A shift-and-add multiplier is a neat way to understand how multiplication works in hardware design. You’ve got the basics down, and I can see why you’d find transitioning to Verilog a bit tricky. Let’s break this down step-by-step!

Setting Up Registers

First, you’ll need to declare your registers. You should have registers for A, B, the result, and a counter to track how many bits you’ve processed. Here’s a simple way to set up your registers:

module shift_add_multiplier (
    input signed [31:0] A, // Your first number (multiplicand)
    input signed [31:0] B, // Your second number (multiplier)
    output reg signed [63:0] result // Result register (wide enough to hold the product)
);

Multiplication Logic

Next, you can use a loop to perform the shift-and-add process. Here’s a basic outline for your main logic:

always @(*) begin
    result = 0; // Initialize result
    // A and B need to be copied since they will be modified
    signed [31:0] a_temp = A;
    signed [31:0] b_temp = B;

    while (b_temp != 0) begin
        if (b_temp[0] == 1) begin
            result = result + a_temp; // Add A to the result if LSB of B is 1
        end
        a_temp = a_temp << 1; // Shift A left
        b_temp = b_temp >> 1; // Shift B right
    end
end

Handling Signed Numbers

Since you want to support signed numbers, ensure that your shifts are performed correctly. In Verilog, shifting a signed number maintains its sign, so you should be good there!

Example Test Bench

To test your multiplier, you could create a simple test bench. Here’s an example you could start with:

module tb_shift_add_multiplier;
    reg signed [31:0] A;
    reg signed [31:0] B;
    wire signed [63:0] result;

    shift_add_multiplier uut (
        .A(A),
        .B(B),
        .result(result)
    );

    initial begin
        // Test Case 1
        A = 5; B = 3; // Expect 15
        #10;
        $display("A = %d, B = %d, Result = %d", A, B, result);

        // Test Case 2
        A = -4; B = 2; // Expect -8
        #10;
        $display("A = %d, B = %d, Result = %d", A, B, result);

        // More test cases can be added here...
        
        $finish;
    end
endmodule

Running the Tests

To simulate the design, you just run your test bench and see if the output matches your expectations. Use a simulator like ModelSim or Vivado. Apply your test cases and check whether the results are what you expect. If you don’t get the correct results, step through your design and see where things might be going wrong.

Conclusion

That’s a simplified overview. The key is to carefully translate the mathematical process of shifting and adding into Verilog code. Once you get the logic down, the syntax will feel more familiar! Keep experimenting with different inputs, and don’t hesitate to ask more questions if you get stuck!