| 1 | /* ****************************************************************** |
| 2 | * bitstream |
| 3 | * Part of FSE library |
| 4 | * Copyright (c) Meta Platforms, Inc. and affiliates. |
| 5 | * |
| 6 | * You can contact the author at : |
| 7 | * - Source repository : https://github.com/Cyan4973/FiniteStateEntropy |
| 8 | * |
| 9 | * This source code is licensed under both the BSD-style license (found in the |
| 10 | * LICENSE file in the root directory of this source tree) and the GPLv2 (found |
| 11 | * in the COPYING file in the root directory of this source tree). |
| 12 | * You may select, at your option, one of the above-listed licenses. |
| 13 | ****************************************************************** */ |
| 14 | #ifndef BITSTREAM_H_MODULE |
| 15 | #define BITSTREAM_H_MODULE |
| 16 | |
| 17 | #if defined (__cplusplus) |
| 18 | extern "C" { |
| 19 | #endif |
| 20 | /* |
| 21 | * This API consists of small unitary functions, which must be inlined for best performance. |
| 22 | * Since link-time-optimization is not available for all compilers, |
| 23 | * these functions are defined into a .h to be included. |
| 24 | */ |
| 25 | |
| 26 | /*-**************************************** |
| 27 | * Dependencies |
| 28 | ******************************************/ |
| 29 | #include "mem.h" /* unaligned access routines */ |
| 30 | #include "compiler.h" /* UNLIKELY() */ |
| 31 | #include "debug.h" /* assert(), DEBUGLOG(), RAWLOG() */ |
| 32 | #include "error_private.h" /* error codes and messages */ |
| 33 | #include "bits.h" /* ZSTD_highbit32 */ |
| 34 | |
| 35 | |
| 36 | /*========================================= |
| 37 | * Target specific |
| 38 | =========================================*/ |
| 39 | #ifndef ZSTD_NO_INTRINSICS |
| 40 | # if (defined(__BMI__) || defined(__BMI2__)) && defined(__GNUC__) |
| 41 | # include <immintrin.h> /* support for bextr (experimental)/bzhi */ |
| 42 | # elif defined(__ICCARM__) |
| 43 | # include <intrinsics.h> |
| 44 | # endif |
| 45 | #endif |
| 46 | |
| 47 | #define STREAM_ACCUMULATOR_MIN_32 25 |
| 48 | #define STREAM_ACCUMULATOR_MIN_64 57 |
| 49 | #define STREAM_ACCUMULATOR_MIN ((U32)(MEM_32bits() ? STREAM_ACCUMULATOR_MIN_32 : STREAM_ACCUMULATOR_MIN_64)) |
| 50 | |
| 51 | |
| 52 | /*-****************************************** |
| 53 | * bitStream encoding API (write forward) |
| 54 | ********************************************/ |
| 55 | /* bitStream can mix input from multiple sources. |
| 56 | * A critical property of these streams is that they encode and decode in **reverse** direction. |
| 57 | * So the first bit sequence you add will be the last to be read, like a LIFO stack. |
| 58 | */ |
| 59 | typedef struct { |
| 60 | size_t bitContainer; |
| 61 | unsigned bitPos; |
| 62 | char* startPtr; |
| 63 | char* ptr; |
| 64 | char* endPtr; |
| 65 | } BIT_CStream_t; |
| 66 | |
