A compressed alternative to the Java BitSet class
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javaewah
README
example.java

README

JavaEWAH
(c) Daniel Lemire,
http://www.daniel-lemire.com/

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).

Unlike the similar compressedbitset, it does not
implement a patented scheme (to D. Lemire's knowledge).

http://code.google.com/p/compressedbitset/

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

Among other possible open source licenses, this
code is licensed under GPL version 3 and 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 ==

javac javaewah/unit.java 
java javaewah/unit


=== Usage ==

See example.java.

=== Warning ==

Don't trust software you downloaded off the internet. When in doubt, 
run the unit tests (javaewah/unit.java). Report bugs when you find them.