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   //

   // Internal wires and regs

   //

   reg [5:0]                            serial_mul_cnt;

   reg                                  mul_free;

   wire [WIDTH-1:0]                     x;

   wire [WIDTH-1:0]                     y;

   reg ex_freeze_r;

   always @( posedge clk)

     if (reset) ex_freeze_r <= 1'b1;

     else       ex_freeze_r <= ex_freeze;

   //

   // Combinatorial logic

   //

   assign x = a_in;

   assign y = b_in;

`ifndef SYNTHESIS

always@(posedge clk)

if((serial_mul_cnt == 6'b000000) && ex_freeze && ex_freeze_r)

begin

   $display("%t %m mul (%x,%x,%x);",$realtime,a_in,b_in,mul_prod_r );

end

`endif

   always @( posedge clk)

     if (reset) begin

        mul_prod_r <=  64'h0000_0000_0000_0000;

        serial_mul_cnt <= 6'd0;

        mul_free <= 1'b1;

     end

     else if (|serial_mul_cnt) begin

        serial_mul_cnt <= serial_mul_cnt - 6'd1;

        if (mul_prod_r[0])

          mul_prod_r[(WIDTH*2)-1:WIDTH-1] <= mul_prod_r[(WIDTH*2)-1:WIDTH] + x;

        else

          mul_prod_r[(WIDTH*2)-1:WIDTH-1] <= {1'b0,mul_prod_r[(WIDTH*2)-1: WIDTH]};

        mul_prod_r[WIDTH-2:0] <= mul_prod_r[WIDTH-1:1];

     end

     else if (alu_op_mul && mul_free) begin

        mul_prod_r <= {32'd0, y};

        mul_free <= 0;

        serial_mul_cnt <= 6'b10_0000;

     end

     else if (!ex_freeze | mul_free) begin

        mul_free <= 1'b1;

     end

   assign mul_stall = (|serial_mul_cnt) | (alu_op_mul & !ex_freeze_r);