| 67 | MEM_STATIC size_t BIT_initCStream(BIT_CStream_t* bitC, void* dstBuffer, size_t dstCapacity); |
| 68 | MEM_STATIC void BIT_addBits(BIT_CStream_t* bitC, size_t value, unsigned nbBits); |
| 69 | MEM_STATIC void BIT_flushBits(BIT_CStream_t* bitC); |
| 70 | MEM_STATIC size_t BIT_closeCStream(BIT_CStream_t* bitC); |
| 71 | |
| 72 | /* Start with initCStream, providing the size of buffer to write into. |
| 73 | * bitStream will never write outside of this buffer. |
| 74 | * `dstCapacity` must be >= sizeof(bitD->bitContainer), otherwise @return will be an error code. |
| 75 | * |
| 76 | * bits are first added to a local register. |
| 77 | * Local register is size_t, hence 64-bits on 64-bits systems, or 32-bits on 32-bits systems. |
| 78 | * Writing data into memory is an explicit operation, performed by the flushBits function. |
| 79 | * Hence keep track how many bits are potentially stored into local register to avoid register overflow. |
| 80 | * After a flushBits, a maximum of 7 bits might still be stored into local register. |
| 81 | * |
| 82 | * Avoid storing elements of more than 24 bits if you want compatibility with 32-bits bitstream readers. |
| 83 | * |
| 84 | * Last operation is to close the bitStream. |
| 85 | * The function returns the final size of CStream in bytes. |
| 86 | * If data couldn't fit into `dstBuffer`, it will return a 0 ( == not storable) |
| 87 | */ |
| 88 | |
| 89 | |
| 90 | /*-******************************************** |
| 91 | * bitStream decoding API (read backward) |
| 92 | **********************************************/ |
| 93 | typedef struct { |
| 94 | size_t bitContainer; |
| 95 | unsigned bitsConsumed; |
| 96 | const char* ptr; |
| 97 | const char* start; |
| 98 | const char* limitPtr; |
| 99 | } BIT_DStream_t; |
| 100 | |
| 101 | typedef enum { BIT_DStream_unfinished = 0, |
| 102 | BIT_DStream_endOfBuffer = 1, |
| 103 | BIT_DStream_completed = 2, |
| 104 | BIT_DStream_overflow = 3 } BIT_DStream_status; /* result of BIT_reloadDStream() */ |
| 105 | /* 1,2,4,8 would be better for bitmap combinations, but slows down performance a bit ... :( */ |
| 106 | |
| 107 | MEM_STATIC size_t BIT_initDStream(BIT_DStream_t* bitD, const void* srcBuffer, size_t srcSize); |
| 108 | MEM_STATIC size_t BIT_readBits(BIT_DStream_t* bitD, unsigned nbBits); |
| 109 | MEM_STATIC BIT_DStream_status BIT_reloadDStream(BIT_DStream_t* bitD); |
| 110 | MEM_STATIC unsigned BIT_endOfDStream(const BIT_DStream_t* bitD); |
| 111 | |
| 112 | |
| 113 | /* Start by invoking BIT_initDStream(). |
| 114 | * A chunk of the bitStream is then stored into a local register. |
| 115 | * Local register size is 64-bits on 64-bits systems, 32-bits on 32-bits systems (size_t). |
| 116 | * You can then retrieve bitFields stored into the local register, **in reverse order**. |
| 117 | * Local register is explicitly reloaded from memory by the BIT_reloadDStream() method. |
