1 /* ******************************************************************
2 * bitstream
3 * Part of FSE library
4 * Copyright (c) 2013-2020, Yann Collet, Facebook, Inc.
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 /*
22 * This API consists of small unitary functions, which must be inlined for best performance.
23 * Since link-time-optimization is not available for all compilers,
24 * these functions are defined into a .h to be included.
25 */
26
27 /*-****************************************
28 * Dependencies
29 ******************************************/
30 #include "mem.h" /* unaligned access routines */
31 #include "compiler.h" /* UNLIKELY() */
32 #include "debug.h" /* assert(), DEBUGLOG(), RAWLOG() */
33 #include "error_private.h" /* error codes and messages */
34
35
36 /*=========================================
37 * Target specific
38 =========================================*/
39 #if defined(__BMI__) && defined(__GNUC__)
40 # include <immintrin.h> /* support for bextr (experimental) */
41 #elif defined(__ICCARM__)
42 # include <intrinsics.h>
43 #endif
44
45 #define STREAM_ACCUMULATOR_MIN_32 25
46 #define STREAM_ACCUMULATOR_MIN_64 57
47 #define STREAM_ACCUMULATOR_MIN ((U32)(MEM_32bits() ? STREAM_ACCUMULATOR_MIN_32 : STREAM_ACCUMULATOR_MIN_64))
48
49
50 /*-******************************************
51 * bitStream encoding API (write forward)
52 ********************************************/
53 /* bitStream can mix input from multiple sources.
54 * A critical property of these streams is that they encode and decode in **reverse** direction.
55 * So the first bit sequence you add will be the last to be read, like a LIFO stack.
56 */
57 typedef struct {
58 size_t bitContainer;
59 unsigned bitPos;
60 char* startPtr;
61 char* ptr;
62 char* endPtr;
63 } BIT_CStream_t;
64
65 MEM_STATIC size_t BIT_initCStream(BIT_CStream_t* bitC, void* dstBuffer, size_t dstCapacity);
66 MEM_STATIC void BIT_addBits(BIT_CStream_t* bitC, size_t value, unsigned nbBits);
67 MEM_STATIC void BIT_flushBits(BIT_CStream_t* bitC);
68 MEM_STATIC size_t BIT_closeCStream(BIT_CStream_t* bitC);
69
70 /* Start with initCStream, providing the size of buffer to write into.
71 * bitStream will never write outside of this buffer.
72 * `dstCapacity` must be >= sizeof(bitD->bitContainer), otherwise @return will be an error code.
73 *
74 * bits are first added to a local register.
75 * Local register is size_t, hence 64-bits on 64-bits systems, or 32-bits on 32-bits systems.
76 * Writing data into memory is an explicit operation, performed by the flushBits function.
77 * Hence keep track how many bits are potentially stored into local register to avoid register overflow.
78 * After a flushBits, a maximum of 7 bits might still be stored into local register.
79 *
80 * Avoid storing elements of more than 24 bits if you want compatibility with 32-bits bitstream readers.
81 *
82 * Last operation is to close the bitStream.
83 * The function returns the final size of CStream in bytes.
84 * If data couldn't fit into `dstBuffer`, it will return a 0 ( == not storable)
85 */
86
87
88 /*-********************************************
89 * bitStream decoding API (read backward)
90 **********************************************/
91 typedef struct {
92 size_t bitContainer;
93 unsigned bitsConsumed;
94 const char* ptr;
95 const char* start;
96 const char* limitPtr;
97 } BIT_DStream_t;
98
99 typedef enum { BIT_DStream_unfinished = 0,
100 BIT_DStream_endOfBuffer = 1,
101 BIT_DStream_completed = 2,
102 BIT_DStream_overflow = 3 } BIT_DStream_status; /* result of BIT_reloadDStream() */
103 /* 1,2,4,8 would be better for bitmap combinations, but slows down performance a bit ... :( */
104
105 MEM_STATIC size_t BIT_initDStream(BIT_DStream_t* bitD, const void* srcBuffer, size_t srcSize);
106 MEM_STATIC size_t BIT_readBits(BIT_DStream_t* bitD, unsigned nbBits);
107 MEM_STATIC BIT_DStream_status BIT_reloadDStream(BIT_DStream_t* bitD);
108 MEM_STATIC unsigned BIT_endOfDStream(const BIT_DStream_t* bitD);
109
110
111 /* Start by invoking BIT_initDStream().
