FFA（快速折叠算法）

				function y = FFA(x, fold_period)
				fold_length = length(x);
				y = 0;
				if (fold_period ~= fold_length) && (fold_period ~= 0) && (fold_period ~= 1)
				    r = fold_length / fold_period; 
				    m = log2(2^nextpow2(r));
				    N = 2^m; 
				    if r < N 
				        x=[x,zeros(1,(N*fold_period - length(x)))];
				    end 
				    fold_length = length(x);
				    for mm = 1 : m   
				        Nmr = 2^mm * fold_period; 
				        for n = 1 : Nmr : fold_length
				            shift_length = 0;
				            step = 0;
				            for k = n : fold_period : (Nmr/2+n-1) 
				                kp = k + Nmr/2; 
				                temp1 = cycle_left_shift(x(kp:(kp+fold_period-1)),...
				                    fold_period,shift_length);
				                temp2 = cycle_left_shift(x(kp:(kp+fold_period-1)),...
				                    fold_period,(shift_length+1));
				                y((k+step*fold_period):(k+(step+1)*fold_period-1)) =...
				                    x(k:(k+fold_period-1)) + temp1; 
				                y((k+(step+1)*fold_period):(k+(step+2)*fold_period-1)) =...
				                    x(k:(k+fold_period-1)) + temp2; 
				                shift_length = shift_length + 1;
				                step = step + 1;
				            end 
				        end 
				        x = y;
				    end
				    y = x;
				else if fold_period == 1
				        for i = 1 : fold_length
				            y(1) = y(1) + x(i);
				        end
				        for j = 2 : fold_length
				            y(j) = y(1);
				        end
				    else
				        y = x;
				    end
				end
				end