input CLOCK;
input START;
input [7:0] C;
input [7:0] D;
output [15:0] P;

reg [15:0] P;
reg [7:0]  M;
reg [7:0]  Q;
reg [7:0]  A;
reg        Qd;
reg [16:0] SHIFT;

integer CNT;

always @(posedge START or posedge CLOCK) begin
    if (START) begin
        P <= 0;
        M <= C;
        Q <= D;
        A <= 0;
        Qd <= 0;
        SHIFT <= 0;

        CNT <= 8;
    end
    else begin
        if (CNT != 0) begin
            case ({Q[0], Qd})
                2'b01: begin
                    A <= A + M;
                    SHIFT <= {A[7], A, Q};
                end

                2'b10: begin
                    A <= A + ~M + 1;
                    SHIFT <= {A[7], A, Q};
                end

                2'b00, 2'b11: begin
                    SHIFT <= {A[7], A, Q};
                end
            endcase
            CNT <= CNT - 1;
        end
        else P <= SHIFT;
    end
end