OrdMap & HashMap

• AVL is not worse than RBTree and is also a feasible way to resolve Hash Collision Attack.
• This package exposes two public structs: OrdMap which implemented by optimized AVL, HashMap whose every index contains an AVL-Tree.
• To improve performance, raw pointer is used frequently. Because Rust uses a similar memory model to C/C++, two classic macros offset_of and container_of are used to dereference member variables into main struct. Fastbin is implemented to reduce the cost of memory allocation.
• insert and remove operations are optimized by selectively skipping AVL Rebalance, because under 95% of indexes, there are less than 3 nodes.

• The whole structure of HashMap is like: ``` HashMap: ------------------------------------------ | HashIndex | HashIndex | ... ------------------------------------------ ---------------- HashIndex: | ...... | ---------------- ---------------- | AVL Node | | ........ | | AVL Root |==> ---------------- ... <==>| ListHead |<==>| ListHead |<==> ... <==> HEAD <==> ... ---------------- ----------------

  InternalHashEntry ---------------- | HashNode | | Value | ----------------

  HashNode ---------------- ----------------- | ...... | | HashValue | | ...... | | Key | ... <==>| AVL Node |<==>| AVL Node |<==> ... ---------------- ----------------- ```

  Usage

Notice the Trait. Usage of most functions is same as STL HashMap, you can find examples in test case or Documentation. impl<K, V, S> HashMap<K, V, S> where K: Ord + Hash, S: BuildHasher impl<K, V> OrdMap<K, V> where K: Ord

Performance Test

Environment

Linux version 4.4.0-1049-aws (buildd@lcy01-amd64-001) (gcc version 5.4.0 20160609 (Ubuntu 5.4.0-6ubuntu1~16.04.5) ) Intel(R) Xeon(R) CPU E5-2676 v3 @ 2.40GHz

AVL Compare with RBTree

cargo run --release --example avl_cmp_rbtree * Obviously, optimized AVL is not worse than RBTree, and with the advantage of smaller height, it works better in searching case. It performs much better in clear case benefit from Fastbin ``` avl tree size 1000000 build time PT0.086414625S contain count 1000000 find time PT0.079008516S remove time PT0.047414057S insert after remove time PT0.068621561S clear time PT0.020838042S

rbtree size 1000000 build time PT0.255747347S contain count 1000000 find time PT0.128373407S remove time PT0.129552620S insert after remove time PT0.256210620S

clear time PT0.051735117S

avl tree size 10000000 build time PT0.996452066S contain count 10000000 find time PT0.862577411S remove time PT0.641826155S insert after remove time PT0.779849807S clear time PT0.206050905S

rbtree size 10000000 build time PT3.348531156S contain count 10000000 find time PT1.482958388S remove time PT1.538498453S insert after remove time PT3.361221077S

clear time PT0.505872813S

```

HashMap Competition

Run command cargo run --release --example hash_map_cmp_string * If the type of key is String, ours performs better in case of insert and search, Because Fastbin makes rehashing run faster and comparable hash node helps to reduce search time. ``` test hash avl map insert time PT0.264062182S max node num of single index: 7 find 1000000, time PT0.232942470S remove time PT0.303657020S

test stl hash map insert time PT0.382943597S find 1000000, time PT0.254504066S

remove time PT0.297953633S

test hash avl map insert time PT1.623697494S max node num of single index: 8 find 5000000, time PT1.374587816S remove time PT1.712209458S

test stl hash map insert time PT2.146439362S find 5000000, time PT1.494242541S

remove time PT1.613802131S

* However, if type is usize|isize|f32... , which means the cost of key comparing and memory copying are low, then STL HashMap sometimes performs better in case of `insert` and `remove`. cargo run --release --example hashmapcmp_usize test hash avl map insert time PT0.134678145S max node num of single index: 8 find 1000000, time PT0.118454962S remove time PT0.126796283S

test stl hash map insert time PT0.126203898S find 1000000, time PT0.099042480S

remove time PT0.104399187S

test hash avl map insert time PT0.996003799S max node num of single index: 8 find 5000000, time PT0.774285169S remove time PT0.836908472S

test stl hash map insert time PT0.982269496S find 5000000, time PT0.868572380S

remove time PT0.835186910S

* When facing Collision Attack, the runtime complexity of STL HashMap can be _O(n^2)_, but ours is _O(n log n)_. cargo run --release --example hashmapcmp_collision test hash avl map insert time PT0.000739762S max node num of single index: 10000 find 10000, time PT0.000690444S remove time PT0.000497103S

test stl hash map insert time PT0.093169479S find 10000, time PT0.079600027S

remove time PT0.089153558S

```