b111)
 begin
 count <= 3'b000;
 flag <= 1'b1;
 end
 else
 begin
 count <= count + 1'b1;
 flag <= 1'b0;
 end 
 shifter[0]<=shifter[7]+dividend;
 shifter[1]<=shifter[0]+dividend;
 shifter[2]<=shifter[1]+dividend;
 shifter[3]<=shifter[2]+dividend;
 shifter[4]<=shifter[3]+dividend;
 shifter[5]<=shifter[4]+dividend;
 shifter[6]<=shifter[5]+dividend;
 shifter[7]<=shifter[6]+dividend;
 end 
 end
 assign remainder = (flag)?shifter:8'hzz;
endmodule