bitstream.h 13 KB

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  1. /* SPDX-License-Identifier: (GPL-2.0 or BSD-2-Clause) */
  2. /*
  3. * bitstream
  4. * Part of FSE library
  5. * header file (to include)
  6. * Copyright (C) 2013-2016, Yann Collet.
  7. *
  8. * You can contact the author at :
  9. * - Source repository : https://github.com/Cyan4973/FiniteStateEntropy
  10. */
  11. #ifndef BITSTREAM_H_MODULE
  12. #define BITSTREAM_H_MODULE
  13. /*
  14. * This API consists of small unitary functions, which must be inlined for best performance.
  15. * Since link-time-optimization is not available for all compilers,
  16. * these functions are defined into a .h to be included.
  17. */
  18. /*-****************************************
  19. * Dependencies
  20. ******************************************/
  21. #include "error_private.h" /* error codes and messages */
  22. #include "mem.h" /* unaligned access routines */
  23. /*=========================================
  24. * Target specific
  25. =========================================*/
  26. #define STREAM_ACCUMULATOR_MIN_32 25
  27. #define STREAM_ACCUMULATOR_MIN_64 57
  28. #define STREAM_ACCUMULATOR_MIN ((U32)(ZSTD_32bits() ? STREAM_ACCUMULATOR_MIN_32 : STREAM_ACCUMULATOR_MIN_64))
  29. /*-******************************************
  30. * bitStream encoding API (write forward)
  31. ********************************************/
  32. /* bitStream can mix input from multiple sources.
  33. * A critical property of these streams is that they encode and decode in **reverse** direction.
  34. * So the first bit sequence you add will be the last to be read, like a LIFO stack.
  35. */
  36. typedef struct {
  37. size_t bitContainer;
  38. int bitPos;
  39. char *startPtr;
  40. char *ptr;
  41. char *endPtr;
  42. } BIT_CStream_t;
  43. ZSTD_STATIC size_t BIT_initCStream(BIT_CStream_t *bitC, void *dstBuffer, size_t dstCapacity);
  44. ZSTD_STATIC void BIT_addBits(BIT_CStream_t *bitC, size_t value, unsigned nbBits);
  45. ZSTD_STATIC void BIT_flushBits(BIT_CStream_t *bitC);
  46. ZSTD_STATIC size_t BIT_closeCStream(BIT_CStream_t *bitC);
  47. /* Start with initCStream, providing the size of buffer to write into.
  48. * bitStream will never write outside of this buffer.
  49. * `dstCapacity` must be >= sizeof(bitD->bitContainer), otherwise @return will be an error code.
  50. *
  51. * bits are first added to a local register.
  52. * Local register is size_t, hence 64-bits on 64-bits systems, or 32-bits on 32-bits systems.
  53. * Writing data into memory is an explicit operation, performed by the flushBits function.
  54. * Hence keep track how many bits are potentially stored into local register to avoid register overflow.
  55. * After a flushBits, a maximum of 7 bits might still be stored into local register.
  56. *
  57. * Avoid storing elements of more than 24 bits if you want compatibility with 32-bits bitstream readers.
  58. *
  59. * Last operation is to close the bitStream.
  60. * The function returns the final size of CStream in bytes.
  61. * If data couldn't fit into `dstBuffer`, it will return a 0 ( == not storable)
  62. */
  63. /*-********************************************
  64. * bitStream decoding API (read backward)
  65. **********************************************/
  66. typedef struct {
  67. size_t bitContainer;
  68. unsigned bitsConsumed;
  69. const char *ptr;
  70. const char *start;
  71. } BIT_DStream_t;
  72. typedef enum {
  73. BIT_DStream_unfinished = 0,
  74. BIT_DStream_endOfBuffer = 1,
  75. BIT_DStream_completed = 2,
  76. BIT_DStream_overflow = 3
  77. } BIT_DStream_status; /* result of BIT_reloadDStream() */
  78. /* 1,2,4,8 would be better for bitmap combinations, but slows down performance a bit ... :( */
  79. ZSTD_STATIC size_t BIT_initDStream(BIT_DStream_t *bitD, const void *srcBuffer, size_t srcSize);
  80. ZSTD_STATIC size_t BIT_readBits(BIT_DStream_t *bitD, unsigned nbBits);
  81. ZSTD_STATIC BIT_DStream_status BIT_reloadDStream(BIT_DStream_t *bitD);
  82. ZSTD_STATIC unsigned BIT_endOfDStream(const BIT_DStream_t *bitD);
  83. /* Start by invoking BIT_initDStream().
  84. * A chunk of the bitStream is then stored into a local register.
  85. * Local register size is 64-bits on 64-bits systems, 32-bits on 32-bits systems (size_t).
