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ffmpeg / libavcodec / bitstream.c @ 2912e87a

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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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 * Copyright (c) 2010 Loren Merritt
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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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 * This file is part of Libav.
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 *
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 * Libav 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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 *
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 * Libav 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 Libav; 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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/**
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 * @file
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 * bitstream api.
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 */
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#include "avcodec.h"
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#include "get_bits.h"
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#include "put_bits.h"
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const uint8_t ff_log2_run[32]={
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 0, 0, 0, 0, 1, 1, 1, 1,
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 2, 2, 2, 2, 3, 3, 3, 3,
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 4, 4, 5, 5, 6, 6, 7, 7,
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 8, 9,10,11,12,13,14,15
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};
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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 *pb, const char *string, int terminate_string)
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{
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    while(*string){
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        put_bits(pb, 8, *string);
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        string++;
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    }
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    if(terminate_string)
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        put_bits(pb, 8, 0);
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}
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void ff_copy_bits(PutBitContext *pb, const uint8_t *src, int length)
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{
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    int words= length>>4;
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    int bits= length&15;
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    int i;
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    if(length==0) return;
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    if(CONFIG_SMALL || words < 16 || put_bits_count(pb)&7){
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        for(i=0; i<words; i++) put_bits(pb, 16, AV_RB16(src + 2*i));
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    }else{
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        for(i=0; put_bits_count(pb)&31; i++)
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            put_bits(pb, 8, src[i]);
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        flush_put_bits(pb);
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        memcpy(put_bits_ptr(pb), src+i, 2*words-i);
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        skip_put_bytes(pb, 2*words-i);
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    }
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    put_bits(pb, bits, AV_RB16(src + 2*words)>>(16-bits));
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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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        if(use_static)
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            abort(); //cant do anything, init_vlc() is used with too little memory
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        vlc->table_allocated += (1 << vlc->bits);
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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 av_always_inline uint32_t bitswap_32(uint32_t x) {
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    return av_reverse[x&0xFF]<<24
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         | av_reverse[(x>>8)&0xFF]<<16
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         | av_reverse[(x>>16)&0xFF]<<8
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         | av_reverse[x>>24];
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}
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typedef struct {
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    uint8_t bits;
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    uint16_t symbol;
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    /** codeword, with the first bit-to-be-read in the msb
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     * (even if intended for a little-endian bitstream reader) */
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    uint32_t code;
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} VLCcode;
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static int compare_vlcspec(const void *a, const void *b)
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{
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    const VLCcode *sa=a, *sb=b;
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    return (sa->code >> 1) - (sb->code >> 1);
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}
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/**
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 * Build VLC decoding tables suitable for use with get_vlc().
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 *
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 * @param vlc            the context to be initted
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 *
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 * @param table_nb_bits  max length of vlc codes to store directly in this table
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 *                       (Longer codes are delegated to subtables.)
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 *
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 * @param nb_codes       number of elements in codes[]
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 *
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 * @param codes          descriptions of the vlc codes
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 *                       These must be ordered such that codes going into the same subtable are contiguous.
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 *                       Sorting by VLCcode.code is sufficient, though not necessary.
