libavcodec/get_bits.h

   1 /*
   2  * Copyright (c) 2004 Michael Niedermayer <michaelni@gmx.at>
   3  *
   4  * This file is part of FFmpeg.
   5  *
   6  * FFmpeg is free software; you can redistribute it and/or
   7  * modify it under the terms of the GNU Lesser General Public
   8  * License as published by the Free Software Foundation; either
   9  * version 2.1 of the License, or (at your option) any later version.
  10  *
  11  * FFmpeg is distributed in the hope that it will be useful,
  12  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  13  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14  * Lesser General Public License for more details.
  15  *
  16  * You should have received a copy of the GNU Lesser General Public
  17  * License along with FFmpeg; if not, write to the Free Software
  18  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  19  */
  20
  21 /**
  22  * @file
  23  * bitstream reader API header.
  24  */
  25
  26 #ifndef AVCODEC_GET_BITS_H
  27 #define AVCODEC_GET_BITS_H
  28
  29 #include <stdint.h>
  30
  31 #include "libavutil/common.h"
  32 #include "libavutil/intreadwrite.h"
  33 #include "libavutil/avassert.h"
  34
  35 #include "defs.h"
  36 #include "mathops.h"
  37 #include "vlc.h"
  38
  39 /*
  40  * Safe bitstream reading:
  41  * optionally, the get_bits API can check to ensure that we
  42  * don't read past input buffer boundaries. This is protected
  43  * with CONFIG_SAFE_BITSTREAM_READER at the global level, and
  44  * then below that with UNCHECKED_BITSTREAM_READER at the per-
  45  * decoder level. This means that decoders that check internally
  46  * can "#define UNCHECKED_BITSTREAM_READER 1" to disable
  47  * overread checks.
  48  * Boundary checking causes a minor performance penalty so for
  49  * applications that won't want/need this, it can be disabled
  50  * globally using "#define CONFIG_SAFE_BITSTREAM_READER 0".
  51  */
  52 #ifndef UNCHECKED_BITSTREAM_READER
  53 #define UNCHECKED_BITSTREAM_READER !CONFIG_SAFE_BITSTREAM_READER
  54 #endif
  55
  56 #ifndef CACHED_BITSTREAM_READER
  57 #define CACHED_BITSTREAM_READER 0
  58 #endif
  59
  60 #if CACHED_BITSTREAM_READER
  61
  62 // we always want the LE implementation, to provide get_bits_le()
  63 #define BITSTREAM_LE
  64
  65 #ifndef BITSTREAM_READER_LE
  66 # define BITSTREAM_BE
  67 # define BITSTREAM_DEFAULT_BE
  68 #endif
  69
  70 #include "bitstream.h"
  71
  72 #undef BITSTREAM_LE
  73 #undef BITSTREAM_BE
  74 #undef BITSTREAM_DEFAULT_BE
  75
  76 typedef BitstreamContext GetBitContext;
  77
  78 #define get_bits_count      bits_tell
  79 #define get_bits_left       bits_left
  80 #define skip_bits_long      bits_skip
  81 #define skip_bits           bits_skip
  82 #define get_bits            bits_read_nz
  83 #define get_bitsz           bits_read
  84 #define get_bits_long       bits_read
  85 #define get_bits1           bits_read_bit
  86 #define get_bits64          bits_read_64
  87 #define get_xbits           bits_read_xbits
  88 #define get_sbits           bits_read_signed_nz
  89 #define get_sbits_long      bits_read_signed
  90 #define show_bits           bits_peek
  91 #define show_bits_long      bits_peek
  92 #define init_get_bits       bits_init
  93 #define init_get_bits8      bits_init8
  94 #define align_get_bits      bits_align
  95 #define get_vlc2            bits_read_vlc
  96 #define get_vlc_multi       bits_read_vlc_multi
  97
  98 #define init_get_bits8_le(s, buffer, byte_size) bits_init8_le((BitstreamContextLE*)s, buffer, byte_size)
  99 #define get_bits_le(s, n)                       bits_read_le((BitstreamContextLE*)s, n)
 100
 101 #define show_bits1(s)       bits_peek(s, 1)
 102 #define skip_bits1(s)       bits_skip(s, 1)
 103
 104 #define skip_1stop_8data_bits bits_skip_1stop_8data
 105
 106 #else   // CACHED_BITSTREAM_READER
 107
 108 typedef struct GetBitContext {
 109     const uint8_t *buffer, *buffer_end;
 110     int index;
 111     int size_in_bits;
 112     int size_in_bits_plus8;
 113 } GetBitContext;
 114
 115 static inline unsigned int get_bits(GetBitContext *s, int n);
 116 static inline void skip_bits(GetBitContext *s, int n);
 117 static inline unsigned int show_bits(GetBitContext *s, int n);
 118
 119 /* Bitstream reader API docs:
 120  * name
 121  *   arbitrary name which is used as prefix for the internal variables
 122  *
 123  * gb
 124  *   getbitcontext
 125  *
 126  * OPEN_READER(name, gb)
 127  *   load gb into local variables
 128  *
 129  * CLOSE_READER(name, gb)
 130  *   store local vars in gb
 131  *
 132  * UPDATE_CACHE(name, gb)
 133  *   Refill the internal cache from the bitstream.
