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4c4e746566
ffmpeg/libavcodec/bitstream.c
Måns Rullgård 4c4e746566 Avoid negative shifts in build_table() 
A shift by a negative amount has undefined behaviour.  Even though
the result of this shift is never used, the shift itself could
cause an exception of some kind.

Originally committed as revision 21939 to svn://svn.ffmpeg.org/ffmpeg/trunk
2010-02-21 15:11:57 +00:00

297 lines
9.3 KiB
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>
*
* 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 libavcodec/bitstream.c
* bitstream api.
*/
#include "avcodec.h"
#include "get_bits.h"
#include "put_bits.h"
const uint8_t ff_log2_run[32]={
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
};
void align_put_bits(PutBitContext *s)
{
#ifdef ALT_BITSTREAM_WRITER
put_bits(s,( - s->index) & 7,0);
#else
put_bits(s,s->bit_left & 7,0);
#endif
}
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 DEBUG_VLC
#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 int build_table(VLC *vlc, int table_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,
uint32_t code_prefix, int n_prefix, int flags)
{
int i, j, k, n, table_size, table_index, nb, n1, index, code_prefix2, symbol;
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);
#ifdef DEBUG_VLC
av_log(NULL,AV_LOG_DEBUG,"new table index=%d size=%d code_prefix=%x n=%d\n",
table_index, table_size, code_prefix, n_prefix);
#endif
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++) {
GET_DATA(n, bits, i, bits_wrap, bits_size);
GET_DATA(code, codes, i, codes_wrap, codes_size);
/* we accept tables with holes */
if (n <= 0)
continue;
if (!symbols)
symbol = i;
else
GET_DATA(symbol, symbols, i, symbols_wrap, symbols_size);
#if defined(DEBUG_VLC) && 0
av_log(NULL,AV_LOG_DEBUG,"i=%d n=%d code=0x%x\n", i, n, code);
#endif
/* if code matches the prefix, it is in the table */
n -= n_prefix;
if (n > 0) {
if(flags & INIT_VLC_LE)
code_prefix2= code & (n_prefix>=32 ? 0xffffffff : (1 << n_prefix)-1);
else
code_prefix2= code >> n;
if (code_prefix2 == code_prefix) {
if (n <= table_nb_bits) {
/* no need to add another table */
j = (code << (table_nb_bits - n)) & (table_size - 1);
nb = 1 << (table_nb_bits - n);
for(k=0;k<nb;k++) {
if(flags & INIT_VLC_LE)
j = (code >> n_prefix) + (k<<n);
#ifdef DEBUG_VLC
av_log(NULL, AV_LOG_DEBUG, "%4x: code=%d n=%d\n",
j, i, n);
#endif
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++;
}
} else {
n -= table_nb_bits;
j = (code >> ((flags & INIT_VLC_LE) ? n_prefix : n)) & ((1 << table_nb_bits) - 1);
#ifdef DEBUG_VLC
av_log(NULL,AV_LOG_DEBUG,"%4x: n=%d (subtable)\n",
j, n);
#endif
/* compute table size */
n1 = -table[j][1]; //bits
if (n > n1)
n1 = n;
table[j][1] = -n1; //bits
}
}
}
}
/* second pass : fill auxillary tables recursively */
for(i=0;i<table_size;i++) {
n = table[i][1]; //bits
if (n < 0) {
n = -n;
if (n > table_nb_bits) {
n = table_nb_bits;
table[i][1] = -n; //bits
}
index = build_table(vlc, n, nb_codes,
bits, bits_wrap, bits_size,
codes, codes_wrap, codes_size,
symbols, symbols_wrap, symbols_size,
(flags & INIT_VLC_LE) ? (code_prefix | (i << n_prefix)) : ((code_prefix << table_nb_bits) | i),
n_prefix + table_nb_bits, flags);
if (index < 0)
return -1;
/* note: realloc has been done, so reload tables */
table = &vlc->table[table_index];
table[i][0] = index; //code
}
}
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)
{
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;
}
#ifdef DEBUG_VLC
av_log(NULL,AV_LOG_DEBUG,"build table nb_codes=%d\n", nb_codes);
#endif
if (build_table(vlc, nb_bits, nb_codes,
bits, bits_wrap, bits_size,
codes, codes_wrap, codes_size,
symbols, symbols_wrap, symbols_size,
0, 0, flags) < 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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