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1 /*
2  * bitstream
3  * Part of FSE library
4  * header file (to include)
5  * Copyright (C) 2013-2016, 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  * This program is free software; you can redistribute it and/or modify it under
33  * the terms of the GNU General Public License version 2 as published by the
34  * Free Software Foundation. This program is dual-licensed; you may select
35  * either version 2 of the GNU General Public License ("GPL") or BSD license
36  * ("BSD").
37  *
38  * You can contact the author at :
39  * - Source repository : https://github.com/Cyan4973/FiniteStateEntropy
40  */
41 #ifndef BITSTREAM_H_MODULE
42 #define BITSTREAM_H_MODULE
43 
44 /*
45 *  This API consists of small unitary functions, which must be inlined for best performance.
46 *  Since link-time-optimization is not available for all compilers,
47 *  these functions are defined into a .h to be included.
48 */
49 
50 /*-****************************************
51 *  Dependencies
52 ******************************************/
53 #include "error_private.h" /* error codes and messages */
54 #include "mem.h"	   /* unaligned access routines */
55 
56 /*=========================================
57 *  Target specific
58 =========================================*/
59 #define STREAM_ACCUMULATOR_MIN_32 25
60 #define STREAM_ACCUMULATOR_MIN_64 57
61 #define STREAM_ACCUMULATOR_MIN ((U32)(ZSTD_32bits() ? STREAM_ACCUMULATOR_MIN_32 : STREAM_ACCUMULATOR_MIN_64))
62 
63 /*-******************************************
64 *  bitStream encoding API (write forward)
65 ********************************************/
66 /* bitStream can mix input from multiple sources.
67 *  A critical property of these streams is that they encode and decode in **reverse** direction.
68 *  So the first bit sequence you add will be the last to be read, like a LIFO stack.
69 */
70 typedef struct {
71 	size_t bitContainer;
72 	int bitPos;
73 	char *startPtr;
74 	char *ptr;
75 	char *endPtr;
76 } BIT_CStream_t;
77 
78 ZSTD_STATIC size_t BIT_initCStream(BIT_CStream_t *bitC, void *dstBuffer, size_t dstCapacity);
79 ZSTD_STATIC void BIT_addBits(BIT_CStream_t *bitC, size_t value, unsigned nbBits);
80 ZSTD_STATIC void BIT_flushBits(BIT_CStream_t *bitC);
81 ZSTD_STATIC size_t BIT_closeCStream(BIT_CStream_t *bitC);
82 
83 /* Start with initCStream, providing the size of buffer to write into.
84 *  bitStream will never write outside of this buffer.
85 *  `dstCapacity` must be >= sizeof(bitD->bitContainer), otherwise @return will be an error code.
86 *
87 *  bits are first added to a local register.
88 *  Local register is size_t, hence 64-bits on 64-bits systems, or 32-bits on 32-bits systems.
89 *  Writing data into memory is an explicit operation, performed by the flushBits function.
90 *  Hence keep track how many bits are potentially stored into local register to avoid register overflow.
91 *  After a flushBits, a maximum of 7 bits might still be stored into local register.
92 *
93 *  Avoid storing elements of more than 24 bits if you want compatibility with 32-bits bitstream readers.
94 *
95 *  Last operation is to close the bitStream.
96 *  The function returns the final size of CStream in bytes.
97 *  If data couldn't fit into `dstBuffer`, it will return a 0 ( == not storable)
98 */
99 
100 /*-********************************************
101 *  bitStream decoding API (read backward)
102 **********************************************/
103 typedef struct {
104 	size_t bitContainer;
105 	unsigned bitsConsumed;
106 	const char *ptr;
107 	const char *start;
108 } BIT_DStream_t;
109 
110 typedef enum {
111 	BIT_DStream_unfinished = 0,
112 	BIT_DStream_endOfBuffer = 1,
113 	BIT_DStream_completed = 2,
114 	BIT_DStream_overflow = 3
115 } BIT_DStream_status; /* result of BIT_reloadDStream() */
116 /* 1,2,4,8 would be better for bitmap combinations, but slows down performance a bit ... :( */
117 
118 ZSTD_STATIC size_t BIT_initDStream(BIT_DStream_t *bitD, const void *srcBuffer, size_t srcSize);
119 ZSTD_STATIC size_t BIT_readBits(BIT_DStream_t *bitD, unsigned nbBits);
120 ZSTD_STATIC BIT_DStream_status BIT_reloadDStream(BIT_DStream_t *bitD);
121 ZSTD_STATIC unsigned BIT_endOfDStream(const BIT_DStream_t *bitD);
122 
123 /* Start by invoking BIT_initDStream().