 134  *   After this call at least MIN_CACHE_BITS will be available.
 135  *
 136  * GET_CACHE(name, gb)
 137  *   Will output the contents of the internal cache,
 138  *   next bit is MSB of 32 or 64 bits (FIXME 64 bits).
 139  *
 140  * SHOW_UBITS(name, gb, num)
 141  *   Will return the next num bits.
 142  *
 143  * SHOW_SBITS(name, gb, num)
 144  *   Will return the next num bits and do sign extension.
 145  *
 146  * SKIP_BITS(name, gb, num)
 147  *   Will skip over the next num bits.
 148  *   Note, this is equivalent to SKIP_CACHE; SKIP_COUNTER.
 149  *
 150  * SKIP_CACHE(name, gb, num)
 151  *   Will remove the next num bits from the cache (note SKIP_COUNTER
 152  *   MUST be called before UPDATE_CACHE / CLOSE_READER).
 153  *
 154  * SKIP_COUNTER(name, gb, num)
 155  *   Will increment the internal bit counter (see SKIP_CACHE & SKIP_BITS).
 156  *
 157  * LAST_SKIP_BITS(name, gb, num)
 158  *   Like SKIP_BITS, to be used if next call is UPDATE_CACHE or CLOSE_READER.
 159  *
 160  * BITS_LEFT(name, gb)
 161  *   Return the number of bits left
 162  *
 163  * For examples see get_bits, show_bits, skip_bits, get_vlc.
 164  */
 165
 166 #if defined LONG_BITSTREAM_READER
 167 #   define MIN_CACHE_BITS 32
 168 #else
 169 #   define MIN_CACHE_BITS 25
 170 #endif
 171
 172 #define OPEN_READER_NOSIZE(name, gb)            \
 173     unsigned int name ## _index = (gb)->index;  \
 174     unsigned int av_unused name ## _cache
 175
 176 #if UNCHECKED_BITSTREAM_READER
 177 #define OPEN_READER(name, gb) OPEN_READER_NOSIZE(name, gb)
 178
 179 #define BITS_AVAILABLE(name, gb) 1
 180 #else
 181 #define OPEN_READER(name, gb)                   \
 182     OPEN_READER_NOSIZE(name, gb);               \
 183     unsigned int name ## _size_plus8 = (gb)->size_in_bits_plus8
 184
 185 #define BITS_AVAILABLE(name, gb) name ## _index < name ## _size_plus8
 186 #endif
 187
 188 #define CLOSE_READER(name, gb) (gb)->index = name ## _index
 189
 190 #define UPDATE_CACHE_BE_EXT(name, gb, bits, dst_bits) name ## _cache = \
 191     AV_RB ## bits((gb)->buffer + (name ## _index >> 3)) << (name ## _index & 7) >> (bits - dst_bits)
 192
 193 #define UPDATE_CACHE_LE_EXT(name, gb, bits, dst_bits) name ## _cache = \
 194     (uint ## dst_bits ## _t)(AV_RL ## bits((gb)->buffer + (name ## _index >> 3)) >> (name ## _index & 7))
 195
 196 /* Using these two macros ensures that 32 bits are available. */
 197 # define UPDATE_CACHE_LE_32(name, gb) UPDATE_CACHE_LE_EXT(name, (gb), 64, 32)
 198
 199 # define UPDATE_CACHE_BE_32(name, gb) UPDATE_CACHE_BE_EXT(name, (gb), 64, 32)
 200
 201 # ifdef LONG_BITSTREAM_READER
 202
