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SubjectRe: [PATCH] rbtree: undo augmented damage -v2
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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.




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