/* ****************************************************************** * bitstream * Part of FSE library * Copyright (c) 2013-2021, Yann Collet, Facebook, Inc. * * You can contact the author at : * - Source repository : https://github.com/Cyan4973/FiniteStateEntropy * * This source code is licensed under both the BSD-style license (found in the * LICENSE file in the root directory of this source tree) and the GPLv2 (found * in the COPYING file in the root directory of this source tree). * You may select, at your option, one of the above-listed licenses. ****************************************************************** */ #ifndef BITSTREAM_H_MODULE #define BITSTREAM_H_MODULE #if defined (__cplusplus) extern "C" { #endif /* * This API consists of small unitary functions, which must be inlined for best performance. * Since link-time-optimization is not available for all compilers, * these functions are defined into a .h to be included. */ /*-**************************************** * Dependencies ******************************************/ #include "mem.h" /* unaligned access routines */ #include "compiler.h" /* UNLIKELY() */ #include "debug.h" /* assert(), DEBUGLOG(), RAWLOG() */ #include "error_private.h" /* error codes and messages */ /*========================================= * Target specific =========================================*/ #ifndef ZSTD_NO_INTRINSICS # if defined(__BMI__) && defined(__GNUC__) # include /* support for bextr (experimental) */ # elif defined(__ICCARM__) # include # endif #endif #define STREAM_ACCUMULATOR_MIN_32 25 #define STREAM_ACCUMULATOR_MIN_64 57 #define STREAM_ACCUMULATOR_MIN ((U32)(MEM_32bits() ? STREAM_ACCUMULATOR_MIN_32 : STREAM_ACCUMULATOR_MIN_64)) /*-****************************************** * bitStream encoding API (write forward) ********************************************/ /* bitStream can mix input from multiple sources. * A critical property of these streams is that they encode and decode in **reverse** direction. * So the first bit sequence you add will be the last to be read, like a LIFO stack. */ typedef struct { size_t bitContainer; unsigned bitPos; char* startPtr; char* ptr; char* endPtr; } BIT_CStream_t; MEM_STATIC size_t BIT_initCStream(BIT_CStream_t* bitC, void* dstBuffer, size_t dstCapacity); MEM_STATIC void BIT_addBits(BIT_CStream_t* bitC, size_t value, unsigned nbBits); MEM_STATIC void BIT_flushBits(BIT_CStream_t* bitC); MEM_STATIC size_t BIT_closeCStream(BIT_CStream_t* bitC); /* Start with initCStream, providing the size of buffer to write into. * bitStream will never write outside of this buffer. * `dstCapacity` must be >= sizeof(bitD->bitContainer), otherwise @return will be an error code. * * bits are first added to a local register. * Local register is size_t, hence 64-bits on 64-bits systems, or 32-bits on 32-bits systems. * Writing data into memory is an explicit operation, performed by the flushBits function. * Hence keep track how many bits are potentially stored into local register to avoid register overflow. * After a flushBits, a maximum of 7 bits might still be stored into local register. * * Avoid storing elements of more than 24 bits if you want compatibility with 32-bits bitstream readers. * * Last operation is to close the bitStream. * The function returns the final size of