Scott Baker | e7144bc | 2019-10-01 14:16:47 -0700 | [diff] [blame^] | 1 | /* ****************************************************************** |
| 2 | bitstream |
| 3 | Part of FSE library |
| 4 | header file (to include) |
| 5 | Copyright (C) 2013-2017, Yann Collet. |
| 6 | |
| 7 | BSD 2-Clause License (http://www.opensource.org/licenses/bsd-license.php) |
| 8 | |
| 9 | Redistribution and use in source and binary forms, with or without |
| 10 | modification, are permitted provided that the following conditions are |
| 11 | met: |
| 12 | |
| 13 | * Redistributions of source code must retain the above copyright |
| 14 | notice, this list of conditions and the following disclaimer. |
| 15 | * Redistributions in binary form must reproduce the above |
| 16 | copyright notice, this list of conditions and the following disclaimer |
| 17 | in the documentation and/or other materials provided with the |
| 18 | distribution. |
| 19 | |
| 20 | THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS |
| 21 | "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT |
| 22 | LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR |
| 23 | A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT |
| 24 | OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, |
| 25 | SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT |
| 26 | LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, |
| 27 | DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY |
| 28 | THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT |
| 29 | (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE |
| 30 | OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. |
| 31 | |
| 32 | You can contact the author at : |
| 33 | - Source repository : https://github.com/Cyan4973/FiniteStateEntropy |
| 34 | ****************************************************************** */ |
| 35 | #ifndef BITSTREAM_H_MODULE |
| 36 | #define BITSTREAM_H_MODULE |
| 37 | |
| 38 | #if defined (__cplusplus) |
| 39 | extern "C" { |
| 40 | #endif |
| 41 | |
| 42 | /* |
| 43 | * This API consists of small unitary functions, which must be inlined for best performance. |
| 44 | * Since link-time-optimization is not available for all compilers, |
| 45 | * these functions are defined into a .h to be included. |
| 46 | */ |
| 47 | |
| 48 | /*-**************************************** |
| 49 | * Dependencies |
| 50 | ******************************************/ |
| 51 | #include "mem.h" /* unaligned access routines */ |
| 52 | #include "error_private.h" /* error codes and messages */ |
| 53 | |
| 54 | |
| 55 | /*-************************************* |
| 56 | * Debug |
| 57 | ***************************************/ |
| 58 | #if defined(BIT_DEBUG) && (BIT_DEBUG>=1) |
| 59 | # include <assert.h> |
| 60 | #else |
| 61 | # ifndef assert |
| 62 | # define assert(condition) ((void)0) |
| 63 | # endif |
| 64 | #endif |
| 65 | |
| 66 | |
| 67 | /*========================================= |
| 68 | * Target specific |
| 69 | =========================================*/ |
