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RLE for Runs of Zero ( RLE0Coder )

Definition

The class RLE0Coder is designed for compressing inputs which contain many runs of the character 0x00. This coder is useful as a preprocessing stage for a Move-To-Front coder. (This stage was suggested by D.J. Wheeler and described by P. Fenwick [32].)
The following combinations of coders often yield very good compression results:

#include < LEDA/coding/RLE0.h >

Creation

RLE0Coder C(streambuf* src_stream = 0, streambuf* tgt_stream = 0, bool own_streams = false)
    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.

RLE0Coder C(const char* src_file_name, const char* tgt_file_name)
    creates an instance C which uses file-streams for input and output.

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.

uint32 C.encode_memory_chunk(const char* in_buf, uint32 in_len, char* out_buf, uint32 out_len)
    encodes the memory chunk starting at in_buf with size in_len into the buffer starting at out_buf with size out_len. The function returns actual length of the encoded chunk which may be smaller than out_len. If the output buffer is too small for the encoded data the failure flag will be set (see below).

uint32 C.decode_memory_chunk(const char* in_buf, uint32 in_len, char* out_buf, uint32 out_len)
    decodes a memory chunk. The meaning of the parameters and the return value is the same as in the previous function.

streambuf* C.get_src_stream() returns the current source stream.

void C.set_src_stream(streambuf* src_stream, bool own_stream = false)
    sets the source stream (cf. constructor).

void C.set_src_file(const char* file_name)
    sets a file as source stream.

streambuf* C.get_tgt_stream() returns the current target stream.

void C.set_tgt_stream(streambuf* tgt_stream, bool own_Stream = false)
    sets the target stream (cf. constructor).

void C.set_tgt_file(const char* file_name)
    sets a file as target stream.

void C.reset() puts C in exactly the same state as the default constructor.

bool C.failed() returns true if an error occured.

bool C.finished() returns true if the coding is finished.

string C.get_description() provides a description for C.


next up previous contents index
Next: Checksummers ( checksummer_base ) Up: Lossless Compression Previous: Move-To-Front Coder II (   Contents   Index
root 2008-01-09