112 * A chunk of the bitStream is then stored into a local register.
113 * Local register size is 64-bits on 64-bits systems, 32-bits on 32-bits systems (size_t).
114 * You can then retrieve bitFields stored into the local register, **in reverse order**.
115 * Local register is explicitly reloaded from memory by the BIT_reloadDStream() method.
116 * A reload guarantee a minimum of ((8*sizeof(bitD->bitContainer))-7) bits when its result is BIT_DStream_unfinished.
117 * Otherwise, it can be less than that, so proceed accordingly.
118 * Checking if DStream has reached its end can be performed with BIT_endOfDStream().
119 */
120
121
122 /*-****************************************
123 * unsafe API
124 ******************************************/
125 MEM_STATIC void BIT_addBitsFast(BIT_CStream_t* bitC, size_t value, unsigned nbBits);
126 /* faster, but works only if value is "clean", meaning all high bits above nbBits are 0 */
127
128 MEM_STATIC void BIT_flushBitsFast(BIT_CStream_t* bitC);
129 /* unsafe version; does not check buffer overflow */
130
131 MEM_STATIC size_t BIT_readBitsFast(BIT_DStream_t* bitD, unsigned nbBits);
132 /* faster, but works only if nbBits >= 1 */
133
134
135
136 /*-**************************************************************
137 * Internal functions
138 ****************************************************************/
BIT_highbit32(U32 val)139 MEM_STATIC unsigned BIT_highbit32 (U32 val)
140 {
141 assert(val != 0);
142 {
143 # if defined(_MSC_VER) /* Visual */
144 unsigned long r=0;
145 return _BitScanReverse ( &r, val ) ? (unsigned)r : 0;
146 # elif defined(__GNUC__) && (__GNUC__ >= 3) /* Use GCC Intrinsic */
147 return __builtin_clz (val) ^ 31;
148 # elif defined(__ICCARM__) /* IAR Intrinsic */
149 return 31 - __CLZ(val);
150 # else /* Software version */
151 static const unsigned DeBruijnClz[32] = { 0, 9, 1, 10, 13, 21, 2, 29,
152 11, 14, 16, 18, 22, 25, 3, 30,
153 8, 12, 20, 28, 15, 17, 24, 7,
154 19, 27, 23, 6, 26, 5, 4, 31 };
155 U32 v = val;
156 v |= v >> 1;
157 v |= v >> 2;
158 v |= v >> 4;
159 v |= v >> 8;
160 v |= v >> 16;
161 return DeBruijnClz[ (U32) (v * 0x07C4ACDDU) >> 27];
162 # endif
163 }
164 }
165
166 /*===== Local Constants =====*/
167 static const unsigned BIT_mask[] = {
168 0, 1, 3, 7, 0xF, 0x1F,
169 0x3F, 0x7F, 0xFF, 0x1FF, 0x3FF, 0x7FF,
170 0xFFF, 0x1FFF, 0x3FFF, 0x7FFF, 0xFFFF, 0x1FFFF,
171 0x3FFFF, 0x7FFFF, 0xFFFFF, 0x1FFFFF, 0x3FFFFF, 0x7FFFFF,
172 0xFFFFFF, 0x1FFFFFF, 0x3FFFFFF, 0x7FFFFFF, 0xFFFFFFF, 0x1FFFFFFF,
173 0x3FFFFFFF, 0x7FFFFFFF}; /* up to 31 bits */
174 #define BIT_MASK_SIZE (sizeof(BIT_mask) / sizeof(BIT_mask[0]))
175
176 /*-**************************************************************
177 * bitStream encoding
178 ****************************************************************/
179 /*! BIT_initCStream() :
180 * `dstCapacity` must be > sizeof(size_t)
181 * @return : 0 if success,
182 * otherwise an error code (can be tested using ERR_isError()) */
BIT_initCStream(BIT_CStream_t * bitC,void * startPtr,size_t dstCapacity)183 MEM_STATIC size_t BIT_initCStream(BIT_CStream_t* bitC,
184 void* startPtr, size_t dstCapacity)
185 {
186 bitC->bitContainer = 0;
187 bitC->bitPos = 0;
188 bitC->startPtr = (char*)startPtr;
189 bitC->ptr = bitC->startPtr;
190 bitC->endPtr = bitC->startPtr + dstCapacity - sizeof(bitC->bitContainer);
191 if (dstCapacity <= sizeof(bitC->bitContainer)) return ERROR(dstSize_tooSmall);
192 return 0;
193 }
194
195 /*! BIT_addBits() :
196 * can add up to 31 bits into `bitC`.