| 70 | #if defined(__BMI__) && defined(__GNUC__) |
| 71 | # include <immintrin.h> /* support for bextr (experimental) */ |
| 72 | #endif |
| 73 | |
| 74 | #define STREAM_ACCUMULATOR_MIN_32 25 |
| 75 | #define STREAM_ACCUMULATOR_MIN_64 57 |
| 76 | #define STREAM_ACCUMULATOR_MIN ((U32)(MEM_32bits() ? STREAM_ACCUMULATOR_MIN_32 : STREAM_ACCUMULATOR_MIN_64)) |
| 77 | |
| 78 | |
| 79 | /*-****************************************** |
| 80 | * bitStream encoding API (write forward) |
| 81 | ********************************************/ |
| 82 | /* bitStream can mix input from multiple sources. |
| 83 | * A critical property of these streams is that they encode and decode in **reverse** direction. |
| 84 | * So the first bit sequence you add will be the last to be read, like a LIFO stack. |
| 85 | */ |
| 86 | typedef struct |
| 87 | { |
| 88 | size_t bitContainer; |
| 89 | unsigned bitPos; |
| 90 | char* startPtr; |
| 91 | char* ptr; |
| 92 | char* endPtr; |
| 93 | } BIT_CStream_t; |
| 94 | |
| 95 | MEM_STATIC size_t BIT_initCStream(BIT_CStream_t* bitC, void* dstBuffer, size_t dstCapacity); |
| 96 | MEM_STATIC void BIT_addBits(BIT_CStream_t* bitC, size_t value, unsigned nbBits); |
| 97 | MEM_STATIC void BIT_flushBits(BIT_CStream_t* bitC); |
| 98 | MEM_STATIC size_t BIT_closeCStream(BIT_CStream_t* bitC); |
| 99 | |
| 100 | /* Start with initCStream, providing the size of buffer to write into. |
| 101 | * bitStream will never write outside of this buffer. |
| 102 | * `dstCapacity` must be >= sizeof(bitD->bitContainer), otherwise @return will be an error code. |
| 103 | * |
| 104 | * bits are first added to a local register. |
| 105 | * Local register is size_t, hence 64-bits on 64-bits systems, or 32-bits on 32-bits systems. |
| 106 | * Writing data into memory is an explicit operation, performed by the flushBits function. |
| 107 | * Hence keep track how many bits are potentially stored into local register to avoid register overflow. |
| 108 | * After a flushBits, a maximum of 7 bits might still be stored into local register. |
| 109 | * |
| 110 | * Avoid storing elements of more than 24 bits if you want compatibility with 32-bits bitstream readers. |
| 111 | * |
| 112 | * Last operation is to close the bitStream. |
| 113 | * The function returns the final size of CStream in bytes. |
| 114 | * If data couldn't fit into `dstBuffer`, it will return a 0 ( == not storable) |
| 115 | */ |
| 116 | |
| 117 | |
| 118 | /*-******************************************** |
| 119 | * bitStream decoding API (read backward) |
| 120 | **********************************************/ |
| 121 | typedef struct |
| 122 | { |
| 123 | size_t bitContainer; |
| 124 | unsigned bitsConsumed; |
| 125 | const char* ptr; |
| 126 | const char* start; |
| 127 | const char* limitPtr; |
| 128 | } BIT_DStream_t; |
| 129 | |
| 130 | typedef enum { BIT_DStream_unfinished = 0, |
| 131 | BIT_DStream_endOfBuffer = 1, |
| 132 | BIT_DStream_completed = 2, |
| 133 | BIT_DStream_overflow = 3 } BIT_DStream_status; /* result of BIT_reloadDStream() */ |
