447 lines
18 KiB
C
447 lines
18 KiB
C
/* ******************************************************************
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* bitstream
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* Part of FSE library
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* Copyright (c) Yann Collet, Facebook, Inc.
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*
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* You can contact the author at :
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* - Source repository : https://github.com/Cyan4973/FiniteStateEntropy
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*
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* This source code is licensed under both the BSD-style license (found in the
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* LICENSE file in the root directory of this source tree) and the GPLv2 (found
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* in the COPYING file in the root directory of this source tree).
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* You may select, at your option, one of the above-listed licenses.
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****************************************************************** */
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#ifndef BITSTREAM_H_MODULE
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#define BITSTREAM_H_MODULE
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/*
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* This API consists of small unitary functions, which must be inlined for best performance.
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* Since link-time-optimization is not available for all compilers,
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* these functions are defined into a .h to be included.
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*/
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/*-****************************************
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* Dependencies
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******************************************/
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#include "mem.h" /* unaligned access routines */
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#include "compiler.h" /* UNLIKELY() */
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#include "debug.h" /* assert(), DEBUGLOG(), RAWLOG() */
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#include "error_private.h" /* error codes and messages */
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/*=========================================
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* Target specific
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=========================================*/
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#define STREAM_ACCUMULATOR_MIN_32 25
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#define STREAM_ACCUMULATOR_MIN_64 57
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#define STREAM_ACCUMULATOR_MIN ((U32)(MEM_32bits() ? STREAM_ACCUMULATOR_MIN_32 : STREAM_ACCUMULATOR_MIN_64))
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/*-******************************************
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* bitStream encoding API (write forward)
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********************************************/
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/* bitStream can mix input from multiple sources.
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* A critical property of these streams is that they encode and decode in **reverse** direction.
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* So the first bit sequence you add will be the last to be read, like a LIFO stack.
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*/
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typedef struct {
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size_t bitContainer;
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unsigned bitPos;
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char* startPtr;
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char* ptr;
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char* endPtr;
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} BIT_CStream_t;
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MEM_STATIC size_t BIT_initCStream(BIT_CStream_t* bitC, void* dstBuffer, size_t dstCapacity);
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MEM_STATIC void BIT_addBits(BIT_CStream_t* bitC, size_t value, unsigned nbBits);
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MEM_STATIC void BIT_flushBits(BIT_CStream_t* bitC);
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MEM_STATIC size_t BIT_closeCStream(BIT_CStream_t* bitC);
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/* Start with initCStream, providing the size of buffer to write into.
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* bitStream will never write outside of this buffer.
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* `dstCapacity` must be >= sizeof(bitD->bitContainer), otherwise @return will be an error code.
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*
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* bits are first added to a local register.
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* Local register is size_t, hence 64-bits on 64-bits systems, or 32-bits on 32-bits systems.
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* Writing data into memory is an explicit operation, performed by the flushBits function.
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* Hence keep track how many bits are potentially stored into local register to avoid register overflow.
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* After a flushBits, a maximum of 7 bits might still be stored into local register.
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*
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* Avoid storing elements of more than 24 bits if you want compatibility with 32-bits bitstream readers.
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*
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* Last operation is to close the bitStream.
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* The function returns the final size of CStream in bytes.
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* If data couldn't fit into `dstBuffer`, it will return a 0 ( == not storable)
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*/
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/*-********************************************
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* bitStream decoding API (read backward)
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**********************************************/
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typedef struct {
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size_t bitContainer;
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unsigned bitsConsumed;
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const char* ptr;
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const char* start;
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const char* limitPtr;
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} BIT_DStream_t;
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typedef enum { BIT_DStream_unfinished = 0,
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BIT_DStream_endOfBuffer = 1,
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BIT_DStream_completed = 2,
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BIT_DStream_overflow = 3 } BIT_DStream_status; /* result of BIT_reloadDStream() */
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/* 1,2,4,8 would be better for bitmap combinations, but slows down performance a bit ... :( */
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MEM_STATIC size_t BIT_initDStream(BIT_DStream_t* bitD, const void* srcBuffer, size_t srcSize);
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MEM_STATIC size_t BIT_readBits(BIT_DStream_t* bitD, unsigned nbBits);
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MEM_STATIC BIT_DStream_status BIT_reloadDStream(BIT_DStream_t* bitD);
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MEM_STATIC unsigned BIT_endOfDStream(const BIT_DStream_t* bitD);
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/* Start by invoking BIT_initDStream().
