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%% Copyright: 2010 Integrated Sytems Laboratory, ETH Zurich
%%            http://www.iis.ee.ethz.ch/~sha3
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function [s] = s0(x)
    a = [0 x(1:31)];
    b = [x(4:32) zeros(1,3)];
    c = circshift(x,[0 -4]);
    d = circshift(x,[0 -19]);
    s = xor(xor(a,b),xor(c,d));