Comment by tzs

I took that into account, although it may not have been clear because I tried to describe it in words rather than code.

What I was suggesting was something like this (in pseudocode):

  int previous_leftmost = 64;
  while (mask != 0) {
    leftmost = find_leftmost(mask);
    mask ^= 1u << leftmost;
    while (--previous_leftmost > leftmost)
      func_false(previous_leftmost);
    func_true(leftmost);
  }