README

JavaEWAH
(c) Daniel Lemire,
http://lemire.me/en/

This is a word-aligned compressed variant of
the Java Bitset class. It uses a 64-bit RLE-like
compression scheme.

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.

Among other possible open source licenses, this
code is licensed under Apache License, Version 2.0 (ASL2.0).

For more details, see the following paper:

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
 
== Unit testing ==

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

mvn test

See 
http://maven.apache.org/guides/introduction/introduction-to-the-lifecycle.html
for details.


=== Usage ==

See example.java.

 
== Maven central repository ==

You can download JavaEWAH from the Maven central repository:
http://repo1.maven.org/maven2/com/googlecode/javaewah/JavaEWAH/

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

<dependencies>
    <dependency>
	<groupId>com.googlecode.javaewah</groupId>
	<artifactId>JavaEWAH</artifactId>
	<version>0.3.1</version>
    </dependency>
</dependencies>