Distributed Memory Techniques for Classical Simulation of Quantum Circuits, Ryan LaRose, June 21, 2018.

Excerpts:

 
QCE does this using an equivalent single loop, e.g. for the Hadamard transformation on qubit i: 
  s2 = sqrt(2)/2;  k = 0;  i1 = 1 << i; // i1 = 0...010...0, i'th bit = 1

  while( k < n) // k will have i'th bit = 0, k1 will have i'th bit = 1
  {
    k1 = k | i1;  t0 = q[k];  t1 = q[k1];

    q[k] = s2*(t0+t1);  q[k1] = s2*(t0-t1);

    ++k;  k += (k & i1); // skip k values with i'th bit = 1
  }