LXR linux/lib/zstd/bitstream.h

   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                        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
 287ZSTD_STATIC size_t BIT_getUpperBits(size_t bitContainer, U32 const start) { return bitContainer >> start; }
 288
 289ZSTD_STATIC size_t BIT_getMiddleBits(size_t bitContainer, U32 const start, U32 const nbBits) { return (bitContainer >> start) & BIT_mask[nbBits]; }
 290
 291ZSTD_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 */
 300ZSTD_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 */
 308ZSTD_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
 314ZSTD_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 */
 321ZSTD_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 */
 330ZSTD_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 */
 342ZSTD_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*/
 375ZSTD_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