| 118 | * A reload guarantee a minimum of ((8*sizeof(bitD->bitContainer))-7) bits when its result is BIT_DStream_unfinished. |
| 119 | * Otherwise, it can be less than that, so proceed accordingly. |
| 120 | * Checking if DStream has reached its end can be performed with BIT_endOfDStream(). |
| 121 | */ |
| 122 | |
| 123 | |
| 124 | /*-**************************************** |
| 125 | * unsafe API |
| 126 | ******************************************/ |
| 127 | MEM_STATIC void BIT_addBitsFast(BIT_CStream_t* bitC, size_t value, unsigned nbBits); |
| 128 | /* faster, but works only if value is "clean", meaning all high bits above nbBits are 0 */ |
| 129 | |
| 130 | MEM_STATIC void BIT_flushBitsFast(BIT_CStream_t* bitC); |
| 131 | /* unsafe version; does not check buffer overflow */ |
| 132 | |
| 133 | MEM_STATIC size_t BIT_readBitsFast(BIT_DStream_t* bitD, unsigned nbBits); |
| 134 | /* faster, but works only if nbBits >= 1 */ |
| 135 | |
| 136 | /*===== Local Constants =====*/ |
| 137 | static const unsigned BIT_mask[] = { |
| 138 | 0, 1, 3, 7, 0xF, 0x1F, |
| 139 | 0x3F, 0x7F, 0xFF, 0x1FF, 0x3FF, 0x7FF, |
| 140 | 0xFFF, 0x1FFF, 0x3FFF, 0x7FFF, 0xFFFF, 0x1FFFF, |
| 141 | 0x3FFFF, 0x7FFFF, 0xFFFFF, 0x1FFFFF, 0x3FFFFF, 0x7FFFFF, |
| 142 | 0xFFFFFF, 0x1FFFFFF, 0x3FFFFFF, 0x7FFFFFF, 0xFFFFFFF, 0x1FFFFFFF, |
| 143 | 0x3FFFFFFF, 0x7FFFFFFF}; /* up to 31 bits */ |
| 144 | #define BIT_MASK_SIZE (sizeof(BIT_mask) / sizeof(BIT_mask[0])) |
| 145 | |
| 146 | /*-************************************************************** |
| 147 | * bitStream encoding |
| 148 | ****************************************************************/ |
| 149 | /*! BIT_initCStream() : |
| 150 | * `dstCapacity` must be > sizeof(size_t) |
| 151 | * @return : 0 if success, |
| 152 | * otherwise an error code (can be tested using ERR_isError()) */ |
| 153 | MEM_STATIC size_t BIT_initCStream(BIT_CStream_t* bitC, |
| 154 | void* startPtr, size_t dstCapacity) |
| 155 | { |
| 156 | bitC->bitContainer = 0; |
| 157 | bitC->bitPos = 0; |
| 158 | bitC->startPtr = (char*)startPtr; |
| 159 | bitC->ptr = bitC->startPtr; |
| 160 | bitC->endPtr = bitC->startPtr + dstCapacity - sizeof(bitC->bitContainer); |
| 161 | if (dstCapacity <= sizeof(bitC->bitContainer)) return ERROR(dstSize_tooSmall); |
| 162 | return 0; |
| 163 | } |
| 164 | |
| 165 | MEM_STATIC FORCE_INLINE_ATTR size_t BIT_getLowerBits(size_t bitContainer, U32 const nbBits) |
| 166 | { |
| 167 | #if defined(STATIC_BMI2) && STATIC_BMI2 == 1 && !defined(ZSTD_NO_INTRINSICS) |
| 168 | return _bzhi_u64(bitContainer, nbBits); |
| 169 | #else |
| 170 | assert(nbBits < BIT_MASK_SIZE); |
| 171 | return bitContainer & BIT_mask[nbBits]; |
| 172 | #endif |
| 173 | } |
| 174 | |
| 175 | /*! BIT_addBits() : |
| 176 | * can add up to 31 bits into `bitC`. |
| 177 | * Note : does not check for register overflow ! */ |
| 178 | MEM_STATIC void BIT_addBits(BIT_CStream_t* bitC, |
| 179 | size_t value, unsigned nbBits) |
| 180 | { |
