treewriter.h

/*
 *  Copyright (c) 2010 The WebM 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_TREEWRITER_H
#define __INC_TREEWRITER_H

/* Trees map alphabets into huffman-like codes suitable for an arithmetic
   bit coder.  Timothy S Murphy  11 October 2004 */

#include "vp8/common/treecoder.h"

#include "boolhuff.h"       /* for now */

typedef BOOL_CODER vp8_writer;

#define vp8_write vp8_encode_bool
#define vp8_write_literal vp8_encode_value
#define vp8_write_bit( W, V) vp8_write( W, V, vp8_prob_half)

#define vp8bc_write vp8bc_write_bool
#define vp8bc_write_literal vp8bc_write_bits
#define vp8bc_write_bit( W, V) vp8bc_write_bits( W, V, 1)


/* Approximate length of an encoded bool in 256ths of a bit at given prob */

#define vp8_cost_zero( x) ( vp8_prob_cost[x])
#define vp8_cost_one( x)  vp8_cost_zero( vp8_complement(x))

#define vp8_cost_bit( x, b) vp8_cost_zero( (b)?  vp8_complement(x) : (x) )

/* VP8BC version is scaled by 2^20 rather than 2^8; see bool_coder.h */


/* Both of these return bits, not scaled bits. */

static unsigned int vp8_cost_branch(const unsigned int ct[2], vp8_prob p)
{
    /* Imitate existing calculation */

    return ((ct[0] * vp8_cost_zero(p))
            + (ct[1] * vp8_cost_one(p))) >> 8;
}

/* Small functions to write explicit values and tokens, as well as
   estimate their lengths. */

static void vp8_treed_write
(
    vp8_writer *const w,
    vp8_tree t,
    const vp8_prob *const p,
    int v,
    int n               /* number of bits in v, assumed nonzero */
)
{
    vp8_tree_index i = 0;

    do
    {
        const int b = (v >> --n) & 1;
        vp8_write(w, b, p[i>>1]);