 203 # define UPDATE_CACHE_LE(name, gb) UPDATE_CACHE_LE_32(name, (gb))
 204
 205 # define UPDATE_CACHE_BE(name, gb) UPDATE_CACHE_BE_32(name, (gb))
 206
 207 #else
 208
 209 # define UPDATE_CACHE_LE(name, gb) UPDATE_CACHE_LE_EXT(name, (gb), 32, 32)
 210
 211 # define UPDATE_CACHE_BE(name, gb) UPDATE_CACHE_BE_EXT(name, (gb), 32, 32)
 212
 213 #endif
 214
 215
 216 #ifdef BITSTREAM_READER_LE
 217
 218 # define UPDATE_CACHE(name, gb) UPDATE_CACHE_LE(name, gb)
 219 # define UPDATE_CACHE_32(name, gb) UPDATE_CACHE_LE_32(name, (gb))
 220
 221 # define SKIP_CACHE(name, gb, num) name ## _cache >>= (num)
 222
 223 #else
 224
 225 # define UPDATE_CACHE(name, gb) UPDATE_CACHE_BE(name, gb)
 226 # define UPDATE_CACHE_32(name, gb) UPDATE_CACHE_BE_32(name, (gb))
 227
 228 # define SKIP_CACHE(name, gb, num) name ## _cache <<= (num)
 229
 230 #endif
 231
 232 #if UNCHECKED_BITSTREAM_READER
 233 #   define SKIP_COUNTER(name, gb, num) name ## _index += (num)
 234 #else
 235 #   define SKIP_COUNTER(name, gb, num) \
 236     name ## _index = FFMIN(name ## _size_plus8, name ## _index + (num))
 237 #endif
 238
 239 #define BITS_LEFT(name, gb) ((int)((gb)->size_in_bits - name ## _index))
 240
 241 #define SKIP_BITS(name, gb, num)                \
 242     do {                                        \
 243         SKIP_CACHE(name, gb, num);              \
 244         SKIP_COUNTER(name, gb, num);            \
 245     } while (0)
 246
 247 #define LAST_SKIP_BITS(name, gb, num) SKIP_COUNTER(name, gb, num)
 248
 249 #define SHOW_UBITS_LE(name, gb, num) zero_extend(name ## _cache, num)
 250 #define SHOW_SBITS_LE(name, gb, num) sign_extend(name ## _cache, num)
 251
 252 #define SHOW_UBITS_BE(name, gb, num) NEG_USR32(name ## _cache, num)
 253 #define SHOW_SBITS_BE(name, gb, num) NEG_SSR32(name ## _cache, num)
 254
 255 #ifdef BITSTREAM_READER_LE
 256 #   define SHOW_UBITS(name, gb, num) SHOW_UBITS_LE(name, gb, num)
 257 #   define SHOW_SBITS(name, gb, num) SHOW_SBITS_LE(name, gb, num)
 258 #else
 259 #   define SHOW_UBITS(name, gb, num) SHOW_UBITS_BE(name, gb, num)
 260 #   define SHOW_SBITS(name, gb, num) SHOW_SBITS_BE(name, gb, num)
 261 #endif
 262
 263 #define GET_CACHE(name, gb) ((uint32_t) name ## _cache)
 264
 265
 266 static inline int get_bits_count(const GetBitContext *s)
 267 {
 268     return s->index;
 269 }
 270
 271 /**
 272  * Skips the specified number of bits.
 273  * @param n the number of bits to skip,
 274  *          For the UNCHECKED_BITSTREAM_READER this must not cause the distance
 275  *          from the start to overflow int32_t. Staying within the bitstream + padding
 276  *          is sufficient, too.
