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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);