CStream in bytes. * If data couldn't fit into `dstBuffer`, it will return a 0 ( == not storable) */ /*-******************************************** * bitStream decoding API (read backward) **********************************************/ typedef struct { size_t bitContainer; unsigned bitsConsumed; const char* ptr; const char* start; const char* limitPtr; } BIT_DStream_t; typedef enum { BIT_DStream_unfinished = 0, BIT_DStream_endOfBuffer = 1, BIT_DStream_completed = 2, BIT_DStream_overflow = 3 } BIT_DStream_status; /* result of BIT_reloadDStream() */ /* 1,2,4,8 would be better for bitmap combinations, but slows down performance a bit ... :( */ MEM_STATIC size_t BIT_initDStream(BIT_DStream_t* bitD, const void* srcBuffer, size_t srcSize); MEM_STATIC size_t BIT_readBits(BIT_DStream_t* bitD, unsigned nbBits); MEM_STATIC BIT_DStream_status BIT_reloadDStream(BIT_DStream_t* bitD); MEM_STATIC unsigned BIT_endOfDStream(const BIT_DStream_t* bitD); /* Start by invoking BIT_initDStream(). * A chunk of the bitStream is then stored into a local register. * Local register size is 64-bits on 64-bits systems, 32-bits on 32-bits systems (size_t). * You can then retrieve bitFields stored into the local register, **in reverse order**. * Local register is explicitly reloaded from memory by the BIT_reloadDStream() method. * A reload guarantee a minimum of ((8*sizeof(bitD->bitContainer))-7) bits when its result is BIT_DStream_unfinished. * Otherwise, it can be less than that, so proceed accordingly. * Checking if DStream has reached its end can be performed with BIT_endOfDStream(). */ /*-**************************************** * unsafe API ******************************************/ MEM_STATIC void BIT_addBitsFast(BIT_CStream_t* bitC, size_t value, unsigned nbBits); /* faster, but works only if value is "clean", meaning all high bits above nbBits are 0 */ MEM_STATIC void BIT_flushBitsFast(BIT_CStream_t* bitC); /* unsafe version; does not check buffer overflow */ MEM_STATIC size_t BIT_readBitsFast(BIT_DStream_t* bitD, unsigned nbBits); /* faster, but works only if nbBits >= 1 */ /*-************************************************************** * Internal functions ****************************************************************/ MEM_STATIC unsigned BIT_highbit32 (U32 val) { assert(val != 0); { # if defined(_MSC_VER) /* Visual */ # if STATIC_BMI2 == 1 return _lzcnt_u32(val) ^ 31; # else unsigned long r = 0; return _BitScanReverse(&r, val) ? (unsigned)r : 0; # endif # elif defined(__GNUC__) && (__GNUC__ >= 3) /* Use GCC Intrinsic */ return __builtin_clz (val) ^ 31; # elif defined(__ICCARM__) /* IAR Intrinsic */ return 31 - __CLZ(val); # else /* Software version */ static const unsigned DeBruijnClz[32] = { 0, 9, 1, 10, 13, 21, 2, 29, 11, 14, 16, 18, 22, 25, 3, 30, 8, 12, 20, 28, 15, 17, 24, 7, 19, 27, 23, 6, 26, 5, 4, 31 }; U32 v = val; v |= v >> 1; v |= v >> 2; v |= v >> 4; v |= v >> 8; v |= v >> 16; return DeBruijnClz[ (U32) (v * 0x07C4ACDDU) >> 27]; # endif } } /*===== Local Constants =====*/ static const unsigned BIT_mask[] = { 0, 1, 3, 7, 0xF, 0x1F, 0x3F, 0x7F, 0xFF, 0x1FF, 0x3FF, 0x7FF, 0xFFF, 0x1FFF, 0x3FFF, 0x7FFF, 0xFFFF, 0x1FFFF, 0x3FFFF, 0x7FFFF, 0xFFFFF, 0x1FFFFF, 0x3FFFFF, 0x7FFFFF, 0xFFFFFF, 0x1FFFFFF, 0x3FFFFFF, 0x7FFFFFF, 0xFFFFFFF, 0x1FFFFFFF, 0x3FFFFFFF, 