projects/linux·blob v4.14 · refs

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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*/
70typedef struct {
71 size_t bitContainer;
72 int bitPos;
73 char *startPtr;
74 char *ptr;
75 char *endPtr;
76} BIT_CStream_t;
77
78ZSTD_STATIC size_t BIT_initCStream(BIT_CStream_t *bitC, void *dstBuffer, size_t dstCapacity);
79ZSTD_STATIC void BIT_addBits(BIT_CStream_t *bitC, size_t value, unsigned nbBits);
80ZSTD_STATIC void BIT_flushBits(BIT_CStream_t *bitC);
81ZSTD_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**********************************************/
103typedef struct {
104 size_t bitContainer;
105 unsigned bitsConsumed;
106 const char *ptr;
107 const char *start;
108} BIT_DStream_t;
109
110typedef 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
118ZSTD_STATIC size_t BIT_initDStream(BIT_DStream_t *bitD, const void *srcBuffer, size_t srcSize);
119ZSTD_STATIC size_t BIT_readBits(BIT_DStream_t *bitD, unsigned nbBits);
120ZSTD_STATIC BIT_DStream_status BIT_reloadDStream(BIT_DStream_t *bitD);
121ZSTD_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******************************************/
136ZSTD_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
139ZSTD_STATIC void BIT_flushBitsFast(BIT_CStream_t *bitC);
140/* unsafe version; does not check buffer overflow */
141
142ZSTD_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****************************************************************/
148ZSTD_STATIC unsigned BIT_highbit32(register U32 val) { return 31 - __builtin_clz(val); }
149
150/*===== Local Constants =====*/
151static 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() ) */
162ZSTD_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 ! */
177ZSTD_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 */
185ZSTD_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 */
193ZSTD_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() */
205ZSTD_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 */
219ZSTD_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*/
239ZSTD_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 case 6: bitD->bitContainer += (size_t)(((const BYTE *)(srcBuffer))[5]) << (sizeof(bitD->bitContainer) * 8 - 24);
263 case 5: bitD->bitContainer += (size_t)(((const BYTE *)(srcBuffer))[4]) << (sizeof(bitD->bitContainer) * 8 - 32);
264 case 4: bitD->bitContainer += (size_t)(((const BYTE *)(srcBuffer))[3]) << 24;
265 case 3: bitD->bitContainer += (size_t)(((const BYTE *)(srcBuffer))[2]) << 16;
266 case 2: bitD->bitContainer += (size_t)(((const BYTE *)(srcBuffer))[1]) << 8;
267 default:;
268 }
269 {
270 BYTE const lastByte = ((const BYTE *)srcBuffer)[srcSize - 1];
271 bitD->bitsConsumed = lastByte ? 8 - BIT_highbit32(lastByte) : 0;
272 if (lastByte == 0)
273 return ERROR(GENERIC); /* endMark not present */
274 }
275 bitD->bitsConsumed += (U32)(sizeof(bitD->bitContainer) - srcSize) * 8;
276 }
277
278 return srcSize;
279}
280
281ZSTD_STATIC size_t BIT_getUpperBits(size_t bitContainer, U32 const start) { return bitContainer >> start; }
282
283ZSTD_STATIC size_t BIT_getMiddleBits(size_t bitContainer, U32 const start, U32 const nbBits) { return (bitContainer >> start) & BIT_mask[nbBits]; }
284
285ZSTD_STATIC size_t BIT_getLowerBits(size_t bitContainer, U32 const nbBits) { return bitContainer & BIT_mask[nbBits]; }
286
287/*! BIT_lookBits() :
288 * Provides next n bits from local register.
289 * local register is not modified.
290 * On 32-bits, maxNbBits==24.
291 * On 64-bits, maxNbBits==56.
