[Lldb-commits] [PATCH] D74759: Treat RangeDataVector as an augmented BST

Wed Feb 19 05:04:46 PST 2020

labath added a comment.

In D74759#1880559 <https://reviews.llvm.org/D74759#1880559>, @jarin wrote:

> In D74759#1880499 <https://reviews.llvm.org/D74759#1880499>, @labath wrote:
>
> > I like this idea a lot, in principle. It is much simpler than a full blown interval tree, and it should give us similar performance characteristics.
> >
> > Have you done a proper complexity analysis here? I doubt the `O(log n)` claim is true in general. It would have to be at least `O(m + log n)` (m - number of elements found), but it's not clear to me whether even this is true in general. (However, I believe this can achieve ~~log(n) for non-degenerate cases.)
>
>
> Thanks for the feedback! We were aiming for something simple and efficient enough. Our preliminary results show that the lookup pretty much disappears even from the profiles it was dominating before.
>
> The implementation is pretty much taken from the "Augmented tree" section of https://en.wikipedia.org/wiki/Interval_tree where we just use the tree induced by the pivots of the binary search as the binary search tree that we augment. I believe the complexity is O(m log n), even though the wikipedia article makes a O(m + log n) claim. This should be still much better than the current O(n) and the memory cost seems to be quite palatable (extra word per symbol).

Ok, I see. Thanks for that reference. The wikipedia description is somewhat short, but I am beginning to understand how this could work. Maybe you could include a pointer to the wikipedia page and/or the book it references next to the algorithm.

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