function [rw] = fold(r)
% [rw] = fold(r)
% Fold left wing of vector in "FFT buffer format"
% onto right wing
% J.O. Smith, 1982-2002

   [m,n] = size(r);
   if m*n ~= m+n-1
     error('fold.m: input must be a vector');
   end
   flipped = 0;
   if (m > n)
     n = m;
     r = r.';
     flipped = 1;
   end
   if n < 3, rw = r; return;
   elseif mod(n,2)==1,
       nt = (n+1)/2;
       rw = [ r(1), r(2:nt) + conj(r(n:-1:nt+1)), ...
             0*ones(1,n-nt) ];
   else
       nt = n/2;
       rf = [r(2:nt),0];
       rf = rf + conj(r(n:-1:nt+1));
       rw = [ r(1) , rf , 0*ones(1,n-nt-1) ];
   end;

   if flipped
     rw = rw.';
   end