| 181 | DEBUG_STATIC_ASSERT(BIT_MASK_SIZE == 32); |
| 182 | assert(nbBits < BIT_MASK_SIZE); |
| 183 | assert(nbBits + bitC->bitPos < sizeof(bitC->bitContainer) * 8); |
| 184 | bitC->bitContainer |= BIT_getLowerBits(value, nbBits) << bitC->bitPos; |
| 185 | bitC->bitPos += nbBits; |
| 186 | } |
| 187 | |
| 188 | /*! BIT_addBitsFast() : |
| 189 | * works only if `value` is _clean_, |
| 190 | * meaning all high bits above nbBits are 0 */ |
| 191 | MEM_STATIC void BIT_addBitsFast(BIT_CStream_t* bitC, |
| 192 | size_t value, unsigned nbBits) |
| 193 | { |
| 194 | assert((value>>nbBits) == 0); |
| 195 | assert(nbBits + bitC->bitPos < sizeof(bitC->bitContainer) * 8); |
| 196 | bitC->bitContainer |= value << bitC->bitPos; |
| 197 | bitC->bitPos += nbBits; |
| 198 | } |
| 199 | |
| 200 | /*! BIT_flushBitsFast() : |
| 201 | * assumption : bitContainer has not overflowed |
| 202 | * unsafe version; does not check buffer overflow */ |
| 203 | MEM_STATIC void BIT_flushBitsFast(BIT_CStream_t* bitC) |
| 204 | { |
| 205 | size_t const nbBytes = bitC->bitPos >> 3; |
| 206 | assert(bitC->bitPos < sizeof(bitC->bitContainer) * 8); |
| 207 | assert(bitC->ptr <= bitC->endPtr); |
| 208 | MEM_writeLEST(bitC->ptr, bitC->bitContainer); |
| 209 | bitC->ptr += nbBytes; |
| 210 | bitC->bitPos &= 7; |
| 211 | bitC->bitContainer >>= nbBytes*8; |
| 212 | } |
| 213 | |
| 214 | /*! BIT_flushBits() : |
| 215 | * assumption : bitContainer has not overflowed |
| 216 | * safe version; check for buffer overflow, and prevents it. |
| 217 | * note : does not signal buffer overflow. |
| 218 | * overflow will be revealed later on using BIT_closeCStream() */ |
| 219 | MEM_STATIC void BIT_flushBits(BIT_CStream_t* bitC) |
| 220 | { |
| 221 | size_t const nbBytes = bitC->bitPos >> 3; |
| 222 | assert(bitC->bitPos < sizeof(bitC->bitContainer) * 8); |
| 223 | assert(bitC->ptr <= bitC->endPtr); |
| 224 | MEM_writeLEST(bitC->ptr, bitC->bitContainer); |
| 225 | bitC->ptr += nbBytes; |
| 226 | if (bitC->ptr > bitC->endPtr) bitC->ptr = bitC->endPtr; |
| 227 | bitC->bitPos &= 7; |
| 228 | bitC->bitContainer >>= nbBytes*8; |
| 229 | } |
| 230 | |
| 231 | /*! BIT_closeCStream() : |
| 232 | * @return : size of CStream, in bytes, |
| 233 | * or 0 if it could not fit into dstBuffer */ |
| 234 | MEM_STATIC size_t BIT_closeCStream(BIT_CStream_t* bitC) |
| 235 | { |
| 236 | BIT_addBitsFast(bitC, 1, 1); /* endMark */ |
| 237 | BIT_flushBits(bitC); |
| 238 | if (bitC->ptr >= bitC->endPtr) return 0; /* overflow detected */ |
| 239 | return (bitC->ptr - bitC->startPtr) + (bitC->bitPos > 0); |
| 240 | } |
| 241 | |
| 242 | |
| 243 | /*-******************************************************** |
| 244 | * bitStream decoding |
| 245 | **********************************************************/ |
| 246 | /*! BIT_initDStream() : |
| 247 | * Initialize a BIT_DStream_t. |
| 248 | * `bitD` : a pointer to an already allocated BIT_DStream_t structure. |
