libavcodec/get_bits.h

   1 /*
   2  * copyright (c) 2004 Michael Niedermayer <michaelni@gmx.at>
   3  *
   4  * This file is part of Libav.
   5  *
   6  * Libav 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  * Libav 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 Libav; 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/log.h"
  34 #include "mathops.h"
  35 #include "vlc.h"
  36
  37 /*
  38  * Safe bitstream reading:
  39  * optionally, the get_bits API can check to ensure that we
  40  * don't read past input buffer boundaries. This is protected
  41  * with CONFIG_SAFE_BITSTREAM_READER at the global level, and
  42  * then below that with UNCHECKED_BITSTREAM_READER at the per-
  43  * decoder level. This means that decoders that check internally
  44  * can "#define UNCHECKED_BITSTREAM_READER 1" to disable
  45  * overread checks.
  46  * Boundary checking causes a minor performance penalty so for
  47  * applications that won't want/need this, it can be disabled
  48  * globally using "#define CONFIG_SAFE_BITSTREAM_READER 0".
  49  */
  50 #ifndef UNCHECKED_BITSTREAM_READER
  51 #define UNCHECKED_BITSTREAM_READER !CONFIG_SAFE_BITSTREAM_READER
  52 #endif
  53
  54 typedef struct GetBitContext {
  55     const uint8_t *buffer, *buffer_end;
  56     int index;
  57     int size_in_bits;
  58 #if !UNCHECKED_BITSTREAM_READER
  59     int size_in_bits_plus8;
  60 #endif
  61 } GetBitContext;
  62
  63 /* Bitstream reader API docs:
  64  * name
  65  *   arbitrary name which is used as prefix for the internal variables
  66  *
  67  * gb
  68  *   getbitcontext
  69  *
  70  * OPEN_READER(name, gb)
  71  *   load gb into local variables
  72  *
  73  * CLOSE_READER(name, gb)
  74  *   store local vars in gb
  75  *
  76  * UPDATE_CACHE(name, gb)
  77  *   Refill the internal cache from the bitstream.
  78  *   After this call at least MIN_CACHE_BITS will be available.
  79  *
  80  * GET_CACHE(name, gb)
  81  *   Will output the contents of the internal cache,
  82  *   next bit is MSB of 32 or 64 bits (FIXME 64 bits).
  83  *
  84  * SHOW_UBITS(name, gb, num)
  85  *   Will return the next num bits.
  86  *
  87  * SHOW_SBITS(name, gb, num)
  88  *   Will return the next num bits and do sign extension.
  89  *
  90  * SKIP_BITS(name, gb, num)
  91  *   Will skip over the next num bits.
  92  *   Note, this is equivalent to SKIP_CACHE; SKIP_COUNTER.
  93  *
  94  * SKIP_CACHE(name, gb, num)
  95  *   Will remove the next num bits from the cache (note SKIP_COUNTER
  96  *   MUST be called before UPDATE_CACHE / CLOSE_READER).
  97  *
  98  * SKIP_COUNTER(name, gb, num)
  99  *   Will increment the internal bit counter (see SKIP_CACHE & SKIP_BITS).
 100  *
 101  * LAST_SKIP_BITS(name, gb, num)
 102  *   Like SKIP_BITS, to be used if next call is UPDATE_CACHE or CLOSE_READER.
 103  *
 104  * For examples see get_bits, show_bits, skip_bits, get_vlc.
