vpx/vp8/common/treecoder.h

/*
 *  Copyright (c) 2010 The VP8 project authors. All Rights Reserved.
 *
 *  Use of this source code is governed by a BSD-style license 
 *  that can be found in the LICENSE file in the root of the source
 *  tree. An additional intellectual property rights grant can be found
 *  in the file PATENTS.  All contributing project authors may 
 *  be found in the AUTHORS file in the root of the source tree.
 */


#ifndef __INC_TREECODER_H
#define __INC_TREECODER_H

typedef unsigned char vp8bc_index_t; // probability index


typedef unsigned char vp8_prob;

#define vp8_prob_half ( (vp8_prob) 128)

typedef signed char vp8_tree_index;
struct bool_coder_spec;

typedef struct bool_coder_spec bool_coder_spec;
typedef struct bool_writer bool_writer;
typedef struct bool_reader bool_reader;

typedef const bool_coder_spec c_bool_coder_spec;
typedef const bool_writer c_bool_writer;
typedef const bool_reader c_bool_reader;



# define vp8_complement( x) (255 - x)


/* We build coding trees compactly in arrays.
   Each node of the tree is a pair of vp8_tree_indices.
   Array index often references a corresponding probability table.
   Index <= 0 means done encoding/decoding and value = -Index,
   Index > 0 means need another bit, specification at index.
   Nonnegative indices are always even;  processing begins at node 0. */

typedef const vp8_tree_index vp8_tree[], *vp8_tree_p;


typedef const struct vp8_token_struct
{
    int value;
    int Len;
} vp8_token;

/* Construct encoding array from tree. */

void vp8_tokens_from_tree(struct vp8_token_struct *, vp8_tree);


/* Convert array of token occurrence counts into a table of probabilities
   for the associated binary encoding tree.  Also writes count of branches
   taken for each node on the tree; this facilitiates decisions as to
   probability updates. */

void vp8_tree_probs_from_distribution(
    int n,                      /* n = size of alphabet */
    vp8_token tok               [ /* n */ ],
    vp8_tree tree,
    vp8_prob probs          [ /* n-1 */ ],
    unsigned int branch_ct       [ /* n-1 */ ] [2],
    const unsigned int num_events[ /* n */ ],
    unsigned int Pfactor,
    int Round
);

/* Variant of above using coder spec rather than hardwired 8-bit probs. */

void vp8bc_tree_probs_from_distribution(
    int n,                      /* n = size of alphabet */
    vp8_token tok               [ /* n */ ],
    vp8_tree tree,
    vp8_prob probs          [ /* n-1 */ ],
    unsigned int branch_ct       [ /* n-1 */ ] [2],
    const unsigned int num_events[ /* n */ ],
    c_bool_coder_spec *s
);


#endif