ref: f347dd3b3d9c1ffef4f707d39208ffa4750370ab
dir: /libentcode/probmod.h/
#if !defined(_probmod_H)
# define _probmod_H (1)
# include "entcode.h"
typedef struct ec_probsamp ec_probsamp;
typedef struct ec_probmod ec_probmod;
/*A sample from a probability distribution.
This is the information needed to encode a symbol or update the decoder
state.*/
struct ec_probsamp{
/*The cumulative frequency of all symbols preceding this one in the
alphabet.*/
unsigned fl;
/*The frequency of the symbol coded.*/
unsigned fs;
/*The total frequency of all symbols in the alphabet.*/
unsigned ft;
};
/*A simple frequency-count probability model.*/
struct ec_probmod{
/*The number of symbols in this context.*/
int sz;
/*The largest power of two less than or equal to sz.*/
int split;
/*The amount by which to increment the frequency count of an observed
symbol.*/
unsigned inc;
/*The current total frequency count.*/
unsigned ft;
/*The maximum total frequency count allowed before the counts are rescaled.
Note that this should be larger than (inc+1>>1)+sz-1, since at most one
rescaling is done per decoded symbol.
Otherwise, this threshold might be exceeded.
This must be less than 2**23 for a range coder, and 2**31 for an
arithmetic coder.*/
unsigned thresh;
/*The binary indexed tree used to keep track of the frequency counts.*/
unsigned *bitree;
};
/*Initializes a probability model of the given size.
The amount to increment and all frequency counts are initialized to 1.
The rescaling threshold is initialized to 2**23.
_sz: The number of symbols in this context.*/
void ec_probmod_init(ec_probmod *_this,unsigned _sz);
/*Initializes a probability model of the given size.
The amount to increment is initialized to 1.
The rescaling threshold is initialized to 2**23.
_sz: The number of symbols in this context.
_counts: The initial frequency count of each symbol.*/
void ec_probmod_init_from_counts(ec_probmod *_this,unsigned _sz,
const unsigned *_counts);
/*Initializes a probability model of the given size.
_sz: The number of symbols in this context.
_inc: The amount by which to increment the frequency count of an observed
symbol.
_thresh: The maximum total frequency count allowed before the counts are
rescaled.
See above for restrictions on this value.
_counts: The initial frequency count of each symbol, or NULL to initialize
each frequency count to 1.*/
void ec_probmod_init_full(ec_probmod *_this,unsigned _sz,unsigned _inc,
unsigned _thresh,const unsigned *_counts);
/*Frees all memory used by this probability model.*/
void ec_probmod_clear(ec_probmod *_this);
#endif