> 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.
>
