FFmpeg
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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 FFmpeg.
10  *
11  * FFmpeg 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  * FFmpeg 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 FFmpeg; if not, write to the Free Software
23  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
24  */
25 
26 /**
27  * @file
28  * bitstream api.
29  */
30 
31 #include "libavutil/atomic.h"
32 #include "libavutil/avassert.h"
33 #include "avcodec.h"
34 #include "internal.h"
35 #include "mathops.h"
36 #include "get_bits.h"
37 #include "put_bits.h"
38 
39 const uint8_t ff_log2_run[41]={
40  0, 0, 0, 0, 1, 1, 1, 1,
41  2, 2, 2, 2, 3, 3, 3, 3,
42  4, 4, 5, 5, 6, 6, 7, 7,
43  8, 9,10,11,12,13,14,15,
44 16,17,18,19,20,21,22,23,
45 24,
46 };
47 
49 {
50  put_bits(s, s->bit_left & 7, 0);
51 }
52 
53 void avpriv_put_string(PutBitContext *pb, const char *string,
54  int terminate_string)
55 {
56  while (*string) {
57  put_bits(pb, 8, *string);
58  string++;
59  }
60  if (terminate_string)
61  put_bits(pb, 8, 0);
62 }
63 
65 {
66  int words = length >> 4;
67  int bits = length & 15;
68  int i;
69 
70  if (length == 0)
71  return;
72 
73  av_assert0(length <= put_bits_left(pb));
74 
75  if (CONFIG_SMALL || words < 16 || put_bits_count(pb) & 7) {
76  for (i = 0; i < words; i++)
77  put_bits(pb, 16, AV_RB16(src + 2 * i));
78  } else {
79  for (i = 0; put_bits_count(pb) & 31; i++)
80  put_bits(pb, 8, src[i]);
81  flush_put_bits(pb);
82  memcpy(put_bits_ptr(pb), src + i, 2 * words - i);
83  skip_put_bytes(pb, 2 * words - i);
84  }
85 
86  put_bits(pb, bits, AV_RB16(src + 2 * words) >> (16 - bits));
87 }
88 
89 /* VLC decoding */
90 
91 #define GET_DATA(v, table, i, wrap, size) \
92 { \
93  const uint8_t *ptr = (const uint8_t *)table + i * wrap; \
94  switch(size) { \
95  case 1: \
96  v = *(const uint8_t *)ptr; \
97  break; \
98  case 2: \
99  v = *(const uint16_t *)ptr; \
100  break; \
101  default: \
102  v = *(const uint32_t *)ptr; \
103  break; \
104  } \
105 }
106 
107 
108 static int alloc_table(VLC *vlc, int size, int use_static)
109 {
110  int index = vlc->table_size;
111 
112  vlc->table_size += size;
113  if (vlc->table_size > vlc->table_allocated) {
114  if (use_static)
115  abort(); // cannot do anything, init_vlc() is used with too little memory
116  vlc->table_allocated += (1 << vlc->bits);
117  vlc->table = av_realloc_f(vlc->table, vlc->table_allocated, sizeof(VLC_TYPE) * 2);
118  if (!vlc->table) {
119  vlc->table_allocated = 0;
120  vlc->table_size = 0;
121  return AVERROR(ENOMEM);
122  }
123  memset(vlc->table + vlc->table_allocated - (1 << vlc->bits), 0, sizeof(VLC_TYPE) * 2 << vlc->bits);
124  }
125  return index;
126 }
127 
128 static av_always_inline uint32_t bitswap_32(uint32_t x)
129 {
130  return (uint32_t)ff_reverse[ x & 0xFF] << 24 |
131  (uint32_t)ff_reverse[(x >> 8) & 0xFF] << 16 |
132  (uint32_t)ff_reverse[(x >> 16) & 0xFF] << 8 |
133  (uint32_t)ff_reverse[ x >> 24];
134 }
135 
136 typedef struct VLCcode {
138  uint16_t symbol;
139  /** codeword, with the first bit-to-be-read in the msb
140  * (even if intended for a little-endian bitstream reader) */
141  uint32_t code;
142 } VLCcode;
143 
144 static int compare_vlcspec(const void *a, const void *b)
145 {
146  const VLCcode *sa = a, *sb = b;
147  return (sa->code >> 1) - (sb->code >> 1);
148 }
149 /**
150  * Build VLC decoding tables suitable for use with get_vlc().