 277  */
 278 static inline void skip_bits_long(GetBitContext *s, int n)
 279 {
 280 #if UNCHECKED_BITSTREAM_READER
 281     s->index += n;
 282 #else
 283     s->index += av_clip(n, -s->index, s->size_in_bits_plus8 - s->index);
 284 #endif
 285 }
 286
 287 /**
 288  * Read MPEG-1 dc-style VLC (sign bit + mantissa with no MSB).
 289  * if MSB not set it is negative
 290  * @param n length in bits
 291  */
 292 static inline int get_xbits(GetBitContext *s, int n)
 293 {
 294     register int sign;
 295     register int32_t cache;
 296     OPEN_READER(re, s);
 297     av_assert2(n>0 && n<=25);
 298     UPDATE_CACHE(re, s);
 299     cache = GET_CACHE(re, s);
 300     sign  = ~cache >> 31;
 301     LAST_SKIP_BITS(re, s, n);
 302     CLOSE_READER(re, s);
 303     return (NEG_USR32(sign ^ cache, n) ^ sign) - sign;
 304 }
 305
 306 static inline int get_xbits_le(GetBitContext *s, int n)
 307 {
 308     register int sign;
 309     register int32_t cache;
 310     OPEN_READER(re, s);
 311     av_assert2(n>0 && n<=25);
 312     UPDATE_CACHE_LE(re, s);
 313     cache = GET_CACHE(re, s);
 314     sign  = sign_extend(~cache, n) >> 31;
 315     LAST_SKIP_BITS(re, s, n);
 316     CLOSE_READER(re, s);
 317     return (zero_extend(sign ^ cache, n) ^ sign) - sign;
 318 }
 319
 320 static inline int get_sbits(GetBitContext *s, int n)
 321 {
 322     register int tmp;
 323     OPEN_READER(re, s);
 324     av_assert2(n>0 && n<=25);
 325     UPDATE_CACHE(re, s);
 326     tmp = SHOW_SBITS(re, s, n);
 327     LAST_SKIP_BITS(re, s, n);
 328     CLOSE_READER(re, s);
 329     return tmp;
 330 }
 331
 332 /**
 333  * Read 1-25 bits.
 334  */
 335 static inline unsigned int get_bits(GetBitContext *s, int n)
 336 {
 337     register unsigned int tmp;
 338     OPEN_READER(re, s);
 339     av_assert2(n>0 && n<=25);
 340     UPDATE_CACHE(re, s);
 341     tmp = SHOW_UBITS(re, s, n);
 342     LAST_SKIP_BITS(re, s, n);
 343     CLOSE_READER(re, s);
 344     av_assert2(tmp < UINT64_C(1) << n);
 345     return tmp;
 346 }
 347
 348 /**
 349  * Read 0-25 bits.
 350  */
 351 static av_always_inline int get_bitsz(GetBitContext *s, int n)
 352 {
 353     return n ? get_bits(s, n) : 0;
 354 }
 355
 356 static inline unsigned int get_bits_le(GetBitContext *s, int n)
 357 {
 358     register int tmp;
 359     OPEN_READER(re, s);
 360     av_assert2(n>0 && n<=25);
 361     UPDATE_CACHE_LE(re, s);
 362     tmp = SHOW_UBITS_LE(re, s, n);
 363     LAST_SKIP_BITS(re, s, n);
 364     CLOSE_READER(re, s);
 365     return tmp;
 366 }
 367
 368 /**
 369  * Show 1-25 bits.
