Rolling Hash C++ Library
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README.md
characterhash.h
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example.cpp
example2.cpp
example3.cpp Reformatting. Aug 20, 2015
example4.cpp
example64bits.cpp Reformatting. Aug 20, 2015
generalhash.h
mersennetwister.h
rabinkarphash.h Reformatting. Aug 20, 2015
speedtesting.cpp
threewisehash.h
unit.cpp Reformatting. Aug 20, 2015
ztimer.h

README.md

Randomized rolling hash functions in C++

Build Status

License: Apache 2.0

What is this?

This is a set of C++ classes implementing various recursive n-gram hashing techniques, also called rolling hashing (http://en.wikipedia.org/wiki/Rolling_hash), including:

  • Randomized Karp-Rabin (sometimes called Rabin-Karp)
  • Hashing by Cyclic Polynomials (also known as Buzhash)
  • Hashing by Irreducible Polynomials

Code sample

    const uint n(3);//hash all sequences of 3 characters
    const uint L(7); // you need 7 bits
    CyclicHash<uint32> hf(n,L );// if you want 64-bit values replace uint32 by uint64
    for(uint32 k = 0; k<n;++k) {
              chartype c = ... ; // grab some character
              hf.eat(c); // feed it to the hasher
    }
    while(...) { // go over your string
       hf.hashvalue; // at all times, this contains the hash value
       chartype c = ... ;// point to the next character
       chartype out = ...; // character we want to forget
       hf.update(out,c); // update hash value
    }

Requirements

A recent GNU GCC C++ compiler or a recent CLANG.

What should I do after I download it?

type:

    make

then

    ./unit

then

    ./speedtesting

References

Daniel Lemire, Owen Kaser: Recursive n-gram hashing is pairwise independent, at best, Computer Speech & Language, Volume 24, Issue 4, October 2010, Pages 698-710 http://arxiv.org/abs/0705.4676

Daniel Lemire, The universality of iterated hashing over variable-length strings, Discrete Applied Mathematics 160 (4-5), 2012. http://arxiv.org/abs/1008.1715

Owen Kaser and Daniel Lemire, Strongly universal string hashing is fast, Computer Journal (2014) 57 (11): 1624-1638. http://arxiv.org/abs/1202.4961