| 134 | /* 1,2,4,8 would be better for bitmap combinations, but slows down performance a bit ... :( */ |
| 135 | |
| 136 | MEM_STATIC size_t BIT_initDStream(BIT_DStream_t* bitD, const void* srcBuffer, size_t srcSize); |
| 137 | MEM_STATIC size_t BIT_readBits(BIT_DStream_t* bitD, unsigned nbBits); |
| 138 | MEM_STATIC BIT_DStream_status BIT_reloadDStream(BIT_DStream_t* bitD); |
| 139 | MEM_STATIC unsigned BIT_endOfDStream(const BIT_DStream_t* bitD); |
| 140 | |
| 141 | |
| 142 | /* Start by invoking BIT_initDStream(). |
| 143 | * A chunk of the bitStream is then stored into a local register. |
| 144 | * Local register size is 64-bits on 64-bits systems, 32-bits on 32-bits systems (size_t). |
| 145 | * You can then retrieve bitFields stored into the local register, **in reverse order**. |
| 146 | * Local register is explicitly reloaded from memory by the BIT_reloadDStream() method. |
| 147 | * A reload guarantee a minimum of ((8*sizeof(bitD->bitContainer))-7) bits when its result is BIT_DStream_unfinished. |
| 148 | * Otherwise, it can be less than that, so proceed accordingly. |
| 149 | * Checking if DStream has reached its end can be performed with BIT_endOfDStream(). |
| 150 | */ |
| 151 | |
| 152 | |
| 153 | /*-**************************************** |
| 154 | * unsafe API |
| 155 | ******************************************/ |
| 156 | MEM_STATIC void BIT_addBitsFast(BIT_CStream_t* bitC, size_t value, unsigned nbBits); |
| 157 | /* faster, but works only if value is "clean", meaning all high bits above nbBits are 0 */ |
| 158 | |
| 159 | MEM_STATIC void BIT_flushBitsFast(BIT_CStream_t* bitC); |
| 160 | /* unsafe version; does not check buffer overflow */ |
| 161 | |
| 162 | MEM_STATIC size_t BIT_readBitsFast(BIT_DStream_t* bitD, unsigned nbBits); |
| 163 | /* faster, but works only if nbBits >= 1 */ |
| 164 | |
| 165 | |
| 166 | |
| 167 | /*-************************************************************** |
| 168 | * Internal functions |
| 169 | ****************************************************************/ |
| 170 | MEM_STATIC unsigned BIT_highbit32 (U32 val) |
| 171 | { |
| 172 | assert(val != 0); |
| 173 | { |
| 174 | # if defined(_MSC_VER) /* Visual */ |
| 175 | unsigned long r=0; |
| 176 | _BitScanReverse ( &r, val ); |
| 177 | return (unsigned) r; |
| 178 | # elif defined(__GNUC__) && (__GNUC__ >= 3) /* Use GCC Intrinsic */ |
| 179 | return 31 - __builtin_clz (val); |
| 180 | # else /* Software version */ |
| 181 | static const unsigned DeBruijnClz[32] = { 0, 9, 1, 10, 13, 21, 2, 29, |
| 182 | 11, 14, 16, 18, 22, 25, 3, 30, |
| 183 | 8, 12, 20, 28, 15, 17, 24, 7, |
| 184 | 19, 27, 23, 6, 26, 5, 4, 31 }; |
| 185 | U32 v = val; |
| 186 | v |= v >> 1; |
| 187 | v |= v >> 2; |
| 188 | v |= v >> 4; |
| 189 | v |= v >> 8; |
| 190 | v |= v >> 16; |
| 191 | return DeBruijnClz[ (U32) (v * 0x07C4ACDDU) >> 27]; |
| 192 | # endif |
| 193 | } |
| 194 | } |
| 195 | |
| 196 | /*===== Local Constants =====*/ |
| 197 | static const unsigned BIT_mask[] = { |
| 198 | 0, 1, 3, 7, 0xF, 0x1F, |