 370  */
 371 static inline unsigned int show_bits(GetBitContext *s, int n)
 372 {
 373     register unsigned int tmp;
 374     OPEN_READER_NOSIZE(re, s);
 375     av_assert2(n>0 && n<=25);
 376     UPDATE_CACHE(re, s);
 377     tmp = SHOW_UBITS(re, s, n);
 378     return tmp;
 379 }
 380
 381 static inline void skip_bits(GetBitContext *s, int n)
 382 {
 383     OPEN_READER(re, s);
 384     LAST_SKIP_BITS(re, s, n);
 385     CLOSE_READER(re, s);
 386 }
 387
 388 static inline unsigned int get_bits1(GetBitContext *s)
 389 {
 390     unsigned int index = s->index;
 391     uint8_t result     = s->buffer[index >> 3];
 392 #ifdef BITSTREAM_READER_LE
 393     result >>= index & 7;
 394     result  &= 1;
 395 #else
 396     result <<= index & 7;
 397     result >>= 8 - 1;
 398 #endif
 399 #if !UNCHECKED_BITSTREAM_READER
 400     if (s->index < s->size_in_bits_plus8)
 401 #endif
 402         index++;
 403     s->index = index;
 404
 405     return result;
 406 }
 407
 408 static inline unsigned int show_bits1(GetBitContext *s)
 409 {
 410     return show_bits(s, 1);
 411 }
 412
 413 static inline void skip_bits1(GetBitContext *s)
 414 {
 415     skip_bits(s, 1);
 416 }
 417
 418 /**
 419  * Read 0-32 bits.
 420  */
 421 static inline unsigned int get_bits_long(GetBitContext *s, int n)
 422 {
 423     av_assert2(n>=0 && n<=32);
 424     if (!n) {
 425         return 0;
 426     } else if ((!HAVE_FAST_64BIT || av_builtin_constant_p(n <= MIN_CACHE_BITS))
 427                && n <= MIN_CACHE_BITS) {
 428         return get_bits(s, n);
 429     } else {
 430 #if HAVE_FAST_64BIT
 431         unsigned tmp;
 432         OPEN_READER(re, s);
 433         UPDATE_CACHE_32(re, s);
 434         tmp = SHOW_UBITS(re, s, n);
 435         LAST_SKIP_BITS(re, s, n);
 436         CLOSE_READER(re, s);
 437         return tmp;
 438 #else
 439 #ifdef BITSTREAM_READER_LE
 440         unsigned ret = get_bits(s, 16);
 441         return ret | (get_bits(s, n - 16) << 16);
 442 #else
 443         unsigned ret = get_bits(s, 16) << (n - 16);
 444         return ret | get_bits(s, n - 16);
 445 #endif
 446 #endif
 447     }
 448 }
 449
 450 /**
 451  * Read 0-64 bits.
 452  */
 453 static inline uint64_t get_bits64(GetBitContext *s, int n)
 454 {
 455     if (n <= 32) {
 456         return get_bits_long(s, n);
 457     } else {
 458 #ifdef BITSTREAM_READER_LE
 459         uint64_t ret = get_bits_long(s, 32);
 460         return ret | (uint64_t) get_bits_long(s, n - 32) << 32;
 461 #else
 462         uint64_t ret = (uint64_t) get_bits_long(s, n - 32) << 32;
 463         return ret | get_bits_long(s, 32);
 464 #endif
 465     }
 466 }
 467
 468 /**
 469  * Read 0-32 bits as a signed integer.
 470  */
 471 static inline int get_sbits_long(GetBitContext *s, int n)
 472 {
 473     // sign_extend(x, 0) is undefined
 474     if (!n)
 475         return 0;
 476
 477     return sign_extend(get_bits_long(s, n), n);
 478 }
 479
 480 /**
 481  * Read 0-64 bits as a signed integer.
 482  */
 483 static inline int64_t get_sbits64(GetBitContext *s, int n)
 484 {
 485     // sign_extend(x, 0) is undefined
 486     if (!n)
 487         return 0;
 488
 489     return sign_extend64(get_bits64(s, n), n);
 490 }
 491
 492 /**
 493  * Show 0-32 bits.
 494  */
 495 static inline unsigned int show_bits_long(GetBitContext *s, int n)
 496 {
 497     if (n <= MIN_CACHE_BITS) {
 498         return show_bits(s, n);
 499     } else {
 500         GetBitContext gb = *s;
 501         return get_bits_long(&gb, n);
 502     }
 503 }
 504
 505
 506 /**
 507  * Initialize GetBitContext.
