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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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* This file is part of FFmpeg.
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* FFmpeg 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 2.1 of the License, or (at your option) any later version.
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* FFmpeg 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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* You should have received a copy of the GNU Lesser General Public
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* License along with FFmpeg; 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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* alternative bitstream reader & writer by Michael Niedermayer <michaelni@gmx.at>
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#include "bitstream.h"
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* Same as av_mallocz_static(), but does a realloc.
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* @param[in] ptr The block of memory to reallocate.
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* @param[in] size The requested size.
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* @return Block of memory of requested size.
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void *ff_realloc_static(void *ptr, unsigned int size);
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void align_put_bits(PutBitContext *s)
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#ifdef ALT_BITSTREAM_WRITER
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put_bits(s,( - s->index) & 7,0);
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put_bits(s,s->bit_left & 7,0);
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void ff_put_string(PutBitContext * pbc, char *s, int put_zero)
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#define GET_DATA(v, table, i, wrap, size) \
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const uint8_t *ptr = (const uint8_t *)table + i * wrap;\
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v = *(const uint8_t *)ptr;\
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v = *(const uint16_t *)ptr;\
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v = *(const uint32_t *)ptr;\
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static int alloc_table(VLC *vlc, int size, int use_static)
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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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vlc->table = ff_realloc_static(vlc->table,
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sizeof(VLC_TYPE) * 2 * vlc->table_allocated);
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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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static int build_table(VLC *vlc, int table_nb_bits,
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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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int i, j, k, n, table_size, table_index, nb, n1, index, code_prefix2;
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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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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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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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/* 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 defined(DEBUG_VLC) && 0
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printf("i=%d n=%d code=0x%x\n", i, n, code);
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/* if code matches the prefix, it is in the table */
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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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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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if(flags & INIT_VLC_LE)
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j = (code >> n_prefix) + (k<<n);
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av_log(NULL, AV_LOG_DEBUG, "%4x: code=%d n=%d\n",
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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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table[j][1] = n; //bits
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table[j][0] = i; //code
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j = (code >> ((flags & INIT_VLC_LE) ? n_prefix : n)) & ((1 << table_nb_bits) - 1);
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printf("%4x: n=%d (subtable)\n",
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/* compute table size */
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n1 = -table[j][1]; //bits
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table[j][1] = -n1; //bits
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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 > table_nb_bits) {
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table[i][1] = -n; //bits
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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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/* 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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/* 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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'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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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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vlc->table_allocated = 0;
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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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printf("build table nb_codes=%d\n", nb_codes);
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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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void free_vlc(VLC *vlc)
added
removed
ffmpeg/libavcodec/bitstream.c