 105  */
 106
 107 #ifdef LONG_BITSTREAM_READER
 108 #   define MIN_CACHE_BITS 32
 109 #else
 110 #   define MIN_CACHE_BITS 25
 111 #endif
 112
 113 #define OPEN_READER_NOSIZE(name, gb)            \
 114     unsigned int name ## _index = (gb)->index;  \
 115     unsigned int av_unused name ## _cache = 0
 116
 117 #if UNCHECKED_BITSTREAM_READER
 118 #define OPEN_READER(name, gb) OPEN_READER_NOSIZE(name, gb)
 119
 120 #define BITS_AVAILABLE(name, gb) 1
 121 #else
 122 #define OPEN_READER(name, gb)                   \
 123     OPEN_READER_NOSIZE(name, gb);               \
 124     unsigned int name ## _size_plus8 = (gb)->size_in_bits_plus8
 125
 126 #define BITS_AVAILABLE(name, gb) name ## _index < name ## _size_plus8
 127 #endif
 128
 129 #define CLOSE_READER(name, gb) (gb)->index = name ## _index
 130
 131 #ifdef BITSTREAM_READER_LE
 132
 133 # ifdef LONG_BITSTREAM_READER
 134 #   define UPDATE_CACHE(name, gb) name ## _cache = \
 135         AV_RL64((gb)->buffer + (name ## _index >> 3)) >> (name ## _index & 7)
 136 # else
 137 #   define UPDATE_CACHE(name, gb) name ## _cache = \
 138         AV_RL32((gb)->buffer + (name ## _index >> 3)) >> (name ## _index & 7)
 139 # endif
 140
 141 # define SKIP_CACHE(name, gb, num) name ## _cache >>= (num)
 142
 143 #else
 144
 145 # ifdef LONG_BITSTREAM_READER
 146 #   define UPDATE_CACHE(name, gb) name ## _cache = \
 147         AV_RB64((gb)->buffer + (name ## _index >> 3)) >> (32 - (name ## _index & 7))
 148 # else
 149 #   define UPDATE_CACHE(name, gb) name ## _cache = \
 150         AV_RB32((gb)->buffer + (name ## _index >> 3)) << (name ## _index & 7)
 151 # endif
 152
 153 # define SKIP_CACHE(name, gb, num) name ## _cache <<= (num)
 154
 155 #endif
 156
 157 #if UNCHECKED_BITSTREAM_READER
 158 #   define SKIP_COUNTER(name, gb, num) name ## _index += (num)
 159 #else
 160 #   define SKIP_COUNTER(name, gb, num) \
 161     name ## _index = FFMIN(name ## _size_plus8, name ## _index + (num))
 162 #endif
 163
 164 #define SKIP_BITS(name, gb, num)                \
 165     do {                                        \
 166         SKIP_CACHE(name, gb, num);              \
 167         SKIP_COUNTER(name, gb, num);            \
 168     } while (0)
 169
 170 #define LAST_SKIP_BITS(name, gb, num) SKIP_COUNTER(name, gb, num)
 171
 172 #ifdef BITSTREAM_READER_LE
 173 #   define SHOW_UBITS(name, gb, num) zero_extend(name ## _cache, num)
 174 #   define SHOW_SBITS(name, gb, num) sign_extend(name ## _cache, num)
 175 #else
 176 #   define SHOW_UBITS(name, gb, num) NEG_USR32(name ## _cache, num)
 177 #   define SHOW_SBITS(name, gb, num) NEG_SSR32(name ## _cache, num)
 178 #endif
 179
 180 #define GET_CACHE(name, gb) ((uint32_t) name ## _cache)
 181
 182 static inline int get_bits_count(const GetBitContext *s)
 183 {
 184     return s->index;
 185 }
 186
 187 static inline void skip_bits_long(GetBitContext *s, int n)
 188 {
 189 #if UNCHECKED_BITSTREAM_READER
 190     s->index += n;
 191 #else
 192     s->index += av_clip(n, -s->index, s->size_in_bits_plus8 - s->index);
 193 #endif
 194 }
 195
 196 /**
 197  * Read MPEG-1 dc-style VLC (sign bit + mantisse with no MSB).
