shithub: libvpx

ref: e237fd7c5ad8c0caf341ca50a4ea65495edce74f
dir: /vp8/decoder/dboolhuff.c/

/*
 *  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.
 */


#include "dboolhuff.h"
#include "vpx_ports/mem.h"
#include "vpx_mem/vpx_mem.h"

int vp8dx_start_decode(BOOL_DECODER *br,
                       const unsigned char *source,
                       unsigned int source_sz)
{
    br->user_buffer_end = source+source_sz;
    br->user_buffer     = source;
    br->value    = 0;
    br->count    = -8;
    br->range    = 255;

    if (source_sz && !source)
        return 1;

    /* Populate the buffer */
    vp8dx_bool_decoder_fill(br);

    return 0;
}


void vp8dx_bool_decoder_fill(BOOL_DECODER *br)
{
    const unsigned char *bufptr;
    const unsigned char *bufend;
    VP8_BD_VALUE         value;
    int                  count;
    bufend = br->user_buffer_end;
    bufptr = br->user_buffer;
    value = br->value;
    count = br->count;

    VP8DX_BOOL_DECODER_FILL(count, value, bufptr, bufend);

    br->user_buffer = bufptr;
    br->value = value;
    br->count = count;
}


#if CONFIG_NEWUPDATE
static int get_unsigned_bits(unsigned num_values)
{
    int cat=0;
    if ((num_values--)<=1) return 0;
    while (num_values>0)
    {
        cat++;
        num_values>>=1;
    }
    return cat;
}

int inv_recenter_nonneg(int v, int m)
{
    if (v>(m<<1)) return v;
    else if ((v&1)==0) return (v>>1)+m;
    else return m-((v+1)>>1);
}

int vp8_decode_uniform(BOOL_DECODER *br, int n)
{
    int v;
    int l=get_unsigned_bits(n);
    int m=(1<<l)-n;
    if (!l) return 0;
    v = vp8_decode_value(br, l-1);
    if (v < m)
        return v;
    else
        return (v<<1)-m+vp8_decode_value(br, 1);
}

int vp8_decode_term_subexp(BOOL_DECODER *br, int k, int num_syms)
{
    int i=0, mk=0, word;
    while (1)
    {
        int b = (i?k+i-1:k);
        int a = (1<<b);
        if (num_syms<=mk+3*a)
        {
            word = vp8_decode_uniform(br, num_syms-mk) + mk;
            break;
        }
        else
        {
            if (vp8_decode_value(br, 1))
            {
                i++;
                mk += a;
            }
            else
            {
                word = vp8_decode_value(br, b) + mk;
                break;
            }
        }
    }
    return word;
}
#endif