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 "mathops.h"
33 #include "get_bits.h"
34 #include "put_bits.h"
35 
36 const uint8_t ff_log2_run[41]={
37  0, 0, 0, 0, 1, 1, 1, 1,
38  2, 2, 2, 2, 3, 3, 3, 3,
39  4, 4, 5, 5, 6, 6, 7, 7,
40  8, 9,10,11,12,13,14,15,
41 16,17,18,19,20,21,22,23,
42 24,
43 };
44 
46 {
47  put_bits(s,s->bit_left & 7,0);
48 }
49 
50 void avpriv_put_string(PutBitContext *pb, const char *string, int terminate_string)
51 {
52  while(*string){
53  put_bits(pb, 8, *string);
54  string++;
55  }
56  if(terminate_string)
57  put_bits(pb, 8, 0);
58 }
59 
60 void avpriv_copy_bits(PutBitContext *pb, const uint8_t *src, int length)
61 {
62  int words= length>>4;
63  int bits= length&15;
64  int i;
65 
66  if(length==0) return;
67 
68  if(CONFIG_SMALL || words < 16 || put_bits_count(pb)&7){
69  for(i=0; i<words; i++) put_bits(pb, 16, AV_RB16(src + 2*i));
70  }else{
71  for(i=0; put_bits_count(pb)&31; i++)
72  put_bits(pb, 8, src[i]);
73  flush_put_bits(pb);
74  memcpy(put_bits_ptr(pb), src+i, 2*words-i);
75  skip_put_bytes(pb, 2*words-i);
76  }
77 
78  put_bits(pb, bits, AV_RB16(src + 2*words)>>(16-bits));
79 }
80 
81 /* VLC decoding */
82 
83 #define GET_DATA(v, table, i, wrap, size) \
84 {\
85  const uint8_t *ptr = (const uint8_t *)table + i * wrap;\
86  switch(size) {\
87  case 1:\
88  v = *(const uint8_t *)ptr;\
89  break;\
90  case 2:\
91  v = *(const uint16_t *)ptr;\
92  break;\
93  default:\
94  v = *(const uint32_t *)ptr;\
95  break;\
96  }\
97 }
98 
99 
100 static int alloc_table(VLC *vlc, int size, int use_static)
101 {
102  int index;
103  index = vlc->table_size;
104  vlc->table_size += size;
105  if (vlc->table_size > vlc->table_allocated) {
106  if(use_static)
107  abort(); // cannot do anything, init_vlc() is used with too little memory
108  vlc->table_allocated += (1 << vlc->bits);
109  vlc->table = av_realloc(vlc->table,
110  sizeof(VLC_TYPE) * 2 * vlc->table_allocated);
111  if (!vlc->table)
112  return -1;
113  }
114  return index;
115 }
116 
117 static av_always_inline uint32_t bitswap_32(uint32_t x) {
118  return (uint32_t)ff_reverse[x&0xFF]<<24
119  | (uint32_t)ff_reverse[(x>>8)&0xFF]<<16
120  | (uint32_t)ff_reverse[(x>>16)&0xFF]<<8
121  | (uint32_t)ff_reverse[x>>24];
122 }
123 
124 typedef struct {
126  uint16_t symbol;
129  uint32_t code;
130 } VLCcode;
131 
132 static int compare_vlcspec(const void *a, const void *b)
133 {
134  const VLCcode *sa=a, *sb=b;
135  return (sa->code >> 1) - (sb->code >> 1);
136 }
137 
152 static int build_table(VLC *vlc, int table_nb_bits, int nb_codes,
153  VLCcode *codes, int flags)
154 {
155  int table_size, table_index, index, code_prefix, symbol, subtable_bits;
156  int i, j, k, n, nb, inc;
157  uint32_t code;
158  VLC_TYPE (*table)[2];
159 
160  table_size = 1 << table_nb_bits;
161  table_index = alloc_table(vlc, table_size, flags & INIT_VLC_USE_NEW_STATIC);
162  av_dlog(NULL, "new table index=%d size=%d\n", table_index, table_size);
163  if (table_index < 0)
164  return -1;
165  table = &vlc->table[table_index];
166 
167  for (i = 0; i < table_size; i++) {
168  table[i][1] = 0; //bits
169  table[i][0] = -1; //codes
170  }
171 
172  /* first pass: map codes and compute auxiliary table sizes */
173  for (i = 0; i < nb_codes; i++) {
174  n = codes[i].bits;
175  code = codes[i].code;
176  symbol = codes[i].symbol;
177  av_dlog(NULL, "i=%d n=%d code=0x%x\n", i, n, code);
178  if (n <= table_nb_bits) {
179  /* no need to add another table */
180  j = code >> (32 - table_nb_bits);
181  nb = 1 << (table_nb_bits - n);
182  inc = 1;
183  if (flags & INIT_VLC_LE) {
184  j = bitswap_32(code);
185  inc = 1 << n;
186  }
187  for (k = 0; k < nb; k++) {
188  av_dlog(NULL, "%4x: code=%d n=%d\n", j, i, n);
189  if (table[j][1] /*bits*/ != 0) {
190  av_log(NULL, AV_LOG_ERROR, "incorrect codes\n");
191  return -1;
192  }
193  table[j][1] = n; //bits
194  table[j][0] = symbol;
195  j += inc;
196  }
197  } else {
198  /* fill auxiliary table recursively */
199  n -= table_nb_bits;
200  code_prefix = code >> (32 - table_nb_bits);
201  subtable_bits = n;
202  codes[i].bits = n;
203  codes[i].code = code << table_nb_bits;
204  for (k = i+1; k < nb_codes; k++) {
205  n = codes[k].bits - table_nb_bits;
206  if (n <= 0)
207  break;
208  code = codes[k].code;
209  if (code >> (32 - table_nb_bits) != code_prefix)
210  break;
211  codes[k].bits = n;
212  codes[k].code = code << table_nb_bits;
213  subtable_bits = FFMAX(subtable_bits, n);
214  }
215  subtable_bits = FFMIN(subtable_bits, table_nb_bits);
216  j = (flags & INIT_VLC_LE) ? bitswap_32(code_prefix) >> (32 - table_nb_bits) : code_prefix;
217  table[j][1] = -subtable_bits;
218  av_dlog(NULL, "%4x: n=%d (subtable)\n",
219  j, codes[i].bits + table_nb_bits);
220  index = build_table(vlc, subtable_bits, k-i, codes+i, flags);
221  if (index < 0)
222  return -1;
223  /* note: realloc has been done, so reload tables */
224  table = &vlc->table[table_index];
225  table[j][0] = index; //code
226  i = k-1;
227  }
228  }
229  return table_index;
230 }
231 
232 
233 /* Build VLC decoding tables suitable for use with get_vlc().
