feature/noverlay 30f5220277 1/3: Comment change: explain inheriting "dirty" offsets

[Stefan Monnier]

branch: feature/noverlay
commit 30f52202775155c1d301af3634d0122c3d7851f8
Author: Matt Armstrong <matt@rfc20.org>
Commit: Matt Armstrong <matt@rfc20.org>

    Comment change: explain inheriting "dirty" offsets
    
    ; * src/itree.c (interval_generator_next): explain why the code
    handles inheriting offsets from dirty nodes.
---
 src/itree.c | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/src/itree.c b/src/itree.c
index de16af5b0c..05851007f5 100644
--- a/src/itree.c
+++ b/src/itree.c
@@ -1086,8 +1086,17 @@ interval_tree_inherit_offset (uintmax_t otick, struct 
interval_node *node)
         node->right->offset += node->offset;
       node->offset = 0;
     }
-  /* FIXME: I wonder when/why this condition can be false, and more generally
-     why we'd want to propagate offsets that may not be fully up-to-date.  */
+  /* FIXME: I wonder when/why this condition can be false, and more
+     generally why we'd want to propagate offsets that may not be
+     fully up-to-date. --stef
+
+     Offsets can be inherited from dirty nodes (with out of date
+     otick) during insert and remove.  Offsets aren't inherited
+     downward from the root for these operations so rotations are
+     performed on potentially "dirty" nodes.  We could fix this by
+     always inheriting offsets downward from the root for every insert
+     and remove.  --matt
+  */
   if (node->parent == ITREE_NULL || node->parent->otick == otick)
     node->otick = otick;
 }