197 * Note : does not check for register overflow ! */
BIT_addBits(BIT_CStream_t * bitC,size_t value,unsigned nbBits)198 MEM_STATIC void BIT_addBits(BIT_CStream_t* bitC,
199 size_t value, unsigned nbBits)
200 {
201 MEM_STATIC_ASSERT(BIT_MASK_SIZE == 32);
202 assert(nbBits < BIT_MASK_SIZE);
203 assert(nbBits + bitC->bitPos < sizeof(bitC->bitContainer) * 8);
204 bitC->bitContainer |= (value & BIT_mask[nbBits]) << bitC->bitPos;
205 bitC->bitPos += nbBits;
206 }
207
208 /*! BIT_addBitsFast() :
209 * works only if `value` is _clean_,
210 * meaning all high bits above nbBits are 0 */
BIT_addBitsFast(BIT_CStream_t * bitC,size_t value,unsigned nbBits)211 MEM_STATIC void BIT_addBitsFast(BIT_CStream_t* bitC,
212 size_t value, unsigned nbBits)
213 {
214 assert((value>>nbBits) == 0);
215 assert(nbBits + bitC->bitPos < sizeof(bitC->bitContainer) * 8);
216 bitC->bitContainer |= value << bitC->bitPos;
217 bitC->bitPos += nbBits;
218 }
219
220 /*! BIT_flushBitsFast() :
221 * assumption : bitContainer has not overflowed
222 * unsafe version; does not check buffer overflow */
BIT_flushBitsFast(BIT_CStream_t * bitC)223 MEM_STATIC void BIT_flushBitsFast(BIT_CStream_t* bitC)
224 {
225 size_t const nbBytes = bitC->bitPos >> 3;
226 assert(bitC->bitPos < sizeof(bitC->bitContainer) * 8);
227 assert(bitC->ptr <= bitC->endPtr);
228 MEM_writeLEST(bitC->ptr, bitC->bitContainer);
229 bitC->ptr += nbBytes;
230 bitC->bitPos &= 7;
231 bitC->bitContainer >>= nbBytes*8;
232 }
233
234 /*! BIT_flushBits() :
235 * assumption : bitContainer has not overflowed
236 * safe version; check for buffer overflow, and prevents it.
237 * note : does not signal buffer overflow.
