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ffmpeg/libavcodec/bitstream.c

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/*
* Common bit i/o utils
* Copyright (c) 2000, 2001 Fabrice Bellard
* Copyright (c) 2002-2004 Michael Niedermayer <michaelni@gmx.at>
* Copyright (c) 2010 Loren Merritt
*
* alternative bitstream reader & writer by Michael Niedermayer <michaelni@gmx.at>
*
* This file is part of FFmpeg.
*
* FFmpeg is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2.1 of the License, or (at your option) any later version.
*
* FFmpeg is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with FFmpeg; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
*/
/**
* @file
* bitstream api.
*/
#include "avcodec.h"
#include "get_bits.h"
#include "put_bits.h"
const uint8_t ff_log2_run[41]={
0, 0, 0, 0, 1, 1, 1, 1,
2, 2, 2, 2, 3, 3, 3, 3,
4, 4, 5, 5, 6, 6, 7, 7,
8, 9,10,11,12,13,14,15,
16,17,18,19,20,21,22,23,
24,
};
void align_put_bits(PutBitContext *s)
{
put_bits(s,s->bit_left & 7,0);
}
void ff_put_string(PutBitContext *pb, const char *string, int terminate_string)
{
while(*string){
put_bits(pb, 8, *string);
string++;
}
if(terminate_string)
put_bits(pb, 8, 0);
}
void ff_copy_bits(PutBitContext *pb, const uint8_t *src, int length)
{
int words= length>>4;
int bits= length&15;
int i;
if(length==0) return;
if(CONFIG_SMALL || words < 16 || put_bits_count(pb)&7){
for(i=0; i<words; i++) put_bits(pb, 16, AV_RB16(src + 2*i));
}else{
for(i=0; put_bits_count(pb)&31; i++)
put_bits(pb, 8, src[i]);
flush_put_bits(pb);
memcpy(put_bits_ptr(pb), src+i, 2*words-i);
skip_put_bytes(pb, 2*words-i);
}
put_bits(pb, bits, AV_RB16(src + 2*words)>>(16-bits));
}
/* VLC decoding */
#define GET_DATA(v, table, i, wrap, size) \
{\
const uint8_t *ptr = (const uint8_t *)table + i * wrap;\
switch(size) {\
case 1:\
v = *(const uint8_t *)ptr;\
break;\
case 2:\
v = *(const uint16_t *)ptr;\
break;\
default:\
v = *(const uint32_t *)ptr;\
break;\
}\
}
static int alloc_table(VLC *vlc, int size, int use_static)
{
int index;
index = vlc->table_size;
vlc->table_size += size;
if (vlc->table_size > vlc->table_allocated) {
if(use_static)
abort(); //cant do anything, init_vlc() is used with too little memory
vlc->table_allocated += (1 << vlc->bits);
vlc->table = av_realloc(vlc->table,
sizeof(VLC_TYPE) * 2 * vlc->table_allocated);
if (!vlc->table)
return -1;
}
return index;
}
static av_always_inline uint32_t bitswap_32(uint32_t x) {
return (uint32_t)av_reverse[x&0xFF]<<24
| (uint32_t)av_reverse[(x>>8)&0xFF]<<16
| (uint32_t)av_reverse[(x>>16)&0xFF]<<8
| (uint32_t)av_reverse[x>>24];
}
typedef struct {
uint8_t bits;
uint16_t symbol;
/** codeword, with the first bit-to-be-read in the msb
* (even if intended for a little-endian bitstream reader) */
uint32_t code;
} VLCcode;
static int compare_vlcspec(const void *a, const void *b)
{
const VLCcode *sa=a, *sb=b;
return (sa->code >> 1) - (sb->code >> 1);
}
/**
* Build VLC decoding tables suitable for use with get_vlc().
*
* @param vlc the context to be initted
*
* @param table_nb_bits max length of vlc codes to store directly in this table
* (Longer codes are delegated to subtables.)
*
* @param nb_codes number of elements in codes[]
*
* @param codes descriptions of the vlc codes
* These must be ordered such that codes going into the same subtable are contiguous.
* Sorting by VLCcode.code is sufficient, though not necessary.
