FFmpeg: libavcodec/get_bits.h Source File

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get_bits.h

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1 /*

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 */

21 /**

22 * @file

23 * bitstream reader API header.

24 */

26 #ifndef AVCODEC_GET_BITS_H

27 #define AVCODEC_GET_BITS_H

29 #include <stdint.h>

31 #include "libavutil/common.h"

32 #include "libavutil/intreadwrite.h"

33 #include "libavutil/log.h"

34 #include "libavutil/avassert.h"

35 #include "mathops.h"

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

54 typedef struct GetBitContext {

55 const uint8_t *buffer, *buffer_end;

56 int index;

57 int size_in_bits;

58 int size_in_bits_plus8;

59 } GetBitContext;

61 #define VLC_TYPE int16_t

63 typedef struct VLC {

64 int bits;

65 VLC_TYPE (*table)[2]; ///< code, bits

66 int table_size, table_allocated;

67 void * volatile init_state;

68 } VLC;

70 typedef struct RL_VLC_ELEM {

71 int16_t level;

72 int8_t len;

73 uint8_t run;

74 } RL_VLC_ELEM;

76 /* Bitstream reader API docs:

77 * name

78 * arbitrary name which is used as prefix for the internal variables

79 *

80 * gb

81 * getbitcontext

82 *

83 * OPEN_READER(name, gb)

84 * load gb into local variables

85 *

86 * CLOSE_READER(name, gb)

87 * store local vars in gb

88 *

89 * UPDATE_CACHE(name, gb)

90 * Refill the internal cache from the bitstream.

91 * After this call at least MIN_CACHE_BITS will be available.

92 *

93 * GET_CACHE(name, gb)

94 * Will output the contents of the internal cache,

95 * next bit is MSB of 32 or 64 bit (FIXME 64bit).

96 *

97 * SHOW_UBITS(name, gb, num)

98 * Will return the next num bits.

99 *

100 * SHOW_SBITS(name, gb, num)

101 * Will return the next num bits and do sign extension.

102 *

103 * SKIP_BITS(name, gb, num)

104 * Will skip over the next num bits.

105 * Note, this is equivalent to SKIP_CACHE; SKIP_COUNTER.

106 *

107 * SKIP_CACHE(name, gb, num)

108 * Will remove the next num bits from the cache (note SKIP_COUNTER

109 * MUST be called before UPDATE_CACHE / CLOSE_READER).

110 *

111 * SKIP_COUNTER(name, gb, num)

112 * Will increment the internal bit counter (see SKIP_CACHE & SKIP_BITS).

113 *

114 * LAST_SKIP_BITS(name, gb, num)

115 * Like SKIP_BITS, to be used if next call is UPDATE_CACHE or CLOSE_READER.

116 *

117 * For examples see get_bits, show_bits, skip_bits, get_vlc.

118 */

119

120 #ifdef LONG_BITSTREAM_READER

121 # define MIN_CACHE_BITS 32

122 #else

123 # define MIN_CACHE_BITS 25

124 #endif

125

126 #if UNCHECKED_BITSTREAM_READER

127 #define OPEN_READER(name, gb) \

128 unsigned int name ## _index = (gb)->index; \

129 unsigned int av_unused name ## _cache

130

131 #define HAVE_BITS_REMAINING(name, gb) 1

132 #else

133 #define OPEN_READER(name, gb) \

134 unsigned int name ## _index = (gb)->index; \

135 unsigned int av_unused name ## _cache = 0; \

136 unsigned int av_unused name ## _size_plus8 = (gb)->size_in_bits_plus8

137

138 #define HAVE_BITS_REMAINING(name, gb) name ## _index < name ## _size_plus8

139 #endif

140

141 #define CLOSE_READER(name, gb) (gb)->index = name ## _index

142

143 # ifdef LONG_BITSTREAM_READER

144

145 # define UPDATE_CACHE_LE(name, gb) name ## _cache = \

146 AV_RL64((gb)->buffer + (name ## _index >> 3)) >> (name ## _index & 7)

147

148 # define UPDATE_CACHE_BE(name, gb) name ## _cache = \

149 AV_RB64((gb)->buffer + (name ## _index >> 3)) >> (32 - (name ## _index & 7))

150

151 #else

152

153 # define UPDATE_CACHE_LE(name, gb) name ## _cache = \

154 AV_RL32((gb)->buffer + (name ## _index >> 3)) >> (name ## _index & 7)

155

156 # define UPDATE_CACHE_BE(name, gb) name ## _cache = \

157 AV_RB32((gb)->buffer + (name ## _index >> 3)) << (name ## _index & 7)

158

159 #endif

160

161

162 #ifdef BITSTREAM_READER_LE

163

164 # define UPDATE_CACHE(name, gb) UPDATE_CACHE_LE(name, gb)

