bitstream.c
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1 /*
2  * Common bit i/o utils
3  * Copyright (c) 2000, 2001 Fabrice Bellard
4  * Copyright (c) 2002-2004 Michael Niedermayer <michaelni@gmx.at>
5  * Copyright (c) 2010 Loren Merritt
6  *
7  * alternative bitstream reader & writer by Michael Niedermayer <michaelni@gmx.at>
8  *
9  * This file is part of Libav.
10  *
11  * Libav is free software; you can redistribute it and/or
12  * modify it under the terms of the GNU Lesser General Public
13  * License as published by the Free Software Foundation; either
14  * version 2.1 of the License, or (at your option) any later version.
15  *
16  * Libav is distributed in the hope that it will be useful,
17  * but WITHOUT ANY WARRANTY; without even the implied warranty of
18  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
19  * Lesser General Public License for more details.
20  *
21  * You should have received a copy of the GNU Lesser General Public
22  * License along with Libav; if not, write to the Free Software
23  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
24  */
25 
31 #include "avcodec.h"
32 #include "get_bits.h"
33 #include "put_bits.h"
34 
35 const uint8_t ff_log2_run[41]={
36  0, 0, 0, 0, 1, 1, 1, 1,
37  2, 2, 2, 2, 3, 3, 3, 3,
38  4, 4, 5, 5, 6, 6, 7, 7,
39  8, 9,10,11,12,13,14,15,
40 16,17,18,19,20,21,22,23,
41 24,
42 };
43 
45 {
46  put_bits(s,s->bit_left & 7,0);
47 }
48 
49 void ff_put_string(PutBitContext *pb, const char *string, int terminate_string)
50 {
51  while(*string){
52  put_bits(pb, 8, *string);
53  string++;
54  }
55  if(terminate_string)
56  put_bits(pb, 8, 0);
57 }
58 
59 void avpriv_copy_bits(PutBitContext *pb, const uint8_t *src, int length)
60 {
61  int words= length>>4;
62  int bits= length&15;
63  int i;
64 
65  if(length==0) return;
66 
67  if(CONFIG_SMALL || words < 16 || put_bits_count(pb)&7){
68  for(i=0; i<words; i++) put_bits(pb, 16, AV_RB16(src + 2*i));
69  }else{
70  for(i=0; put_bits_count(pb)&31; i++)
71  put_bits(pb, 8, src[i]);
72  flush_put_bits(pb);
73  memcpy(put_bits_ptr(pb), src+i, 2*words-i);
74  skip_put_bytes(pb, 2*words-i);
75  }
76 
77  put_bits(pb, bits, AV_RB16(src + 2*words)>>(16-bits));
78 }
79 
80 /* VLC decoding */
81 
82 #define GET_DATA(v, table, i, wrap, size) \
83 {\
84  const uint8_t *ptr = (const uint8_t *)table + i * wrap;\
85  switch(size) {\
86  case 1:\
87  v = *(const uint8_t *)ptr;\
88  break;\
89  case 2:\
90  v = *(const uint16_t *)ptr;\
91  break;\
92  default:\
93  v = *(const uint32_t *)ptr;\
94  break;\
95  }\
96 }
97 
98 
99 static int alloc_table(VLC *vlc, int size, int use_static)
100 {
101  int index;
102  index = vlc->table_size;
103  vlc->table_size += size;
104  if (vlc->table_size > vlc->table_allocated) {
105  if(use_static)
106  abort(); // cannot do anything, init_vlc() is used with too little memory
107  vlc->table_allocated += (1 << vlc->bits);
108  vlc->table = av_realloc(vlc->table,
109  sizeof(VLC_TYPE) * 2 * vlc->table_allocated);
110  if (!vlc->table)
111  return -1;
112  }
113  return index;
114 }
115 
116 static av_always_inline uint32_t bitswap_32(uint32_t x) {
117  return (uint32_t)av_reverse[x&0xFF]<<24
118  | (uint32_t)av_reverse[(x>>8)&0xFF]<<16
119  | (uint32_t)av_reverse[(x>>16)&0xFF]<<8
120  | (uint32_t)av_reverse[x>>24];
121 }
122 
123 typedef struct {
124  uint8_t bits;
125  uint16_t symbol;
128  uint32_t code;
129 } VLCcode;
130 
131 static int compare_vlcspec(const void *a, const void *b)
132 {
133  const VLCcode *sa=a, *sb=b;
134  return (sa->code >> 1) - (sb->code >> 1);
135 }
136 
151 static int build_table(VLC *vlc, int table_nb_bits, int nb_codes,
152  VLCcode *codes, int flags)
153 {
154  int table_size, table_index, index, code_prefix, symbol, subtable_bits;
155  int i, j, k, n, nb, inc;
156  uint32_t code;
157  VLC_TYPE (*table)[2];
158 
159  table_size = 1 << table_nb_bits;
160  table_index = alloc_table(vlc, table_size, flags & INIT_VLC_USE_NEW_STATIC);
161  av_dlog(NULL, "new table index=%d size=%d\n", table_index, table_size);
162  if (table_index < 0)
163  return -1;
164  table = &vlc->table[table_index];
165 
166  for (i = 0; i < table_size; i++) {
167  table[i][1] = 0; //bits
168  table[i][0] = -1; //codes
169  }
170 
171  /* first pass: map codes and compute auxillary table sizes */
172  for (i = 0; i < nb_codes; i++) {
173  n = codes[i].bits;
174  code = codes[i].code;
175  symbol = codes[i].symbol;
176  av_dlog(NULL, "i=%d n=%d code=0x%x\n", i, n, code);
177  if (n <= table_nb_bits) {
178  /* no need to add another table */
179  j = code >> (32 - table_nb_bits);