| 199 | 0x3F, 0x7F, 0xFF, 0x1FF, 0x3FF, 0x7FF, |
| 200 | 0xFFF, 0x1FFF, 0x3FFF, 0x7FFF, 0xFFFF, 0x1FFFF, |
| 201 | 0x3FFFF, 0x7FFFF, 0xFFFFF, 0x1FFFFF, 0x3FFFFF, 0x7FFFFF, |
| 202 | 0xFFFFFF, 0x1FFFFFF, 0x3FFFFFF, 0x7FFFFFF, 0xFFFFFFF, 0x1FFFFFFF, |
| 203 | 0x3FFFFFFF, 0x7FFFFFFF}; /* up to 31 bits */ |
| 204 | #define BIT_MASK_SIZE (sizeof(BIT_mask) / sizeof(BIT_mask[0])) |
| 205 | |
| 206 | /*-************************************************************** |
| 207 | * bitStream encoding |
| 208 | ****************************************************************/ |
| 209 | /*! BIT_initCStream() : |
| 210 | * `dstCapacity` must be > sizeof(size_t) |
| 211 | * @return : 0 if success, |
| 212 | * otherwise an error code (can be tested using ERR_isError()) */ |
| 213 | MEM_STATIC size_t BIT_initCStream(BIT_CStream_t* bitC, |
| 214 | void* startPtr, size_t dstCapacity) |
| 215 | { |
| 216 | bitC->bitContainer = 0; |
| 217 | bitC->bitPos = 0; |
| 218 | bitC->startPtr = (char*)startPtr; |
| 219 | bitC->ptr = bitC->startPtr; |
| 220 | bitC->endPtr = bitC->startPtr + dstCapacity - sizeof(bitC->bitContainer); |
| 221 | if (dstCapacity <= sizeof(bitC->bitContainer)) return ERROR(dstSize_tooSmall); |
| 222 | return 0; |
| 223 | } |
| 224 | |
| 225 | /*! BIT_addBits() : |
| 226 | * can add up to 31 bits into `bitC`. |
| 227 | * Note : does not check for register overflow ! */ |
| 228 | MEM_STATIC void BIT_addBits(BIT_CStream_t* bitC, |
| 229 | size_t value, unsigned nbBits) |
| 230 | { |
| 231 | MEM_STATIC_ASSERT(BIT_MASK_SIZE == 32); |
| 232 | assert(nbBits < BIT_MASK_SIZE); |
| 233 | assert(nbBits + bitC->bitPos < sizeof(bitC->bitContainer) * 8); |
| 234 | bitC->bitContainer |= (value & BIT_mask[nbBits]) << bitC->bitPos; |
| 235 | bitC->bitPos += nbBits; |
| 236 | } |
| 237 | |
| 238 | /*! BIT_addBitsFast() : |
| 239 | * works only if `value` is _clean_, meaning all high bits above nbBits are 0 */ |
| 240 | MEM_STATIC void BIT_addBitsFast(BIT_CStream_t* bitC, |
| 241 | size_t value, unsigned nbBits) |
| 242 | { |
| 243 | assert((value>>nbBits) == 0); |
| 244 | assert(nbBits + bitC->bitPos < sizeof(bitC->bitContainer) * 8); |
| 245 | bitC->bitContainer |= value << bitC->bitPos; |
| 246 | bitC->bitPos += nbBits; |
| 247 | } |
| 248 | |
| 249 | /*! BIT_flushBitsFast() : |
| 250 | * assumption : bitContainer has not overflowed |
| 251 | * unsafe version; does not check buffer overflow */ |
| 252 | MEM_STATIC void BIT_flushBitsFast(BIT_CStream_t* bitC) |
| 253 | { |
| 254 | size_t const nbBytes = bitC->bitPos >> 3; |
| 255 | assert(bitC->bitPos < sizeof(bitC->bitContainer) * 8); |
| 256 | MEM_writeLEST(bitC->ptr, bitC->bitContainer); |
| 257 | bitC->ptr += nbBytes; |
| 258 | assert(bitC->ptr <= bitC->endPtr); |
| 259 | bitC->bitPos &= 7; |
| 260 | bitC->bitContainer >>= nbBytes*8; |
| 261 | } |
| 262 | |
| 263 | /*! BIT_flushBits() : |
| 264 | * assumption : bitContainer has not overflowed |
| 265 | * safe version; check for buffer overflow, and prevents it. |
| 266 | * note : does not signal buffer overflow. |
