ffa.m

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