124 *  A chunk of the bitStream is then stored into a local register.
125 *  Local register size is 64-bits on 64-bits systems, 32-bits on 32-bits systems (size_t).
126 *  You can then retrieve bitFields stored into the local register, **in reverse order**.
127 *  Local register is explicitly reloaded from memory by the BIT_reloadDStream() method.
128 *  A reload guarantee a minimum of ((8*sizeof(bitD->bitContainer))-7) bits when its result is BIT_DStream_unfinished.
129 *  Otherwise, it can be less than that, so proceed accordingly.
130 *  Checking if DStream has reached its end can be performed with BIT_endOfDStream().
131 */
132 
133 /*-****************************************
134 *  unsafe API
135 ******************************************/
136 ZSTD_STATIC void BIT_addBitsFast(BIT_CStream_t *bitC, size_t value, unsigned nbBits);
137 /* faster, but works only if value is "clean", meaning all high bits above nbBits are 0 */
138 
139 ZSTD_STATIC void BIT_flushBitsFast(BIT_CStream_t *bitC);
140 /* unsafe version; does not check buffer overflow */
141 
142 ZSTD_STATIC size_t BIT_readBitsFast(BIT_DStream_t *bitD, unsigned nbBits);
143 /* faster, but works only if nbBits >= 1 */
144 
145 /*-**************************************************************
146 *  Internal functions
147 ****************************************************************/
BIT_highbit32(register U32 val)148 ZSTD_STATIC unsigned BIT_highbit32(register U32 val) { return 31 - __builtin_clz(val); }
149 
150 /*=====    Local Constants   =====*/
151 static const unsigned BIT_mask[] = {0,       1,       3,       7,	0xF,      0x1F,     0x3F,     0x7F,      0xFF,
152 				    0x1FF,   0x3FF,   0x7FF,   0xFFF,    0x1FFF,   0x3FFF,   0x7FFF,   0xFFFF,    0x1FFFF,
153 				    0x3FFFF, 0x7FFFF, 0xFFFFF, 0x1FFFFF, 0x3FFFFF, 0x7FFFFF, 0xFFFFFF, 0x1FFFFFF, 0x3FFFFFF}; /* up to 26 bits */
154 
155 /*-**************************************************************
156 *  bitStream encoding
157 ****************************************************************/
158 /*! BIT_initCStream() :
159  *  `dstCapacity` must be > sizeof(void*)
160  *  @return : 0 if success,
161 			  otherwise an error code (can be tested using ERR_isError() ) */
BIT_initCStream(BIT_CStream_t * bitC,void * startPtr,size_t dstCapacity)162 ZSTD_STATIC size_t BIT_initCStream(BIT_CStream_t *bitC, void *startPtr, size_t dstCapacity)
163 {
164 	bitC->bitContainer = 0;
165 	bitC->bitPos = 0;
166 	bitC->startPtr = (char *)startPtr;
167 	bitC->ptr = bitC->startPtr;
168 	bitC->endPtr = bitC->startPtr + dstCapacity - sizeof(bitC->ptr);
169 	if (dstCapacity <= sizeof(bitC->ptr))
170 		return ERROR(dstSize_tooSmall);
171 	return 0;
172 }
173 
174 /*! BIT_addBits() :
175 	can add up to 26 bits into `bitC`.