| 267 | * overflow will be revealed later on using BIT_closeCStream() */ |
| 268 | MEM_STATIC void BIT_flushBits(BIT_CStream_t* bitC) |
| 269 | { |
| 270 | size_t const nbBytes = bitC->bitPos >> 3; |
| 271 | assert(bitC->bitPos < sizeof(bitC->bitContainer) * 8); |
| 272 | MEM_writeLEST(bitC->ptr, bitC->bitContainer); |
| 273 | bitC->ptr += nbBytes; |
| 274 | if (bitC->ptr > bitC->endPtr) bitC->ptr = bitC->endPtr; |
| 275 | bitC->bitPos &= 7; |
| 276 | bitC->bitContainer >>= nbBytes*8; |
| 277 | } |
| 278 | |
| 279 | /*! BIT_closeCStream() : |
| 280 | * @return : size of CStream, in bytes, |
| 281 | * or 0 if it could not fit into dstBuffer */ |
| 282 | MEM_STATIC size_t BIT_closeCStream(BIT_CStream_t* bitC) |
| 283 | { |
| 284 | BIT_addBitsFast(bitC, 1, 1); /* endMark */ |
| 285 | BIT_flushBits(bitC); |
| 286 | if (bitC->ptr >= bitC->endPtr) return 0; /* overflow detected */ |
| 287 | return (bitC->ptr - bitC->startPtr) + (bitC->bitPos > 0); |
| 288 | } |
| 289 | |
| 290 | |
| 291 | /*-******************************************************** |
| 292 | * bitStream decoding |
| 293 | **********************************************************/ |
| 294 | /*! BIT_initDStream() : |
| 295 | * Initialize a BIT_DStream_t. |
| 296 | * `bitD` : a pointer to an already allocated BIT_DStream_t structure. |
| 297 | * `srcSize` must be the *exact* size of the bitStream, in bytes. |
| 298 | * @return : size of stream (== srcSize), or an errorCode if a problem is detected |
| 299 | */ |
| 300 | MEM_STATIC size_t BIT_initDStream(BIT_DStream_t* bitD, const void* srcBuffer, size_t srcSize) |
| 301 | { |
| 302 | if (srcSize < 1) { memset(bitD, 0, sizeof(*bitD)); return ERROR(srcSize_wrong); } |
| 303 | |
| 304 | bitD->start = (const char*)srcBuffer; |
| 305 | bitD->limitPtr = bitD->start + sizeof(bitD->bitContainer); |
| 306 | |
| 307 | if (srcSize >= sizeof(bitD->bitContainer)) { /* normal case */ |
| 308 | bitD->ptr = (const char*)srcBuffer + srcSize - sizeof(bitD->bitContainer); |
| 309 | bitD->bitContainer = MEM_readLEST(bitD->ptr); |
| 310 | { BYTE const lastByte = ((const BYTE*)srcBuffer)[srcSize-1]; |
| 311 | bitD->bitsConsumed = lastByte ? 8 - BIT_highbit32(lastByte) : 0; /* ensures bitsConsumed is always set */ |
| 312 | if (lastByte == 0) return ERROR(GENERIC); /* endMark not present */ } |
| 313 | } else { |
| 314 | bitD->ptr = bitD->start; |
| 315 | bitD->bitContainer = *(const BYTE*)(bitD->start); |
| 316 | switch(srcSize) |
| 317 | { |
| 318 | case 7: bitD->bitContainer += (size_t)(((const BYTE*)(srcBuffer))[6]) << (sizeof(bitD->bitContainer)*8 - 16); |
| 319 | /* fall-through */ |
| 320 | |
| 321 | case 6: bitD->bitContainer += (size_t)(((const BYTE*)(srcBuffer))[5]) << (sizeof(bitD->bitContainer)*8 - 24); |
| 322 | /* fall-through */ |
| 323 | |
| 324 | case 5: bitD->bitContainer += (size_t)(((const BYTE*)(srcBuffer))[4]) << (sizeof(bitD->bitContainer)*8 - 32); |
| 325 | /* fall-through */ |
| 326 | |
| 327 | case 4: bitD->bitContainer += (size_t)(((const BYTE*)(srcBuffer))[3]) << 24; |
