module multiplier(prod, busy, mc, mp, clk, start);
output [5:0] prod;
output busy;
input [2:0] mc, mp;
input clk, start;
reg [2:0] A, Q, M;
reg Q_1;
reg [3:0] count;

wire [2:0] sum, difference;

always @(posedge clk)
begin
    if (start) begin
        A <= 3'b0;
        M <= mc;
        Q <= mp;
        Q_1 <= 1'b0;
        count <= 4'b0;
    end
    else begin
        case ({Q[0], Q_1})
            2'b0_1 : {A, Q, Q_1} <= {sum[2], sum, Q};
            2'b1_0 : {A, Q, Q_1} <= {difference[2], difference, Q};
            default: {A, Q, Q_1} <= {A[2], A, Q};
        endcase
        count <= count + 1'b1;
    end
end

alu adder (sum, A, M, 1'b0);
alu subtracter (difference, A, ~M, 1'b1);

assign prod = {A, Q};
assign busy = (count < 2);



endmodule
//The following is an alu.
//It is an adder, but capable of subtraction:
//Recall that subtraction means adding the two's complement--
//a - b = a + (-b) = a + (inverted b + 1)
//The 1 will be coming in as cin (carry-in)
module alu(out, a, b, cin);
output [2:0] out;
input [2:0] a;
input [2:0] b;
input cin;

assign out = a + b + cin;

endmodule