165

166 # define SKIP_CACHE(name, gb, num) name ## _cache >>= (num)

167

168 #else

169

170 # define UPDATE_CACHE(name, gb) UPDATE_CACHE_BE(name, gb)

171

172 # define SKIP_CACHE(name, gb, num) name ## _cache <<= (num)

173

174 #endif

175

176 #if UNCHECKED_BITSTREAM_READER

177 # define SKIP_COUNTER(name, gb, num) name ## _index += (num)

178 #else

179 # define SKIP_COUNTER(name, gb, num) \

180 name ## _index = FFMIN(name ## _size_plus8, name ## _index + (num))

181 #endif

182

183 #define SKIP_BITS(name, gb, num) \

184 do { \

185 SKIP_CACHE(name, gb, num); \

186 SKIP_COUNTER(name, gb, num); \

187 } while (0)

188

189 #define LAST_SKIP_BITS(name, gb, num) SKIP_COUNTER(name, gb, num)

190

191 #define SHOW_UBITS_LE(name, gb, num) zero_extend(name ## _cache, num)

192 #define SHOW_SBITS_LE(name, gb, num) sign_extend(name ## _cache, num)

193

194 #define SHOW_UBITS_BE(name, gb, num) NEG_USR32(name ## _cache, num)

195 #define SHOW_SBITS_BE(name, gb, num) NEG_SSR32(name ## _cache, num)

196

197 #ifdef BITSTREAM_READER_LE

198 # define SHOW_UBITS(name, gb, num) SHOW_UBITS_LE(name, gb, num)

199 # define SHOW_SBITS(name, gb, num) SHOW_SBITS_LE(name, gb, num)

200 #else

201 # define SHOW_UBITS(name, gb, num) SHOW_UBITS_BE(name, gb, num)

202 # define SHOW_SBITS(name, gb, num) SHOW_SBITS_BE(name, gb, num)

203 #endif

204

205 #define GET_CACHE(name, gb) ((uint32_t) name ## _cache)

206

207 static inline int get_bits_count(const GetBitContext *s)

208 {

209 return s->index;

210 }

211

212 static inline void skip_bits_long(GetBitContext *s, int n)

213 {

214 #if UNCHECKED_BITSTREAM_READER

215 s->index += n;

216 #else

217 s->index += av_clip(n, -s->index, s->size_in_bits_plus8 - s->index);

218 #endif

219 }

220

221 /**

222 * read mpeg1 dc style vlc (sign bit + mantisse with no MSB).

223 * if MSB not set it is negative

224 * @param n length in bits

225 */

226 static inline int get_xbits(GetBitContext *s, int n)

227 {

228 register int sign;

229 register int32_t cache;

230 OPEN_READER(re, s);

231 av_assert2(n>0 && n<=25);

232 UPDATE_CACHE(re, s);

233 cache = GET_CACHE(re, s);

234 sign = ~cache >> 31;

235 LAST_SKIP_BITS(re, s, n);

236 CLOSE_READER(re, s);

237 return (NEG_USR32(sign ^ cache, n) ^ sign) - sign;

238 }

239

240 static inline int get_sbits(GetBitContext *s, int n)

241 {

242 register int tmp;

243 OPEN_READER(re, s);

244 av_assert2(n>0 && n<=25);

245 UPDATE_CACHE(re, s);

246 tmp = SHOW_SBITS(re, s, n);

247 LAST_SKIP_BITS(re, s, n);

248 CLOSE_READER(re, s);

249 return tmp;

250 }

251

252 /**

253 * Read 1-25 bits.

254 */

255 static inline unsigned int get_bits(GetBitContext *s, int n)

256 {

257 register int tmp;

258 OPEN_READER(re, s);

259 av_assert2(n>0 && n<=25);

260 UPDATE_CACHE(re, s);

261 tmp = SHOW_UBITS(re, s, n);

262 LAST_SKIP_BITS(re, s, n);

263 CLOSE_READER(re, s);

264 return tmp;

265 }

266

267 static inline unsigned int get_bits_le(GetBitContext *s, int n)

268 {

269 register int tmp;

270 OPEN_READER(re, s);

271 av_assert2(n>0 && n<=25);

272 UPDATE_CACHE_LE(re, s);

273 tmp = SHOW_UBITS_LE(re, s, n);

274 LAST_SKIP_BITS(re, s, n);

275 CLOSE_READER(re, s);

276 return tmp;

277 }

278

279 /**

280 * Show 1-25 bits.