292 * @return : value extracted
293 */
294ZSTD_STATIC size_t BIT_lookBits(const BIT_DStream_t *bitD, U32 nbBits)
295{
296 U32 const bitMask = sizeof(bitD->bitContainer) * 8 - 1;
297 return ((bitD->bitContainer << (bitD->bitsConsumed & bitMask)) >> 1) >> ((bitMask - nbBits) & bitMask);
298}
299
300/*! BIT_lookBitsFast() :
301* unsafe version; only works only if nbBits >= 1 */
302ZSTD_STATIC size_t BIT_lookBitsFast(const BIT_DStream_t *bitD, U32 nbBits)
303{
304 U32 const bitMask = sizeof(bitD->bitContainer) * 8 - 1;
305 return (bitD->bitContainer << (bitD->bitsConsumed & bitMask)) >> (((bitMask + 1) - nbBits) & bitMask);
306}
307
308ZSTD_STATIC void BIT_skipBits(BIT_DStream_t *bitD, U32 nbBits) { bitD->bitsConsumed += nbBits; }
309
310/*! BIT_readBits() :
311 * Read (consume) next n bits from local register and update.
312 * Pay attention to not read more than nbBits contained into local register.
313 * @return : extracted value.
314 */
315ZSTD_STATIC size_t BIT_readBits(BIT_DStream_t *bitD, U32 nbBits)
316{
317 size_t const value = BIT_lookBits(bitD, nbBits);
318 BIT_skipBits(bitD, nbBits);
319 return value;
320}
321
322/*! BIT_readBitsFast() :
323* unsafe version; only works only if nbBits >= 1 */
324ZSTD_STATIC size_t BIT_readBitsFast(BIT_DStream_t *bitD, U32 nbBits)
325{
326 size_t const value = BIT_lookBitsFast(bitD, nbBits);
327 BIT_skipBits(bitD, nbBits);
328 return value;
329}
330
331/*! BIT_reloadDStream() :
332* Refill `bitD` from buffer previously set in BIT_initDStream() .
333* This function is safe, it guarantees it will not read beyond src buffer.
334* @return : status of `BIT_DStream_t` internal register.
335 if status == BIT_DStream_unfinished, internal register is filled with >= (sizeof(bitD->bitContainer)*8 - 7) bits */
336ZSTD_STATIC BIT_DStream_status BIT_reloadDStream(BIT_DStream_t *bitD)
337{
338 if (bitD->bitsConsumed > (sizeof(bitD->bitContainer) * 8)) /* should not happen => corruption detected */
339 return BIT_DStream_overflow;
340
341 if (bitD->ptr >= bitD->start + sizeof(bitD->bitContainer)) {
342 bitD->ptr -= bitD->bitsConsumed >> 3;
343 bitD->bitsConsumed &= 7;
344 bitD->bitContainer = ZSTD_readLEST(bitD->ptr);
345 return BIT_DStream_unfinished;
346 }
347 if (bitD->ptr == bitD->start) {
348 if (bitD->bitsConsumed < sizeof(bitD->bitContainer) * 8)
349 return BIT_DStream_endOfBuffer;
350 return BIT_DStream_completed;
351 }
352 {
353 U32 nbBytes = bitD->bitsConsumed >> 3;
354 BIT_DStream_status result = BIT_DStream_unfinished;
355 if (bitD->ptr - nbBytes < bitD->start) {
356 nbBytes = (U32)(bitD->ptr - bitD->start); /* ptr > start */
357 result = BIT_DStream_endOfBuffer;
358 }
359 bitD->ptr -= nbBytes;
360 bitD->bitsConsumed -= nbBytes * 8;
361 bitD->bitContainer = ZSTD_readLEST(bitD->ptr); /* reminder : srcSize > sizeof(bitD) */
362 return result;
363 }
364}
365
366/*! BIT_endOfDStream() :
367* @return Tells if DStream has exactly reached its end (all bits consumed).
368*/
369ZSTD_STATIC unsigned BIT_endOfDStream(const BIT_DStream_t *DStream)
370{
371 return ((DStream->ptr == DStream->start) && (DStream->bitsConsumed == sizeof(DStream->bitContainer) * 8));
372}
373
374#endif /* BITSTREAM_H_MODULE */