176 	Does not check for register overflow ! */
BIT_addBits(BIT_CStream_t * bitC,size_t value,unsigned nbBits)177 ZSTD_STATIC void BIT_addBits(BIT_CStream_t *bitC, size_t value, unsigned nbBits)
178 {
179 	bitC->bitContainer |= (value & BIT_mask[nbBits]) << bitC->bitPos;
180 	bitC->bitPos += nbBits;
181 }
182 
183 /*! BIT_addBitsFast() :
184  *  works only if `value` is _clean_, meaning all high bits above nbBits are 0 */
BIT_addBitsFast(BIT_CStream_t * bitC,size_t value,unsigned nbBits)185 ZSTD_STATIC void BIT_addBitsFast(BIT_CStream_t *bitC, size_t value, unsigned nbBits)
186 {
187 	bitC->bitContainer |= value << bitC->bitPos;
188 	bitC->bitPos += nbBits;
189 }
190 
191 /*! BIT_flushBitsFast() :
192  *  unsafe version; does not check buffer overflow */
BIT_flushBitsFast(BIT_CStream_t * bitC)193 ZSTD_STATIC void BIT_flushBitsFast(BIT_CStream_t *bitC)
194 {
195 	size_t const nbBytes = bitC->bitPos >> 3;
196 	ZSTD_writeLEST(bitC->ptr, bitC->bitContainer);
197 	bitC->ptr += nbBytes;
198 	bitC->bitPos &= 7;
199 	bitC->bitContainer >>= nbBytes * 8; /* if bitPos >= sizeof(bitContainer)*8 --> undefined behavior */
200 }
201 
202 /*! BIT_flushBits() :
203  *  safe version; check for buffer overflow, and prevents it.
204  *  note : does not signal buffer overflow. This will be revealed later on using BIT_closeCStream() */
BIT_flushBits(BIT_CStream_t * bitC)205 ZSTD_STATIC void BIT_flushBits(BIT_CStream_t *bitC)
206 {
207 	size_t const nbBytes = bitC->bitPos >> 3;
208 	ZSTD_writeLEST(bitC->ptr, bitC->bitContainer);
209 	bitC->ptr += nbBytes;
210 	if (bitC->ptr > bitC->endPtr)
211 		bitC->ptr = bitC->endPtr;
212 	bitC->bitPos &= 7;
213 	bitC->bitContainer >>= nbBytes * 8; /* if bitPos >= sizeof(bitContainer)*8 --> undefined behavior */
214 }
215 
216 /*! BIT_closeCStream() :
217  *  @return : size of CStream, in bytes,
218 			  or 0 if it could not fit into dstBuffer */
BIT_closeCStream(BIT_CStream_t * bitC)219 ZSTD_STATIC size_t BIT_closeCStream(BIT_CStream_t *bitC)
220 {
221 	BIT_addBitsFast(bitC, 1, 1); /* endMark */
222 	BIT_flushBits(bitC);
223 
224 	if (bitC->ptr >= bitC->endPtr)
225 		return 0; /* doesn't fit within authorized budget : cancel */
226 
227 	return (bitC->ptr - bitC->startPtr) + (bitC->bitPos > 0);
228 }
229 
230 /*-********************************************************
231 * bitStream decoding
232 **********************************************************/
233 /*! BIT_initDStream() :
234 *   Initialize a BIT_DStream_t.
235 *   `bitD` : a pointer to an already allocated BIT_DStream_t structure.
236 *   `srcSize` must be the *exact* size of the bitStream, in bytes.