  86. * You can then retrieve bitFields stored into the local register, **in reverse order**.
  87. * Local register is explicitly reloaded from memory by the BIT_reloadDStream() method.
  88. * A reload guarantee a minimum of ((8*sizeof(bitD->bitContainer))-7) bits when its result is BIT_DStream_unfinished.
  89. * Otherwise, it can be less than that, so proceed accordingly.
  90. * Checking if DStream has reached its end can be performed with BIT_endOfDStream().
  91. */
  92. /*-****************************************
  93. * unsafe API
  94. ******************************************/
  95. ZSTD_STATIC void BIT_addBitsFast(BIT_CStream_t *bitC, size_t value, unsigned nbBits);
  96. /* faster, but works only if value is "clean", meaning all high bits above nbBits are 0 */
  97. ZSTD_STATIC void BIT_flushBitsFast(BIT_CStream_t *bitC);
  98. /* unsafe version; does not check buffer overflow */
  99. ZSTD_STATIC size_t BIT_readBitsFast(BIT_DStream_t *bitD, unsigned nbBits);
  100. /* faster, but works only if nbBits >= 1 */
  101. /*-**************************************************************
  102. * Internal functions
  103. ****************************************************************/
  104. ZSTD_STATIC unsigned BIT_highbit32(register U32 val) { return 31 - __builtin_clz(val); }
  105. /*===== Local Constants =====*/
  106. static const unsigned BIT_mask[] = {0, 1, 3, 7, 0xF, 0x1F, 0x3F, 0x7F, 0xFF,
  107. 0x1FF, 0x3FF, 0x7FF, 0xFFF, 0x1FFF, 0x3FFF, 0x7FFF, 0xFFFF, 0x1FFFF,
  108. 0x3FFFF, 0x7FFFF, 0xFFFFF, 0x1FFFFF, 0x3FFFFF, 0x7FFFFF, 0xFFFFFF, 0x1FFFFFF, 0x3FFFFFF}; /* up to 26 bits */
  109. /*-**************************************************************
  110. * bitStream encoding
  111. ****************************************************************/
  112. /*! BIT_initCStream() :
  113. * `dstCapacity` must be > sizeof(void*)
  114. * @return : 0 if success,
  115. otherwise an error code (can be tested using ERR_isError() ) */
  116. ZSTD_STATIC size_t BIT_initCStream(BIT_CStream_t *bitC, void *startPtr, size_t dstCapacity)
  117. {
  118. bitC->bitContainer = 0;
  119. bitC->bitPos = 0;
  120. bitC->startPtr = (char *)startPtr;
  121. bitC->ptr = bitC->startPtr;
  122. bitC->endPtr = bitC->startPtr + dstCapacity - sizeof(bitC->ptr);
  123. if (dstCapacity <= sizeof(bitC->ptr))
  124. return ERROR(dstSize_tooSmall);
  125. return 0;
  126. }
  127. /*! BIT_addBits() :
  128. can add up to 26 bits into `bitC`.
  129. Does not check for register overflow ! */
  130. ZSTD_STATIC void BIT_addBits(BIT_CStream_t *bitC, size_t value, unsigned nbBits)
  131. {
  132. bitC->bitContainer |= (value & BIT_mask[nbBits]) << bitC->bitPos;
  133. bitC->bitPos += nbBits;
  134. }
  135. /*! BIT_addBitsFast() :
  136. * works only if `value` is _clean_, meaning all high bits above nbBits are 0 */
  137. ZSTD_STATIC void BIT_addBitsFast(BIT_CStream_t *bitC, size_t value, unsigned nbBits)
  138. {
  139. bitC->bitContainer |= value << bitC->bitPos;
  140. bitC->bitPos += nbBits;
  141. }
  142. /*! BIT_flushBitsFast() :
  143. * unsafe version; does not check buffer overflow */
  144. ZSTD_STATIC void BIT_flushBitsFast(BIT_CStream_t *bitC)
  145. {
  146. size_t const nbBytes = bitC->bitPos >> 3;
  147. ZSTD_writeLEST(bitC->ptr, bitC->bitContainer);
  148. bitC->ptr += nbBytes;
  149. bitC->bitPos &= 7;
  150. bitC->bitContainer >>= nbBytes * 8; /* if bitPos >= sizeof(bitContainer)*8 --> undefined behavior */
  151. }
  152. /*! BIT_flushBits() :
  153. * safe version; check for buffer overflow, and prevents it.