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* A chunk of the bitStream is then stored into a local register.
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* Local register size is 64-bits on 64-bits systems, 32-bits on 32-bits systems (size_t).
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* You can then retrieve bitFields stored into the local register, **in reverse order**.
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* Local register is explicitly reloaded from memory by the BIT_reloadDStream() method.
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* A reload guarantee a minimum of ((8*sizeof(bitD->bitContainer))-7) bits when its result is BIT_DStream_unfinished.
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* Otherwise, it can be less than that, so proceed accordingly.
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* Checking if DStream has reached its end can be performed with BIT_endOfDStream().
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*/
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/*-****************************************
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* unsafe API
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******************************************/
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MEM_STATIC void BIT_addBitsFast(BIT_CStream_t* bitC, size_t value, unsigned nbBits);
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/* faster, but works only if value is "clean", meaning all high bits above nbBits are 0 */
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MEM_STATIC void BIT_flushBitsFast(BIT_CStream_t* bitC);
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/* unsafe version; does not check buffer overflow */
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MEM_STATIC size_t BIT_readBitsFast(BIT_DStream_t* bitD, unsigned nbBits);
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/* faster, but works only if nbBits >= 1 */
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/*-**************************************************************
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* Internal functions
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****************************************************************/
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MEM_STATIC unsigned BIT_highbit32 (U32 val)
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{
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assert(val != 0);
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{
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# if (__GNUC__ >= 3) /* Use GCC Intrinsic */
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return __builtin_clz (val) ^ 31;
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# else /* Software version */
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static const unsigned DeBruijnClz[32] = { 0, 9, 1, 10, 13, 21, 2, 29,
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11, 14, 16, 18, 22, 25, 3, 30,
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8, 12, 20, 28, 15, 17, 24, 7,
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19, 27, 23, 6, 26, 5, 4, 31 };
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U32 v = val;
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v |= v >> 1;
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v |= v >> 2;
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v |= v >> 4;
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v |= v >> 8;
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v |= v >> 16;
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return DeBruijnClz[ (U32) (v * 0x07C4ACDDU) >> 27];
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# endif
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}
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}
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/*===== Local Constants =====*/
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static const unsigned BIT_mask[] = {
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0, 1, 3, 7, 0xF, 0x1F,
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0x3F, 0x7F, 0xFF, 0x1FF, 0x3FF, 0x7FF,
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0xFFF, 0x1FFF, 0x3FFF, 0x7FFF, 0xFFFF, 0x1FFFF,
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0x3FFFF, 0x7FFFF, 0xFFFFF, 0x1FFFFF, 0x3FFFFF, 0x7FFFFF,
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0xFFFFFF, 0x1FFFFFF, 0x3FFFFFF, 0x7FFFFFF, 0xFFFFFFF, 0x1FFFFFFF,
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0x3FFFFFFF, 0x7FFFFFFF}; /* up to 31 bits */
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#define BIT_MASK_SIZE (sizeof(BIT_mask) / sizeof(BIT_mask[0]))
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/*-**************************************************************
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* bitStream encoding
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****************************************************************/
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/*! BIT_initCStream() :
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* `dstCapacity` must be > sizeof(size_t)
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* @return : 0 if success,
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* otherwise an error code (can be tested using ERR_isError()) */
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MEM_STATIC size_t BIT_initCStream(BIT_CStream_t* bitC,
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void* startPtr, size_t dstCapacity)
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{
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bitC->bitContainer = 0;
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bitC->bitPos = 0;
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bitC->startPtr = (char*)startPtr;
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bitC->ptr = bitC->startPtr;
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bitC->endPtr = bitC->startPtr + dstCapacity - sizeof(bitC->bitContainer);
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if (dstCapacity <= sizeof(bitC->bitContainer)) return ERROR(dstSize_tooSmall);
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return 0;
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}
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/*! BIT_addBits() :
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* can add up to 31 bits into `bitC`.
