20'd0: instruction <= 32'h20110001; // addi    $s1,    $zero,  1
20'd1: instruction <= 32'h20120002; // addi    $s2,    $zero,  2
20'd2: instruction <= 32'h02319820; // add     $s3,    $s1,    $s1
20'd3: instruction <= 32'h02719820; // add     $s3,    $s3,    $s1
20'd4: instruction <= 32'h20140003; // addi    $s4,    $zero,  3
20'd5: instruction <= 32'h02729820; // add     $s3,    $s3,    $s2