  154. * note : does not signal buffer overflow. This will be revealed later on using BIT_closeCStream() */
  155. ZSTD_STATIC void BIT_flushBits(BIT_CStream_t *bitC)
  156. {
  157. size_t const nbBytes = bitC->bitPos >> 3;
  158. ZSTD_writeLEST(bitC->ptr, bitC->bitContainer);
  159. bitC->ptr += nbBytes;
  160. if (bitC->ptr > bitC->endPtr)
  161. bitC->ptr = bitC->endPtr;
  162. bitC->bitPos &= 7;
  163. bitC->bitContainer >>= nbBytes * 8; /* if bitPos >= sizeof(bitContainer)*8 --> undefined behavior */
  164. }
  165. /*! BIT_closeCStream() :
  166. * @return : size of CStream, in bytes,
  167. or 0 if it could not fit into dstBuffer */
  168. ZSTD_STATIC size_t BIT_closeCStream(BIT_CStream_t *bitC)
  169. {
  170. BIT_addBitsFast(bitC, 1, 1); /* endMark */
  171. BIT_flushBits(bitC);
  172. if (bitC->ptr >= bitC->endPtr)
  173. return 0; /* doesn't fit within authorized budget : cancel */
  174. return (bitC->ptr - bitC->startPtr) + (bitC->bitPos > 0);
  175. }
  176. /*-********************************************************
  177. * bitStream decoding
  178. **********************************************************/
  179. /*! BIT_initDStream() :
  180. * Initialize a BIT_DStream_t.
  181. * `bitD` : a pointer to an already allocated BIT_DStream_t structure.
  182. * `srcSize` must be the *exact* size of the bitStream, in bytes.
  183. * @return : size of stream (== srcSize) or an errorCode if a problem is detected
  184. */
  185. ZSTD_STATIC size_t BIT_initDStream(BIT_DStream_t *bitD, const void *srcBuffer, size_t srcSize)
  186. {
  187. if (srcSize < 1) {
  188. memset(bitD, 0, sizeof(*bitD));
  189. return ERROR(srcSize_wrong);
  190. }
  191. if (srcSize >= sizeof(bitD->bitContainer)) { /* normal case */
  192. bitD->start = (const char *)srcBuffer;
  193. bitD->ptr = (const char *)srcBuffer + srcSize - sizeof(bitD->bitContainer);
  194. bitD->bitContainer = ZSTD_readLEST(bitD->ptr);
  195. {
  196. BYTE const lastByte = ((const BYTE *)srcBuffer)[srcSize - 1];
  197. bitD->bitsConsumed = lastByte ? 8 - BIT_highbit32(lastByte) : 0; /* ensures bitsConsumed is always set */
  198. if (lastByte == 0)
  199. return ERROR(GENERIC); /* endMark not present */
  200. }
  201. } else {
  202. bitD->start = (const char *)srcBuffer;
  203. bitD->ptr = bitD->start;
  204. bitD->bitContainer = *(const BYTE *)(bitD->start);
  205. switch (srcSize) {
  206. case 7: bitD->bitContainer += (size_t)(((const BYTE *)(srcBuffer))[6]) << (sizeof(bitD->bitContainer) * 8 - 16);
  207. case 6: bitD->bitContainer += (size_t)(((const BYTE *)(srcBuffer))[5]) << (sizeof(bitD->bitContainer) * 8 - 24);
  208. case 5: bitD->bitContainer += (size_t)(((const BYTE *)(srcBuffer))[4]) << (sizeof(bitD->bitContainer) * 8 - 32);
  209. case 4: bitD->bitContainer += (size_t)(((const BYTE *)(srcBuffer))[3]) << 24;
  210. case 3: bitD->bitContainer += (size_t)(((const BYTE *)(srcBuffer))[2]) << 16;
  211. case 2: bitD->bitContainer += (size_t)(((const BYTE *)(srcBuffer))[1]) << 8;
  212. default:;
  213. }
  214. {
  215. BYTE const lastByte = ((const BYTE *)srcBuffer)[srcSize - 1];
  216. bitD->bitsConsumed = lastByte ? 8 - BIT_highbit32(lastByte) : 0;
  217. if (lastByte == 0)
  218. return ERROR(GENERIC); /* endMark not present */
  219. }
  220. bitD->bitsConsumed += (U32)(sizeof(bitD->bitContainer) - srcSize) * 8;
  221. }
  222. return srcSize;
  223. }
  224. ZSTD_STATIC size_t BIT_getUpperBits(size_t bitContainer, U32 const start) { return bitContainer >> start; }
  225. ZSTD_STATIC size_t BIT_getMiddleBits(size_t bitContainer, U32 const start, U32 const nbBits) { return (bitContainer >> start) & BIT_mask[nbBits]; }
  226. ZSTD_STATIC size_t BIT_getLowerBits(size_t bitContainer, U32 const nbBits) { return bitContainer & BIT_mask[nbBits]; }
  227. /*! BIT_lookBits() :
  228. * Provides next n bits from local register.
