/* String manipulator FSM that removes the second 1 from any
 * set of consecutive 1 inputs.
 */
module fsm (input  logic clk, reset, in,
            output logic out);

	// present and next state
	enum logic [1:0] {S0, S1, S3} ps, ns;
	
	// next state logic
	always_comb
		case (ps)
			S0: if (in) ns = S1;
			    else    ns = S0;
			S1: if (in) ns = S3;
				 else		ns = S0;
			S3: if (in) ns = S3;
				 else		ns = S0;
		endcase
		
	// output logic
	assign out = in & (ps[1] | ~ps[0]);
	
	// sequential logic (DFFs)
	// synchronous reset
	always_ff @(posedge clk)
		if (reset)
			ps <= S0;  // reset state
		else
			ps <= ns;
	
endmodule  // fsm