`timescale 1ns/1ns module calculation( input clk, input rst_n, input [3:0] a, input [3:0] b, output [8:0] c ); reg [8:0] a_r,b_r; reg [8:0] c_r; always @(posedge clk or negedge rst_n) if(~rst_n)begin a_r <= 9'd0; b_r <= 9'd0; end else begin a_r <= a; b_r <= b; end always @(posedge clk or...