| 249 | * `srcSize` must be the *exact* size of the bitStream, in bytes. |
| 250 | * @return : size of stream (== srcSize), or an errorCode if a problem is detected |
| 251 | */ |
| 252 | MEM_STATIC size_t BIT_initDStream(BIT_DStream_t* bitD, const void* srcBuffer, size_t srcSize) |
| 253 | { |
| 254 | if (srcSize < 1) { ZSTD_memset(bitD, 0, sizeof(*bitD)); return ERROR(srcSize_wrong); } |
| 255 | |
| 256 | bitD->start = (const char*)srcBuffer; |
| 257 | bitD->limitPtr = bitD->start + sizeof(bitD->bitContainer); |
| 258 | |
| 259 | if (srcSize >= sizeof(bitD->bitContainer)) { /* normal case */ |
| 260 | bitD->ptr = (const char*)srcBuffer + srcSize - sizeof(bitD->bitContainer); |
| 261 | bitD->bitContainer = MEM_readLEST(bitD->ptr); |
| 262 | { BYTE const lastByte = ((const BYTE*)srcBuffer)[srcSize-1]; |
| 263 | bitD->bitsConsumed = lastByte ? 8 - ZSTD_highbit32(lastByte) : 0; /* ensures bitsConsumed is always set */ |
| 264 | if (lastByte == 0) return ERROR(GENERIC); /* endMark not present */ } |
| 265 | } else { |
| 266 | bitD->ptr = bitD->start; |
| 267 | bitD->bitContainer = *(const BYTE*)(bitD->start); |
| 268 | switch(srcSize) |
| 269 | { |
| 270 | case 7: bitD->bitContainer += (size_t)(((const BYTE*)(srcBuffer))[6]) << (sizeof(bitD->bitContainer)*8 - 16); |
| 271 | ZSTD_FALLTHROUGH; |
| 272 | |
| 273 | case 6: bitD->bitContainer += (size_t)(((const BYTE*)(srcBuffer))[5]) << (sizeof(bitD->bitContainer)*8 - 24); |
| 274 | ZSTD_FALLTHROUGH; |
| 275 | |
| 276 | case 5: bitD->bitContainer += (size_t)(((const BYTE*)(srcBuffer))[4]) << (sizeof(bitD->bitContainer)*8 - 32); |
| 277 | ZSTD_FALLTHROUGH; |
| 278 | |
| 279 | case 4: bitD->bitContainer += (size_t)(((const BYTE*)(srcBuffer))[3]) << 24; |
| 280 | ZSTD_FALLTHROUGH; |
| 281 | |
| 282 | case 3: bitD->bitContainer += (size_t)(((const BYTE*)(srcBuffer))[2]) << 16; |
| 283 | ZSTD_FALLTHROUGH; |
| 284 | |
| 285 | case 2: bitD->bitContainer += (size_t)(((const BYTE*)(srcBuffer))[1]) << 8; |
| 286 | ZSTD_FALLTHROUGH; |
| 287 | |
| 288 | default: break; |
| 289 | } |
| 290 | { BYTE const lastByte = ((const BYTE*)srcBuffer)[srcSize-1]; |
| 291 | bitD->bitsConsumed = lastByte ? 8 - ZSTD_highbit32(lastByte) : 0; |
| 292 | if (lastByte == 0) return ERROR(corruption_detected); /* endMark not present */ |
| 293 | } |
| 294 | bitD->bitsConsumed += (U32)(sizeof(bitD->bitContainer) - srcSize)*8; |
| 295 | } |
| 296 | |
| 297 | return srcSize; |
| 298 | } |
| 299 | |
| 300 | MEM_STATIC FORCE_INLINE_ATTR size_t BIT_getUpperBits(size_t bitContainer, U32 const start) |
| 301 | { |
| 302 | return bitContainer >> start; |
| 303 | } |
| 304 | |
| 305 | MEM_STATIC FORCE_INLINE_ATTR size_t BIT_getMiddleBits(size_t bitContainer, U32 const start, U32 const nbBits) |
| 306 | { |
| 307 | U32 const regMask = sizeof(bitContainer)*8 - 1; |
| 308 | /* if start > regMask, bitstream is corrupted, and result is undefined */ |
