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ffmpeg / libavcodec / bitstream.c @ 5509bffa

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/*
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 * Common bit i/o utils
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 * Copyright (c) 2000, 2001 Fabrice Bellard.
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 * Copyright (c) 2002-2004 Michael Niedermayer <michaelni@gmx.at>
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 *
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 * This library is free software; you can redistribute it and/or
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 * modify it under the terms of the GNU Lesser General Public
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 * License as published by the Free Software Foundation; either
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 * version 2 of the License, or (at your option) any later version.
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 *
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 * This library is distributed in the hope that it will be useful,
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 * but WITHOUT ANY WARRANTY; without even the implied warranty of
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 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
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 * Lesser General Public License for more details.
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 *
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 * You should have received a copy of the GNU Lesser General Public
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 * License along with this library; if not, write to the Free Software
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 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
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 *
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 * alternative bitstream reader & writer by Michael Niedermayer <michaelni@gmx.at>
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 */
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/**
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 * @file bitstream.c
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 * bitstream api.
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 */
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#include "avcodec.h"
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#include "bitstream.h"
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void align_put_bits(PutBitContext *s)
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{
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#ifdef ALT_BITSTREAM_WRITER
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    put_bits(s,(  - s->index) & 7,0);
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#else
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    put_bits(s,s->bit_left & 7,0);
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#endif
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}
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void ff_put_string(PutBitContext * pbc, char *s, int put_zero)
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{
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    while(*s){
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        put_bits(pbc, 8, *s);
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        s++;
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    }
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    if(put_zero)
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        put_bits(pbc, 8, 0);
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}
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/* bit input functions */
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/**
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 * reads 0-32 bits.
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 */
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unsigned int get_bits_long(GetBitContext *s, int n){
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    if(n<=17) return get_bits(s, n);
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    else{
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        int ret= get_bits(s, 16) << (n-16);
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        return ret | get_bits(s, n-16);
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    }
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}
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/**
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 * shows 0-32 bits.
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 */
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unsigned int show_bits_long(GetBitContext *s, int n){
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    if(n<=17) return show_bits(s, n);
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    else{
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        GetBitContext gb= *s;
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        int ret= get_bits_long(s, n);
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        *s= gb;
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        return ret;
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    }
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}
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void align_get_bits(GetBitContext *s)
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{
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    int n= (-get_bits_count(s)) & 7;
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    if(n) skip_bits(s, n);
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}
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int check_marker(GetBitContext *s, const char *msg)
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{
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    int bit= get_bits1(s);
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    if(!bit)
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            av_log(NULL, AV_LOG_INFO, "Marker bit missing %s\n", msg);
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    return bit;
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}
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/* VLC decoding */
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//#define DEBUG_VLC
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#define GET_DATA(v, table, i, wrap, size) \
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{\
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    const uint8_t *ptr = (const uint8_t *)table + i * wrap;\
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    switch(size) {\
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    case 1:\
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        v = *(const uint8_t *)ptr;\
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        break;\
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    case 2:\
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        v = *(const uint16_t *)ptr;\
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        break;\
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    default:\
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        v = *(const uint32_t *)ptr;\
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        break;\
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    }\
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}
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static int alloc_table(VLC *vlc, int size, int use_static)
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{
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    int index;
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    index = vlc->table_size;
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    vlc->table_size += size;
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    if (vlc->table_size > vlc->table_allocated) {
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        vlc->table_allocated += (1 << vlc->bits);
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        if(use_static)
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            vlc->table = av_realloc_static(vlc->table,
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                                           sizeof(VLC_TYPE) * 2 * vlc->table_allocated);
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        else
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            vlc->table = av_realloc(vlc->table,
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                                    sizeof(VLC_TYPE) * 2 * vlc->table_allocated);
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        if (!vlc->table)
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            return -1;
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    }
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    return index;
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}
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static int build_table(VLC *vlc, int table_nb_bits,
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                       int nb_codes,
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                       const void *bits, int bits_wrap, int bits_size,
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                       const void *codes, int codes_wrap, int codes_size,
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                       uint32_t code_prefix, int n_prefix, int flags)
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{
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    int i, j, k, n, table_size, table_index, nb, n1, index, code_prefix2;
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    uint32_t code;
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    VLC_TYPE (*table)[2];
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    table_size = 1 << table_nb_bits;
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    table_index = alloc_table(vlc, table_size, flags & INIT_VLC_USE_STATIC);
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#ifdef DEBUG_VLC
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    printf("new table index=%d size=%d code_prefix=%x n=%d\n",
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           table_index, table_size, code_prefix, n_prefix);
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#endif
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    if (table_index < 0)
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        return -1;
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    table = &vlc->table[table_index];
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    for(i=0;i<table_size;i++) {
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        table[i][1] = 0; //bits
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        table[i][0] = -1; //codes