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* Note : does not check for register overflow ! */
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MEM_STATIC void BIT_addBits(BIT_CStream_t* bitC,
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size_t value, unsigned nbBits)
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{
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DEBUG_STATIC_ASSERT(BIT_MASK_SIZE == 32);
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assert(nbBits < BIT_MASK_SIZE);
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assert(nbBits + bitC->bitPos < sizeof(bitC->bitContainer) * 8);
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bitC->bitContainer |= (value & BIT_mask[nbBits]) << bitC->bitPos;
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bitC->bitPos += nbBits;
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}
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/*! BIT_addBitsFast() :
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* works only if `value` is _clean_,
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* meaning all high bits above nbBits are 0 */
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MEM_STATIC void BIT_addBitsFast(BIT_CStream_t* bitC,
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size_t value, unsigned nbBits)
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{
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assert((value>>nbBits) == 0);
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assert(nbBits + bitC->bitPos < sizeof(bitC->bitContainer) * 8);
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bitC->bitContainer |= value << bitC->bitPos;
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bitC->bitPos += nbBits;
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}
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/*! BIT_flushBitsFast() :
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* assumption : bitContainer has not overflowed
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* unsafe version; does not check buffer overflow */
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MEM_STATIC void BIT_flushBitsFast(BIT_CStream_t* bitC)
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{
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size_t const nbBytes = bitC->bitPos >> 3;
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assert(bitC->bitPos < sizeof(bitC->bitContainer) * 8);
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assert(bitC->ptr <= bitC->endPtr);
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MEM_writeLEST(bitC->ptr, bitC->bitContainer);
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bitC->ptr += nbBytes;
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bitC->bitPos &= 7;
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bitC->bitContainer >>= nbBytes*8;
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}
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/*! BIT_flushBits() :
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* assumption : bitContainer has not overflowed
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* safe version; check for buffer overflow, and prevents it.
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* note : does not signal buffer overflow.
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* overflow will be revealed later on using BIT_closeCStream() */
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MEM_STATIC void BIT_flushBits(BIT_CStream_t* bitC)
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{
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size_t const nbBytes = bitC->bitPos >> 3;
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assert(bitC->bitPos < sizeof(bitC->bitContainer) * 8);
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assert(bitC->ptr <= bitC->endPtr);
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MEM_writeLEST(bitC->ptr, bitC->bitContainer);
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bitC->ptr += nbBytes;
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if (bitC->ptr > bitC->endPtr) bitC->ptr = bitC->endPtr;
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bitC->bitPos &= 7;
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bitC->bitContainer >>= nbBytes*8;
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}
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/*! BIT_closeCStream() :
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* @return : size of CStream, in bytes,
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* or 0 if it could not fit into dstBuffer */
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MEM_STATIC size_t BIT_closeCStream(BIT_CStream_t* bitC)
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{
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BIT_addBitsFast(bitC, 1, 1); /* endMark */
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BIT_flushBits(bitC);
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if (bitC->ptr >= bitC->endPtr) return 0; /* overflow detected */
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return (bitC->ptr - bitC->startPtr) + (bitC->bitPos > 0);
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}
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/*-********************************************************
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* bitStream decoding
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**********************************************************/
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/*! BIT_initDStream() :
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* Initialize a BIT_DStream_t.
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* `bitD` : a pointer to an already allocated BIT_DStream_t structure.
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* `srcSize` must be the *exact* size of the bitStream, in bytes.