281 */

282 static inline unsigned int show_bits(GetBitContext *s, int n)

283 {

284 register int tmp;

285 OPEN_READER(re, s);

286 av_assert2(n>0 && n<=25);

287 UPDATE_CACHE(re, s);

288 tmp = SHOW_UBITS(re, s, n);

289 return tmp;

290 }

291

292 static inline void skip_bits(GetBitContext *s, int n)

293 {

294 OPEN_READER(re, s);

295 LAST_SKIP_BITS(re, s, n);

296 CLOSE_READER(re, s);

297 }

298

299 static inline unsigned int get_bits1(GetBitContext *s)

300 {

301 unsigned int index = s->index;

302 uint8_t result = s->buffer[index >> 3];

303 #ifdef BITSTREAM_READER_LE

304 result >>= index & 7;

305 result &= 1;

306 #else

307 result <<= index & 7;

308 result >>= 8 - 1;

309 #endif

310 #if !UNCHECKED_BITSTREAM_READER

311 if (s->index < s->size_in_bits_plus8)

312 #endif

313 index++;

314 s->index = index;

315

316 return result;

317 }

318

319 static inline unsigned int show_bits1(GetBitContext *s)

320 {

321 return show_bits(s, 1);

322 }

323

324 static inline void skip_bits1(GetBitContext *s)

325 {

326 skip_bits(s, 1);

327 }

328

329 /**

330 * Read 0-32 bits.

331 */

332 static inline unsigned int get_bits_long(GetBitContext *s, int n)

333 {

334 if (!n) {

335 return 0;

336 } else if (n <= MIN_CACHE_BITS) {

337 return get_bits(s, n);

338 } else {

339 #ifdef BITSTREAM_READER_LE

340 unsigned ret = get_bits(s, 16);

341 return ret | (get_bits(s, n - 16) << 16);

342 #else

343 unsigned ret = get_bits(s, 16) << (n - 16);

344 return ret | get_bits(s, n - 16);

345 #endif

346 }

347 }

348

349 /**

350 * Read 0-64 bits.

351 */

352 static inline uint64_t get_bits64(GetBitContext *s, int n)

353 {

354 if (n <= 32) {

355 return get_bits_long(s, n);

356 } else {

357 #ifdef BITSTREAM_READER_LE

358 uint64_t ret = get_bits_long(s, 32);

359 return ret | (uint64_t) get_bits_long(s, n - 32) << 32;

360 #else

361 uint64_t ret = (uint64_t) get_bits_long(s, n - 32) << 32;

362 return ret | get_bits_long(s, 32);

363 #endif

364 }

365 }

366

367 /**

368 * Read 0-32 bits as a signed integer.

369 */

370 static inline int get_sbits_long(GetBitContext *s, int n)

371 {

372 return sign_extend(get_bits_long(s, n), n);

373 }

374

375 /**

376 * Show 0-32 bits.

377 */

378 static inline unsigned int show_bits_long(GetBitContext *s, int n)

379 {

380 if (n <= MIN_CACHE_BITS) {

381 return show_bits(s, n);

382 } else {

383 GetBitContext gb = *s;

384 return get_bits_long(&gb, n);

385 }

386 }

387

388 static inline int check_marker(GetBitContext *s, const char *msg)

389 {

390 int bit = get_bits1(s);

391 if (!bit)

392 av_log(NULL, AV_LOG_INFO, "Marker bit missing %s\n", msg);

393

394 return bit;

395 }

396

397 /**

398 * Initialize GetBitContext.

399 * @param buffer bitstream buffer, must be FF_INPUT_BUFFER_PADDING_SIZE bytes

400 * larger than the actual read bits because some optimized bitstream

401 * readers read 32 or 64 bit at once and could read over the end

402 * @param bit_size the size of the buffer in bits

403 * @return 0 on success, AVERROR_INVALIDDATA if the buffer_size would overflow.

404 */

405 static inline int init_get_bits(GetBitContext *s, const uint8_t *buffer,

406 int bit_size)

407 {

408 int buffer_size;

409 int ret = 0;

410

411 if (bit_size >= INT_MAX - 7 || bit_size < 0 || !buffer) {

412 buffer_size = bit_size = 0;

413 buffer = NULL;

414 ret = AVERROR_INVALIDDATA;

415 }

416

417 buffer_size = (bit_size + 7) >> 3;

418

419 s->buffer = buffer;

420 s->size_in_bits = bit_size;

421 s->size_in_bits_plus8 = bit_size + 8;

422 s->buffer_end = buffer + buffer_size;

423 s->index = 0;

424

425 return ret;

426 }

427

428 /**

429 * Initialize GetBitContext.