| 328 | /* fall-through */ |
| 329 | |
| 330 | case 3: bitD->bitContainer += (size_t)(((const BYTE*)(srcBuffer))[2]) << 16; |
| 331 | /* fall-through */ |
| 332 | |
| 333 | case 2: bitD->bitContainer += (size_t)(((const BYTE*)(srcBuffer))[1]) << 8; |
| 334 | /* fall-through */ |
| 335 | |
| 336 | default: break; |
| 337 | } |
| 338 | { BYTE const lastByte = ((const BYTE*)srcBuffer)[srcSize-1]; |
| 339 | bitD->bitsConsumed = lastByte ? 8 - BIT_highbit32(lastByte) : 0; |
| 340 | if (lastByte == 0) return ERROR(corruption_detected); /* endMark not present */ |
| 341 | } |
| 342 | bitD->bitsConsumed += (U32)(sizeof(bitD->bitContainer) - srcSize)*8; |
| 343 | } |
| 344 | |
| 345 | return srcSize; |
| 346 | } |
| 347 | |
| 348 | MEM_STATIC size_t BIT_getUpperBits(size_t bitContainer, U32 const start) |
| 349 | { |
| 350 | return bitContainer >> start; |
| 351 | } |
| 352 | |
| 353 | MEM_STATIC size_t BIT_getMiddleBits(size_t bitContainer, U32 const start, U32 const nbBits) |
| 354 | { |
| 355 | #if defined(__BMI__) && defined(__GNUC__) && __GNUC__*1000+__GNUC_MINOR__ >= 4008 /* experimental */ |
| 356 | # if defined(__x86_64__) |
| 357 | if (sizeof(bitContainer)==8) |
| 358 | return _bextr_u64(bitContainer, start, nbBits); |
| 359 | else |
| 360 | # endif |
| 361 | return _bextr_u32(bitContainer, start, nbBits); |
| 362 | #else |
| 363 | assert(nbBits < BIT_MASK_SIZE); |
| 364 | return (bitContainer >> start) & BIT_mask[nbBits]; |
| 365 | #endif |
| 366 | } |
| 367 | |
| 368 | MEM_STATIC size_t BIT_getLowerBits(size_t bitContainer, U32 const nbBits) |
| 369 | { |
| 370 | assert(nbBits < BIT_MASK_SIZE); |
| 371 | return bitContainer & BIT_mask[nbBits]; |
| 372 | } |
| 373 | |
| 374 | /*! BIT_lookBits() : |
| 375 | * Provides next n bits from local register. |
| 376 | * local register is not modified. |
| 377 | * On 32-bits, maxNbBits==24. |
| 378 | * On 64-bits, maxNbBits==56. |
| 379 | * @return : value extracted */ |
| 380 | MEM_STATIC size_t BIT_lookBits(const BIT_DStream_t* bitD, U32 nbBits) |
| 381 | { |
| 382 | #if defined(__BMI__) && defined(__GNUC__) /* experimental; fails if bitD->bitsConsumed + nbBits > sizeof(bitD->bitContainer)*8 */ |
| 383 | return BIT_getMiddleBits(bitD->bitContainer, (sizeof(bitD->bitContainer)*8) - bitD->bitsConsumed - nbBits, nbBits); |
| 384 | #else |
| 385 | U32 const regMask = sizeof(bitD->bitContainer)*8 - 1; |
| 386 | return ((bitD->bitContainer << (bitD->bitsConsumed & regMask)) >> 1) >> ((regMask-nbBits) & regMask); |
| 387 | #endif |
| 388 | } |
| 389 | |
| 390 | /*! BIT_lookBitsFast() : |
| 391 | * unsafe version; only works if nbBits >= 1 */ |
| 392 | MEM_STATIC size_t BIT_lookBitsFast(const BIT_DStream_t* bitD, U32 nbBits) |
| 393 | { |
| 394 | U32 const regMask = sizeof(bitD->bitContainer)*8 - 1; |
| 395 | assert(nbBits >= 1); |
| 396 | return (bitD->bitContainer << (bitD->bitsConsumed & regMask)) >> (((regMask+1)-nbBits) & regMask); |
| 397 | } |
| 398 | |
| 399 | MEM_STATIC void BIT_skipBits(BIT_DStream_t* bitD, U32 nbBits) |
