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    <h1>CodeMirror: Verilog mode</h1>

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/* Verilog demo code */

module butterfly
  #(
    parameter WIDTH = 32,
    parameter MWIDTH = 1
    )
   (
    input wire                     clk,
    input wire                     rst_n,
    // m_in contains data that passes through this block with no change.
    input wire [MWIDTH-1:0]        m_in,
    // The twiddle factor.
    input wire signed [WIDTH-1:0]  w,
    // XA
    input wire signed [WIDTH-1:0]  xa,
    // XB
    input wire signed [WIDTH-1:0]  xb,
    // Set to 1 when new data is present on inputs.
    input wire                     x_nd,
    // delayed version of m_in.
    output reg [MWIDTH-1:0]        m_out,
    // YA = XA + W*XB
    // YB = XA - W*XB
    output wire signed [WIDTH-1:0] ya,
    output wire signed [WIDTH-1:0] yb,
    output reg                     y_nd,
    output reg                     error
    );

   // Set wire to the real and imag parts for convenience.
   wire signed [WIDTH/2-1:0]        xa_re;
   wire signed [WIDTH/2-1:0]        xa_im;
   assign xa_re = xa[WIDTH-1:WIDTH/2];
   assign xa_im = xa[WIDTH/2-1:0];
   wire signed [WIDTH/2-1: 0]       ya_re;
   wire signed [WIDTH/2-1: 0]       ya_im;
   assign ya = {ya_re, ya_im};
   wire signed [WIDTH/2-1: 0]       yb_re;
   wire signed [WIDTH/2-1: 0]       yb_im;
   assign yb = {yb_re, yb_im};

   // Delayed stuff.
   reg signed [WIDTH/2-1:0]         xa_re_z;
   reg signed [WIDTH/2-1:0]         xa_im_z;
   // Output of multiplier
   wire signed [WIDTH-1:0]          xbw;
   wire signed [WIDTH/2-1:0]        xbw_re;
   wire signed [WIDTH/2-1:0]        xbw_im;
   assign xbw_re = xbw[WIDTH-1:WIDTH/2];
   assign xbw_im = xbw[WIDTH/2-1:0];
   // Do summing
   // I don't think we should get overflow here because of the
   // size of the twiddle factors.
   // If we do testing should catch it.
   assign ya_re = xa_re_z + xbw_re;
   assign ya_im = xa_im_z + xbw_im;
   assign yb_re = xa_re_z - xbw_re;
   assign yb_im = xa_im_z - xbw_im;
   
   // Create the multiply module.
   multiply_complex #(WIDTH) multiply_complex_0
     (.clk(clk),
      .rst_n(rst_n),
      .x(xb),
      .y(w),
      .z(xbw)
      );

  always @ (posedge clk)
    begin
       if (!rst_n)
         begin
            y_nd <= 1'b0;
            error <= 1'b0;
         end
       else
         begin
            // Set delay for x_nd_old and m.
            y_nd <= x_nd;
            m_out <= m_in;
            if (x_nd)
              begin
                 xa_re_z <= xa_re/2;
                 xa_im_z <= xa_im/2;
              end
         end
    end
   
endmodule
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    <p>Simple mode that tries to handle Verilog-like languages as well as it
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