Messages in this thread | | | Subject | Re: [PATCH] rbtree: undo augmented damage -v2 | From | Suresh Siddha <> | Date | Wed, 02 Jun 2010 14:11:14 -0700 |
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On Tue, 2010-06-01 at 11:42 -0700, Peter Zijlstra wrote: > On Tue, 2010-06-01 at 11:09 -0700, Venkatesh Pallipadi wrote: > > On Tue, Jun 1, 2010 at 10:42 AM, Peter Zijlstra <peterz@infradead.org> wrote: > > > On Tue, 2010-06-01 at 10:34 -0700, Venkatesh Pallipadi wrote: > > >> > > >> Yes. This will cover all the cases on insert. But on erase, there is > > >> still a case where a rotate of sibling node is done during the > > >> re-coloration process. There we have a child change on sibling's > > >> child. I am not able to think of any easy way to handle that case. > > > > > > Let me go draw some figures with pen and paper to match up the erase > > > path with the rb_augment_erase_begin() code, because I can't quite spot > > > the case we're missing. > > > > > > If you have it handy, ascii art might help.. > > > > It is this case > > > > P > > / \ > > N S > > / \ > > SL SR > > > > changing to > > > > P > > / \ > > N SL > > \ > > S > > \ > > SR > > Right, but see: http://en.wikipedia.org/wiki/Red-black_tree > That is delete_case5, however then we fall into delete_case6 and perform > a left rotation. > > So suppose we start with the tree: > > P P P SL > / \ / \ / \ / \ > D S --> N S --> N SL --> P S > \ / \ / \ \ / \ > N SL SR SL* SR S* N SR > \ > SR > > and then remove D, delete case 5 and finally delete case 6, * marks red. > > rb_augment_erase_begin(D) will return N, and then rb_augment_path(N) > will re-augment: N, P, SL and S.
P SL / \ / \ N S ---> N S / / \ / \ C SL SR C SR
If P needs to be removed, we need to re-augment S also in this case, right? It looks like we are not handling this case.
thanks, suresh
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