mul4b_addtree.v

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module mul4b_addtree(mul_a,mul_b,mul_out,clk,rst_n);

parameter MUL_WIDTH = 4;
parameter MUL_RESULT = 8;

input     [MUL_WIDTH-1:0]      mul_a;
input     [MUL_WIDTH-1:0]      mul_b;
input                          clk;
input                          rst_n;

output    [MUL_RESULT-1:0]     mul_out;

reg       [MUL_RESULT-1:0]     mul_out;
reg       [MUL_RESULT-1:0]     stored0;
reg       [MUL_RESULT-1:0]     stored1;
reg       [MUL_RESULT-1:0]     stored2;
reg       [MUL_RESULT-1:0]     stored3;
reg       [MUL_RESULT-1:0]     add01;
reg       [MUL_RESULT-1:0]     add23;


always @(posedge clk or negedge rst_n)
begin
  if(!rst_n)
    begin
      mul_out <= 8'b0000_0000;
      stored0 <= 8'b0000_0000;
      stored1 <= 8'b0000_0000;
      stored2 <= 8'b0000_0000;
      stored3 <= 8'b0000_0000;
      add01 <= 8'b0000_0000;
      add23 <= 8'b0000_0000;
    end
  else
    begin
      stored3 <= mul_b[3]?{1'b0,mul_a,3'b0} : 8'b0;
      stored2 <= mul_b[2]?{2'b0,mul_a,2'b0} : 8'b0;
      stored1 <= mul_b[1]?{3'b0,mul_a,1'b0} : 8'b0;
      stored0 <= mul_b[0]?{4'b0,mul_a} : 8'b0;
      add01 <= stored1 + stored0;
      add23 <= stored3 + stored2;
      mul_out <= add01 + add23;
    end
end
endmodule