/* * Copyright (c) 2016-2020, Yann Collet, Facebook, Inc. * All rights reserved. * * 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. */ /* zstd_decompress_block : * this module takes care of decompressing _compressed_ block */ /*-******************************************************* * Dependencies *********************************************************/ #include /* memcpy, memmove, memset */ #include "../common/compiler.h" /* prefetch */ #include "../common/cpu.h" /* bmi2 */ #include "../common/mem.h" /* low level memory routines */ #define FSE_STATIC_LINKING_ONLY #include "../common/fse.h" #define HUF_STATIC_LINKING_ONLY #include "../common/huf.h" #include "../common/zstd_internal.h" #include "zstd_decompress_internal.h" /* ZSTD_DCtx */ #include "zstd_ddict.h" /* ZSTD_DDictDictContent */ #include "zstd_decompress_block.h" /*_******************************************************* * Macros **********************************************************/ /* These two optional macros force the use one way or another of the two * ZSTD_decompressSequences implementations. You can't force in both directions * at the same time. */ #if defined(ZSTD_FORCE_DECOMPRESS_SEQUENCES_SHORT) && \ defined(ZSTD_FORCE_DECOMPRESS_SEQUENCES_LONG) #error "Cannot force the use of the short and the long ZSTD_decompressSequences variants!" #endif /*_******************************************************* * Memory operations **********************************************************/ static void ZSTD_copy4(void* dst, const void* src) { memcpy(dst, src, 4); } /*-************************************************************* * Block decoding ***************************************************************/ /*! ZSTD_getcBlockSize() : * Provides the size of compressed block from block header `src` */ size_t ZSTD_getcBlockSize(const void* src, size_t srcSize, blockProperties_t* bpPtr) { RETURN_ERROR_IF(srcSize < ZSTD_blockHeaderSize, srcSize_wrong, ""); { U32 const cBlockHeader = MEM_readLE24(src); U32 const cSize = cBlockHeader >> 3; bpPtr->lastBlock = cBlockHeader & 1; bpPtr->blockType = (blockType_e)((cBlockHeader >> 1) & 3); bpPtr->origSize = cSize; /* only useful for RLE */ if (bpPtr->blockType == bt_rle) return 1; RETURN_ERROR_IF(bpPtr->blockType == bt_reserved, corruption_detected, ""); return cSize; } } /* Hidden declaration for fullbench */ size_t ZSTD_decodeLiteralsBlock(ZSTD_DCtx* dctx, const void* src, size_t srcSize); /*! ZSTD_decodeLiteralsBlock() : * @return : nb of bytes read from src (< srcSize ) * note : symbol not declared but exposed for fullbench */ size_t ZSTD_decodeLiteralsBlock(ZSTD_DCtx* dctx, const void* src, size_t srcSize) /* note : srcSize < BLOCKSIZE */ { DEBUGLOG(5, "ZSTD_decodeLiteralsBlock"); RETURN_ERROR_IF(srcSize < MIN_CBLOCK_SIZE, corruption_detected, ""); { const BYTE* const istart = (const BYTE*) src; symbolEncodingType_e const litEncType = (symbolEncodingType_e)(istart[0] & 3); switch(litEncType) { case set_repeat: DEBUGLOG(5, "set_repeat flag : re-using stats from previous compressed literals block"); RETURN_ERROR_IF(dctx->litEntropy==0, dictionary_corrupted, ""); /* fall-through */ case set_compressed: RETURN_ERROR_IF(srcSize < 5, corruption_detected, "srcSize >= MIN_CBLOCK_SIZE == 3; here we need up to 5 for case 3"); { size_t lhSize, litSize, litCSize; U32 singleStream=0; U32 const lhlCode = (istart[0] >> 2) & 3; U32 const lhc = MEM_readLE32(istart); size_t hufSuccess; switch(lhlCode) { case 0: case 1: default: /* note : default is impossible, since lhlCode into [0..3] */ /* 2 - 2 - 10 - 10 */ singleStream = !lhlCode; lhSize = 3; litSize = (lhc >> 4) & 0x3FF; litCSize = (lhc >> 14) & 0x3FF; break; case 2: /* 2 - 2 - 14 - 14 */ lhSize = 4; litSize = (lhc >> 4) & 0x3FFF; litCSize = lhc >> 18; break; case 3: /* 2 - 2 - 18 - 18 */ lhSize = 5; litSize = (lhc >> 4) & 0x3FFFF; litCSize = (lhc >> 22) + ((size_t)istart[4] << 10); break; } RETURN_ERROR_IF(litSize > ZSTD_BLOCKSIZE_MAX, corruption_detected, ""); RETURN_ERROR_IF(litCSize + lhSize > srcSize, corruption_detected, ""); /* prefetch huffman table if cold */ if (dctx->ddictIsCold && (litSize > 768 /* heuristic */)) { PREFETCH_AREA(dctx->HUFptr, sizeof(dctx->entropy.hufTable)); } if (litEncType==set_repeat) { if (singleStream) { hufSuccess = HUF_decompress1X_usingDTable_bmi2( dctx->litBuffer, litSize, istart+lhSize, litCSize, dctx->HUFptr, dctx->bmi2); } else { hufSuccess = HUF_decompress4X_usingDTable_bmi2( dctx->litBuffer, litSize, istart+lhSize, litCSize, dctx->HUFptr, dctx->bmi2); } } else { if (singleStream) { #if defined(HUF_FORCE_DECOMPRESS_X2) hufSuccess = HUF_decompress1X_DCtx_wksp( dctx->entropy.hufTable, dctx->litBuffer, litSize, istart+lhSize, litCSize, dctx->workspace, sizeof(dctx->workspace)); #else hufSuccess = HUF_decompress1X1_DCtx_wksp_bmi2( dctx->entropy.hufTable, dctx->litBuffer, litSize, istart+lhSize, litCSize, dctx->workspace, sizeof(dctx->workspace), dctx->bmi2); #endif } else { hufSuccess = HUF_decompress4X_hufOnly_wksp_bmi2( dctx->entropy.hufTable, dctx->litBuffer, litSize, istart+lhSize, litCSize, dctx->workspace, sizeof(dctx->workspace), dctx->bmi2); } } RETURN_ERROR_IF(HUF_isError(hufSuccess), corruption_detected, ""); dctx->litPtr = dctx->litBuffer; dctx->litSize = litSize; dctx->litEntropy = 1; if (litEncType==set_compressed) dctx->HUFptr = dctx->entropy.hufTable; memset(dctx->litBuffer + dctx->litSize, 0, WILDCOPY_OVERLENGTH); return litCSize + lhSize; } case set_basic: { size_t litSize, lhSize; U32 const lhlCode = ((istart[0]) >> 2) & 3; switch(lhlCode) { case 0: case 2: default: /* note : default is impossible, since lhlCode into [0..3] */ lhSize = 1; litSize = istart[0] >> 3; break; case 1: lhSize = 2; litSize = MEM_readLE16(istart) >> 4; break; case 3: lhSize = 3; litSize = MEM_readLE24(istart) >> 4; break; } if (lhSize+litSize+WILDCOPY_OVERLENGTH > srcSize) { /* risk reading beyond src buffer with wildcopy */ RETURN_ERROR_IF(litSize+lhSize > srcSize, corruption_detected, ""); memcpy(dctx->litBuffer, istart+lhSize, litSize); dctx->litPtr = dctx->litBuffer; dctx->litSize = litSize; memset(dctx->litBuffer + dctx->litSize, 0, WILDCOPY_OVERLENGTH); return lhSize+litSize; } /* direct reference into compressed stream */ dctx->litPtr = istart+lhSize; dctx->litSize = litSize; return lhSize+litSize; } case set_rle: { U32 const lhlCode = ((istart[0]) >> 2) & 3; size_t litSize, lhSize; switch(lhlCode) { case 0: case 2: default: /* note : default is impossible, since