function[u]=algspa(N,u0,X)
N=4; u0=7;X=[1 0 1 0];
u=[];val=u0;
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for iter=1:P_MAX
 xor=0;

 u=[u val];
 lung=length(u);

 for i=1:N
   xor=bitxor(bitget(u(lung),i),xor);
 end
 val=bitshift(u(lung),-1);
 val=bitset(val,N,xor);

 disp('val =');
 val
 if (val==u(1))
       break;
   end
 end
%%%%%%%%%%%%%%%%%%%%