Formula for lbzip2, a parallel bzip2 compatible (un)archiver.

lbzip2 is a bzip2 compatible compressor and decompressor, but it also makes use of multiple cores, something that bzip2 does not do. This is very useful for anyone who has to shuffle compressed data around. bzip2 is a very good compression algorithm, but it itself is slow during compression and decompression compared to gzip. lbzip2 fixes this by allowing the (de)compression to occur on multiple cores. API mirrors that of bzip2.