237 *   @return : size of stream (== srcSize) or an errorCode if a problem is detected
238 */
BIT_initDStream(BIT_DStream_t * bitD,const void * srcBuffer,size_t srcSize)239 ZSTD_STATIC size_t BIT_initDStream(BIT_DStream_t *bitD, const void *srcBuffer, size_t srcSize)
240 {
241 	if (srcSize < 1) {
242 		memset(bitD, 0, sizeof(*bitD));
243 		return ERROR(srcSize_wrong);
244 	}
245 
246 	if (srcSize >= sizeof(bitD->bitContainer)) { /* normal case */
247 		bitD->start = (const char *)srcBuffer;
248 		bitD->ptr = (const char *)srcBuffer + srcSize - sizeof(bitD->bitContainer);
249 		bitD->bitContainer = ZSTD_readLEST(bitD->ptr);
250 		{
251 			BYTE const lastByte = ((const BYTE *)srcBuffer)[srcSize - 1];
252 			bitD->bitsConsumed = lastByte ? 8 - BIT_highbit32(lastByte) : 0; /* ensures bitsConsumed is always set */
253 			if (lastByte == 0)
254 				return ERROR(GENERIC); /* endMark not present */
255 		}
256 	} else {
257 		bitD->start = (const char *)srcBuffer;
258 		bitD->ptr = bitD->start;
259 		bitD->bitContainer = *(const BYTE *)(bitD->start);
260 		switch (srcSize) {
261 		case 7: bitD->bitContainer += (size_t)(((const BYTE *)(srcBuffer))[6]) << (sizeof(bitD->bitContainer) * 8 - 16);
262 			fallthrough;
263 		case 6: bitD->bitContainer += (size_t)(((const BYTE *)(srcBuffer))[5]) << (sizeof(bitD->bitContainer) * 8 - 24);
264 			fallthrough;
265 		case 5: bitD->bitContainer += (size_t)(((const BYTE *)(srcBuffer))[4]) << (sizeof(bitD->bitContainer) * 8 - 32);
266 			fallthrough;
267 		case 4: bitD->bitContainer += (size_t)(((const BYTE *)(srcBuffer))[3]) << 24;
268 			fallthrough;
269 		case 3: bitD->bitContainer += (size_t)(((const BYTE *)(srcBuffer))[2]) << 16;
270 			fallthrough;
271 		case 2: bitD->bitContainer += (size_t)(((const BYTE *)(srcBuffer))[1]) << 8;
272 			fallthrough;
273 		default:;
274 		}
275 		{
276 			BYTE const lastByte = ((const BYTE *)srcBuffer)[srcSize - 1];
277 			bitD->bitsConsumed = lastByte ? 8 - BIT_highbit32(lastByte) : 0;
278 			if (lastByte == 0)
279 				return ERROR(GENERIC); /* endMark not present */
280 		}
281 		bitD->bitsConsumed += (U32)(sizeof(bitD->bitContainer) - srcSize) * 8;
282 	}
283 
284 	return srcSize;
285 }
286 
BIT_getUpperBits(size_t bitContainer,U32 const start)287 ZSTD_STATIC size_t BIT_getUpperBits(size_t bitContainer, U32 const start) { return bitContainer >> start; }
288 
BIT_getMiddleBits(size_t bitContainer,U32 const start,U32 const nbBits)289 ZSTD_STATIC size_t BIT_getMiddleBits(size_t bitContainer, U32 const start, U32 const nbBits) { return (bitContainer >> start) & BIT_mask[nbBits]; }
290 
BIT_getLowerBits(size_t bitContainer,U32 const nbBits)291 ZSTD_STATIC size_t BIT_getLowerBits(size_t bitContainer, U32 const nbBits) { return bitContainer & BIT_mask[nbBits]; }
292 
293 /*! BIT_lookBits() :
294  *  Provides next n bits from local register.
295  *  local register is not modified.
296  *  On 32-bits, maxNbBits==24.
297  *  On 64-bits, maxNbBits==56.
298  *  @return : value extracted
299  */
BIT_lookBits(const BIT_DStream_t * bitD,U32 nbBits)300 ZSTD_STATIC size_t BIT_lookBits(const BIT_DStream_t *bitD, U32 nbBits)
301 {
302 	U32 const bitMask = sizeof(bitD->bitContainer) * 8 - 1;
303 	return ((bitD->bitContainer << (bitD->bitsConsumed & bitMask)) >> 1) >> ((bitMask - nbBits) & bitMask);
304 }
305 
306 /*! BIT_lookBitsFast() :
307 *   unsafe version; only works only if nbBits >= 1 */
BIT_lookBitsFast(const BIT_DStream_t * bitD,U32 nbBits)308 ZSTD_STATIC size_t BIT_lookBitsFast(const BIT_DStream_t *bitD, U32 nbBits)
309 {
310 	U32 const bitMask = sizeof(bitD->bitContainer) * 8 - 1;
311 	return (bitD->bitContainer << (bitD->bitsConsumed & bitMask)) >> (((bitMask + 1) - nbBits) & bitMask);
312 }
313 
BIT_skipBits(BIT_DStream_t * bitD,U32 nbBits)314 ZSTD_STATIC void BIT_skipBits(BIT_DStream_t *bitD, U32 nbBits) { bitD->bitsConsumed += nbBits; }
315 
316 /*! BIT_readBits() :
317  *  Read (consume) next n bits from local register and update.
