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Elastic Binary Trees (2011)
Administrivia This article was initially posted on Wikipedia in 2008, which explains why it's written at the 3rd person and looks familiar...
In order to store a duplicate key, we grow a binary sub-tree at the place where the leaf was to be located, using the same algorithm as for the upper tree, but with negative bit offsets. Conversely, EB trees heavily rely on bit-addressable data (typically integers), which confer them a very high performance due to the cheap operations involved, but limit their application field. ACL: string and IP address matches rely on EB trees so that even very large pattern file do not cause any noticeable slowdown (eg: full internet BGP routing table).
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