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 */
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static int build_table(VLC *vlc, int table_nb_bits, int nb_codes,
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                       VLCcode *codes, int flags)
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{
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    int table_size, table_index, index, code_prefix, symbol, subtable_bits;
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    int i, j, k, n, nb, inc;
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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_NEW_STATIC);
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#ifdef DEBUG_VLC
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    av_log(NULL,AV_LOG_DEBUG,"new table index=%d size=%d\n",
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           table_index, table_size);
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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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        n = codes[i].bits;
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        code = codes[i].code;
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        symbol = codes[i].symbol;
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#if defined(DEBUG_VLC) && 0
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        av_log(NULL,AV_LOG_DEBUG,"i=%d n=%d code=0x%x\n", i, n, code);
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#endif
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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 >> (32 - table_nb_bits);
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            nb = 1 << (table_nb_bits - n);
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            inc = 1;
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            if (flags & INIT_VLC_LE) {
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                j = bitswap_32(code);
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                inc = 1 << n;
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            }
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            for (k = 0; k < nb; k++) {
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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] = symbol;
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                j += inc;
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            }
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        } else {
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            /* fill auxiliary table recursively */
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            n -= table_nb_bits;
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            code_prefix = code >> (32 - table_nb_bits);
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            subtable_bits = n;
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            codes[i].bits = n;
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            codes[i].code = code << table_nb_bits;
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            for (k = i+1; k < nb_codes; k++) {
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                n = codes[k].bits - table_nb_bits;
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                if (n <= 0)
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                    break;
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                code = codes[k].code;
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                if (code >> (32 - table_nb_bits) != code_prefix)
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                    break;
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                codes[k].bits = n;
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                codes[k].code = code << table_nb_bits;
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                subtable_bits = FFMAX(subtable_bits, n);
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            }
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            subtable_bits = FFMIN(subtable_bits, table_nb_bits);
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            j = (flags & INIT_VLC_LE) ? bitswap_32(code_prefix) >> (32 - table_nb_bits) : code_prefix;
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            table[j][1] = -subtable_bits;
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#ifdef DEBUG_VLC
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            av_log(NULL,AV_LOG_DEBUG,"%4x: n=%d (subtable)\n",
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                   j, codes[i].bits + table_nb_bits);
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#endif
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            index = build_table(vlc, subtable_bits, k-i, codes+i, 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[j][0] = index; //code
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            i = k-1;
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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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   'symbols' : table which gives the values to be returned from get_vlc().
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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', 'codes', and 'symbols' 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_sparse(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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             const void *symbols, int symbols_wrap, int symbols_size,
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             int flags)
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{
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    VLCcode *buf;
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    int i, j, ret;
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    vlc->bits = nb_bits;
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    if(flags & INIT_VLC_USE_NEW_STATIC){
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        if(vlc->table_size && vlc->table_size == vlc->table_allocated){
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            return 0;
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        }else if(vlc->table_size){
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            abort(); // fatal error, we are called on a partially initialized table
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        }
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    }else {
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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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    }
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#ifdef DEBUG_VLC
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    av_log(NULL,AV_LOG_DEBUG,"build table nb_codes=%d\n", nb_codes);
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#endif
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    buf = av_malloc((nb_codes+1)*sizeof(VLCcode));
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    assert(symbols_size <= 2 || !symbols);
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    j = 0;
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#define COPY(condition)\
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    for (i = 0; i < nb_codes; i++) {\
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        GET_DATA(buf[j].bits, bits, i, bits_wrap, bits_size);\
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        if (!(condition))\
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            continue;\
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        GET_DATA(buf[j].code, codes, i, codes_wrap, codes_size);\
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        if (flags & INIT_VLC_LE)\
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            buf[j].code = bitswap_32(buf[j].code);\
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        else\
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            buf[j].code <<= 32 - buf[j].bits;\
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        if (symbols)\
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            GET_DATA(buf[j].symbol, symbols, i, symbols_wrap, symbols_size)\
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        else\
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            buf[j].symbol = i;\
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        j++;\
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    }
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    COPY(buf[j].bits > nb_bits);
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    // qsort is the slowest part of init_vlc, and could probably be improved or avoided
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    qsort(buf, j, sizeof(VLCcode), compare_vlcspec);
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    COPY(buf[j].bits && buf[j].bits <= nb_bits);
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    nb_codes = j;
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    ret = build_table(vlc, nb_bits, nb_codes, buf, flags);
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    av_free(buf);
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    if (ret < 0) {
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        av_freep(&vlc->table);
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        return -1;
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    }
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    if((flags & INIT_VLC_USE_NEW_STATIC) && vlc->table_size != vlc->table_allocated)
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        av_log(NULL, AV_LOG_ERROR, "needed %d had %d\n", vlc->table_size, vlc->table_allocated);
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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_freep(&vlc->table);
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}
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