151  *
152  * @param vlc the context to be initted
153  *
154  * @param table_nb_bits max length of vlc codes to store directly in this table
155  * (Longer codes are delegated to subtables.)
156  *
157  * @param nb_codes number of elements in codes[]
158  *
159  * @param codes descriptions of the vlc codes
160  * These must be ordered such that codes going into the same subtable are contiguous.
161  * Sorting by VLCcode.code is sufficient, though not necessary.
162  */
163 static int build_table(VLC *vlc, int table_nb_bits, int nb_codes,
164  VLCcode *codes, int flags)
165 {
166  int table_size, table_index, index, code_prefix, symbol, subtable_bits;
167  int i, j, k, n, nb, inc;
168  uint32_t code;
169  volatile VLC_TYPE (* volatile table)[2]; // the double volatile is needed to prevent a internal compiler error in gcc 4.2
170 
171  table_size = 1 << table_nb_bits;
172  if (table_nb_bits > 30)
173  return -1;
174  table_index = alloc_table(vlc, table_size, flags & INIT_VLC_USE_NEW_STATIC);
175  ff_dlog(NULL, "new table index=%d size=%d\n", table_index, table_size);
176  if (table_index < 0)
177  return table_index;
178  table = (volatile VLC_TYPE (*)[2])&vlc->table[table_index];
179 
180  /* first pass: map codes and compute auxiliary table sizes */
181  for (i = 0; i < nb_codes; i++) {
182  n = codes[i].bits;
183  code = codes[i].code;
184  symbol = codes[i].symbol;
185  ff_dlog(NULL, "i=%d n=%d code=0x%x\n", i, n, code);
186  if (n <= table_nb_bits) {
187  /* no need to add another table */
188  j = code >> (32 - table_nb_bits);
189  nb = 1 << (table_nb_bits - n);
190  inc = 1;
191  if (flags & INIT_VLC_LE) {
192  j = bitswap_32(code);
193  inc = 1 << n;
194  }
195  for (k = 0; k < nb; k++) {
196  int bits = table[j][1];
197  ff_dlog(NULL, "%4x: code=%d n=%d\n", j, i, n);
198  if (bits != 0 && bits != n) {
199  av_log(NULL, AV_LOG_ERROR, "incorrect codes\n");
200  return AVERROR_INVALIDDATA;
201  }
202  table[j][1] = n; //bits
203  table[j][0] = symbol;
204  j += inc;
205  }
206  } else {
207  /* fill auxiliary table recursively */
208  n -= table_nb_bits;
209  code_prefix = code >> (32 - table_nb_bits);
210  subtable_bits = n;
211  codes[i].bits = n;
212  codes[i].code = code << table_nb_bits;
213  for (k = i+1; k < nb_codes; k++) {
214  n = codes[k].bits - table_nb_bits;
215  if (n <= 0)
216  break;
217  code = codes[k].code;
218  if (code >> (32 - table_nb_bits) != code_prefix)
219  break;
220  codes[k].bits = n;
221  codes[k].code = code << table_nb_bits;
222  subtable_bits = FFMAX(subtable_bits, n);
223  }
224  subtable_bits = FFMIN(subtable_bits, table_nb_bits);
225  j = (flags & INIT_VLC_LE) ? bitswap_32(code_prefix) >> (32 - table_nb_bits) : code_prefix;
226  table[j][1] = -subtable_bits;
227  ff_dlog(NULL, "%4x: n=%d (subtable)\n",
228  j, codes[i].bits + table_nb_bits);
229  index = build_table(vlc, subtable_bits, k-i, codes+i, flags);
230  if (index < 0)
231  return index;
232  /* note: realloc has been done, so reload tables */
233  table = (volatile VLC_TYPE (*)[2])&vlc->table[table_index];
234  table[j][0] = index; //code
235  i = k-1;
236  }
237  }
238 
239  for (i = 0; i < table_size; i++) {
240  if (table[i][1] == 0) //bits
241  table[i][0] = -1; //codes
242  }
243 
244  return table_index;
245 }
246 
247 
248 /* Build VLC decoding tables suitable for use with get_vlc().
249 
250  'nb_bits' set thee decoding table size (2^nb_bits) entries. The
251  bigger it is, the faster is the decoding. But it should not be too
252  big to save memory and L1 cache. '9' is a good compromise.
253 
254  'nb_codes' : number of vlcs codes
255 
256  'bits' : table which gives the size (in bits) of each vlc code.