 508  * @param buffer bitstream buffer, must be AV_INPUT_BUFFER_PADDING_SIZE bytes
 509  *        larger than the actual read bits because some optimized bitstream
 510  *        readers read 32 or 64 bit at once and could read over the end
 511  * @param bit_size the size of the buffer in bits
 512  * @return 0 on success, AVERROR_INVALIDDATA if the buffer_size would overflow.
 513  */
 514 static inline int init_get_bits(GetBitContext *s, const uint8_t *buffer,
 515                                 int bit_size)
 516 {
 517     int buffer_size;
 518     int ret = 0;
 519
 520     if (bit_size >= INT_MAX - FFMAX(7, AV_INPUT_BUFFER_PADDING_SIZE*8) || bit_size < 0 || !buffer) {
 521         bit_size    = 0;
 522         buffer      = NULL;
 523         ret         = AVERROR_INVALIDDATA;
 524     }
 525
 526     buffer_size = (bit_size + 7) >> 3;
 527
 528     s->buffer             = buffer;
 529     s->size_in_bits       = bit_size;
 530     s->size_in_bits_plus8 = bit_size + 8;
 531     s->buffer_end         = buffer + buffer_size;
 532     s->index              = 0;
 533
 534     return ret;
 535 }
 536
 537 /**
 538  * Initialize GetBitContext.
 539  * @param buffer bitstream buffer, must be AV_INPUT_BUFFER_PADDING_SIZE bytes
 540  *        larger than the actual read bits because some optimized bitstream
 541  *        readers read 32 or 64 bit at once and could read over the end
 542  * @param byte_size the size of the buffer in bytes
 543  * @return 0 on success, AVERROR_INVALIDDATA if the buffer_size would overflow.
 544  */
 545 static inline int init_get_bits8(GetBitContext *s, const uint8_t *buffer,
 546                                  int byte_size)
 547 {
 548     if (byte_size > INT_MAX / 8 || byte_size < 0)
 549         byte_size = -1;
 550     return init_get_bits(s, buffer, byte_size * 8);
 551 }
 552
 553 static inline int init_get_bits8_le(GetBitContext *s, const uint8_t *buffer,
 554                                     int byte_size)
 555 {
 556     if (byte_size > INT_MAX / 8 || byte_size < 0)
 557         byte_size = -1;
 558     return init_get_bits(s, buffer, byte_size * 8);
 559 }
 560
 561 static inline const uint8_t *align_get_bits(GetBitContext *s)
 562 {
 563     int n = -get_bits_count(s) & 7;
 564     if (n)
 565         skip_bits(s, n);
 566     return s->buffer + (s->index >> 3);
 567 }
 568
 569 /**
 570  * If the vlc code is invalid and max_depth=1, then no bits will be removed.
 571  * If the vlc code is invalid and max_depth>1, then the number of bits removed
 572  * is undefined.
 573  */
 574 #define GET_VLC(code, name, gb, table, bits, max_depth)         \
 575     do {                                                        \
 576         int n, nb_bits;                                         \
 577         unsigned int index;                                     \
 578                                                                 \
 579         index = SHOW_UBITS(name, gb, bits);                     \
 580         code  = table[index].sym;                               \
 581         n     = table[index].len;                               \
 582                                                                 \
 583         if (max_depth > 1 && n < 0) {                           \
 584             LAST_SKIP_BITS(name, gb, bits);                     \
 585             UPDATE_CACHE(name, gb);                             \
 586                                                                 \
 587             nb_bits = -n;                                       \
 588                                                                 \
 589             index = SHOW_UBITS(name, gb, nb_bits) + code;       \
 590             code  = table[index].sym;                           \
 591             n     = table[index].len;                           \
 592             if (max_depth > 2 && n < 0) {                       \
 593                 LAST_SKIP_BITS(name, gb, nb_bits);              \
 594                 UPDATE_CACHE(name, gb);                         \
 595                                                                 \
 596                 nb_bits = -n;                                   \
 597                                                                 \
 598                 index = SHOW_UBITS(name, gb, nb_bits) + code;   \
 599                 code  = table[index].sym;                       \
 600                 n     = table[index].len;                       \
 601             }                                                   \
 602         }                                                       \
 603         SKIP_BITS(name, gb, n);                                 \
