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 "mathops.h"
35 #include "get_bits.h"
36 #include "put_bits.h"
37 
38 const uint8_t ff_log2_run[41]={
39  0, 0, 0, 0, 1, 1, 1, 1,
40  2, 2, 2, 2, 3, 3, 3, 3,
41  4, 4, 5, 5, 6, 6, 7, 7,
42  8, 9,10,11,12,13,14,15,
43 16,17,18,19,20,21,22,23,
44 24,
45 };
46 
48 {
49  put_bits(s, s->bit_left & 7, 0);
50 }
51 
52 void avpriv_put_string(PutBitContext *pb, const char *string,
53  int terminate_string)
54 {
55  while (*string) {
56  put_bits(pb, 8, *string);
57  string++;
58  }
59  if (terminate_string)
60  put_bits(pb, 8, 0);
61 }
62 
64 {
65  int words = length >> 4;
66  int bits = length & 15;
67  int i;
68 
69  if (length == 0)
70  return;
71 
72  if (CONFIG_SMALL || words < 16 || put_bits_count(pb) & 7) {
73  for (i = 0; i < words; i++)
74  put_bits(pb, 16, AV_RB16(src + 2 * i));
75  } else {
76  for (i = 0; put_bits_count(pb) & 31; i++)
77  put_bits(pb, 8, src[i]);
78  flush_put_bits(pb);
79  memcpy(put_bits_ptr(pb), src + i, 2 * words - i);
80  skip_put_bytes(pb, 2 * words - i);
81  }
82 
83  put_bits(pb, bits, AV_RB16(src + 2 * words) >> (16 - bits));
84 }
85 
86 /* VLC decoding */
87 
88 #define GET_DATA(v, table, i, wrap, size) \
89 { \
90  const uint8_t *ptr = (const uint8_t *)table + i * wrap; \
91  switch(size) { \
92  case 1: \
93  v = *(const uint8_t *)ptr; \
94  break; \
95  case 2: \
96  v = *(const uint16_t *)ptr; \
97  break; \
98  default: \
99  v = *(const uint32_t *)ptr; \
100  break; \
101  } \
102 }
103 
104 
105 static int alloc_table(VLC *vlc, int size, int use_static)
106 {
107  int index = vlc->table_size;
108 
109  vlc->table_size += size;
110  if (vlc->table_size > vlc->table_allocated) {
111  if (use_static)
112  abort(); // cannot do anything, init_vlc() is used with too little memory
113  vlc->table_allocated += (1 << vlc->bits);
114  vlc->table = av_realloc_f(vlc->table, vlc->table_allocated, sizeof(VLC_TYPE) * 2);
115  if (!vlc->table) {
116  vlc->table_allocated = 0;
117  vlc->table_size = 0;
118  return AVERROR(ENOMEM);
119  }
120  memset(vlc->table + vlc->table_allocated - (1 << vlc->bits), 0, sizeof(VLC_TYPE) * 2 << vlc->bits);
121  }
122  return index;
123 }
124 
125 static av_always_inline uint32_t bitswap_32(uint32_t x)
126 {
127  return (uint32_t)ff_reverse[ x & 0xFF] << 24 |
128  (uint32_t)ff_reverse[(x >> 8) & 0xFF] << 16 |
129  (uint32_t)ff_reverse[(x >> 16) & 0xFF] << 8 |
130  (uint32_t)ff_reverse[ x >> 24];
131 }
132 
133 typedef struct {
135  uint16_t symbol;
136  /** codeword, with the first bit-to-be-read in the msb
137  * (even if intended for a little-endian bitstream reader) */
138  uint32_t code;
139 } VLCcode;
140 
141 static int compare_vlcspec(const void *a, const void *b)
142 {
143  const VLCcode *sa = a, *sb = b;
144  return (sa->code >> 1) - (sb->code >> 1);
145 }
146 /**
147  * Build VLC decoding tables suitable for use with get_vlc().
148  *
149  * @param vlc the context to be initted
150  *
151  * @param table_nb_bits max length of vlc codes to store directly in this table
152  * (Longer codes are delegated to subtables.)
153  *
154  * @param nb_codes number of elements in codes[]
155  *
156  * @param codes descriptions of the vlc codes
157  * These must be ordered such that codes going into the same subtable are contiguous.
