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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/avassert.h"
32 #include "avcodec.h"
33 #include "mathops.h"
34 #include "get_bits.h"
35 #include "put_bits.h"
36 
37 const uint8_t ff_log2_run[41]={
38  0, 0, 0, 0, 1, 1, 1, 1,
39  2, 2, 2, 2, 3, 3, 3, 3,
40  4, 4, 5, 5, 6, 6, 7, 7,
41  8, 9,10,11,12,13,14,15,
42 16,17,18,19,20,21,22,23,
43 24,
44 };
45 
47 {
48  put_bits(s,s->bit_left & 7,0);
49 }
50 
51 void avpriv_put_string(PutBitContext *pb, const char *string, int terminate_string)
52 {
53  while(*string){
54  put_bits(pb, 8, *string);
55  string++;
56  }
57  if(terminate_string)
58  put_bits(pb, 8, 0);
59 }
60 
61 void avpriv_copy_bits(PutBitContext *pb, const uint8_t *src, int length)
62 {
63  int words= length>>4;
64  int bits= length&15;
65  int i;
66 
67  if(length==0) return;
68 
69  if(CONFIG_SMALL || words < 16 || put_bits_count(pb)&7){
70  for(i=0; i<words; i++) put_bits(pb, 16, AV_RB16(src + 2*i));
71  }else{
72  for(i=0; put_bits_count(pb)&31; i++)
73  put_bits(pb, 8, src[i]);
74  flush_put_bits(pb);
75  memcpy(put_bits_ptr(pb), src+i, 2*words-i);
76  skip_put_bytes(pb, 2*words-i);
77  }
78 
79  put_bits(pb, bits, AV_RB16(src + 2*words)>>(16-bits));
80 }
81 
82 /* VLC decoding */
83 
84 #define GET_DATA(v, table, i, wrap, size) \
85 {\
86  const uint8_t *ptr = (const uint8_t *)table + i * wrap;\
87  switch(size) {\
88  case 1:\
89  v = *(const uint8_t *)ptr;\
90  break;\
91  case 2:\
92  v = *(const uint16_t *)ptr;\
93  break;\
94  default:\
95  v = *(const uint32_t *)ptr;\
96  break;\
97  }\
98 }
99 
100 
101 static int alloc_table(VLC *vlc, int size, int use_static)
102 {
103  int index;
104  index = vlc->table_size;
105  vlc->table_size += size;
106  if (vlc->table_size > vlc->table_allocated) {
107  if(use_static)
108  abort(); // cannot do anything, init_vlc() is used with too little memory
109  vlc->table_allocated += (1 << vlc->bits);
110  vlc->table = av_realloc_f(vlc->table,
111  vlc->table_allocated, sizeof(VLC_TYPE) * 2);
112  if (!vlc->table)
113  return -1;
114  }
115  return index;
116 }
117 
118 static av_always_inline uint32_t bitswap_32(uint32_t x) {
119  return (uint32_t)ff_reverse[x&0xFF]<<24
120  | (uint32_t)ff_reverse[(x>>8)&0xFF]<<16
121  | (uint32_t)ff_reverse[(x>>16)&0xFF]<<8
122  | (uint32_t)ff_reverse[x>>24];
123 }
124 
125 typedef struct {
127  uint16_t symbol;
128  /** codeword, with the first bit-to-be-read in the msb
129  * (even if intended for a little-endian bitstream reader) */
130  uint32_t code;
131 } VLCcode;
132 
133 static int compare_vlcspec(const void *a, const void *b)
134 {
135  const VLCcode *sa=a, *sb=b;
136  return (sa->code >> 1) - (sb->code >> 1);
137 }
138 
139 /**
140  * Build VLC decoding tables suitable for use with get_vlc().
141  *
142  * @param vlc the context to be initted
143  *
144  * @param table_nb_bits max length of vlc codes to store directly in this table
145  * (Longer codes are delegated to subtables.)
146  *
147  * @param nb_codes number of elements in codes[]
148  *
149  * @param codes descriptions of the vlc codes
150  * These must be ordered such that codes going into the same subtable are contiguous.
151  * Sorting by VLCcode.code is sufficient, though not necessary.
