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) 20022004 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 021101301 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 032 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) << (n16); 
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return ret  get_bits(s, n16); 
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} 
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} 
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/**

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* shows 032 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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