 198  * if MSB not set it is negative
 199  * @param n length in bits
 200  */
 201 static inline int get_xbits(GetBitContext *s, int n)
 202 {
 203     register int sign;
 204     register int32_t cache;
 205     OPEN_READER(re, s);
 206     UPDATE_CACHE(re, s);
 207     cache = GET_CACHE(re, s);
 208     sign  = ~cache >> 31;
 209     LAST_SKIP_BITS(re, s, n);
 210     CLOSE_READER(re, s);
 211     return (NEG_USR32(sign ^ cache, n) ^ sign) - sign;
 212 }
 213
 214 static inline int get_sbits(GetBitContext *s, int n)
 215 {
 216     register int tmp;
 217     OPEN_READER(re, s);
 218     UPDATE_CACHE(re, s);
 219     tmp = SHOW_SBITS(re, s, n);
 220     LAST_SKIP_BITS(re, s, n);
 221     CLOSE_READER(re, s);
 222     return tmp;
 223 }
 224
 225 /**
 226  * Read 1-25 bits.
 227  */
 228 static inline unsigned int get_bits(GetBitContext *s, int n)
 229 {
 230     register int tmp;
 231     OPEN_READER(re, s);
 232     UPDATE_CACHE(re, s);
 233     tmp = SHOW_UBITS(re, s, n);
 234     LAST_SKIP_BITS(re, s, n);
 235     CLOSE_READER(re, s);
 236     return tmp;
 237 }
 238
 239 /**
 240  * Read 0-25 bits.
 241  */
 242 static av_always_inline int get_bitsz(GetBitContext *s, int n)
 243 {
 244     return n ? get_bits(s, n) : 0;
 245 }
 246
 247 /**
 248  * Show 1-25 bits.
 249  */
 250 static inline unsigned int show_bits(GetBitContext *s, int n)
 251 {
 252     register int tmp;
 253     OPEN_READER_NOSIZE(re, s);
 254     UPDATE_CACHE(re, s);
 255     tmp = SHOW_UBITS(re, s, n);
 256     return tmp;
 257 }
 258
 259 static inline void skip_bits(GetBitContext *s, int n)
 260 {
 261     OPEN_READER(re, s);
 262     UPDATE_CACHE(re, s);
 263     LAST_SKIP_BITS(re, s, n);
 264     CLOSE_READER(re, s);
 265 }
 266
 267 static inline unsigned int get_bits1(GetBitContext *s)
 268 {
 269     unsigned int index = s->index;
 270     uint8_t result     = s->buffer[index >> 3];
 271 #ifdef BITSTREAM_READER_LE
 272     result >>= index & 7;
 273     result  &= 1;
 274 #else
 275     result <<= index & 7;
 276     result >>= 8 - 1;
 277 #endif
 278 #if !UNCHECKED_BITSTREAM_READER
 279     if (s->index < s->size_in_bits_plus8)
 280 #endif
 281         index++;
 282     s->index = index;
 283
 284     return result;
 285 }
 286
 287 static inline unsigned int show_bits1(GetBitContext *s)
 288 {
 289     return show_bits(s, 1);
 290 }
 291
 292 static inline void skip_bits1(GetBitContext *s)
 293 {
 294     skip_bits(s, 1);
 295 }
 296
 297 /**
 298  * Read 0-32 bits.
 299  */
 300 static inline unsigned int get_bits_long(GetBitContext *s, int n)
 301 {
 302     if (n <= MIN_CACHE_BITS) {
 303         return get_bits(s, n);
 304     } else {
 305 #ifdef BITSTREAM_READER_LE
 306         int ret = get_bits(s, 16);
 307         return ret | (get_bits(s, n - 16) << 16);
 308 #else
 309         int ret = get_bits(s, 16) << (n - 16);
 310         return ret | get_bits(s, n - 16);
 311 #endif
 312     }
 313 }
 314
 315 /*
 316  * Read 0-64 bits.
 317  */
 318 static inline uint64_t get_bits64(GetBitContext *s, int n)
 319 {
 320     if (n <= 32) {
 321         return get_bits_long(s, n);
 322     } else {
 323 #ifdef BITSTREAM_READER_LE
 324         uint64_t ret = get_bits_long(s, 32);
 325         return ret | (uint64_t) get_bits_long(s, n - 32) << 32;
 326 #else
 327         uint64_t ret = (uint64_t) get_bits_long(s, n - 32) << 32;
 328         return ret | get_bits_long(s, 32);
 329 #endif
 330     }
 331 }
 332
 333 /**
 334  * Read 0-32 bits as a signed integer.