180  nb = 1 << (table_nb_bits - n);
181  inc = 1;
182  if (flags & INIT_VLC_LE) {
183  j = bitswap_32(code);
184  inc = 1 << n;
185  }
186  for (k = 0; k < nb; k++) {
187  av_dlog(NULL, "%4x: code=%d n=%d\n", j, i, n);
188  if (table[j][1] /*bits*/ != 0) {
189  av_log(NULL, AV_LOG_ERROR, "incorrect codes\n");
190  return -1;
191  }
192  table[j][1] = n; //bits
193  table[j][0] = symbol;
194  j += inc;
195  }
196  } else {
197  /* fill auxiliary table recursively */
198  n -= table_nb_bits;
199  code_prefix = code >> (32 - table_nb_bits);
200  subtable_bits = n;
201  codes[i].bits = n;
202  codes[i].code = code << table_nb_bits;
203  for (k = i+1; k < nb_codes; k++) {
204  n = codes[k].bits - table_nb_bits;
205  if (n <= 0)
206  break;
207  code = codes[k].code;
208  if (code >> (32 - table_nb_bits) != code_prefix)
209  break;
210  codes[k].bits = n;
211  codes[k].code = code << table_nb_bits;
212  subtable_bits = FFMAX(subtable_bits, n);
213  }
214  subtable_bits = FFMIN(subtable_bits, table_nb_bits);
215  j = (flags & INIT_VLC_LE) ? bitswap_32(code_prefix) >> (32 - table_nb_bits) : code_prefix;
216  table[j][1] = -subtable_bits;
217  av_dlog(NULL, "%4x: n=%d (subtable)\n",
218  j, codes[i].bits + table_nb_bits);
219  index = build_table(vlc, subtable_bits, k-i, codes+i, flags);
220  if (index < 0)
221  return -1;
222  /* note: realloc has been done, so reload tables */
223  table = &vlc->table[table_index];
224  table[j][0] = index; //code
225  i = k-1;
226  }
227  }
228  return table_index;
229 }
230 
231 
232 /* Build VLC decoding tables suitable for use with get_vlc().
233 
234  'nb_bits' set thee decoding table size (2^nb_bits) entries. The
235  bigger it is, the faster is the decoding. But it should not be too
236  big to save memory and L1 cache. '9' is a good compromise.
237 
238  'nb_codes' : number of vlcs codes
239 
240  'bits' : table which gives the size (in bits) of each vlc code.
241 
242  'codes' : table which gives the bit pattern of of each vlc code.
243 
244  'symbols' : table which gives the values to be returned from get_vlc().
245 
246  'xxx_wrap' : give the number of bytes between each entry of the
247  'bits' or 'codes' tables.
248 
249  'xxx_size' : gives the number of bytes of each entry of the 'bits'
250  or 'codes' tables.
251 
252  'wrap' and 'size' allows to use any memory configuration and types
253  (byte/word/long) to store the 'bits', 'codes', and 'symbols' tables.
254 
255  'use_static' should be set to 1 for tables, which should be freed
256  with av_free_static(), 0 if ff_free_vlc() will be used.
257 */
258 int ff_init_vlc_sparse(VLC *vlc, int nb_bits, int nb_codes,
259  const void *bits, int bits_wrap, int bits_size,
260  const void *codes, int codes_wrap, int codes_size,
261  const void *symbols, int symbols_wrap, int symbols_size,
262  int flags)
263 {
264  VLCcode *buf;
265  int i, j, ret;
266 
267  vlc->bits = nb_bits;
268  if(flags & INIT_VLC_USE_NEW_STATIC){
269  if(vlc->table_size && vlc->table_size == vlc->table_allocated){
270  return 0;
271  }else if(vlc->table_size){
272  abort(); // fatal error, we are called on a partially initialized table
273  }
274  }else {
275  vlc->table = NULL;
276  vlc->table_allocated = 0;
277  vlc->table_size = 0;
278  }
279 
280  av_dlog(NULL, "build table nb_codes=%d\n", nb_codes);
281 
282  buf = av_malloc((nb_codes+1)*sizeof(VLCcode));
283 
284  assert(symbols_size <= 2 || !symbols);
285  j = 0;
286 #define COPY(condition)\
287  for (i = 0; i < nb_codes; i++) {\
288  GET_DATA(buf[j].bits, bits, i, bits_wrap, bits_size);\
289  if (!(condition))\
290  continue;\
291  GET_DATA(buf[j].code, codes, i, codes_wrap, codes_size);\
292  if (flags & INIT_VLC_LE)\
293  buf[j].code = bitswap_32(buf[j].code);\
294  else\
295  buf[j].code <<= 32 - buf[j].bits;\
296  if (symbols)\
297  GET_DATA(buf[j].symbol, symbols, i, symbols_wrap, symbols_size)\
298  else\
299  buf[j].symbol = i;\
300  j++;\
301  }
302  COPY(buf[j].bits > nb_bits);
303  // qsort is the slowest part of init_vlc, and could probably be improved or avoided
304  qsort(buf, j, sizeof(VLCcode), compare_vlcspec);
305  COPY(buf[j].bits && buf[j].bits <= nb_bits);
306  nb_codes = j;
307 
308  ret = build_table(vlc, nb_bits, nb_codes, buf, flags);
309 
310  av_free(buf);
311  if (ret < 0) {
312  av_freep(&vlc->table);
313  return -1;
314  }
315  if((flags & INIT_VLC_USE_NEW_STATIC) && vlc->table_size != vlc->table_allocated)
316  av_log(NULL, AV_LOG_ERROR, "needed %d had %d\n", vlc->table_size, vlc->table_allocated);
317  return 0;
318 }
319 
320 
321 void ff_free_vlc(VLC *vlc)
322 {
323  av_freep(&vlc->table);
324 }
325