Will fail in case nodes addreess are not monotonically increase/decrease:

Test(SampleTests, TwoNodesTileFourNodesLoopRandomOrder) {
  Node n[6];

  // 4 -> 1 -> 3 -> 0 -> 5 -> 2
  //           ^              |
  //           +--------------+

  n[4].next = &n[1];
  n[1].next = &n[3];
  n[3].next = &n[0];
  n[0].next = &n[5];
  n[5].next = &n[2];
  n[2].next = &n[3];
  
  Node* startNode = &n[4];
  int actual = loop_size(startNode);
  cr_assert_eq(actual, 4,
    "Incorrect answer for TwoNodesTileFourNodesLoopRandomOrder");
}

Hi, maybe my answer came too late. I had the same problem. In toAscii85, if the input string contains only zeros and less than 4 bytes, you should return <!!> if it only contains one zero, <!!!> for two zeros and <!!!!> for 3 zeros. On the other hand, if n = 0 (string length=0) you must return <~~>.