| 400 | { |
| 401 | bitD->bitsConsumed += nbBits; |
| 402 | } |
| 403 | |
| 404 | /*! BIT_readBits() : |
| 405 | * Read (consume) next n bits from local register and update. |
| 406 | * Pay attention to not read more than nbBits contained into local register. |
| 407 | * @return : extracted value. */ |
| 408 | MEM_STATIC size_t BIT_readBits(BIT_DStream_t* bitD, U32 nbBits) |
| 409 | { |
| 410 | size_t const value = BIT_lookBits(bitD, nbBits); |
| 411 | BIT_skipBits(bitD, nbBits); |
| 412 | return value; |
| 413 | } |
| 414 | |
| 415 | /*! BIT_readBitsFast() : |
| 416 | * unsafe version; only works only if nbBits >= 1 */ |
| 417 | MEM_STATIC size_t BIT_readBitsFast(BIT_DStream_t* bitD, U32 nbBits) |
| 418 | { |
| 419 | size_t const value = BIT_lookBitsFast(bitD, nbBits); |
| 420 | assert(nbBits >= 1); |
| 421 | BIT_skipBits(bitD, nbBits); |
| 422 | return value; |
| 423 | } |
| 424 | |
| 425 | /*! BIT_reloadDStream() : |
| 426 | * Refill `bitD` from buffer previously set in BIT_initDStream() . |
| 427 | * This function is safe, it guarantees it will not read beyond src buffer. |
| 428 | * @return : status of `BIT_DStream_t` internal register. |
| 429 | * when status == BIT_DStream_unfinished, internal register is filled with at least 25 or 57 bits */ |
| 430 | MEM_STATIC BIT_DStream_status BIT_reloadDStream(BIT_DStream_t* bitD) |
| 431 | { |
| 432 | if (bitD->bitsConsumed > (sizeof(bitD->bitContainer)*8)) /* overflow detected, like end of stream */ |
| 433 | return BIT_DStream_overflow; |
| 434 | |
| 435 | if (bitD->ptr >= bitD->limitPtr) { |
| 436 | bitD->ptr -= bitD->bitsConsumed >> 3; |
| 437 | bitD->bitsConsumed &= 7; |
| 438 | bitD->bitContainer = MEM_readLEST(bitD->ptr); |
| 439 | return BIT_DStream_unfinished; |
| 440 | } |
| 441 | if (bitD->ptr == bitD->start) { |
| 442 | if (bitD->bitsConsumed < sizeof(bitD->bitContainer)*8) return BIT_DStream_endOfBuffer; |
| 443 | return BIT_DStream_completed; |
| 444 | } |
| 445 | /* start < ptr < limitPtr */ |
| 446 | { U32 nbBytes = bitD->bitsConsumed >> 3; |
| 447 | BIT_DStream_status result = BIT_DStream_unfinished; |
| 448 | if (bitD->ptr - nbBytes < bitD->start) { |
| 449 | nbBytes = (U32)(bitD->ptr - bitD->start); /* ptr > start */ |
| 450 | result = BIT_DStream_endOfBuffer; |
| 451 | } |
| 452 | bitD->ptr -= nbBytes; |
| 453 | bitD->bitsConsumed -= nbBytes*8; |
| 454 | bitD->bitContainer = MEM_readLEST(bitD->ptr); /* reminder : srcSize > sizeof(bitD->bitContainer), otherwise bitD->ptr == bitD->start */ |
| 455 | return result; |
| 456 | } |
| 457 | } |
| 458 | |
| 459 | /*! BIT_endOfDStream() : |
| 460 | * @return : 1 if DStream has _exactly_ reached its end (all bits consumed). |
| 461 | */ |
| 462 | MEM_STATIC unsigned BIT_endOfDStream(const BIT_DStream_t* DStream) |
| 463 | { |
| 464 | return ((DStream->ptr == DStream->start) && (DStream->bitsConsumed == sizeof(DStream->bitContainer)*8)); |
| 465 | } |
| 466 | |
| 467 | #if defined (__cplusplus) |
| 468 | } |
| 469 | #endif |
| 470 | |
| 471 | #endif /* BITSTREAM_H_MODULE */ |