238 * overflow will be revealed later on using BIT_closeCStream() */
BIT_flushBits(BIT_CStream_t * bitC)239 MEM_STATIC void BIT_flushBits(BIT_CStream_t* bitC)
240 {
241 size_t const nbBytes = bitC->bitPos >> 3;
242 assert(bitC->bitPos < sizeof(bitC->bitContainer) * 8);
243 assert(bitC->ptr <= bitC->endPtr);
244 MEM_writeLEST(bitC->ptr, bitC->bitContainer);
245 bitC->ptr += nbBytes;
246 if (bitC->ptr > bitC->endPtr) bitC->ptr = bitC->endPtr;
247 bitC->bitPos &= 7;
248 bitC->bitContainer >>= nbBytes*8;
249 }
250
251 /*! BIT_closeCStream() :
252 * @return : size of CStream, in bytes,
253 * or 0 if it could not fit into dstBuffer */
BIT_closeCStream(BIT_CStream_t * bitC)254 MEM_STATIC size_t BIT_closeCStream(BIT_CStream_t* bitC)
255 {
256 BIT_addBitsFast(bitC, 1, 1); /* endMark */
257 BIT_flushBits(bitC);
258 if (bitC->ptr >= bitC->endPtr) return 0; /* overflow detected */
259 return (bitC->ptr - bitC->startPtr) + (bitC->bitPos > 0);
260 }
261
262
263 /*-********************************************************
264 * bitStream decoding
265 **********************************************************/
266 /*! BIT_initDStream() :
267 * Initialize a BIT_DStream_t.
268 * `bitD` : a pointer to an already allocated BIT_DStream_t structure.
269 * `srcSize` must be the *exact* size of the bitStream, in bytes.
270 * @return : size of stream (== srcSize), or an errorCode if a problem is detected
271 */
BIT_initDStream(BIT_DStream_t * bitD,const void * srcBuffer,size_t srcSize)272 MEM_STATIC size_t BIT_initDStream(BIT_DStream_t* bitD, const void* srcBuffer, size_t srcSize)
273 {
274 if (srcSize < 1) { memset(bitD, 0, sizeof(*bitD)); return ERROR(srcSize_wrong); }
275
276 bitD->start = (const char*)srcBuffer;
277 bitD->limitPtr = bitD->start + sizeof(bitD->bitContainer);
278
279 if (srcSize >= sizeof(bitD->bitContainer)) { /* normal case */
280 bitD->ptr = (const char*)srcBuffer + srcSize - sizeof(bitD->bitContainer);
281 bitD->bitContainer = MEM_readLEST(bitD->ptr);
282 { BYTE const lastByte = ((const BYTE*)srcBuffer)[srcSize-1];
283 bitD->bitsConsumed = lastByte ? 8 - BIT_highbit32(lastByte) : 0; /* ensures bitsConsumed is always set */
284 if (lastByte == 0) return ERROR(GENERIC); /* endMark not present */ }
285 } else {
286 bitD->ptr = bitD->start;
287 bitD->bitContainer = *(const BYTE*)(bitD->start);
288 switch(srcSize)
289 {
290 case 7: bitD->bitContainer += (size_t)(((const BYTE*)(srcBuffer))[6]) << (sizeof(bitD->bitContainer)*8 - 16);
291 /* fall-through */
292
293 case 6: bitD->bitContainer += (size_t)(((const BYTE*)(srcBuffer))[5]) << (sizeof(bitD->bitContainer)*8 - 24);
294 /* fall-through */
295
296 case 5: bitD->bitContainer += (size_t)(((const BYTE*)(srcBuffer))[4]) << (sizeof(bitD->bitContainer)*8 - 32);
297 /* fall-through */
298
299 case 4: bitD->bitContainer += (size_t)(((const BYTE*)(srcBuffer))[3]) << 24;
300 /* fall-through */
301
302 case 3: bitD->bitContainer += (size_t)(((const BYTE*)(srcBuffer))[2]) << 16;