257 
258  'codes' : table which gives the bit pattern of of each vlc code.
259 
260  'symbols' : table which gives the values to be returned from get_vlc().
261 
262  'xxx_wrap' : give the number of bytes between each entry of the
263  'bits' or 'codes' tables.
264 
265  'xxx_size' : gives the number of bytes of each entry of the 'bits'
266  or 'codes' tables.
267 
268  'wrap' and 'size' allows to use any memory configuration and types
269  (byte/word/long) to store the 'bits', 'codes', and 'symbols' tables.
270 
271  'use_static' should be set to 1 for tables, which should be freed
272  with av_free_static(), 0 if ff_free_vlc() will be used.
273 */
274 int ff_init_vlc_sparse(VLC *vlc_arg, int nb_bits, int nb_codes,
275  const void *bits, int bits_wrap, int bits_size,
276  const void *codes, int codes_wrap, int codes_size,
277  const void *symbols, int symbols_wrap, int symbols_size,
278  int flags)
279 {
280  VLCcode *buf;
281  int i, j, ret;
282  VLCcode localbuf[1500]; // the maximum currently needed is 1296 by rv34
283  VLC localvlc, *vlc;
284 
285  vlc = vlc_arg;
286  vlc->bits = nb_bits;
287  if (flags & INIT_VLC_USE_NEW_STATIC) {
288  av_assert0(nb_codes + 1 <= FF_ARRAY_ELEMS(localbuf));
289  buf = localbuf;
290  localvlc = *vlc_arg;
291  vlc = &localvlc;
292  vlc->table_size = 0;
293  } else {
294  vlc->table = NULL;
295  vlc->table_allocated = 0;
296  vlc->table_size = 0;
297 
298  buf = av_malloc_array((nb_codes + 1), sizeof(VLCcode));
299  if (!buf)
300  return AVERROR(ENOMEM);
301  }
302 
303 
304  av_assert0(symbols_size <= 2 || !symbols);
305  j = 0;
306 #define COPY(condition)\
307  for (i = 0; i < nb_codes; i++) { \
308  GET_DATA(buf[j].bits, bits, i, bits_wrap, bits_size); \
309  if (!(condition)) \
310  continue; \
311  if (buf[j].bits > 3*nb_bits || buf[j].bits>32) { \
312  av_log(NULL, AV_LOG_ERROR, "Too long VLC (%d) in init_vlc\n", buf[j].bits);\
313  if (!(flags & INIT_VLC_USE_NEW_STATIC)) \
314  av_free(buf); \
315  return -1; \
316  } \
317  GET_DATA(buf[j].code, codes, i, codes_wrap, codes_size); \
318  if (buf[j].code >= (1LL<<buf[j].bits)) { \
319  av_log(NULL, AV_LOG_ERROR, "Invalid code in init_vlc\n"); \
320  if (!(flags & INIT_VLC_USE_NEW_STATIC)) \
321  av_free(buf); \
322  return -1; \
323  } \
324  if (flags & INIT_VLC_LE) \
325  buf[j].code = bitswap_32(buf[j].code); \
326  else \
327  buf[j].code <<= 32 - buf[j].bits; \
328  if (symbols) \
329  GET_DATA(buf[j].symbol, symbols, i, symbols_wrap, symbols_size) \
330  else \
331  buf[j].symbol = i; \
332  j++; \
333  }
334  COPY(buf[j].bits > nb_bits);
335  // qsort is the slowest part of init_vlc, and could probably be improved or avoided
336  qsort(buf, j, sizeof(VLCcode), compare_vlcspec);
337  COPY(buf[j].bits && buf[j].bits <= nb_bits);
338  nb_codes = j;
339 
340  ret = build_table(vlc, nb_bits, nb_codes, buf, flags);
341 
342  if (flags & INIT_VLC_USE_NEW_STATIC) {
343  if(vlc->table_size != vlc->table_allocated)
344  av_log(NULL, AV_LOG_ERROR, "needed %d had %d\n", vlc->table_size, vlc->table_allocated);
345 
346  av_assert0(ret >= 0);
347  *vlc_arg = *vlc;
348  } else {
349  av_free(buf);
350  if (ret < 0) {
351  av_freep(&vlc->table);
352  return ret;
353  }
354  }
355  return 0;
356 }
357 
358 
359 void ff_free_vlc(VLC *vlc)
360 {
361  av_freep(&vlc->table);
362 }