430 * @param buffer bitstream buffer, must be FF_INPUT_BUFFER_PADDING_SIZE bytes

431 * larger than the actual read bits because some optimized bitstream

432 * readers read 32 or 64 bit at once and could read over the end

433 * @param byte_size the size of the buffer in bytes

434 * @return 0 on success, AVERROR_INVALIDDATA if the buffer_size would overflow.

435 */

436 static inline int init_get_bits8(GetBitContext *s, const uint8_t *buffer,

437 int byte_size)

438 {

439 if (byte_size > INT_MAX / 8 || byte_size < 0)

440 byte_size = -1;

441 return init_get_bits(s, buffer, byte_size * 8);

442 }

443

444 static inline const uint8_t *align_get_bits(GetBitContext *s)

445 {

446 int n = -get_bits_count(s) & 7;

447 if (n)

448 skip_bits(s, n);

449 return s->buffer + (s->index >> 3);

450 }

451

452 #define init_vlc(vlc, nb_bits, nb_codes, \

453 bits, bits_wrap, bits_size, \

454 codes, codes_wrap, codes_size, \

455 flags) \

456 ff_init_vlc_sparse(vlc, nb_bits, nb_codes, \

457 bits, bits_wrap, bits_size, \

458 codes, codes_wrap, codes_size, \

459 NULL, 0, 0, flags)

460

461 int ff_init_vlc_sparse(VLC *vlc, int nb_bits, int nb_codes,

462 const void *bits, int bits_wrap, int bits_size,

463 const void *codes, int codes_wrap, int codes_size,

464 const void *symbols, int symbols_wrap, int symbols_size,

465 int flags);

466 void ff_free_vlc(VLC *vlc);

467

468 #define INIT_VLC_LE 2

469 #define INIT_VLC_USE_NEW_STATIC 4

470

471 #define INIT_VLC_STATIC(vlc, bits, a, b, c, d, e, f, g, static_size) \

472 do { \

473 static VLC_TYPE table[static_size][2]; \

474 (vlc)->table = table; \

475 (vlc)->table_allocated = static_size; \

476 init_vlc(vlc, bits, a, b, c, d, e, f, g, INIT_VLC_USE_NEW_STATIC); \

477 } while (0)

478

479 /**

480 * If the vlc code is invalid and max_depth=1, then no bits will be removed.

481 * If the vlc code is invalid and max_depth>1, then the number of bits removed

482 * is undefined.

483 */

484 #define GET_VLC(code, name, gb, table, bits, max_depth) \

485 do { \

486 int n, nb_bits; \

487 unsigned int index; \

488 \

489 index = SHOW_UBITS(name, gb, bits); \

490 code = table[index][0]; \

491 n = table[index][1]; \

492 \

493 if (max_depth > 1 && n < 0) { \

494 LAST_SKIP_BITS(name, gb, bits); \

495 UPDATE_CACHE(name, gb); \

496 \

497 nb_bits = -n; \

498 \

499 index = SHOW_UBITS(name, gb, nb_bits) + code; \

500 code = table[index][0]; \

501 n = table[index][1]; \

502 if (max_depth > 2 && n < 0) { \

503 LAST_SKIP_BITS(name, gb, nb_bits); \

504 UPDATE_CACHE(name, gb); \

505 \

506 nb_bits = -n; \

507 \

508 index = SHOW_UBITS(name, gb, nb_bits) + code; \

509 code = table[index][0]; \

510 n = table[index][1]; \

511 } \

512 } \

513 SKIP_BITS(name, gb, n); \

514 } while (0)

515

516 #define GET_RL_VLC(level, run, name, gb, table, bits, \

517 max_depth, need_update) \

518 do { \

519 int n, nb_bits; \

520 unsigned int index; \

521 \

522 index = SHOW_UBITS(name, gb, bits); \

523 level = table[index].level; \

524 n = table[index].len; \

525 \

526 if (max_depth > 1 && n < 0) { \

527 SKIP_BITS(name, gb, bits); \

528 if (need_update) { \

529 UPDATE_CACHE(name, gb); \

530 } \

531 \

532 nb_bits = -n; \

533 \

534 index = SHOW_UBITS(name, gb, nb_bits) + level; \

535 level = table[index].level; \

536 n = table[index].len; \

537 } \

538 run = table[index].run; \

539 SKIP_BITS(name, gb, n); \

540 } while (0)

541

542 /**

543 * Parse a vlc code.

