module tb2lf; // testbench for the 8-bit unsigned Ladner-Fischer adder
              // exhaustive checking of all 256*256*2 possible cases

reg  [7:0] a, b;  // 8-bit operands
reg  c0;          // carry input
wire [7:0] s;     // 8-bit sum output
wire c8;          // carry output
reg  [8:0] check; // 9-bit value used to check correctess
integer    i, j, k;     // loop variables
integer    num_correct; // counter to keep track of the number correct
integer    num_wrong;   // counter to keep track of the number wrong

// instantiate the 8-bit Ladner-Fischer adder
ladner_fischer lf1(a, b, c0, s, c8);

// exhaustive checking
initial begin
    // initialize the counter variables
    num_correct = 0; num_wrong = 0;

    // loop through all possible cases and record the results
    for (i = 0; i < 256; i = i + 1) begin
        a = i;
        for (j = 0; j < 256; j = j + 1) begin
            b = j;
            for (k = 0; k < 2; k = k + 1) begin
                c0 = k;
                check = a + b + c0;
 
                // compute and check the product
                #10 if ({c8, s} == check)
                   num_correct = num_correct + 1;
                else
                   num_wrong = num_wrong + 1;
 
    // following line is for debugging
    // $display($time, "  %d + %d + %d = %d (%d)", a, b, c0, {c8, s}, check);

            end
        end
    end
 
    // print the final counter values
    $display("num_correct = %d, num_wrong = %d", num_correct, num_wrong);

end

endmodule