esneider

I wrote that algorithm! A year later I found Hacker's delight, a wonderful book that had a much "faster" version of the same algorithm (less ops).

For anyone interested in this kind of things, you should go read that book. It actually is a delight.

Fair enough... I thought it would be more difficult/inefficient to check for cyclic hierarchies, but it wasn't.

Fixed! Thanks.

Yep, you can also do

  void *p;
  free(p);
  free(p);

Don't get me wrong, I get where you are going. But C philosophy is that libraries shouldn't do expensive checking to detect programmers' errors.