function y = GrayCoding(x,Nbits);
% y = GrayCoding(x,Nbits);
%
% reverses the systematic Gray code of the Nbit number x.

% S Weiss, 10/10/2000


% x in [0; 2^Nbits-1]

y = 0;
dummy = 0;

for i = Nbits:-1:1,
    A = floor(x/2^(i-1));
    if (A==1)    		% i-th bit is set
	x = x - 2^(i-1);
    end;
    if (A~=dummy),
       y = y+2^(i-1);
       dummy = 1;
    else
       dummy = 0;	
    end;
end;