  229. * local register is not modified.
  230. * On 32-bits, maxNbBits==24.
  231. * On 64-bits, maxNbBits==56.
  232. * @return : value extracted
  233. */
  234. ZSTD_STATIC size_t BIT_lookBits(const BIT_DStream_t *bitD, U32 nbBits)
  235. {
  236. U32 const bitMask = sizeof(bitD->bitContainer) * 8 - 1;
  237. return ((bitD->bitContainer << (bitD->bitsConsumed & bitMask)) >> 1) >> ((bitMask - nbBits) & bitMask);
  238. }
  239. /*! BIT_lookBitsFast() :
  240. * unsafe version; only works only if nbBits >= 1 */
  241. ZSTD_STATIC size_t BIT_lookBitsFast(const BIT_DStream_t *bitD, U32 nbBits)
  242. {
  243. U32 const bitMask = sizeof(bitD->bitContainer) * 8 - 1;
  244. return (bitD->bitContainer << (bitD->bitsConsumed & bitMask)) >> (((bitMask + 1) - nbBits) & bitMask);
  245. }
  246. ZSTD_STATIC void BIT_skipBits(BIT_DStream_t *bitD, U32 nbBits) { bitD->bitsConsumed += nbBits; }
  247. /*! BIT_readBits() :
  248. * Read (consume) next n bits from local register and update.
  249. * Pay attention to not read more than nbBits contained into local register.
  250. * @return : extracted value.
  251. */
  252. ZSTD_STATIC size_t BIT_readBits(BIT_DStream_t *bitD, U32 nbBits)
  253. {
  254. size_t const value = BIT_lookBits(bitD, nbBits);
  255. BIT_skipBits(bitD, nbBits);
  256. return value;
  257. }
  258. /*! BIT_readBitsFast() :
  259. * unsafe version; only works only if nbBits >= 1 */
  260. ZSTD_STATIC size_t BIT_readBitsFast(BIT_DStream_t *bitD, U32 nbBits)
  261. {
  262. size_t const value = BIT_lookBitsFast(bitD, nbBits);
  263. BIT_skipBits(bitD, nbBits);
  264. return value;
  265. }
  266. /*! BIT_reloadDStream() :
  267. * Refill `bitD` from buffer previously set in BIT_initDStream() .
  268. * This function is safe, it guarantees it will not read beyond src buffer.
  269. * @return : status of `BIT_DStream_t` internal register.
  270. if status == BIT_DStream_unfinished, internal register is filled with >= (sizeof(bitD->bitContainer)*8 - 7) bits */
  271. ZSTD_STATIC BIT_DStream_status BIT_reloadDStream(BIT_DStream_t *bitD)
  272. {
  273. if (bitD->bitsConsumed > (sizeof(bitD->bitContainer) * 8)) /* should not happen => corruption detected */
  274. return BIT_DStream_overflow;
  275. if (bitD->ptr >= bitD->start + sizeof(bitD->bitContainer)) {
  276. bitD->ptr -= bitD->bitsConsumed >> 3;
  277. bitD->bitsConsumed &= 7;
  278. bitD->bitContainer = ZSTD_readLEST(bitD->ptr);
  279. return BIT_DStream_unfinished;
  280. }
  281. if (bitD->ptr == bitD->start) {
  282. if (bitD->bitsConsumed < sizeof(bitD->bitContainer) * 8)
  283. return BIT_DStream_endOfBuffer;
  284. return BIT_DStream_completed;
  285. }
  286. {
  287. U32 nbBytes = bitD->bitsConsumed >> 3;
  288. BIT_DStream_status result = BIT_DStream_unfinished;
  289. if (bitD->ptr - nbBytes < bitD->start) {
  290. nbBytes = (U32)(bitD->ptr - bitD->start); /* ptr > start */
  291. result = BIT_DStream_endOfBuffer;
  292. }
  293. bitD->ptr -= nbBytes;
  294. bitD->bitsConsumed -= nbBytes * 8;
  295. bitD->bitContainer = ZSTD_readLEST(bitD->ptr); /* reminder : srcSize > sizeof(bitD) */
  296. return result;
  297. }
  298. }
  299. /*! BIT_endOfDStream() :
  300. * @return Tells if DStream has exactly reached its end (all bits consumed).
  301. */
  302. ZSTD_STATIC unsigned BIT_endOfDStream(const BIT_DStream_t *DStream)
  303. {
  304. return ((DStream->ptr == DStream->start) && (DStream->bitsConsumed == sizeof(DStream->bitContainer) * 8));
  305. }
  306. #endif /* BITSTREAM_H_MODULE */