| 309 | assert(nbBits < BIT_MASK_SIZE); |
| 310 | /* x86 transform & ((1 << nbBits) - 1) to bzhi instruction, it is better |
| 311 | * than accessing memory. When bmi2 instruction is not present, we consider |
| 312 | * such cpus old (pre-Haswell, 2013) and their performance is not of that |
| 313 | * importance. |
| 314 | */ |
| 315 | #if defined(__x86_64__) || defined(_M_X86) |
| 316 | return (bitContainer >> (start & regMask)) & ((((U64)1) << nbBits) - 1); |
| 317 | #else |
| 318 | return (bitContainer >> (start & regMask)) & BIT_mask[nbBits]; |
| 319 | #endif |
| 320 | } |
| 321 | |
| 322 | /*! BIT_lookBits() : |
| 323 | * Provides next n bits from local register. |
| 324 | * local register is not modified. |
| 325 | * On 32-bits, maxNbBits==24. |
| 326 | * On 64-bits, maxNbBits==56. |
| 327 | * @return : value extracted */ |
| 328 | MEM_STATIC FORCE_INLINE_ATTR size_t BIT_lookBits(const BIT_DStream_t* bitD, U32 nbBits) |
| 329 | { |
| 330 | /* arbitrate between double-shift and shift+mask */ |
| 331 | #if 1 |
| 332 | /* if bitD->bitsConsumed + nbBits > sizeof(bitD->bitContainer)*8, |
| 333 | * bitstream is likely corrupted, and result is undefined */ |
| 334 | return BIT_getMiddleBits(bitD->bitContainer, (sizeof(bitD->bitContainer)*8) - bitD->bitsConsumed - nbBits, nbBits); |
| 335 | #else |
| 336 | /* this code path is slower on my os-x laptop */ |
| 337 | U32 const regMask = sizeof(bitD->bitContainer)*8 - 1; |
| 338 | return ((bitD->bitContainer << (bitD->bitsConsumed & regMask)) >> 1) >> ((regMask-nbBits) & regMask); |
| 339 | #endif |
| 340 | } |
| 341 | |
| 342 | /*! BIT_lookBitsFast() : |
| 343 | * unsafe version; only works if nbBits >= 1 */ |
| 344 | MEM_STATIC size_t BIT_lookBitsFast(const BIT_DStream_t* bitD, U32 nbBits) |
| 345 | { |
| 346 | U32 const regMask = sizeof(bitD->bitContainer)*8 - 1; |
| 347 | assert(nbBits >= 1); |
| 348 | return (bitD->bitContainer << (bitD->bitsConsumed & regMask)) >> (((regMask+1)-nbBits) & regMask); |
| 349 | } |
| 350 | |
| 351 | MEM_STATIC FORCE_INLINE_ATTR void BIT_skipBits(BIT_DStream_t* bitD, U32 nbBits) |
| 352 | { |
| 353 | bitD->bitsConsumed += nbBits; |
| 354 | } |
| 355 | |
| 356 | /*! BIT_readBits() : |
| 357 | * Read (consume) next n bits from local register and update. |
| 358 | * Pay attention to not read more than nbBits contained into local register. |
| 359 | * @return : extracted value. */ |
| 360 | MEM_STATIC FORCE_INLINE_ATTR size_t BIT_readBits(BIT_DStream_t* bitD, unsigned nbBits) |
| 361 | { |
| 362 | size_t const value = BIT_lookBits(bitD, nbBits); |
| 363 | BIT_skipBits(bitD, nbBits); |
| 364 | return value; |
| 365 | } |
| 366 | |
| 367 | /*! BIT_readBitsFast() : |
| 368 | * unsafe version; only works if nbBits >= 1 */ |
| 369 | MEM_STATIC size_t BIT_readBitsFast(BIT_DStream_t* bitD, unsigned nbBits) |
| 370 | { |
| 371 | size_t const value = BIT_lookBitsFast(bitD, nbBits); |
| 372 | assert(nbBits >= 1); |