lhlCode into [0..3] */ lhSize = 1; litSize = istart[0] >> 3; break; case 1: lhSize = 2; litSize = MEM_readLE16(istart) >> 4; break; case 3: lhSize = 3; litSize = MEM_readLE24(istart) >> 4; RETURN_ERROR_IF(srcSize<4, corruption_detected, "srcSize >= MIN_CBLOCK_SIZE == 3; here we need lhSize+1 = 4"); break; } RETURN_ERROR_IF(litSize > ZSTD_BLOCKSIZE_MAX, corruption_detected, ""); memset(dctx->litBuffer, istart[lhSize], litSize + WILDCOPY_OVERLENGTH); dctx->litPtr = dctx->litBuffer; dctx->litSize = litSize; return lhSize+1; } default: RETURN_ERROR(corruption_detected, "impossible"); } } } /* Default FSE distribution tables. * These are pre-calculated FSE decoding tables using default distributions as defined in specification : * https://github.com/facebook/zstd/blob/master/doc/zstd_compression_format.md#default-distributions * They were generated programmatically with following method : * - start from default distributions, present in /lib/common/zstd_internal.h * - generate tables normally, using ZSTD_buildFSETable() * - printout the content of tables * - pretify output, report below, test with fuzzer to ensure it's correct */ /* Default FSE distribution table for Literal Lengths */ static const ZSTD_seqSymbol LL_defaultDTable[(1<tableLog = 0; DTableH->fastMode = 0; cell->nbBits = 0; cell->nextState = 0; assert(nbAddBits < 255); cell->nbAdditionalBits = (BYTE)nbAddBits; cell->baseValue = baseValue; } /* ZSTD_buildFSETable() : * generate FSE decoding table for one symbol (ll, ml or off) * cannot fail if input is valid => * all inputs are presumed validated at this stage */ void ZSTD_buildFSETable(ZSTD_seqSymbol* dt, const short* normalizedCounter, unsigned maxSymbolValue, const U32* baseValue, const U32* nbAdditionalBits, unsigned tableLog) { ZSTD_seqSymbol* const tableDecode = dt+1; U16 symbolNext[MaxSeq+1]; U32 const maxSV1 = maxSymbolValue + 1; U32 const tableSize = 1 << tableLog; U32 highThreshold = tableSize-1; /* Sanity Checks */ assert(maxSymbolValue <= MaxSeq); assert(tableLog <= MaxFSELog); /* Init, lay down lowprob symbols */ { ZSTD_seqSymbol_header DTableH; DTableH.tableLog = tableLog; DTableH.fastMode = 1; { S16 const largeLimit= (S16)(1 << (tableLog-1)); U32 s; for (s=0; s= largeLimit) DTableH.fastMode=0; assert(normalizedCounter[s]>=0); symbolNext[s] = (U16)normalizedCounter[s]; } } } memcpy(dt, &DTableH, sizeof(DTableH)); } /* Spread symbols */ { U32 const tableMask = tableSize-1; U32 const step = FSE_TABLESTEP(tableSize); U32 s, position = 0; for (s=0; s highThreshold) position = (position + step) & tableMask; /* lowprob area */ } } assert(position == 0); /* position must reach all cells once, otherwise normalizedCounter is incorrect */ } /* Build Decoding table */ { U32 u; for (u=0; u max, corruption_detected, ""); { U32 const symbol = *(const BYTE*)src; U32 const baseline = baseValue[symbol]; U32 const nbBits = nbAdditionalBits[symbol]; ZSTD_buildSeqTable_rle(DTableSpace, baseline, nbBits); } *DTablePtr = DTableSpace; return 1; case set_basic : *DTablePtr = defaultTable; return 0; case set_repeat: RETURN_ERROR_IF(!flagRepeatTable, corruption_detected, ""); /* prefetch FSE table if used */ if (ddictIsCold && (nbSeq > 24 /* heuristic */)) { const void* const