152  */
153 static int build_table(VLC *vlc, int table_nb_bits, int nb_codes,
154  VLCcode *codes, int flags)
155 {
156  int table_size, table_index, index, code_prefix, symbol, subtable_bits;
157  int i, j, k, n, nb, inc;
158  uint32_t code;
159  VLC_TYPE (*table)[2];
160 
161  table_size = 1 << table_nb_bits;
162  if (table_nb_bits > 30)
163  return -1;
164  table_index = alloc_table(vlc, table_size, flags & INIT_VLC_USE_NEW_STATIC);
165  av_dlog(NULL, "new table index=%d size=%d\n", table_index, table_size);
166  if (table_index < 0)
167  return -1;
168  table = &vlc->table[table_index];
169 
170  for (i = 0; i < table_size; i++) {
171  table[i][1] = 0; //bits
172  table[i][0] = -1; //codes
173  }
174 
175  /* first pass: map codes and compute auxiliary table sizes */
176  for (i = 0; i < nb_codes; i++) {
177  n = codes[i].bits;
178  code = codes[i].code;
179  symbol = codes[i].symbol;
180  av_dlog(NULL, "i=%d n=%d code=0x%x\n", i, n, code);
181  if (n <= table_nb_bits) {
182  /* no need to add another table */
183  j = code >> (32 - table_nb_bits);
184  nb = 1 << (table_nb_bits - n);
185  inc = 1;
186  if (flags & INIT_VLC_LE) {
187  j = bitswap_32(code);
188  inc = 1 << n;
189  }
190  for (k = 0; k < nb; k++) {
191  av_dlog(NULL, "%4x: code=%d n=%d\n", j, i, n);
192  if (table[j][1] /*bits*/ != 0) {
193  av_log(NULL, AV_LOG_ERROR, "incorrect codes\n");
194  return -1;
195  }
196  table[j][1] = n; //bits
197  table[j][0] = symbol;
198  j += inc;
199  }
200  } else {
201  /* fill auxiliary table recursively */
202  n -= table_nb_bits;
203  code_prefix = code >> (32 - table_nb_bits);
204  subtable_bits = n;
205  codes[i].bits = n;
206  codes[i].code = code << table_nb_bits;
207  for (k = i+1; k < nb_codes; k++) {
208  n = codes[k].bits - table_nb_bits;
209  if (n <= 0)
210  break;
211  code = codes[k].code;
212  if (code >> (32 - table_nb_bits) != code_prefix)
213  break;
214  codes[k].bits = n;
215  codes[k].code = code << table_nb_bits;
216  subtable_bits = FFMAX(subtable_bits, n);
217  }
218  subtable_bits = FFMIN(subtable_bits, table_nb_bits);
219  j = (flags & INIT_VLC_LE) ? bitswap_32(code_prefix) >> (32 - table_nb_bits) : code_prefix;
220  table[j][1] = -subtable_bits;
221  av_dlog(NULL, "%4x: n=%d (subtable)\n",
222  j, codes[i].bits + table_nb_bits);
223  index = build_table(vlc, subtable_bits, k-i, codes+i, flags);
224  if (index < 0)
225  return -1;
226  /* note: realloc has been done, so reload tables */
227  table = &vlc->table[table_index];
228  table[j][0] = index; //code
229  i = k-1;
230  }
231  }
232  return table_index;
233 }
234 
235 
236 /* Build VLC decoding tables suitable for use with get_vlc().
237 
238  'nb_bits' set thee decoding table size (2^nb_bits) entries. The
239  bigger it is, the faster is the decoding. But it should not be too
240  big to save memory and L1 cache. '9' is a good compromise.
241 
242  'nb_codes' : number of vlcs codes
243 
244  'bits' : table which gives the size (in bits) of each vlc code.
245 
246  'codes' : table which gives the bit pattern of of each vlc code.
247 
248  'symbols' : table which gives the values to be returned from get_vlc().
249 
250  'xxx_wrap' : give the number of bytes between each entry of the
251  'bits' or 'codes' tables.
252 
253  'xxx_size' : gives the number of bytes of each entry of the 'bits'
254  or 'codes' tables.
255 
256  'wrap' and 'size' allows to use any memory configuration and types
257  (byte/word/long) to store the 'bits', 'codes', and 'symbols' tables.
258 
259  'use_static' should be set to 1 for tables, which should be freed
260  with av_free_static(), 0 if ff_free_vlc() will be used.
261 */
262 int ff_init_vlc_sparse(VLC *vlc, int nb_bits, int nb_codes,
263  const void *bits, int bits_wrap, int bits_size,
264  const void *codes, int codes_wrap, int codes_size,
265  const void *symbols, int symbols_wrap, int symbols_size,
266  int flags)
267 {
268  VLCcode *buf;
269  int i, j, ret;
270 
271  vlc->bits = nb_bits;
272  if(flags & INIT_VLC_USE_NEW_STATIC){
273  VLC dyn_vlc = *vlc;
274 
275  if (vlc->table_size)
276  return 0;
277 
278  ret = ff_init_vlc_sparse(&dyn_vlc, nb_bits, nb_codes,
279  bits, bits_wrap, bits_size,
280  codes, codes_wrap, codes_size,
281  symbols, symbols_wrap, symbols_size,
282  flags & ~INIT_VLC_USE_NEW_STATIC);
283  av_assert0(ret >= 0);
284  av_assert0(dyn_vlc.table_size <= vlc->table_allocated);
285  if(dyn_vlc.table_size < vlc->table_allocated)
286  av_log(NULL, AV_LOG_ERROR, "needed %d had %d\n", dyn_vlc.table_size, vlc->table_allocated);
287  memcpy(vlc->table, dyn_vlc.table, dyn_vlc.table_size * sizeof(*vlc->table));
288  vlc->table_size = dyn_vlc.table_size;
289  ff_free_vlc(&dyn_vlc);
290  return 0;
291  }else {
292  vlc->table = NULL;
293  vlc->table_allocated = 0;
294  vlc->table_size = 0;
295  }
296 
297  av_dlog(NULL, "build table nb_codes=%d\n", nb_codes);
298 
299  buf = av_malloc((nb_codes+1)*sizeof(VLCcode));
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  GET_DATA(buf[j].code, codes, i, codes_wrap, codes_size);\
309  if (flags & INIT_VLC_LE)\
310  buf[j].code = bitswap_32(buf[j].code);\
311  else\
312  buf[j].code <<= 32 - buf[j].bits;\
313  if (symbols)\
314  GET_DATA(buf[j].symbol, symbols, i, symbols_wrap, symbols_size)\
315  else\
316  buf[j].symbol = i;\
317  j++;\
318  }
319  COPY(buf[j].bits > nb_bits);
320  // qsort is the slowest part of init_vlc, and could probably be improved or avoided
321  qsort(buf, j, sizeof(VLCcode), compare_vlcspec);
322  COPY(buf[j].bits && buf[j].bits <= nb_bits);
323  nb_codes = j;
324 
325  ret = build_table(vlc, nb_bits, nb_codes, buf, flags);
326 
327  av_free(buf);
328  if (ret < 0) {
329  av_freep(&vlc->table);
330  return -1;
331  }
332  return 0;
333 }
334 
335 
336 void ff_free_vlc(VLC *vlc)
337 {
338  av_freep(&vlc->table);
339 }