 604     } while (0)
 605
 606 #define GET_RL_VLC(level, run, name, gb, table, bits,  \
 607                    max_depth, need_update)                      \
 608     do {                                                        \
 609         int n, nb_bits;                                         \
 610         unsigned int index;                                     \
 611                                                                 \
 612         index = SHOW_UBITS(name, gb, bits);                     \
 613         level = table[index].level;                             \
 614         n     = table[index].len;                               \
 615                                                                 \
 616         if (max_depth > 1 && n < 0) {                           \
 617             SKIP_BITS(name, gb, bits);                          \
 618             if (need_update) {                                  \
 619                 UPDATE_CACHE(name, gb);                         \
 620             }                                                   \
 621                                                                 \
 622             nb_bits = -n;                                       \
 623                                                                 \
 624             index = SHOW_UBITS(name, gb, nb_bits) + level;      \
 625             level = table[index].level;                         \
 626             n     = table[index].len;                           \
 627             if (max_depth > 2 && n < 0) {                       \
 628                 LAST_SKIP_BITS(name, gb, nb_bits);              \
 629                 if (need_update) {                              \
 630                     UPDATE_CACHE(name, gb);                     \
 631                 }                                               \
 632                 nb_bits = -n;                                   \
 633                                                                 \
 634                 index = SHOW_UBITS(name, gb, nb_bits) + level;  \
 635                 level = table[index].level;                     \
 636                 n     = table[index].len;                       \
 637             }                                                   \
 638         }                                                       \
 639         run = table[index].run;                                 \
 640         SKIP_BITS(name, gb, n);                                 \
 641     } while (0)
 642
 643 /**
 644  * Parse a vlc code.
 645  * @param bits is the number of bits which will be read at once, must be
 646  *             identical to nb_bits in vlc_init()
 647  * @param max_depth is the number of times bits bits must be read to completely
 648  *                  read the longest vlc code
 649  *                  = (max_vlc_length + bits - 1) / bits
 650  * @returns the code parsed or -1 if no vlc matches
 651  */
 652 static av_always_inline int get_vlc2(GetBitContext *s, const VLCElem *table,
 653                                      int bits, int max_depth)
 654 {
 655     int code;
 656
 657     OPEN_READER(re, s);
 658     UPDATE_CACHE(re, s);
 659
 660     GET_VLC(code, re, s, table, bits, max_depth);
 661
 662     CLOSE_READER(re, s);
 663
 664     return code;
 665 }
 666
 667 static inline int get_vlc_multi(GetBitContext *s, uint8_t *dst,
 668                                 const VLC_MULTI_ELEM *const Jtable,
 669                                 const VLCElem *const table,
 670                                 const int bits, const int max_depth,
 671                                 const int symbols_size)
 672 {
 673     dst[0] = get_vlc2(s, table, bits, max_depth);
 674     return 1;
 675 }
 676
 677 static inline int decode012(GetBitContext *gb)
 678 {
 679     int n;
 680     n = get_bits1(gb);
 681     if (n == 0)
 682         return 0;
 683     else
 684         return get_bits1(gb) + 1;
 685 }
 686
 687 static inline int decode210(GetBitContext *gb)
 688 {
 689     if (get_bits1(gb))
 690         return 0;
 691     else
 692         return 2 - get_bits1(gb);
 693 }
 694
 695 static inline int get_bits_left(GetBitContext *gb)
 696 {
 697     return gb->size_in_bits - get_bits_count(gb);
 698 }
 699
 700 static inline int skip_1stop_8data_bits(GetBitContext *gb)
 701 {
 702     if (get_bits_left(gb) <= 0)
 703         return AVERROR_INVALIDDATA;
 704
 705     while (get_bits1(gb)) {
 706         skip_bits(gb, 8);
 707         if (get_bits_left(gb) <= 0)
 708             return AVERROR_INVALIDDATA;
 709     }
 710
 711     return 0;
 712 }
 713
 714 #endif // CACHED_BITSTREAM_READER
 715
 716 #endif /* AVCODEC_GET_BITS_H */