// mult_20x20_carsav.v
//
// 20 x 20-bit signed pipelined multiplier
//    with two product outputs that are meant to simulate carry-save format.
//    They are a valid carry-save format but are not exactly what would 
//    normally appear with a real hardware multiplier.
//    Inputs and outputs are registered.
//
// 2006/02/18  Written

`timescale 10ps/1ps
`celldefine
module mult_20x20_carsav (
   ina,
   inb,
   out_0,
   out_1,
   clk
   );

   input         [19:0]         ina;
   input         [19:0]         inb;
   input                        clk;

   output        [39:0]         out_0;
   output        [39:0]         out_1;


   //----- declarations
   reg         [19:0]           r_ina;
   reg         [19:0]           r_inb;
   wire        [39:0]           c_out_0;
   wire        [39:0]           c_out_1;
   reg         [39:0]           out_0;
   reg         [39:0]           out_1;
   

   //----- main
   // ina = ina[18:0] - (ina[19] << 19);
   // inb = inb[18:0] - (inb[19] << 19);

   assign c_out_0 =   r_inb[18:0]      * (r_ina[18:0] - (r_ina[19] << 19));
   assign c_out_1 = -(r_inb[19] << 19) * (r_ina[18:0] - (r_ina[19] << 19));

   always @(posedge clk) begin
      r_ina   <= #1 ina;
      r_inb   <= #1 inb;
      out_0   <= #1 c_out_0;
      out_1   <= #1 c_out_1;
   end


endmodule  // mult_20x20_carsav
`endcelldefine