303 /* fall-through */
304
305 case 2: bitD->bitContainer += (size_t)(((const BYTE*)(srcBuffer))[1]) << 8;
306 /* fall-through */
307
308 default: break;
309 }
310 { BYTE const lastByte = ((const BYTE*)srcBuffer)[srcSize-1];
311 bitD->bitsConsumed = lastByte ? 8 - BIT_highbit32(lastByte) : 0;
312 if (lastByte == 0) return ERROR(corruption_detected); /* endMark not present */
313 }
314 bitD->bitsConsumed += (U32)(sizeof(bitD->bitContainer) - srcSize)*8;
315 }
316
317 return srcSize;
318 }
319
BIT_getUpperBits(size_t bitContainer,U32 const start)320 MEM_STATIC size_t BIT_getUpperBits(size_t bitContainer, U32 const start)
321 {
322 return bitContainer >> start;
323 }
324
BIT_getMiddleBits(size_t bitContainer,U32 const start,U32 const nbBits)325 MEM_STATIC size_t BIT_getMiddleBits(size_t bitContainer, U32 const start, U32 const nbBits)
326 {
327 U32 const regMask = sizeof(bitContainer)*8 - 1;
328 /* if start > regMask, bitstream is corrupted, and result is undefined */
329 assert(nbBits < BIT_MASK_SIZE);
330 return (bitContainer >> (start & regMask)) & BIT_mask[nbBits];
331 }
332
BIT_getLowerBits(size_t bitContainer,U32 const nbBits)333 MEM_STATIC size_t BIT_getLowerBits(size_t bitContainer, U32 const nbBits)
334 {
335 assert(nbBits < BIT_MASK_SIZE);
336 return bitContainer & BIT_mask[nbBits];
337 }
338
339 /*! BIT_lookBits() :
340 * Provides next n bits from local register.
341 * local register is not modified.
342 * On 32-bits, maxNbBits==24.
343 * On 64-bits, maxNbBits==56.
344 * @return : value extracted */
BIT_lookBits(const BIT_DStream_t * bitD,U32 nbBits)345 MEM_STATIC size_t BIT_lookBits(const BIT_DStream_t* bitD, U32 nbBits)
346 {
347 /* arbitrate between double-shift and shift+mask */
348 #if 1
349 /* if bitD->bitsConsumed + nbBits > sizeof(bitD->bitContainer)*8,
350 * bitstream is likely corrupted, and result is undefined */
351 return BIT_getMiddleBits(bitD->bitContainer, (sizeof(bitD->bitContainer)*8) - bitD->bitsConsumed - nbBits, nbBits);
352 #else
353 /* this code path is slower on my os-x laptop */
354 U32 const regMask = sizeof(bitD->bitContainer)*8 - 1;
355 return ((bitD->bitContainer << (bitD->bitsConsumed & regMask)) >> 1) >> ((regMask-nbBits) & regMask);
356 #endif
357 }
358
359 /*! BIT_lookBitsFast() :
360 * unsafe version; only works if nbBits >= 1 */
BIT_lookBitsFast(const BIT_DStream_t * bitD,U32 nbBits)361 MEM_STATIC size_t BIT_lookBitsFast(const BIT_DStream_t* bitD, U32 nbBits)
362 {
363 U32 const regMask = sizeof(bitD->bitContainer)*8 - 1;
364 assert(nbBits >= 1);
365 return (bitD->bitContainer << (bitD->bitsConsumed & regMask)) >> (((regMask+1)-nbBits) & regMask);
366 }
367
BIT_skipBits(BIT_DStream_t * bitD,U32 nbBits)368 MEM_STATIC void BIT_skipBits(BIT_DStream_t* bitD, U32 nbBits)
369 {
370 bitD->bitsConsumed += nbBits;
371 }
372
373 /*! BIT_readBits() :
374 * Read (consume) next n bits from local register and update.
375 * Pay attention to not read more than nbBits contained into local register.