| 373 | BIT_skipBits(bitD, nbBits); |
| 374 | return value; |
| 375 | } |
| 376 | |
| 377 | /*! BIT_reloadDStreamFast() : |
| 378 | * Similar to BIT_reloadDStream(), but with two differences: |
| 379 | * 1. bitsConsumed <= sizeof(bitD->bitContainer)*8 must hold! |
| 380 | * 2. Returns BIT_DStream_overflow when bitD->ptr < bitD->limitPtr, at this |
| 381 | * point you must use BIT_reloadDStream() to reload. |
| 382 | */ |
| 383 | MEM_STATIC BIT_DStream_status BIT_reloadDStreamFast(BIT_DStream_t* bitD) |
| 384 | { |
| 385 | if (UNLIKELY(bitD->ptr < bitD->limitPtr)) |
| 386 | return BIT_DStream_overflow; |
| 387 | assert(bitD->bitsConsumed <= sizeof(bitD->bitContainer)*8); |
| 388 | bitD->ptr -= bitD->bitsConsumed >> 3; |
| 389 | bitD->bitsConsumed &= 7; |
| 390 | bitD->bitContainer = MEM_readLEST(bitD->ptr); |
| 391 | return BIT_DStream_unfinished; |
| 392 | } |
| 393 | |
| 394 | /*! BIT_reloadDStream() : |
| 395 | * Refill `bitD` from buffer previously set in BIT_initDStream() . |
| 396 | * This function is safe, it guarantees it will not read beyond src buffer. |
| 397 | * @return : status of `BIT_DStream_t` internal register. |
| 398 | * when status == BIT_DStream_unfinished, internal register is filled with at least 25 or 57 bits */ |
| 399 | MEM_STATIC FORCE_INLINE_ATTR BIT_DStream_status BIT_reloadDStream(BIT_DStream_t* bitD) |
| 400 | { |
| 401 | if (bitD->bitsConsumed > (sizeof(bitD->bitContainer)*8)) /* overflow detected, like end of stream */ |
| 402 | return BIT_DStream_overflow; |
| 403 | |
| 404 | if (bitD->ptr >= bitD->limitPtr) { |
| 405 | return BIT_reloadDStreamFast(bitD); |
| 406 | } |
| 407 | if (bitD->ptr == bitD->start) { |
| 408 | if (bitD->bitsConsumed < sizeof(bitD->bitContainer)*8) return BIT_DStream_endOfBuffer; |
| 409 | return BIT_DStream_completed; |
| 410 | } |
| 411 | /* start < ptr < limitPtr */ |
| 412 | { U32 nbBytes = bitD->bitsConsumed >> 3; |
| 413 | BIT_DStream_status result = BIT_DStream_unfinished; |
| 414 | if (bitD->ptr - nbBytes < bitD->start) { |
| 415 | nbBytes = (U32)(bitD->ptr - bitD->start); /* ptr > start */ |
| 416 | result = BIT_DStream_endOfBuffer; |
| 417 | } |
| 418 | bitD->ptr -= nbBytes; |
| 419 | bitD->bitsConsumed -= nbBytes*8; |
| 420 | bitD->bitContainer = MEM_readLEST(bitD->ptr); /* reminder : srcSize > sizeof(bitD->bitContainer), otherwise bitD->ptr == bitD->start */ |
| 421 | return result; |
| 422 | } |
| 423 | } |
| 424 | |
| 425 | /*! BIT_endOfDStream() : |
| 426 | * @return : 1 if DStream has _exactly_ reached its end (all bits consumed). |
| 427 | */ |
| 428 | MEM_STATIC unsigned BIT_endOfDStream(const BIT_DStream_t* DStream) |
| 429 | { |
| 430 | return ((DStream->ptr == DStream->start) && (DStream->bitsConsumed == sizeof(DStream->bitContainer)*8)); |
| 431 | } |
| 432 | |
| 433 | #if defined (__cplusplus) |
| 434 | } |
| 435 | #endif |
| 436 | |
| 437 | #endif /* BITSTREAM_H_MODULE */ |