*/
static int build_table(VLC *vlc, int table_nb_bits, int nb_codes,
VLCcode *codes, int flags)
{
int table_size, table_index, index, code_prefix, symbol, subtable_bits;
int i, j, k, n, nb, inc;
uint32_t code;
VLC_TYPE (*table)[2];
table_size = 1 << table_nb_bits;
table_index = alloc_table(vlc, table_size, flags & INIT_VLC_USE_NEW_STATIC);
av_dlog(NULL, "new table index=%d size=%d\n", table_index, table_size);
if (table_index < 0)
return -1;
table = &vlc->table[table_index];
for (i = 0; i < table_size; i++) {
table[i][1] = 0; //bits
table[i][0] = -1; //codes
}
/* first pass: map codes and compute auxillary table sizes */
for (i = 0; i < nb_codes; i++) {
n = codes[i].bits;
code = codes[i].code;
symbol = codes[i].symbol;
av_dlog(NULL, "i=%d n=%d code=0x%x\n", i, n, code);
if (n <= table_nb_bits) {
/* no need to add another table */
j = code >> (32 - table_nb_bits);
nb = 1 << (table_nb_bits - n);
inc = 1;
if (flags & INIT_VLC_LE) {
j = bitswap_32(code);
inc = 1 << n;
}
for (k = 0; k < nb; k++) {
av_dlog(NULL, "%4x: code=%d n=%d\n", j, i, n);
if (table[j][1] /*bits*/ != 0) {
av_log(NULL, AV_LOG_ERROR, "incorrect codes\n");
return -1;
}
table[j][1] = n; //bits
table[j][0] = symbol;
j += inc;
}
} else {
/* fill auxiliary table recursively */
n -= table_nb_bits;
code_prefix = code >> (32 - table_nb_bits);
subtable_bits = n;
codes[i].bits = n;
codes[i].code = code << table_nb_bits;
for (k = i+1; k < nb_codes; k++) {
n = codes[k].bits - table_nb_bits;
if (n <= 0)
break;
code = codes[k].code;
if (code >> (32 - table_nb_bits) != code_prefix)
break;
codes[k].bits = n;
codes[k].code = code << table_nb_bits;
subtable_bits = FFMAX(subtable_bits, n);
}
subtable_bits = FFMIN(subtable_bits, table_nb_bits);
j = (flags & INIT_VLC_LE) ? bitswap_32(code_prefix) >> (32 - table_nb_bits) : code_prefix;
table[j][1] = -subtable_bits;
av_dlog(NULL, "%4x: n=%d (subtable)\n",
j, codes[i].bits + table_nb_bits);
index = build_table(vlc, subtable_bits, k-i, codes+i, flags);
if (index < 0)
return -1;
/* note: realloc has been done, so reload tables */
table = &vlc->table[table_index];
table[j][0] = index; //code
i = k-1;
}
}
return table_index;
}
/* Build VLC decoding tables suitable for use with get_vlc().
'nb_bits' set thee decoding table size (2^nb_bits) entries. The
bigger it is, the faster is the decoding. But it should not be too
big to save memory and L1 cache. '9' is a good compromise.
'nb_codes' : number of vlcs codes
'bits' : table which gives the size (in bits) of each vlc code.
'codes' : table which gives the bit pattern of of each vlc code.
'symbols' : table which gives the values to be returned from get_vlc().
'xxx_wrap' : give the number of bytes between each entry of the
'bits' or 'codes' tables.
'xxx_size' : gives the number of bytes of each entry of the 'bits'
or 'codes' tables.
'wrap' and 'size' allows to use any memory configuration and types
(byte/word/long) to store the 'bits', 'codes', and 'symbols' tables.
'use_static' should be set to 1 for tables, which should be freed
with av_free_static(), 0 if free_vlc() will be used.
*/
int init_vlc_sparse(VLC *vlc, int nb_bits, int nb_codes,
const void *bits, int bits_wrap, int bits_size,
const void *codes, int codes_wrap, int codes_size,
const void *symbols, int symbols_wrap, int symbols_size,
int flags)
{
VLCcode *buf;
int i, j, ret;
vlc->bits = nb_bits;
if(flags & INIT_VLC_USE_NEW_STATIC){
if(vlc->table_size && vlc->table_size == vlc->table_allocated){
return 0;
}else if(vlc->table_size){
abort(); // fatal error, we are called on a partially initialized table
}
}else {
vlc->table = NULL;
vlc->table_allocated = 0;
vlc->table_size = 0;
}
av_dlog(NULL, "build table nb_codes=%d\n", nb_codes);
buf = av_malloc((nb_codes+1)*sizeof(VLCcode));
assert(symbols_size <= 2 || !symbols);
j = 0;
#define COPY(condition)\
for (i = 0; i < nb_codes; i++) {\
GET_DATA(buf[j].bits, bits, i, bits_wrap, bits_size);\
if (!(condition))\
continue;\
GET_DATA(buf[j].code, codes, i, codes_wrap, codes_size);\
if (flags & INIT_VLC_LE)\
buf[j].code = bitswap_32(buf[j].code);\
else\
buf[j].code <<= 32 - buf[j].bits;\
if (symbols)\
GET_DATA(buf[j].symbol, symbols, i, symbols_wrap, symbols_size)\
else\
buf[j].symbol = i;\
j++;\
}
COPY(buf[j].bits > nb_bits);
// qsort is the slowest part of init_vlc, and could probably be improved or avoided
qsort(buf, j, sizeof(VLCcode), compare_vlcspec);
COPY(buf[j].bits && buf[j].bits <= nb_bits);
nb_codes = j;
ret = build_table(vlc, nb_bits, nb_codes, buf, flags);
av_free(buf);
if (ret < 0) {
av_freep(&vlc->table);
return -1;
}
if((flags & INIT_VLC_USE_NEW_STATIC) && vlc->table_size != vlc->table_allocated)
av_log(NULL, AV_LOG_ERROR, "needed %d had %d\n", vlc->table_size, vlc->table_allocated);
return 0;
}
void free_vlc(VLC *vlc)
{
av_freep(&vlc->table);
}
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