yovnchine/EWAHBoolArray

Compressed bitset in C++
Daniel Lemire



== What is this? ==

The class EWAHBoolArray is a compressed bitset data structure.

== Licensing ==

Apache License 2.0. (Other licenses are possible.)

== Limitations ==

Because of the compression type being used, you must set the bits
in increasing order (no random access).


== STL and copy constructors ==

I expect most people to construct rather large bitmaps. For this
reason, you should avoid copies.

Thus, the code will warn you against doing this:

    EWAHBoolArray<uword> bitset1;
    bitset1.set(1);
    bitset1.set(2);
    bitset1.set(1000);
    bitset1.set(1001);
    vector< EWAHBoolArray<uword> > testVec;
    testVec.push_back(bitset1);

Instead, do this:

    vector< EWAHBoolArray<uword> > testVec(1);
    testVec[0].set(1);
    testVec[0].set(2);
    testVec[0].set(1000);
    testVec[0].set(1001);


Or you can use the "swap" method.

    EWAHBoolArray<uword> bitset1;
    bitset1.set(1);
    bitset1.set(2);
    bitset1.set(1000);
    bitset1.set(1001);
    vector< EWAHBoolArray<uword> > testVec(1);
    testVec.swap(bitset1);


== Dependencies ==

None. (Will work under MacOS or Linux easily.)

== Usage ==

make
./unit
make example
./example

== Example ==

Please see example.cpp

== Ruby wrapper ==

Josh Ferguson wrote a wrapper for Ruby. 
The implementation is packaged and installable as a ruby gem.

You can install it by typing:

gem install ewah-bitset

== Further reading ==

Please see

Daniel Lemire, Owen Kaser, Kamel Aouiche, Sorting improves
word-aligned bitmap indexes. Data & Knowledge Engineering 69 (1),
pages 3-28, 2010.
http://arxiv.org/abs/0901.3751

== Warning ==

Please don't trust this software. Run your own unit tests. Report bugs.
yovnchine / EWAHBoolArray

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