cross correlation vs FFT

Dear all,

I have two signals which I want to test the correlation of the image by
comparing two procedures, the cross correlation and fast fourier
transform. I do that in matlab, but I have a problem that I don't know how
to use a function correctly. Here is my code;



xt = 2*(rand (1024,1)-0.5);

yt = rand (1024,1);        
for i=1:1024;
    yt(i)=0;
end;

i=1;
for hh=501:532;             
    yt(i)=xt(hh);
    i=i+1;
end;

rk = rand (1024,1);                           
for g=1:1024;               
    rk(g) = 0;               
end;                        

%-----------------------------------------------------------------------
%calculation using normal cross correlation.

for k=0:992;                
    j=1;
    for i=k:31+k;
        rk(k+1) = rk(k+1) + xt(i+1)*yt(j);
        j = j+1;
    end;
    rk(k+1) = rk(k+1)/32;
end;

for k=993:1023;
    j=1;
    d=0;
    for i=k:31+k;
        if i<=1023;
            rk(k+1) = rk(k+1) + xt(i+1)*yt(j);
        else;                                       
            rk(k+1) = rk(k+1) + xt(d+1)*yt(j);
            d=d+1;
        end;
        j = j+1;
    end;
    rk(k+1) = rk(k+1)/32;
end;

%-----------------------------------------------------------------------
%calculation using FFT correlation.

N=32;
r1=fft(xt);
r2=fft(yt);
r3=conj(r2);
z=(ifft(r1.*r3))/N;



As you can see that I have generated two random signals from -1 to 1 for
1,024 points, one fo xt and another one for yt. Then I copied 501 to 532
from xt into yt at the first 32 points of yt and for other points I set to
zero for testing purpose. 

I tried to calculate the cross correlation by using function 'crosscorr'
and 'xcorr' from matlab but neither of these gave me the result of 1024
points as I expected. It gave me the double size (2048 points) instead
which I don't know why. So I did the calculation by using equation of
cross correlation by theory I have read, which is 

r(k)= 1/N(Ex(n)y(n-k)) where E=summation of n=0 to N

The graph I got from this equation was matched with those I got from FFT
that I have done at the end, which should be corrected because I followed
the procedure exactly, but I still need to know how to use the matlab
function to do the cross correlation since it will save time when I
increase the number N points and also for the 2D correlation I won't have
to think all of those equation again.

I'm doing this for a first time and don't have much knowledge on this, so
thanks for any help.

regards,
sangthong