double and algorithm in Verilog

Code Verilog - [expand]
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module multiplier(
    input [7:0] a,
    input [7:0] b,
    input clk,
    input reset,
    output reg[7:0] out
    );
reg [7:0] s1,s2,b2;
wire [7:0]t1,t2,u;
wire bi;
reg [2:0] count;
assign bi=b2[7];
assign u= bi? s2:s1;
///////// calculate t1= 2u mod p(31)///////
left_shift shift1(u,t1);
//////// calculate t2= s1+s2 mod p/////
adder_dub add1(s1,s2,1'b0,t2);
 
always @ (posedge clk)
 
if (~reset)
begin
s1=0; s2= a;
count= 3'd7;
 
end
/////////////////////////////////////////////////////////////////////////////
else begin 
if (count >= 0) begin
 
if (bi==1)
begin
s1=t1;
s2=t2;
end
else begin
s1=t2;
s2=t1;
end
count= count-1;
end
out<= s1;
end
//////////////// left shift of input b//////////////////////
always @(posedge clk)
if (~reset) begin
b2=b;
end
else begin
b2= {b2[6:0],1'b0};
end
endmodule