pStart = *DTablePtr; size_t const pSize = sizeof(ZSTD_seqSymbol) * (SEQSYMBOL_TABLE_SIZE(maxLog)); PREFETCH_AREA(pStart, pSize); } return 0; case set_compressed : { unsigned tableLog; S16 norm[MaxSeq+1]; size_t const headerSize = FSE_readNCount(norm, &max, &tableLog, src, srcSize); RETURN_ERROR_IF(FSE_isError(headerSize), corruption_detected, ""); RETURN_ERROR_IF(tableLog > maxLog, corruption_detected, ""); ZSTD_buildFSETable(DTableSpace, norm, max, baseValue, nbAdditionalBits, tableLog); *DTablePtr = DTableSpace; return headerSize; } default : assert(0); RETURN_ERROR(GENERIC, "impossible"); } } size_t ZSTD_decodeSeqHeaders(ZSTD_DCtx* dctx, int* nbSeqPtr, const void* src, size_t srcSize) { const BYTE* const istart = (const BYTE* const)src; const BYTE* const iend = istart + srcSize; const BYTE* ip = istart; int nbSeq; DEBUGLOG(5, "ZSTD_decodeSeqHeaders"); /* check */ RETURN_ERROR_IF(srcSize < MIN_SEQUENCES_SIZE, srcSize_wrong, ""); /* SeqHead */ nbSeq = *ip++; if (!nbSeq) { *nbSeqPtr=0; RETURN_ERROR_IF(srcSize != 1, srcSize_wrong, ""); return 1; } if (nbSeq > 0x7F) { if (nbSeq == 0xFF) { RETURN_ERROR_IF(ip+2 > iend, srcSize_wrong, ""); nbSeq = MEM_readLE16(ip) + LONGNBSEQ, ip+=2; } else { RETURN_ERROR_IF(ip >= iend, srcSize_wrong, ""); nbSeq = ((nbSeq-0x80)<<8) + *ip++; } } *nbSeqPtr = nbSeq; /* FSE table descriptors */ RETURN_ERROR_IF(ip+1 > iend, srcSize_wrong, ""); /* minimum possible size: 1 byte for symbol encoding types */ { symbolEncodingType_e const LLtype = (symbolEncodingType_e)(*ip >> 6); symbolEncodingType_e const OFtype = (symbolEncodingType_e)((*ip >> 4) & 3); symbolEncodingType_e const MLtype = (symbolEncodingType_e)((*ip >> 2) & 3); ip++; /* Build DTables */ { size_t const llhSize = ZSTD_buildSeqTable(dctx->entropy.LLTable, &dctx->LLTptr, LLtype, MaxLL, LLFSELog, ip, iend-ip, LL_base, LL_bits, LL_defaultDTable, dctx->fseEntropy, dctx->ddictIsCold, nbSeq); RETURN_ERROR_IF(ZSTD_isError(llhSize), corruption_detected, "ZSTD_buildSeqTable failed"); ip += llhSize; } { size_t const ofhSize = ZSTD_buildSeqTable(dctx->entropy.OFTable, &dctx->OFTptr, OFtype, MaxOff, OffFSELog, ip, iend-ip, OF_base, OF_bits, OF_defaultDTable, dctx->fseEntropy, dctx->ddictIsCold, nbSeq); RETURN_ERROR_IF(ZSTD_isError(ofhSize), corruption_detected, "ZSTD_buildSeqTable failed"); ip += ofhSize; } { size_t const mlhSize = ZSTD_buildSeqTable(dctx->entropy.MLTable, &dctx->MLTptr, MLtype, MaxML, MLFSELog, ip, iend-ip, ML_base, ML_bits, ML_defaultDTable, dctx->fseEntropy, dctx->ddictIsCold, nbSeq); RETURN_ERROR_IF(ZSTD_isError(mlhSize), corruption_detected, "ZSTD_buildSeqTable failed"); ip += mlhSize; } } return ip-istart; } typedef struct { size_t litLength; size_t matchLength; size_t offset; const BYTE* match; } seq_t; typedef struct { size_t state; const ZSTD_seqSymbol* table; } ZSTD_fseState; typedef struct { BIT_DStream_t DStream; ZSTD_fseState stateLL; ZSTD_fseState stateOffb; ZSTD_fseState stateML; size_t prevOffset[ZSTD_REP_NUM]; const BYTE* prefixStart; const BYTE* dictEnd; size_t pos; } seqState_t; /*! ZSTD_overlapCopy8() : * Copies 8 bytes from ip to op and updates op and ip where ip <= op. * If the offset is < 8 then the offset is spread to at least 8 bytes. * * Precondition: *ip <= *op * Postcondition: *op - *op >= 8 */ HINT_INLINE void ZSTD_overlapCopy8(BYTE** op, BYTE const** ip, size_t offset) { assert(*ip <= *op); if (offset < 8) { /* close range match, overlap */ static const U32 dec32table[] = { 0, 1, 2, 1, 4, 4, 4, 4 }; /* added */ static const int dec64table[] = { 8, 8, 8, 7, 8, 9,10,11 }; /* subtracted */ int const sub2 = dec64table[offset]; (*op)[0] = (*ip)[0]; (*op)[1] = (*ip)[1]; (*op)[2] = (*ip)[2]; (*op)[3] = (*ip)[3]; *ip += dec32table[offset]; ZSTD_copy4(*op+4, *ip); *ip -= sub2; } else { ZSTD_copy8(*op, *ip); } *ip += 8; *op += 8; assert(*op - *ip >= 8); } /*! ZSTD_safecopy() : * Specialized version of memcpy() that is allowed to READ up to WILDCOPY_OVERLENGTH past the input buffer * and write up to 16 bytes past oend_w (op >= oend_w is allowed). * This function is only called in the uncommon case where the sequence is near the end of the block. It * should be fast for a single long sequence, but can be slow for several short sequences. * * @param ovtype controls the overlap detection * - ZSTD_no_overlap: The source and destination are guaranteed to be at least WILDCOPY_VECLEN bytes apart. * - ZSTD_overlap_src_before_dst: The src and dst may overlap and may be any distance apart. * The src buffer must be before the dst buffer. */ static void ZSTD_safecopy(BYTE* op, BYTE* const oend_w, BYTE const* ip, ptrdiff_t length, ZSTD_overlap_e ovtype) { ptrdiff_t const diff = op - ip; BYTE* const oend = op + length; assert((ovtype == ZSTD_no_overlap && (diff <= -8 || diff >= 8 || op >= oend_w)) || (ovtype == ZSTD_overlap_src_before_dst && diff >= 0)); if (length < 8) { /* Handle short lengths. */ while (op < oend) *op++ = *ip++; return; } if (ovtype == ZSTD_overlap_src_before_dst) { /* Copy 8 bytes and ensure the offset >= 8 when there can be overlap. */ assert(length >= 8); ZSTD_overlapCopy8(&op, &ip, diff); assert(op - ip >= 8); assert(op <= oend); } if (oend <= oend_w) { /* No risk of overwrite. */ ZSTD_wildcopy(op, ip, length, ovtype); return; } if (op <= oend_w) { /* Wildcopy until we get close to the end. */ assert(oend > oend_w); ZSTD_wildcopy(op, ip, oend_w - op, ovtype); ip += oend_w - op; op = oend_w; } /* Handle the leftovers. */ while (op < oend) *op++ = *ip++; } /* ZSTD_execSequenceEnd(): * This version handles cases that are near the end of the output buffer. It requires * more careful checks to make sure there is no overflow. By separating out these hard * and unlikely cases, we can speed up the common cases. * * NOTE: This function needs to be fast for a single long sequence, but doesn't need * to be optimized for many small sequences, since those fall into ZSTD_execSequence(). */ FORCE_NOINLINE size_t ZSTD_execSequenceEnd(BYTE* op, BYTE* const oend, seq_t sequence, const BYTE** litPtr, const BYTE* const litLimit, const BYTE* const prefixStart, const BYTE* const virtualStart, const BYTE* const dictEnd) { BYTE* const oLitEnd = op + sequence.litLength; size_t const sequenceLength = sequence.litLength + sequence.matchLength; const BYTE* const iLitEnd = *litPtr + sequence.litLength; const BYTE* match = oLitEnd - sequence.offset; BYTE* const oend_w = oend - WILDCOPY_OVERLENGTH; /* bounds checks : careful of address space overflow in 32-bit