Version 5.0 The LEDA User Manual

9.9 Burrows-Wheeler Transform ( BWTCoder )
1. Definition
The class BWTCoder applies the Burrows-Wheeler transform [18] (in encoding mode)
or its reversal (in decoding mode) to the input stream. To be more precise, in encoding
mode the input stream is partitioned in blocks and the transformation is applied to each
block. The size of the blocks, i.e. the number of characters per block, can be specified by
the user.
This transformation does not compress the input but it can be used as a preprocessing
step for other coders. Applying BWTCoder first often improves the overall compression
rates. The following combinations yield very good compression results:
• CoderPipe3
• CoderPipe4
#include < LEDA/coding/BWT.h >
2. Creation
BWTCoder C(streambuf ∗ src stream = 0, streambuf ∗ tgt stream = 0,
bool own streams = false, uint32 block size = DefaultBlockSize);
creates an instance C which uses the given source and target
streams. If own streams is set, then C is responsible for the destruction
of the streams, otherwise the pointers src stream and tgt stream
must be valid during the life-time of C. The block size can be controlled
via block size.
BWTCoder
C(const char ∗ src file name, const char ∗ tgt file name,
uint32 block size = DefaultBlockSize);
creates an instance C which uses file-streams for input and output.
The block size can be controlled via block size.
3. Operations
Standard Operations
void C.encode( ) encodes the source stream and writes the output to
the target stream.
void C.decode( ) decodes the source stream and writes the output to
the target stream.