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* @return : size of stream (== srcSize), or an errorCode if a problem is detected
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*/
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MEM_STATIC size_t BIT_initDStream(BIT_DStream_t* bitD, const void* srcBuffer, size_t srcSize)
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{
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if (srcSize < 1) { ZSTD_memset(bitD, 0, sizeof(*bitD)); return ERROR(srcSize_wrong); }
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bitD->start = (const char*)srcBuffer;
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bitD->limitPtr = bitD->start + sizeof(bitD->bitContainer);
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if (srcSize >= sizeof(bitD->bitContainer)) { /* normal case */
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bitD->ptr = (const char*)srcBuffer + srcSize - sizeof(bitD->bitContainer);
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bitD->bitContainer = MEM_readLEST(bitD->ptr);
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{ BYTE const lastByte = ((const BYTE*)srcBuffer)[srcSize-1];
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bitD->bitsConsumed = lastByte ? 8 - BIT_highbit32(lastByte) : 0; /* ensures bitsConsumed is always set */
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if (lastByte == 0) return ERROR(GENERIC); /* endMark not present */ }
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} else {
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bitD->ptr = bitD->start;
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bitD->bitContainer = *(const BYTE*)(bitD->start);
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switch(srcSize)
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{
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case 7: bitD->bitContainer += (size_t)(((const BYTE*)(srcBuffer))[6]) << (sizeof(bitD->bitContainer)*8 - 16);
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ZSTD_FALLTHROUGH;
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case 6: bitD->bitContainer += (size_t)(((const BYTE*)(srcBuffer))[5]) << (sizeof(bitD->bitContainer)*8 - 24);
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ZSTD_FALLTHROUGH;
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case 5: bitD->bitContainer += (size_t)(((const BYTE*)(srcBuffer))[4]) << (sizeof(bitD->bitContainer)*8 - 32);
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ZSTD_FALLTHROUGH;
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case 4: bitD->bitContainer += (size_t)(((const BYTE*)(srcBuffer))[3]) << 24;
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ZSTD_FALLTHROUGH;
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case 3: bitD->bitContainer += (size_t)(((const BYTE*)(srcBuffer))[2]) << 16;
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ZSTD_FALLTHROUGH;
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case 2: bitD->bitContainer += (size_t)(((const BYTE*)(srcBuffer))[1]) << 8;
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ZSTD_FALLTHROUGH;
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default: break;
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}
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{ BYTE const lastByte = ((const BYTE*)srcBuffer)[srcSize-1];
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bitD->bitsConsumed = lastByte ? 8 - BIT_highbit32(lastByte) : 0;
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if (lastByte == 0) return ERROR(corruption_detected); /* endMark not present */
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}
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bitD->bitsConsumed += (U32)(sizeof(bitD->bitContainer) - srcSize)*8;
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}
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return srcSize;
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}
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MEM_STATIC FORCE_INLINE_ATTR size_t BIT_getUpperBits(size_t bitContainer, U32 const start)
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{
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return bitContainer >> start;
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}
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MEM_STATIC FORCE_INLINE_ATTR size_t BIT_getMiddleBits(size_t bitContainer, U32 const start, U32 const nbBits)
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{
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U32 const regMask = sizeof(bitContainer)*8 - 1;
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/* if start > regMask, bitstream is corrupted, and result is undefined */
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assert(nbBits < BIT_MASK_SIZE);
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/* x86 transform & ((1 << nbBits) - 1) to bzhi instruction, it is better
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* than accessing memory. When bmi2 instruction is not present, we consider
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* such cpus old (pre-Haswell, 2013) and their performance is not of that
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* importance.
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*/
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#if defined(__x86_64__) || defined(_M_X86)
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return (bitContainer >> (start & regMask)) & ((((U64)1) << nbBits) - 1);
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#else
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return (bitContainer >> (start & regMask)) & BIT_mask[nbBits];
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#endif
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}
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MEM_STATIC FORCE_INLINE_ATTR size_t BIT_getLowerBits(size_t bitContainer, U32 const nbBits)
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{
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assert(nbBits < BIT_MASK_SIZE);
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return bitContainer & BIT_mask[nbBits];
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}
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/*! BIT_lookBits() :
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* Provides next n bits from local register.
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* local register is not modified.
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* On 32-bits, maxNbBits==24.
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* On 64-bits, maxNbBits==56.
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* @return : value extracted */
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MEM_STATIC FORCE_INLINE_ATTR size_t BIT_lookBits(const BIT_DStream_t* bitD, U32 nbBits)
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{
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/* arbitrate between double-shift and shift+mask */
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#if 1
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/* if bitD->bitsConsumed + nbBits > sizeof(bitD->bitContainer)*8,
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* bitstream is likely corrupted, and result is undefined */
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return BIT_getMiddleBits(bitD->bitContainer, (sizeof(bitD->bitContainer)*8) - bitD->bitsConsumed - nbBits, nbBits);
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#else
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/* this code path is slower on my os-x laptop */
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U32 const regMask = sizeof(bitD->bitContainer)*8 - 1;
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return ((bitD->bitContainer << (bitD->bitsConsumed & regMask)) >> 1) >> ((regMask-nbBits) & regMask);
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#endif
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}
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/*! BIT_lookBitsFast() :
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* unsafe version; only works if nbBits >= 1 */
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MEM_STATIC size_t BIT_lookBitsFast(const BIT_DStream_t* bitD, U32 nbBits)
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{
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U32 const regMask = sizeof(bitD->bitContainer)*8 - 1;
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assert(nbBits >= 1);
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return (bitD->bitContainer << (bitD->bitsConsumed & regMask)) >> (((regMask+1)-nbBits) & regMask);
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}
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MEM_STATIC FORCE_INLINE_ATTR void BIT_skipBits(BIT_DStream_t* bitD, U32 nbBits)
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{
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bitD->bitsConsumed += nbBits;
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}
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/*! BIT_readBits() :
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* Read (consume) next n bits from local register and update.