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    }
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    /* first pass: map codes and compute auxillary table sizes */
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    for(i=0;i<nb_codes;i++) {
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        GET_DATA(n, bits, i, bits_wrap, bits_size);
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        GET_DATA(code, codes, i, codes_wrap, codes_size);
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        /* we accept tables with holes */
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        if (n <= 0)
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            continue;
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#if defined(DEBUG_VLC) && 0
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        printf("i=%d n=%d code=0x%x\n", i, n, code);
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#endif
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        /* if code matches the prefix, it is in the table */
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        n -= n_prefix;
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        if(flags & INIT_VLC_LE)
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            code_prefix2= code & (n_prefix>=32 ? 0xffffffff : (1 << n_prefix)-1);
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        else
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            code_prefix2= code >> n;
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        if (n > 0 && code_prefix2 == code_prefix) {
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            if (n <= table_nb_bits) {
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                /* no need to add another table */
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                j = (code << (table_nb_bits - n)) & (table_size - 1);
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                nb = 1 << (table_nb_bits - n);
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                for(k=0;k<nb;k++) {
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                    if(flags & INIT_VLC_LE)
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                        j = (code >> n_prefix) + (k<<n);
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#ifdef DEBUG_VLC
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                    av_log(NULL, AV_LOG_DEBUG, "%4x: code=%d n=%d\n",
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                           j, i, n);
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#endif
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                    if (table[j][1] /*bits*/ != 0) {
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                        av_log(NULL, AV_LOG_ERROR, "incorrect codes\n");
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                        return -1;
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                    }
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                    table[j][1] = n; //bits
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                    table[j][0] = i; //code
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                    j++;
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                }
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            } else {
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                n -= table_nb_bits;
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                j = (code >> ((flags & INIT_VLC_LE) ? n_prefix : n)) & ((1 << table_nb_bits) - 1);
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#ifdef DEBUG_VLC
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                printf("%4x: n=%d (subtable)\n",
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                       j, n);
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#endif
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                /* compute table size */
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                n1 = -table[j][1]; //bits
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                if (n > n1)
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                    n1 = n;
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                table[j][1] = -n1; //bits
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            }
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        }
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    }
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    /* second pass : fill auxillary tables recursively */
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    for(i=0;i<table_size;i++) {
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        n = table[i][1]; //bits
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        if (n < 0) {
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            n = -n;
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            if (n > table_nb_bits) {
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                n = table_nb_bits;
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                table[i][1] = -n; //bits
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            }
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            index = build_table(vlc, n, nb_codes,
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                                bits, bits_wrap, bits_size,
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                                codes, codes_wrap, codes_size,
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                                (flags & INIT_VLC_LE) ? (code_prefix | (i << n_prefix)) : ((code_prefix << table_nb_bits) | i),
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                                n_prefix + table_nb_bits, flags);
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            if (index < 0)
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                return -1;
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            /* note: realloc has been done, so reload tables */
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            table = &vlc->table[table_index];
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            table[i][0] = index; //code
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        }
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    }
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    return table_index;
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}
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/* Build VLC decoding tables suitable for use with get_vlc().
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   'nb_bits' set thee decoding table size (2^nb_bits) entries. The
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   bigger it is, the faster is the decoding. But it should not be too
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   big to save memory and L1 cache. '9' is a good compromise.
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   'nb_codes' : number of vlcs codes
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   'bits' : table which gives the size (in bits) of each vlc code.
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   'codes' : table which gives the bit pattern of of each vlc code.
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   'xxx_wrap' : give the number of bytes between each entry of the
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   'bits' or 'codes' tables.
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   'xxx_size' : gives the number of bytes of each entry of the 'bits'
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   or 'codes' tables.
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   'wrap' and 'size' allows to use any memory configuration and types
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   (byte/word/long) to store the 'bits' and 'codes' tables.
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   'use_static' should be set to 1 for tables, which should be freed
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   with av_free_static(), 0 if free_vlc() will be used.
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*/
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int init_vlc(VLC *vlc, int nb_bits, int nb_codes,
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             const void *bits, int bits_wrap, int bits_size,
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             const void *codes, int codes_wrap, int codes_size,
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             int use_static)
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{
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    vlc->bits = nb_bits;
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    if(!use_static) {
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        vlc->table = NULL;
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        vlc->table_allocated = 0;
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        vlc->table_size = 0;
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    } else {
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        /* Static tables are initially always NULL, return
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           if vlc->table != NULL to avoid double allocation */
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        if(vlc->table)
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            return 0;
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    }
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#ifdef DEBUG_VLC
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    printf("build table nb_codes=%d\n", nb_codes);
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#endif
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    if (build_table(vlc, nb_bits, nb_codes,
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                    bits, bits_wrap, bits_size,
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                    codes, codes_wrap, codes_size,
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                    0, 0, use_static) < 0) {
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        av_free(vlc->table);
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        return -1;
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    }
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    return 0;
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}
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void free_vlc(VLC *vlc)
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{
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    av_free(vlc->table);
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}
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