Autocorrelation function without using xcorr

Hello, I have this code trying to plot the autocorrelation of signal E1 without xcorr function

E1f=[E1 zeros(1,1249)];

for L = 0:length(E1)

 for j = 1 : length(E1)

    Rxx(j) = (E1f(j)*E1f(j+L)); 
 end

Rxx_sum(L+1) = sum(Rxx);

Rxx = 0;

end

t1=0:1:length(E1);

plot(t1,Rxx_sum);

However i don't the same result using xcorr. E1 is a vector of complex numbers and has a length of [1,1249]

What am I doing wrong?