158  * Sorting by VLCcode.code is sufficient, though not necessary.
159  */
160 static int build_table(VLC *vlc, int table_nb_bits, int nb_codes,
161  VLCcode *codes, int flags)
162 {
163  int table_size, table_index, index, code_prefix, symbol, subtable_bits;
164  int i, j, k, n, nb, inc;
165  uint32_t code;
166  volatile VLC_TYPE (* volatile table)[2]; // the double volatile is needed to prevent a internal compiler error in gcc 4.2
167 
168  table_size = 1 << table_nb_bits;
169  if (table_nb_bits > 30)
170  return -1;
171  table_index = alloc_table(vlc, table_size, flags & INIT_VLC_USE_NEW_STATIC);
172  av_dlog(NULL, "new table index=%d size=%d\n", table_index, table_size);
173  if (table_index < 0)
174  return table_index;
175  table = (volatile VLC_TYPE (*)[2])&vlc->table[table_index];
176 
177  /* first pass: map codes and compute auxiliary table sizes */
178  for (i = 0; i < nb_codes; i++) {
179  n = codes[i].bits;
180  code = codes[i].code;
181  symbol = codes[i].symbol;
182  av_dlog(NULL, "i=%d n=%d code=0x%x\n", i, n, code);
183  if (n <= table_nb_bits) {
184  /* no need to add another table */
185  j = code >> (32 - table_nb_bits);
186  nb = 1 << (table_nb_bits - n);
187  inc = 1;
188  if (flags & INIT_VLC_LE) {
189  j = bitswap_32(code);
190  inc = 1 << n;
191  }
192  for (k = 0; k < nb; k++) {
193  int bits = table[j][1];
194  av_dlog(NULL, "%4x: code=%d n=%d\n", j, i, n);
195  if (bits != 0 && bits != n) {
196  av_log(NULL, AV_LOG_ERROR, "incorrect codes\n");
197  return AVERROR_INVALIDDATA;
198  }
199  table[j][1] = n; //bits
200  table[j][0] = symbol;
201  j += inc;
202  }
203  } else {
204  /* fill auxiliary table recursively */
205  n -= table_nb_bits;
206  code_prefix = code >> (32 - table_nb_bits);
207  subtable_bits = n;
208  codes[i].bits = n;
209  codes[i].code = code << table_nb_bits;
210  for (k = i+1; k < nb_codes; k++) {
211  n = codes[k].bits - table_nb_bits;
212  if (n <= 0)
213  break;
214  code = codes[k].code;
215  if (code >> (32 - table_nb_bits) != code_prefix)
216  break;
217  codes[k].bits = n;
218  codes[k].code = code << table_nb_bits;
219  subtable_bits = FFMAX(subtable_bits, n);
220  }
221  subtable_bits = FFMIN(subtable_bits, table_nb_bits);
222  j = (flags & INIT_VLC_LE) ? bitswap_32(code_prefix) >> (32 - table_nb_bits) : code_prefix;
223  table[j][1] = -subtable_bits;
224  av_dlog(NULL, "%4x: n=%d (subtable)\n",
225  j, codes[i].bits + table_nb_bits);
226  index = build_table(vlc, subtable_bits, k-i, codes+i, flags);
227  if (index < 0)
228  return index;
229  /* note: realloc has been done, so reload tables */
230  table = (volatile VLC_TYPE (*)[2])&vlc->table[table_index];
231  table[j][0] = index; //code
232  i = k-1;
233  }
234  }
235 
236  for (i = 0; i < table_size; i++) {
237  if (table[i][1] == 0) //bits
238  table[i][0] = -1; //codes
239  }
240 
241  return table_index;
242 }
243 
244 
245 /* Build VLC decoding tables suitable for use with get_vlc().
246 
247  'nb_bits' set thee decoding table size (2^nb_bits) entries. The
248  bigger it is, the faster is the decoding. But it should not be too
249  big to save memory and L1 cache. '9' is a good compromise.
250 
251  'nb_codes' : number of vlcs codes
252 
253  'bits' : table which gives the size (in bits) of each vlc code.
254 
255  'codes' : table which gives the bit pattern of of each vlc code.
256 
257  'symbols' : table which gives the values to be returned from get_vlc().
