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/*
* bintree.c: Bintree model of WFA tree
*
* Written by: Ullrich Hafner
*
* This file is part of FIASCO (Fractal Image And Sequence COdec)
* Copyright (C) 1994-2000 Ullrich Hafner
*/
/*
* $Date: 2000/06/14 20:50:51 $
* $Author: hafner $
* $Revision: 5.1 $
* $State: Exp $
*/
#include "config.h"
#include "types.h"
#include "macros.h"
#include "error.h"
#include <math.h>
#include "bintree.h"
#include "misc.h"
#include "cwfa.h"
/*****************************************************************************
public code
*****************************************************************************/
void
tree_update (bool_t child, unsigned level, tree_t *model)
/*
* Update tree model of given 'level'.
*
* No return value.
*
* Side effects:
* tree model is changed.
*/
{
if (!child)
model->total [level]++;
else
{
model->counts [level]++;
model->total [level]++;
}
}
real_t
tree_bits (bool_t child, unsigned level, const tree_t *model)
/*
* Compute number of bits needed for coding element 'child' of the bintree.
* For each 'level' a different context is used.
*
* Return value:
* # bits
*/
{
real_t prob = model->counts [level] / (real_t) model->total [level];
return child ? - log2 (prob) : - log2 (1 - prob);
}
void
init_tree_model (tree_t *tree_model)
/*
* Initialize the model for the tree.
* Symbol RANGE is synonymous with the '0' symbol and
* symbol NO_RANGE is synonymous with the '1' symbol of the binary coder.
* The 'count' array counts the number of NO_RANGE symbols.
*
* No return value.
*/
{
unsigned level;
unsigned counts_0 [MAXLEVEL] = {20, 17, 15, 10, 5, 4, 3,
2, 1, 1, 1, 1, 1, 1, 1,
1, 1, 1, 1 , 1, 1, 1};
unsigned counts_1 [MAXLEVEL] = {1 , 1, 1, 1, 1, 1, 1,
1, 1, 2, 3, 5, 10, 15, 20,
25, 30, 35, 60, 60, 60, 60};
for (level = 0; level < MAXLEVEL ; level++)
{
tree_model->counts [level] = counts_1 [level];
tree_model->total [level] = counts_0 [level] + counts_1 [level];
}
}
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