https://github.com/chaelim/HAMT

Hash Array Mapped Trie (C++ Templates)
https://github.com/chaelim/HAMT

Last synced: 3 months ago
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Hash Array Mapped Trie (C++ Templates)

• Host: GitHub
• URL: https://github.com/chaelim/HAMT
• Owner: chaelim
• License: mit
• Created: 2012-10-22T05:01:35.000Z (over 12 years ago)
• Default Branch: master
• Last Pushed: 2023-04-24T18:17:35.000Z (almost 2 years ago)
• Last Synced: 2024-08-02T01:22:12.050Z (6 months ago)
• Language: C
• Homepage:
• Size: 120 KB
• Stars: 123
• Watchers: 8
• Forks: 14
• Open Issues: 1
• Metadata Files:
  • Readme: README.md
  • License: LICENSE

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README

        
[![Build status](https://ci.appveyor.com/api/projects/status/qtyham872bkcbdwm/branch/dev?svg=true)](https://ci.appveyor.com/project/chaelim/hamt)

C++ Template class implementation of Hash Array Mapped Trie

================================

Do you want space-efficient and fast hash table? HAMT is just here for you. Based on the paper [Ideal Hash Trees by Phil Bagwell](http://lampwww.epfl.ch/papers/idealhashtrees.pdf), and as the title stated, it has really ideal features as a hash table as below.

Features

-------------------------

 * No initial root hash table required.

   _(Empty hash table just takes 8 bytes in 32 bit build or 12 bytes in 64 bit build.)_

 * No stop the world rehashing.

 * Faster and smaller.

 * Constant add/delete O(1) operations

 * C++ Template implementation can be easily used to any data type.

 * 32 bit hash key and 32 bit bitmap to index subhash array.

 * 32 bit integer and string (ANSI and Unicode) hash key templates are included.

 * Expected tree depth: ![equation](http://latex.codecogs.com/gif.latex?O%28%5Clog_%7B2%5EW%7D%28n%29%29).  

     w = 5  

     n : number of elements stored in the trie

 * Hamming weight of bitmap can be caculated using POPCNT(Population count) CPU intruction (introduced in Nehalem-base and Barcelona microarchitecture CPU). POPCNT can speed up overall performance about 10%.

Test program build notes

-------------------------

 * Open and compile Test\IdealHash.sln

 * To enable POPCNT CPU instruction, change 0 to 1 in "#define SSE42_POPCNT 0". POPCNT is SSE4 CPU instruction start supported since Intel Nehalem and AMD Barcelona.

 * References on POPCNT:

    - http://en.wikipedia.org/wiki/SSE4#POPCNT_and_LZCNT

    - http://developer.amd.com/community/blog/barcelona-processor-feature-advanced-bit-manipulation-abm/

More information

-------------------------

 * [Ideal Hash Trees by Phil Bagwell](http://lampwww.epfl.ch/papers/idealhashtrees.pdf).

 * [Wikipedia on Hash array mapped trie](http://en.wikipedia.org/wiki/Hash_array_mapped_trie).

 * [Ideal Hash Tries: an implementation in C++](http://www.altdevblogaday.com/2011/03/22/ideal-hash-tries-an-implementation-in-c/).

 * [POPCNT Instruction](http://en.wikipedia.org/wiki/SSE4#POPCNT_and_LZCNT)