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* Pay attention to not read more than nbBits contained into local register.
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* @return : extracted value. */
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MEM_STATIC FORCE_INLINE_ATTR size_t BIT_readBits(BIT_DStream_t* bitD, unsigned nbBits)
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{
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size_t const value = BIT_lookBits(bitD, nbBits);
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BIT_skipBits(bitD, nbBits);
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return value;
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}
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/*! BIT_readBitsFast() :
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* unsafe version; only works only if nbBits >= 1 */
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MEM_STATIC size_t BIT_readBitsFast(BIT_DStream_t* bitD, unsigned nbBits)
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{
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size_t const value = BIT_lookBitsFast(bitD, nbBits);
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assert(nbBits >= 1);
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BIT_skipBits(bitD, nbBits);
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return value;
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}
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/*! BIT_reloadDStreamFast() :
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* Similar to BIT_reloadDStream(), but with two differences:
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* 1. bitsConsumed <= sizeof(bitD->bitContainer)*8 must hold!
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* 2. Returns BIT_DStream_overflow when bitD->ptr < bitD->limitPtr, at this
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* point you must use BIT_reloadDStream() to reload.
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*/
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MEM_STATIC BIT_DStream_status BIT_reloadDStreamFast(BIT_DStream_t* bitD)
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{
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if (UNLIKELY(bitD->ptr < bitD->limitPtr))
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return BIT_DStream_overflow;
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assert(bitD->bitsConsumed <= sizeof(bitD->bitContainer)*8);
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bitD->ptr -= bitD->bitsConsumed >> 3;
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bitD->bitsConsumed &= 7;
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bitD->bitContainer = MEM_readLEST(bitD->ptr);
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return BIT_DStream_unfinished;
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}
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/*! BIT_reloadDStream() :
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* Refill `bitD` from buffer previously set in BIT_initDStream() .
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* This function is safe, it guarantees it will not read beyond src buffer.
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* @return : status of `BIT_DStream_t` internal register.
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* when status == BIT_DStream_unfinished, internal register is filled with at least 25 or 57 bits */
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MEM_STATIC BIT_DStream_status BIT_reloadDStream(BIT_DStream_t* bitD)
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{
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if (bitD->bitsConsumed > (sizeof(bitD->bitContainer)*8)) /* overflow detected, like end of stream */
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return BIT_DStream_overflow;
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if (bitD->ptr >= bitD->limitPtr) {
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return BIT_reloadDStreamFast(bitD);
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}
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if (bitD->ptr == bitD->start) {
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if (bitD->bitsConsumed < sizeof(bitD->bitContainer)*8) return BIT_DStream_endOfBuffer;
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return BIT_DStream_completed;
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}
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/* start < ptr < limitPtr */
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{ U32 nbBytes = bitD->bitsConsumed >> 3;
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BIT_DStream_status result = BIT_DStream_unfinished;
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if (bitD->ptr - nbBytes < bitD->start) {
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nbBytes = (U32)(bitD->ptr - bitD->start); /* ptr > start */
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result = BIT_DStream_endOfBuffer;
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}
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bitD->ptr -= nbBytes;
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bitD->bitsConsumed -= nbBytes*8;
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bitD->bitContainer = MEM_readLEST(bitD->ptr); /* reminder : srcSize > sizeof(bitD->bitContainer), otherwise bitD->ptr == bitD->start */
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|
return result;
|
|
}
|
|
}
|
|
|
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/*! 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));
|
|
}
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|
|
|
|
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#endif /* BITSTREAM_H_MODULE */
|