module rgst #(
	parameter w = 8	//register's width
)(
	input clk,
	input rst_b,	//asynchronous reset; active low
	input [w-1:0] d,
	input ld,
	input clr,	//synchronous reset; active high
	output reg [w-1:0] q
);

	always @ (posedge clk, negedge rst_b)
		if (!rst_b)
			q <= 1'd0;
		else if (clr)
			q <= 1'd0;
		else if (ld)
			q <= d;
endmodule

module atan_const (input [3:0] itr, output reg [15:0] atan);
  always @ (*)
    case (itr)
      4'd0:   atan = 16'h3244;
      4'd1:   atan = 16'h1dac;
      4'd2:   atan = 16'h0fae;
      4'd3:   atan = 16'h07f5;
      4'd4:   atan = 16'h03ff;
      4'd5:   atan = 16'h0200;
      4'd6:   atan = 16'h0100;
      4'd7:   atan = 16'h0080;
      4'd8:   atan = 16'h0040;
      4'd9:   atan = 16'h0020;
      4'd10:  atan = 16'h0010;
      4'd11:  atan = 16'h0008;
      4'd12:  atan = 16'h0004;
      4'd13:  atan = 16'h0002;
      4'd14:  atan = 16'h0001;
      default:atan = 16'h0000;
    endcase
endmodule

module cntr #(parameter w=8)(input clk, rst_b, c_up, clr, output reg [w-1] q);
  always @ (posedge clk, negedge rst_b)
    if (!rst_b)
			q <= 1'd0;
		else if (clr)
			q <= 1'd0;
		else
		  q<=q+c_up;
endmodule

module add_sub (input [15:0] a, b,input s, output [15:0] o);
  assign o = s ? a-b : a+b;
endmodule

module arsh (input [15:0] a, input [3:0] i, output [15:0] o);
  assign o=$unsigned($signed(a)>>>i);
endmodule

module cntr_u(input clk, rst_b, bgn, [3:0] itr, output fin, ld, init);
  reg [2:0] st; wire [2;0] st_next;
  assign st_next[0] = st[0]&~bgn|st[2];
  assign st_next[1] = st[0]& bgn | st[1] &(itr!=4'd15);
  assign st_next[2] = st[1]&(itr==4'd15);
  assign init =st[0]& bgn;
  assign ld=st[0]&bgn|st[1];
  assign fin = st[2];
  always @ (posedge clk,negedge rst_b)
    if(!rst_b)
      st<=3'd1;
    else
      st<=st_next;
endmodule

module cordic (input clk, rst_b, bgn, [15:0] theta, output fin , [15:0] cos);
  wire [15:0] x_new, x_out, y_new, y_out,z_new, z_out,atan,x_rsh,y_rsh;
  wire [3:0] i;
  wire init, ld;
  ctrl_u          u0(.clk(clk),.rst_b(rst_b),.bgn(bgn),.itr(i),.fin(fin), .ld(ld),.init(init));
  cntr #(.w(4))   u1(.clk(clk),.rst_b(rst_b),.c_up(ld),.clr(init),.q(i));
  atan_const      u2(.itr(i),.atan(atan));
  rgst #(.w(16))  u3(.clk(clk),.rst_b(rst_b),.ld(ld),.clr(1'd0),.d(x_new),.q(x_out));
  arsh            u4(.a(y_out),.o(y_rsh));
  add_sub         u5(.a(x_out), .b(y_rsh),.s(~z_out[15]),.o(x_new));
  rgst #(.w(16))  u6(.clk(clk),.rst_b(rst_b),.ld(ld),.clr(1'd0),.d(y_new),.q(y_out));
  arsh            u7(.a(x_out),.o(x_rsh));
  add_sub         u8(.a(y_out), .b(x_rsh),.s(z_out[15]),.o(y_new));
  rgst #(.w(16))  u9(.clk(clk),.rst_b(rst_b),.ld(ld),.clr(1'd0),.d(z_new),.q(z_out));
  add_sub         u10(.a(z_out), .b(atan),.s(~z_out[15]),.o(z_new));
  assign cos+fin?x_out:16'bz;
endmodule

module cordic_tb(output reg clk, rst_b, bgn, [15:0] theta,output fin, [15:0] cos);