0x7FFFFFFF}; /* up to 31 bits */ #define BIT_MASK_SIZE (sizeof(BIT_mask) / sizeof(BIT_mask[0])) /*-************************************************************** * bitStream encoding ****************************************************************/ /*! BIT_initCStream() : * `dstCapacity` must be > sizeof(size_t) * @return : 0 if success, * otherwise an error code (can be tested using ERR_isError()) */ MEM_STATIC size_t BIT_initCStream(BIT_CStream_t* bitC, void* startPtr, size_t dstCapacity) { bitC->bitContainer = 0; bitC->bitPos = 0; bitC->startPtr = (char*)startPtr; bitC->ptr = bitC->startPtr; bitC->endPtr = bitC->startPtr + dstCapacity - sizeof(bitC->bitContainer); if (dstCapacity <= sizeof(bitC->bitContainer)) return ERROR(dstSize_tooSmall); return 0; } /*! BIT_addBits() : * can add up to 31 bits into `bitC`. * Note : does not check for register overflow ! */ MEM_STATIC void BIT_addBits(BIT_CStream_t* bitC, size_t value, unsigned nbBits) { DEBUG_STATIC_ASSERT(BIT_MASK_SIZE == 32); assert(nbBits < BIT_MASK_SIZE); assert(nbBits + bitC->bitPos < sizeof(bitC->bitContainer) * 8); bitC->bitContainer |= (value & BIT_mask[nbBits]) << bitC->bitPos; bitC->bitPos += nbBits; } /*! BIT_addBitsFast() : * works only if `value` is _clean_, * meaning all high bits above nbBits are 0 */ MEM_STATIC void BIT_addBitsFast(BIT_CStream_t* bitC, size_t value, unsigned nbBits) { assert((value>>nbBits) == 0); assert(nbBits + bitC->bitPos < sizeof(bitC->bitContainer) * 8); bitC->bitContainer |= value << bitC->bitPos; bitC->bitPos += nbBits; } /*! BIT_flushBitsFast() : * assumption : bitContainer has not overflowed * unsafe version; does not check buffer overflow */ MEM_STATIC void BIT_flushBitsFast(BIT_CStream_t* bitC) { size_t const nbBytes = bitC->bitPos >> 3; assert(bitC->bitPos < sizeof(bitC->bitContainer) * 8); assert(bitC->ptr <= bitC->endPtr); MEM_writeLEST(bitC->ptr, bitC->bitContainer); bitC->ptr += nbBytes; bitC->bitPos &= 7; bitC->bitContainer >>= nbBytes*8; } /*! BIT_flushBits() : * assumption : bitContainer has not overflowed * safe version; check for buffer overflow, and prevents it. * note : does not signal buffer overflow. * overflow will be revealed later on using BIT_closeCStream() */ MEM_STATIC void BIT_flushBits(BIT_CStream_t* bitC) { size_t const nbBytes = bitC->bitPos >> 3; assert(bitC->bitPos < sizeof(bitC->bitContainer) * 8); assert(bitC->ptr <= bitC->endPtr); MEM_writeLEST(bitC->ptr, bitC->bitContainer); bitC->ptr += nbBytes; if (bitC->ptr > bitC->endPtr) bitC->ptr = bitC->endPtr; bitC->bitPos &= 7; bitC->bitContainer >>= nbBytes*8; } /*! BIT_closeCStream() : * @return : size of CStream, in bytes, * or 0 if it could not fit into dstBuffer */ MEM_STATIC size_t BIT_closeCStream(BIT_CStream_t* bitC) { BIT_addBitsFast(bitC, 1, 1); /* endMark */ BIT_flushBits(bitC); if (bitC->ptr >= bitC->endPtr) return 0; /* overflow detected */ return (bitC->ptr - bitC->startPtr) + (bitC->bitPos > 0); } /*-******************************************************** * bitStream decoding **********************************************************/ /*! BIT_initDStream() : * Initialize a BIT_DStream_t. * `bitD` : a pointer to an already allocated BIT_DStream_t structure. * `srcSize` must be the *exact* size of the bitStream, in bytes. * @return : size of stream (== srcSize), or an