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@perma/map

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Immutable hash maps implemented as hash array papped tries

github.com/gozala/perma-map.git

gozala/perma-map

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# @perma/map Hash Array Map Trie (HAMT) implementation based on [CHAMP][] paper and inspired by [Clojure][]. Library provides a builder API inspired by clojure [transient][]s that can be utilized for bulk updates. ## Status Prototype implements hash-array map tries (HAMT) by synthesizing [CHAMP][] algorithm with HAMTs used by [IPFS UnixFS][] and [IPLD HAMT][]. [CHAMP][] algorithm utilized several optimizations that are incompatible with [IPFS UnixFS][] and [IPLD HAMT][], this implementation attempts to utilize those optimizations at runtime and provide a way to map it to [IPFS UnixFS][] compatible representation. ## Optimizations [CHAMP][] algorithm exploits branching factor of `32` because it can be manipulated efficiently on 32-bit processors. It also allows storing HAMT bitmaps in a single integer. In order to support [IPFS UnixFS][] implementation (which uses `256` factor by default) branching factor is configurable, but relevant optimizations only apply when branching factor of `32` is used. It is also worth noting that even with branching factor of `32` it can store large amount of entries in a relatively shallow tree e.g. tree 6 levels deep could store around `33,554,432` entries. ## Credits - [Leveling up Clojure’s Hash Maps](https://bendyworks.com/blog/leveling-clojures-hash-maps) - [Hash Array Mapped Tries](https://worace.works/2016/05/24/hash-array-mapped-tries/) - [Optimizing Hash-Array Mapped Tries for Fast and Lean Immutable JVM Collections](https://michael.steindorfer.name/publications/oopsla15.pdf) - [Lean Hash Array Mapped Trie (Lean Map)](https://github.com/bendyworks/lean-map) - [Ideal hash trees](http://lampwww.epfl.ch/papers/idealhashtrees.pdf) [ipfs unixfs]: https://github.com/ipfs/specs/blob/main/UNIXFS.md [champ]: https://michael.steindorfer.name/publications/oopsla15.pdf [ipld hamt]: https://ipld.io/specs/advanced-data-layouts/hamt/spec/ [clojure]: https://clojure.org/ [transient]: https://clojure.org/reference/transients