function y = circonvt(x1,x2,N)% N-point circular convolution between x1 and x2: (time-domain)% -------------------------------------------------------------% [y] = circonvt(x1,x2,N)%  y = output sequence containing the circular convolution% x1 = input sequence of length N1 <= N% x2 = input sequence of length N2 <= N%  N = size of circular buffer%  Method: y(n) = sum (x1(m)*x2((n-m) mod N))% Check for length of x1if length(x1) > N        error('N must be >= the length of x1')end% Check for length of x2if length(x2) > N        error('N must be >= the length of x2')endx1=[x1 zeros(1,N-length(x1))];x2=[x2 zeros(1,N-length(x2))];m = [0:1:N-1];x2 = x2(mod(-m,N)+1);H = zeros(N,N);for n = 1:1:N	H(n,:) = cirshftt(x2,n-1,N);endy = x1*H';