errorCode if a problem is detected */ MEM_STATIC size_t BIT_initDStream(BIT_DStream_t* bitD, const void* srcBuffer, size_t srcSize) { if (srcSize < 1) { ZSTD_memset(bitD, 0, sizeof(*bitD)); return ERROR(srcSize_wrong); } bitD->start = (const char*)srcBuffer; bitD->limitPtr = bitD->start + sizeof(bitD->bitContainer); if (srcSize >= sizeof(bitD->bitContainer)) { /* normal case */ bitD->ptr = (const char*)srcBuffer + srcSize - sizeof(bitD->bitContainer); bitD->bitContainer = MEM_readLEST(bitD->ptr); { BYTE const lastByte = ((const BYTE*)srcBuffer)[srcSize-1]; bitD->bitsConsumed = lastByte ? 8 - BIT_highbit32(lastByte) : 0; /* ensures bitsConsumed is always set */ if (lastByte == 0) return ERROR(GENERIC); /* endMark not present */ } } else { bitD->ptr = bitD->start; bitD->bitContainer = *(const BYTE*)(bitD->start); switch(srcSize) { case 7: bitD->bitContainer += (size_t)(((const BYTE*)(srcBuffer))[6]) << (sizeof(bitD->bitContainer)*8 - 16); /* fall-through */ case 6: bitD->bitContainer += (size_t)(((const BYTE*)(srcBuffer))[5]) << (sizeof(bitD->bitContainer)*8 - 24); /* fall-through */ case 5: bitD->bitContainer += (size_t)(((const BYTE*)(srcBuffer))[4]) << (sizeof(bitD->bitContainer)*8 - 32); /* fall-through */ case 4: bitD->bitContainer += (size_t)(((const BYTE*)(srcBuffer))[3]) << 24; /* fall-through */ case 3: bitD->bitContainer += (size_t)(((const BYTE*)(srcBuffer))[2]) << 16; /* fall-through */ case 2: bitD->bitContainer += (size_t)(((const BYTE*)(srcBuffer))[1]) << 8; /* fall-through */ default: break; } { BYTE const lastByte = ((const BYTE*)srcBuffer)[srcSize-1]; bitD->bitsConsumed = lastByte ? 8 - BIT_highbit32(lastByte) : 0; if (lastByte == 0) return ERROR(corruption_detected); /* endMark not present */ } bitD->bitsConsumed += (U32)(sizeof(bitD->bitContainer) - srcSize)*8; } return srcSize; } MEM_STATIC FORCE_INLINE_ATTR size_t BIT_getUpperBits(size_t bitContainer, U32 const start) { return bitContainer >> start; } MEM_STATIC FORCE_INLINE_ATTR size_t BIT_getMiddleBits(size_t bitContainer, U32 const start, U32 const nbBits) { U32 const regMask = sizeof(bitContainer)*8 - 1; /* if start > regMask, bitstream is corrupted, and result is undefined */ assert(nbBits < BIT_MASK_SIZE); return (bitContainer >> (start & regMask)) & BIT_mask[nbBits]; } MEM_STATIC FORCE_INLINE_ATTR size_t BIT_getLowerBits(size_t bitContainer, U32 const nbBits) { #if defined(STATIC_BMI2) && STATIC_BMI2 == 1 return _bzhi_u64(bitContainer, nbBits); #else assert(nbBits < BIT_MASK_SIZE); return bitContainer & BIT_mask[nbBits]; #endif } /*! BIT_lookBits() : * Provides next n bits from local register. * local register is not modified. * On 32-bits, maxNbBits==24. * On 64-bits, maxNbBits==56. * @return : value extracted */ MEM_STATIC FORCE_INLINE_ATTR size_t BIT_lookBits(const BIT_DStream_t* bitD, U32 nbBits) { /* arbitrate between double-shift and shift+mask */ #if 1 /* if bitD->bitsConsumed + nbBits > sizeof(bitD->bitContainer)*8, * bitstream is likely corrupted, and result is undefined */ return BIT_getMiddleBits(bitD->bitContainer, (sizeof(bitD->bitContainer)*8) - bitD->bitsConsumed - nbBits, nbBits); #else /* this code path is slower on my os-x laptop */ U32 const regMask = sizeof(bitD->bitContainer)*8 - 1; return ((bitD->bitContainer << (bitD->bitsConsumed & regMask)) >> 