Version 5.0 The LEDA User Manual

9.2 Static Arithmetic Coder ( A0sCoder )
1. 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 >
2. 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.
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.
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).