376 * @return : extracted value. */
BIT_readBits(BIT_DStream_t * bitD,unsigned nbBits)377 MEM_STATIC size_t BIT_readBits(BIT_DStream_t* bitD, unsigned nbBits)
378 {
379 size_t const value = BIT_lookBits(bitD, nbBits);
380 BIT_skipBits(bitD, nbBits);
381 return value;
382 }
383
384 /*! BIT_readBitsFast() :
385 * unsafe version; only works only if nbBits >= 1 */
BIT_readBitsFast(BIT_DStream_t * bitD,unsigned nbBits)386 MEM_STATIC size_t BIT_readBitsFast(BIT_DStream_t* bitD, unsigned nbBits)
387 {
388 size_t const value = BIT_lookBitsFast(bitD, nbBits);
389 assert(nbBits >= 1);
390 BIT_skipBits(bitD, nbBits);
391 return value;
392 }
393
394 /*! BIT_reloadDStreamFast() :
395 * Similar to BIT_reloadDStream(), but with two differences:
396 * 1. bitsConsumed <= sizeof(bitD->bitContainer)*8 must hold!
397 * 2. Returns BIT_DStream_overflow when bitD->ptr < bitD->limitPtr, at this
398 * point you must use BIT_reloadDStream() to reload.
399 */
BIT_reloadDStreamFast(BIT_DStream_t * bitD)400 MEM_STATIC BIT_DStream_status BIT_reloadDStreamFast(BIT_DStream_t* bitD)
401 {
402 if (UNLIKELY(bitD->ptr < bitD->limitPtr))
403 return BIT_DStream_overflow;
404 assert(bitD->bitsConsumed <= sizeof(bitD->bitContainer)*8);
405 bitD->ptr -= bitD->bitsConsumed >> 3;
406 bitD->bitsConsumed &= 7;
407 bitD->bitContainer = MEM_readLEST(bitD->ptr);
408 return BIT_DStream_unfinished;
409 }
410
411 /*! BIT_reloadDStream() :
412 * Refill `bitD` from buffer previously set in BIT_initDStream() .
413 * This function is safe, it guarantees it will not read beyond src buffer.
414 * @return : status of `BIT_DStream_t` internal register.
415 * when status == BIT_DStream_unfinished, internal register is filled with at least 25 or 57 bits */
BIT_reloadDStream(BIT_DStream_t * bitD)416 MEM_STATIC BIT_DStream_status BIT_reloadDStream(BIT_DStream_t* bitD)
417 {
418 if (bitD->bitsConsumed > (sizeof(bitD->bitContainer)*8)) /* overflow detected, like end of stream */
419 return BIT_DStream_overflow;
420
421 if (bitD->ptr >= bitD->limitPtr) {
422 return BIT_reloadDStreamFast(bitD);
423 }
424 if (bitD->ptr == bitD->start) {
425 if (bitD->bitsConsumed < sizeof(bitD->bitContainer)*8) return BIT_DStream_endOfBuffer;
426 return BIT_DStream_completed;
427 }
428 /* start < ptr < limitPtr */
429 { U32 nbBytes = bitD->bitsConsumed >> 3;
430 BIT_DStream_status result = BIT_DStream_unfinished;
431 if (bitD->ptr - nbBytes < bitD->start) {
432 nbBytes = (U32)(bitD->ptr - bitD->start); /* ptr > start */
433 result = BIT_DStream_endOfBuffer;
434 }
435 bitD->ptr -= nbBytes;
436 bitD->bitsConsumed -= nbBytes*8;
437 bitD->bitContainer = MEM_readLEST(bitD->ptr); /* reminder : srcSize > sizeof(bitD->bitContainer), otherwise bitD->ptr == bitD->start */
438 return result;
439 }
440 }
441
442 /*! BIT_endOfDStream() :
443 * @return : 1 if DStream has _exactly_ reached its end (all bits consumed).
444 */
BIT_endOfDStream(const BIT_DStream_t * DStream)445 MEM_STATIC unsigned BIT_endOfDStream(const BIT_DStream_t* DStream)
446 {
447 return ((DStream->ptr == DStream->start) && (DStream->bitsConsumed == sizeof(DStream->bitContainer)*8));
448 }
449
450 #if defined (__cplusplus)
451 }
452 #endif
453
454 #endif /* BITSTREAM_H_MODULE */
455