1) >> ((regMask-nbBits) & regMask); #endif } /*! BIT_lookBitsFast() : * unsafe version; only works if nbBits >= 1 */ MEM_STATIC size_t BIT_lookBitsFast(const BIT_DStream_t* bitD, U32 nbBits) { U32 const regMask = sizeof(bitD->bitContainer)*8 - 1; assert(nbBits >= 1); return (bitD->bitContainer << (bitD->bitsConsumed & regMask)) >> (((regMask+1)-nbBits) & regMask); } MEM_STATIC FORCE_INLINE_ATTR void BIT_skipBits(BIT_DStream_t* bitD, U32 nbBits) { bitD->bitsConsumed += nbBits; } /*! BIT_readBits() : * Read (consume) next n bits from local register and update. * Pay attention to not read more than nbBits contained into local register. * @return : extracted value. */ MEM_STATIC FORCE_INLINE_ATTR size_t BIT_readBits(BIT_DStream_t* bitD, unsigned nbBits) { size_t const value = BIT_lookBits(bitD, nbBits); BIT_skipBits(bitD, nbBits); return value; } /*! BIT_readBitsFast() : * unsafe version; only works only if nbBits >= 1 */ MEM_STATIC size_t BIT_readBitsFast(BIT_DStream_t* bitD, unsigned nbBits) { size_t const value = BIT_lookBitsFast(bitD, nbBits); assert(nbBits >= 1); BIT_skipBits(bitD, nbBits); return value; } /*! BIT_reloadDStreamFast() : * Similar to BIT_reloadDStream(), but with two differences: * 1. bitsConsumed <= sizeof(bitD->bitContainer)*8 must hold! * 2. Returns BIT_DStream_overflow when bitD->ptr < bitD->limitPtr, at this * point you must use BIT_reloadDStream() to reload. */ MEM_STATIC BIT_DStream_status BIT_reloadDStreamFast(BIT_DStream_t* bitD) { if (UNLIKELY(bitD->ptr < bitD->limitPtr)) return BIT_DStream_overflow; assert(bitD->bitsConsumed <= sizeof(bitD->bitContainer)*8); bitD->ptr -= bitD->bitsConsumed >> 3; bitD->bitsConsumed &= 7; bitD->bitContainer = MEM_readLEST(bitD->ptr); return BIT_DStream_unfinished; } /*! BIT_reloadDStream() : * Refill `bitD` from buffer previously set in BIT_initDStream() . * This function is safe, it guarantees it will not read beyond src buffer. * @return : status of `BIT_DStream_t` internal register. * when status == BIT_DStream_unfinished, internal register is filled with at least 25 or 57 bits */ MEM_STATIC BIT_DStream_status BIT_reloadDStream(BIT_DStream_t* bitD) { if (bitD->bitsConsumed > (sizeof(bitD->bitContainer)*8)) /* overflow detected, like end of stream */ return BIT_DStream_overflow; if (bitD->ptr >= bitD->limitPtr) { return BIT_reloadDStreamFast(bitD); } if (bitD->ptr == bitD->start) { if (bitD->bitsConsumed < sizeof(bitD->bitContainer)*8) return BIT_DStream_endOfBuffer; return BIT_DStream_completed; } /* start < ptr < limitPtr */ { U32 nbBytes = bitD->bitsConsumed >> 3; BIT_DStream_status result = BIT_DStream_unfinished; if (bitD->ptr - nbBytes < bitD->start) { nbBytes = (U32)(bitD->ptr - bitD->start); /* ptr > start */ result = BIT_DStream_endOfBuffer; } bitD->ptr -= nbBytes; bitD->bitsConsumed -= nbBytes*8; bitD->bitContainer = MEM_readLEST(bitD->ptr); /* reminder : srcSize > sizeof(bitD->bitContainer), otherwise bitD->ptr == bitD->start */ return result; } } /*! BIT_endOfDStream() : * @return : 1 if DStream has _exactly_ reached its end (all bits consumed). */ MEM_STATIC unsigned BIT_endOfDStream(const BIT_DStream_t* DStream) { return ((DStream->ptr == DStream->start) && (DStream->bitsConsumed == sizeof(DStream->bitContainer)*8)); } #if defined (__cplusplus) } #endif #endif /* BITSTREAM_H_MODULE */