544 * @param bits is the number of bits which will be read at once, must be

545 * identical to nb_bits in init_vlc()

546 * @param max_depth is the number of times bits bits must be read to completely

547 * read the longest vlc code

548 * = (max_vlc_length + bits - 1) / bits

549 */

550 static av_always_inline int get_vlc2(GetBitContext *s, VLC_TYPE (*table)[2],

551 int bits, int max_depth)

552 {

553 int code;

554

555 OPEN_READER(re, s);

556 UPDATE_CACHE(re, s);

557

558 GET_VLC(code, re, s, table, bits, max_depth);

559

560 CLOSE_READER(re, s);

561

562 return code;

563 }

564

565 static inline int decode012(GetBitContext *gb)

566 {

567 int n;

568 n = get_bits1(gb);

569 if (n == 0)

570 return 0;

571 else

572 return get_bits1(gb) + 1;

573 }

574

575 static inline int decode210(GetBitContext *gb)

576 {

577 if (get_bits1(gb))

578 return 0;

579 else

580 return 2 - get_bits1(gb);

581 }

582

583 static inline int get_bits_left(GetBitContext *gb)

584 {

585 return gb->size_in_bits - get_bits_count(gb);

586 }

587

588 //#define TRACE

589

590 #ifdef TRACE

591 static inline void print_bin(int bits, int n)

592 {

593 int i;

594

595 for (i = n - 1; i >= 0; i--)

596 av_log(NULL, AV_LOG_DEBUG, "%d", (bits >> i) & 1);

597 for (i = n; i < 24; i++)

598 av_log(NULL, AV_LOG_DEBUG, " ");

599 }

600

601 static inline int get_bits_trace(GetBitContext *s, int n, const char *file,

602 const char *func, int line)

603 {

604 int r = get_bits(s, n);

605

606 print_bin(r, n);

607 av_log(NULL, AV_LOG_DEBUG, "%5d %2d %3d bit @%5d in %s %s:%d\n",

608 r, n, r, get_bits_count(s) - n, file, func, line);

609

610 return r;

611 }

612

613 static inline int get_vlc_trace(GetBitContext *s, VLC_TYPE (*table)[2],

614 int bits, int max_depth, const char *file,

615 const char *func, int line)

616 {

617 int show = show_bits(s, 24);

618 int pos = get_bits_count(s);

619 int r = get_vlc2(s, table, bits, max_depth);

620 int len = get_bits_count(s) - pos;

621 int bits2 = show >> (24 - len);

622

623 print_bin(bits2, len);

624

625 av_log(NULL, AV_LOG_DEBUG, "%5d %2d %3d vlc @%5d in %s %s:%d\n",

626 bits2, len, r, pos, file, func, line);

627

628 return r;

629 }

630

631 static inline int get_xbits_trace(GetBitContext *s, int n, const char *file,

632 const char *func, int line)

633 {

634 int show = show_bits(s, n);

635 int r = get_xbits(s, n);

636

637 print_bin(show, n);

638 av_log(NULL, AV_LOG_DEBUG, "%5d %2d %3d xbt @%5d in %s %s:%d\n",

639 show, n, r, get_bits_count(s) - n, file, func, line);

640

641 return r;

642 }

643

644 #define get_bits(s, n) get_bits_trace(s , n, __FILE__, __PRETTY_FUNCTION__, __LINE__)

645 #define get_bits1(s) get_bits_trace(s, 1, __FILE__, __PRETTY_FUNCTION__, __LINE__)

646 #define get_xbits(s, n) get_xbits_trace(s, n, __FILE__, __PRETTY_FUNCTION__, __LINE__)

647

648 #define get_vlc(s, vlc) get_vlc_trace(s, (vlc)->table, (vlc)->bits, 3, __FILE__, __PRETTY_FUNCTION__, __LINE__)

649 #define get_vlc2(s, tab, bits, max) get_vlc_trace(s, tab, bits, max, __FILE__, __PRETTY_FUNCTION__, __LINE__)

650

651 #define tprintf(p, ...) av_log(p, AV_LOG_DEBUG, __VA_ARGS__)

652

653 #else //TRACE

654 #define tprintf(p, ...) { }

655 #endif

656

657 #endif /* AVCODEC_GET_BITS_H */

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