 335  */
 336 static inline int get_sbits_long(GetBitContext *s, int n)
 337 {
 338     return sign_extend(get_bits_long(s, n), n);
 339 }
 340
 341 /**
 342  * Show 0-32 bits.
 343  */
 344 static inline unsigned int show_bits_long(GetBitContext *s, int n)
 345 {
 346     if (n <= MIN_CACHE_BITS) {
 347         return show_bits(s, n);
 348     } else {
 349         GetBitContext gb = *s;
 350         return get_bits_long(&gb, n);
 351     }
 352 }
 353
 354 /**
 355  * Initialize GetBitContext.
 356  * @param buffer bitstream buffer, must be AV_INPUT_BUFFER_PADDING_SIZE bytes
 357  *        larger than the actual read bits because some optimized bitstream
 358  *        readers read 32 or 64 bit at once and could read over the end
 359  * @param bit_size the size of the buffer in bits
 360  * @return 0 on success, AVERROR_INVALIDDATA if the buffer_size would overflow.
 361  */
 362 static inline int init_get_bits(GetBitContext *s, const uint8_t *buffer,
 363                                 int bit_size)
 364 {
 365     int buffer_size;
 366     int ret = 0;
 367
 368     if (bit_size > INT_MAX - 7 || bit_size < 0 || !buffer) {
 369         bit_size    = 0;
 370         buffer      = NULL;
 371         ret         = AVERROR_INVALIDDATA;
 372     }
 373
 374     buffer_size = (bit_size + 7) >> 3;
 375
 376     s->buffer             = buffer;
 377     s->size_in_bits       = bit_size;
 378 #if !UNCHECKED_BITSTREAM_READER
 379     s->size_in_bits_plus8 = bit_size + 8;
 380 #endif
 381     s->buffer_end         = buffer + buffer_size;
 382     s->index              = 0;
 383
 384     return ret;
 385 }
 386
 387 /**
 388  * Initialize GetBitContext.
 389  * @param buffer bitstream buffer, must be AV_INPUT_BUFFER_PADDING_SIZE bytes
 390  *        larger than the actual read bits because some optimized bitstream
 391  *        readers read 32 or 64 bit at once and could read over the end
 392  * @param byte_size the size of the buffer in bytes
 393  * @return 0 on success, AVERROR_INVALIDDATA if the buffer_size would overflow.
 394  */
 395 static inline int init_get_bits8(GetBitContext *s, const uint8_t *buffer,
 396                                  int byte_size)
 397 {
 398     if (byte_size > INT_MAX / 8)
 399         return AVERROR_INVALIDDATA;
 400     return init_get_bits(s, buffer, byte_size * 8);
 401 }
 402
 403 static inline const uint8_t *align_get_bits(GetBitContext *s)
 404 {
 405     int n = -get_bits_count(s) & 7;
 406     if (n)
 407         skip_bits(s, n);
 408     return s->buffer + (s->index >> 3);
 409 }
 410
 411 /**
 412  * If the vlc code is invalid and max_depth=1, then no bits will be removed.
 413  * If the vlc code is invalid and max_depth>1, then the number of bits removed
 414  * is undefined.