234 
235  'nb_bits' set thee decoding table size (2^nb_bits) entries. The
236  bigger it is, the faster is the decoding. But it should not be too
237  big to save memory and L1 cache. '9' is a good compromise.
238 
239  'nb_codes' : number of vlcs codes
240 
241  'bits' : table which gives the size (in bits) of each vlc code.
242 
243  'codes' : table which gives the bit pattern of of each vlc code.
244 
245  'symbols' : table which gives the values to be returned from get_vlc().
246 
247  'xxx_wrap' : give the number of bytes between each entry of the
248  'bits' or 'codes' tables.
249 
250  'xxx_size' : gives the number of bytes of each entry of the 'bits'
251  or 'codes' tables.
252 
253  'wrap' and 'size' allows to use any memory configuration and types
254  (byte/word/long) to store the 'bits', 'codes', and 'symbols' tables.
255 
256  'use_static' should be set to 1 for tables, which should be freed
257  with av_free_static(), 0 if ff_free_vlc() will be used.
258 */
259 int ff_init_vlc_sparse(VLC *vlc, int nb_bits, int nb_codes,
260  const void *bits, int bits_wrap, int bits_size,
261  const void *codes, int codes_wrap, int codes_size,
262  const void *symbols, int symbols_wrap, int symbols_size,
263  int flags)
264 {
265  VLCcode *buf;
266  int i, j, ret;
267 
268  vlc->bits = nb_bits;
269  if(flags & INIT_VLC_USE_NEW_STATIC){
270  if(vlc->table_size && vlc->table_size == vlc->table_allocated){
271  return 0;
272  }else if(vlc->table_size){
273  abort(); // fatal error, we are called on a partially initialized table
274  }
275  }else {
276  vlc->table = NULL;
277  vlc->table_allocated = 0;
278  vlc->table_size = 0;
279  }
280 
281  av_dlog(NULL, "build table nb_codes=%d\n", nb_codes);
282 
283  buf = av_malloc((nb_codes+1)*sizeof(VLCcode));
284 
285  assert(symbols_size <= 2 || !symbols);
286  j = 0;
287 #define COPY(condition)\
288  for (i = 0; i < nb_codes; i++) {\
289  GET_DATA(buf[j].bits, bits, i, bits_wrap, bits_size);\
290  if (!(condition))\
291  continue;\
292  GET_DATA(buf[j].code, codes, i, codes_wrap, codes_size);\
293  if (flags & INIT_VLC_LE)\
294  buf[j].code = bitswap_32(buf[j].code);\
295  else\
296  buf[j].code <<= 32 - buf[j].bits;\
297  if (symbols)\
298  GET_DATA(buf[j].symbol, symbols, i, symbols_wrap, symbols_size)\
299  else\
300  buf[j].symbol = i;\
301  j++;\
302  }
303  COPY(buf[j].bits > nb_bits);
304  // qsort is the slowest part of init_vlc, and could probably be improved or avoided
305  qsort(buf, j, sizeof(VLCcode), compare_vlcspec);
306  COPY(buf[j].bits && buf[j].bits <= nb_bits);
307  nb_codes = j;
308 
309  ret = build_table(vlc, nb_bits, nb_codes, buf, flags);
310 
311  av_free(buf);
312  if (ret < 0) {
313  av_freep(&vlc->table);
314  return -1;
315  }
316  if((flags & INIT_VLC_USE_NEW_STATIC) && vlc->table_size != vlc->table_allocated)
317  av_log(NULL, AV_LOG_ERROR, "needed %d had %d\n", vlc->table_size, vlc->table_allocated);
318  return 0;
319 }
320 
321 
322 void ff_free_vlc(VLC *vlc)
323 {
324  av_freep(&vlc->table);
325 }