vpx/vp8/encoder/boolhuff.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.
 */


/****************************************************************************
*
*   Module Title :     boolhuff.h
*
*   Description  :     Bool Coder header file.
*
****************************************************************************/
#ifndef __INC_BOOLHUFF_H
#define __INC_BOOLHUFF_H

#include "vpx_ports/mem.h"

typedef struct
{
    unsigned int lowvalue;
    unsigned int range;
    unsigned int value;
    int count;
    unsigned int pos;
    unsigned char *buffer;

    // Variables used to track bit costs without outputing to the bitstream
    unsigned int  measure_cost;
    unsigned long bit_counter;
} BOOL_CODER;

extern void vp8_start_encode(BOOL_CODER *bc, unsigned char *buffer);

extern void vp8_encode_value(BOOL_CODER *br, int data, int bits);
extern void vp8_stop_encode(BOOL_CODER *bc);
extern const unsigned int vp8_prob_cost[256];


DECLARE_ALIGNED(16, extern const unsigned char, vp8_norm[256]);


static void vp8_encode_bool(BOOL_CODER *br, int bit, int probability)
{
    unsigned int split;
    int count = br->count;
    unsigned int range = br->range;
    unsigned int lowvalue = br->lowvalue;
    register unsigned int shift;

#ifdef ENTROPY_STATS
#if defined(SECTIONBITS_OUTPUT)

    if (bit)
        Sectionbits[active_section] += vp8_prob_cost[255-probability];
    else
        Sectionbits[active_section] += vp8_prob_cost[probability];

#endif
#endif

    split = 1 + (((range - 1) * probability) >> 8);

    range = split;

    if (bit)
    {
        lowvalue += split;
        range = br->range - split;
    }

    shift = vp8_norm[range];

    range <<= shift;
    count += shift;

    if (count >= 0)
    {
        int offset = shift - count;

        if ((lowvalue << (offset - 1)) & 0x80000000)
        {
            int x = br->pos - 1;

            while (x >= 0 && br->buffer[x] == 0xff)
            {
                br->buffer[x] = (unsigned char)0;
                x--;
            }

            br->buffer[x] += 1;
        }

        br->buffer[br->pos++] = (lowvalue >> (24 - offset));
        lowvalue <<= offset;
        shift = count;
        lowvalue &= 0xffffff;
        count -= 8 ;
    }

    lowvalue <<= shift;
    br->count = count;
    br->lowvalue = lowvalue;
    br->range = range;
}

#endif