 415  */
 416 #define GET_VLC(code, name, gb, table, bits, max_depth)         \
 417     do {                                                        \
 418         int n, nb_bits;                                         \
 419         unsigned int index;                                     \
 420                                                                 \
 421         index = SHOW_UBITS(name, gb, bits);                     \
 422         code  = table[index][0];                                \
 423         n     = table[index][1];                                \
 424                                                                 \
 425         if (max_depth > 1 && n < 0) {                           \
 426             LAST_SKIP_BITS(name, gb, bits);                     \
 427             UPDATE_CACHE(name, gb);                             \
 428                                                                 \
 429             nb_bits = -n;                                       \
 430                                                                 \
 431             index = SHOW_UBITS(name, gb, nb_bits) + code;       \
 432             code  = table[index][0];                            \
 433             n     = table[index][1];                            \
 434             if (max_depth > 2 && n < 0) {                       \
 435                 LAST_SKIP_BITS(name, gb, nb_bits);              \
 436                 UPDATE_CACHE(name, gb);                         \
 437                                                                 \
 438                 nb_bits = -n;                                   \
 439                                                                 \
 440                 index = SHOW_UBITS(name, gb, nb_bits) + code;   \
 441                 code  = table[index][0];                        \
 442                 n     = table[index][1];                        \
 443             }                                                   \
 444         }                                                       \
 445         SKIP_BITS(name, gb, n);                                 \
 446     } while (0)
 447
 448 #define GET_RL_VLC(level, run, name, gb, table, bits,           \
 449                    max_depth, need_update)                      \
 450     do {                                                        \
 451         int n, nb_bits;                                         \
 452         unsigned int index;                                     \
 453                                                                 \
 454         index = SHOW_UBITS(name, gb, bits);                     \
 455         level = table[index].level;                             \
 456         n     = table[index].len;                               \
 457                                                                 \
 458         if (max_depth > 1 && n < 0) {                           \
 459             SKIP_BITS(name, gb, bits);                          \
 460             if (need_update) {                                  \
 461                 UPDATE_CACHE(name, gb);                         \
 462             }                                                   \
 463                                                                 \
 464             nb_bits = -n;                                       \
 465                                                                 \
 466             index = SHOW_UBITS(name, gb, nb_bits) + level;      \
 467             level = table[index].level;                         \
 468             n     = table[index].len;                           \
 469             if (max_depth > 2 && n < 0) {                       \
 470                 LAST_SKIP_BITS(name, gb, nb_bits);              \
 471                 if (need_update) {                              \
 472                     UPDATE_CACHE(name, gb);                     \
 473                 }                                               \
 474                 nb_bits = -n;                                   \
 475                                                                 \
 476                 index = SHOW_UBITS(name, gb, nb_bits) + level;  \
 477                 level = table[index].level;                     \
 478                 n     = table[index].len;                       \
 479             }                                                   \
 480         }                                                       \
 481         run = table[index].run;                                 \
 482         SKIP_BITS(name, gb, n);                                 \
 483     } while (0)
 484
 485 /**
 486  * Parse a vlc code.
 487  * @param bits is the number of bits which will be read at once, must be
 488  *             identical to nb_bits in init_vlc()
 489  * @param max_depth is the number of times bits bits must be read to completely
 490  *                  read the longest vlc code
 491  *                  = (max_vlc_length + bits - 1) / bits
 492  */
 493 static av_always_inline int get_vlc2(GetBitContext *s, VLC_TYPE (*table)[2],
 494                                      int bits, int max_depth)
 495 {
 496     int code;
 497
 498     OPEN_READER(re, s);
 499     UPDATE_CACHE(re, s);
 500
 501     GET_VLC(code, re, s, table, bits, max_depth);
 502
 503     CLOSE_READER(re, s);
 504
 505     return code;
 506 }
 507
 508 static inline int decode012(GetBitContext *gb)
 509 {
 510     int n;
 511     n = get_bits1(gb);
 512     if (n == 0)
 513         return 0;
 514     else
 515         return get_bits1(gb) + 1;
 516 }
 517
 518 static inline int decode210(GetBitContext *gb)
 519 {
 520     if (get_bits1(gb))
 521         return 0;
 522     else
 523         return 2 - get_bits1(gb);
 524 }
 525
 526 static inline int get_bits_left(GetBitContext *gb)
 527 {
 528     return gb->size_in_bits - get_bits_count(gb);
 529 }
 530
 531 #endif /* AVCODEC_GET_BITS_H */