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Static Arithmetic Coder ( A0sCoder )

Definition

An instance C of A0sCoder is a static arithmetic coder of order zero. (We assume that the reader is familiar with the definition of the class A0Coder from the previous section.) A0sCoder is called static because it uses a fixed model for encoding. The input is scanned twice. In the first scan the frequencies of the characters are counted. This information is used to precompute the model. In the second scan the actual coding takes place.
Since the model is fixed the static coder is usually faster than the adaptive coder (despite the two scans) but the compression rates are often slightly inferior.

#include < LEDA/coding/arithmetic_coding.h >

Creation

A0sCoder 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.

A0sCoder 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: Prediction by Partial Matching Up: Lossless Compression Previous: Adaptive Arithmetic Coder (   Contents   Index
root 2008-01-09