318  *  Pay attention to not read more than nbBits contained into local register.
319  *  @return : extracted value.
320  */
BIT_readBits(BIT_DStream_t * bitD,U32 nbBits)321 ZSTD_STATIC size_t BIT_readBits(BIT_DStream_t *bitD, U32 nbBits)
322 {
323 	size_t const value = BIT_lookBits(bitD, nbBits);
324 	BIT_skipBits(bitD, nbBits);
325 	return value;
326 }
327 
328 /*! BIT_readBitsFast() :
329 *   unsafe version; only works only if nbBits >= 1 */
BIT_readBitsFast(BIT_DStream_t * bitD,U32 nbBits)330 ZSTD_STATIC size_t BIT_readBitsFast(BIT_DStream_t *bitD, U32 nbBits)
331 {
332 	size_t const value = BIT_lookBitsFast(bitD, nbBits);
333 	BIT_skipBits(bitD, nbBits);
334 	return value;
335 }
336 
337 /*! BIT_reloadDStream() :
338 *   Refill `bitD` from buffer previously set in BIT_initDStream() .
339 *   This function is safe, it guarantees it will not read beyond src buffer.
340 *   @return : status of `BIT_DStream_t` internal register.
341 			  if status == BIT_DStream_unfinished, internal register is filled with >= (sizeof(bitD->bitContainer)*8 - 7) bits */
BIT_reloadDStream(BIT_DStream_t * bitD)342 ZSTD_STATIC BIT_DStream_status BIT_reloadDStream(BIT_DStream_t *bitD)
343 {
344 	if (bitD->bitsConsumed > (sizeof(bitD->bitContainer) * 8)) /* should not happen => corruption detected */
345 		return BIT_DStream_overflow;
346 
347 	if (bitD->ptr >= bitD->start + sizeof(bitD->bitContainer)) {
348 		bitD->ptr -= bitD->bitsConsumed >> 3;
349 		bitD->bitsConsumed &= 7;
350 		bitD->bitContainer = ZSTD_readLEST(bitD->ptr);
351 		return BIT_DStream_unfinished;
352 	}
353 	if (bitD->ptr == bitD->start) {
354 		if (bitD->bitsConsumed < sizeof(bitD->bitContainer) * 8)
355 			return BIT_DStream_endOfBuffer;
356 		return BIT_DStream_completed;
357 	}
358 	{
359 		U32 nbBytes = bitD->bitsConsumed >> 3;
360 		BIT_DStream_status result = BIT_DStream_unfinished;
361 		if (bitD->ptr - nbBytes < bitD->start) {
362 			nbBytes = (U32)(bitD->ptr - bitD->start); /* ptr > start */
363 			result = BIT_DStream_endOfBuffer;
364 		}
365 		bitD->ptr -= nbBytes;
366 		bitD->bitsConsumed -= nbBytes * 8;
367 		bitD->bitContainer = ZSTD_readLEST(bitD->ptr); /* reminder : srcSize > sizeof(bitD) */
368 		return result;
369 	}
370 }
371 
372 /*! BIT_endOfDStream() :
373 *   @return Tells if DStream has exactly reached its end (all bits consumed).
374 */
BIT_endOfDStream(const BIT_DStream_t * DStream)375 ZSTD_STATIC unsigned BIT_endOfDStream(const BIT_DStream_t *DStream)
376 {
377 	return ((DStream->ptr == DStream->start) && (DStream->bitsConsumed == sizeof(DStream->bitContainer) * 8));
378 }
379 
380 #endif /* BITSTREAM_H_MODULE */
381