258 
259  'xxx_wrap' : give the number of bytes between each entry of the
260  'bits' or 'codes' tables.
261 
262  'xxx_size' : gives the number of bytes of each entry of the 'bits'
263  or 'codes' tables.
264 
265  'wrap' and 'size' allows to use any memory configuration and types
266  (byte/word/long) to store the 'bits', 'codes', and 'symbols' tables.
267 
268  'use_static' should be set to 1 for tables, which should be freed
269  with av_free_static(), 0 if ff_free_vlc() will be used.
270 */
271 int ff_init_vlc_sparse(VLC *vlc_arg, int nb_bits, int nb_codes,
272  const void *bits, int bits_wrap, int bits_size,
273  const void *codes, int codes_wrap, int codes_size,
274  const void *symbols, int symbols_wrap, int symbols_size,
275  int flags)
276 {
277  VLCcode *buf;
278  int i, j, ret;
279  VLCcode localbuf[1500]; // the maximum currently needed is 1296 by rv34
280  VLC localvlc, *vlc;
281 
282  vlc = vlc_arg;
283  vlc->bits = nb_bits;
284  if (flags & INIT_VLC_USE_NEW_STATIC) {
285  av_assert0(nb_codes + 1 <= FF_ARRAY_ELEMS(localbuf));
286  buf = localbuf;
287  localvlc = *vlc_arg;
288  vlc = &localvlc;
289  vlc->table_size = 0;
290  } else {
291  vlc->table = NULL;
292  vlc->table_allocated = 0;
293  vlc->table_size = 0;
294 
295  buf = av_malloc_array((nb_codes + 1), sizeof(VLCcode));
296  if (!buf)
297  return AVERROR(ENOMEM);
298  }
299 
300 
301  av_assert0(symbols_size <= 2 || !symbols);
302  j = 0;
303 #define COPY(condition)\
304  for (i = 0; i < nb_codes; i++) { \
305  GET_DATA(buf[j].bits, bits, i, bits_wrap, bits_size); \
306  if (!(condition)) \
307  continue; \
308  if (buf[j].bits > 3*nb_bits || buf[j].bits>32) { \
309  av_log(NULL, AV_LOG_ERROR, "Too long VLC (%d) in init_vlc\n", buf[j].bits);\
310  if (!(flags & INIT_VLC_USE_NEW_STATIC)) \
311  av_free(buf); \
312  return -1; \
313  } \
314  GET_DATA(buf[j].code, codes, i, codes_wrap, codes_size); \
315  if (buf[j].code >= (1LL<<buf[j].bits)) { \
316  av_log(NULL, AV_LOG_ERROR, "Invalid code in init_vlc\n"); \
317  if (!(flags & INIT_VLC_USE_NEW_STATIC)) \
318  av_free(buf); \
319  return -1; \
320  } \
321  if (flags & INIT_VLC_LE) \
322  buf[j].code = bitswap_32(buf[j].code); \
323  else \
324  buf[j].code <<= 32 - buf[j].bits; \
325  if (symbols) \
326  GET_DATA(buf[j].symbol, symbols, i, symbols_wrap, symbols_size) \
327  else \
328  buf[j].symbol = i; \
329  j++; \
330  }
331  COPY(buf[j].bits > nb_bits);
332  // qsort is the slowest part of init_vlc, and could probably be improved or avoided
333  qsort(buf, j, sizeof(VLCcode), compare_vlcspec);
334  COPY(buf[j].bits && buf[j].bits <= nb_bits);
335  nb_codes = j;
336 
337  ret = build_table(vlc, nb_bits, nb_codes, buf, flags);
338 
339  if (flags & INIT_VLC_USE_NEW_STATIC) {
340  if(vlc->table_size != vlc->table_allocated)
341  av_log(NULL, AV_LOG_ERROR, "needed %d had %d\n", vlc->table_size, vlc->table_allocated);
342 
343  av_assert0(ret >= 0);
344  *vlc_arg = *vlc;
345  } else {
346  av_free(buf);
347  if (ret < 0) {
348  av_freep(&vlc->table);
349  return ret;
350  }
351  }
352  return 0;
353 }
354 
355 
356 void ff_free_vlc(VLC *vlc)
357 {
358  av_freep(&vlc->table);
359 }