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A compressed alternative to the Java BitSet class
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(c) 2009-2012
Daniel Lemire (, 
Cliff Moon (, 
David McIntosh (,
and Robert Becho (
This code is licensed under Apache License, Version 2.0 (ASL2.0).

This is a word-aligned compressed variant of
the Java Bitset class. It uses a 64-bit RLE-like
compression scheme. It can be used to implement
bitmap indexes.

The goal of word-aligned compression is not to 
achieve the best compression, but rather to 
improve query processing time. Hence, we try
to save CPU cycles, maybe at the expense of
storage. However, the EWAH scheme we implemented
is always more efficient storage-wise than an
uncompressed bitmap (as implemented in the java
BitSet class by Sun).

For better performance, use a 64-bit JVM over
64-bit CPUs.

For more details regarding the compression format, please
see Section 3 of the following paper:

Daniel Lemire, Owen Kaser, Kamel Aouiche, Sorting improves word-aligned bitmap indexes. Data & Knowledge Engineering 69 (1), pages 3-28, 2010.
 (The PDF file is freely available on the arXiv site.)
== Unit testing ==

As of October 2011, this packages relies on Maven. To
test it:

mvn test

for details.

=== Usage ==


== Maven central repository ==

You can download JavaEWAH from the Maven central repository:

You can also specify the dependency in the Maven "pom.xml" file:


Naturally, you should replace "version" by the version
you desire.
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