mode */ RETURN_ERROR_IF(sequenceLength > (size_t)(oend - op), dstSize_tooSmall, "last match must fit within dstBuffer"); RETURN_ERROR_IF(sequence.litLength > (size_t)(litLimit - *litPtr), corruption_detected, "try to read beyond literal buffer"); assert(op < op + sequenceLength); assert(oLitEnd < op + sequenceLength); /* copy literals */ ZSTD_safecopy(op, oend_w, *litPtr, sequence.litLength, ZSTD_no_overlap); op = oLitEnd; *litPtr = iLitEnd; /* copy Match */ if (sequence.offset > (size_t)(oLitEnd - prefixStart)) { /* offset beyond prefix */ RETURN_ERROR_IF(sequence.offset > (size_t)(oLitEnd - virtualStart), corruption_detected, ""); match = dictEnd - (prefixStart-match); if (match + sequence.matchLength <= dictEnd) { memmove(oLitEnd, match, sequence.matchLength); return sequenceLength; } /* span extDict & currentPrefixSegment */ { size_t const length1 = dictEnd - match; memmove(oLitEnd, match, length1); op = oLitEnd + length1; sequence.matchLength -= length1; match = prefixStart; } } ZSTD_safecopy(op, oend_w, match, sequence.matchLength, ZSTD_overlap_src_before_dst); return sequenceLength; } HINT_INLINE size_t ZSTD_execSequence(BYTE* op, BYTE* const oend, seq_t sequence, const BYTE** litPtr, const BYTE* const litLimit, const BYTE* const prefixStart, const BYTE* const virtualStart, const BYTE* const dictEnd) { BYTE* const oLitEnd = op + sequence.litLength; size_t const sequenceLength = sequence.litLength + sequence.matchLength; BYTE* const oMatchEnd = op + sequenceLength; /* risk : address space overflow (32-bits) */ BYTE* const oend_w = oend - WILDCOPY_OVERLENGTH; /* risk : address space underflow on oend=NULL */ const BYTE* const iLitEnd = *litPtr + sequence.litLength; const BYTE* match = oLitEnd - sequence.offset; assert(op != NULL /* Precondition */); assert(oend_w < oend /* No underflow */); /* Handle edge cases in a slow path: * - Read beyond end of literals * - Match end is within WILDCOPY_OVERLIMIT of oend * - 32-bit mode and the match length overflows */ if (UNLIKELY( iLitEnd > litLimit || oMatchEnd > oend_w || (MEM_32bits() && (size_t)(oend - op) < sequenceLength + WILDCOPY_OVERLENGTH))) return ZSTD_execSequenceEnd(op, oend, sequence, litPtr, litLimit, prefixStart, virtualStart, dictEnd); /* Assumptions (everything else goes into ZSTD_execSequenceEnd()) */ assert(op <= oLitEnd /* No overflow */); assert(oLitEnd < oMatchEnd /* Non-zero match & no overflow */); assert(oMatchEnd <= oend /* No underflow */); assert(iLitEnd <= litLimit /* Literal length is in bounds */); assert(oLitEnd <= oend_w /* Can wildcopy literals */); assert(oMatchEnd <= oend_w /* Can wildcopy matches */); /* Copy Literals: * Split out litLength <= 16 since it is nearly always true. +1.6% on gcc-9. * We likely don't need the full 32-byte wildcopy. */ assert(WILDCOPY_OVERLENGTH >= 16); ZSTD_copy16(op, (*litPtr)); if (UNLIKELY(sequence.litLength > 16)) { ZSTD_wildcopy(op+16, (*litPtr)+16, sequence.litLength-16, ZSTD_no_overlap); } op = oLitEnd; *litPtr = iLitEnd; /* update for next sequence */ /* Copy Match */ if (sequence.offset > (size_t)(oLitEnd - prefixStart)) { /* offset beyond prefix -> go into extDict */ RETURN_ERROR_IF(UNLIKELY(sequence.offset > (size_t)(oLitEnd - virtualStart)), corruption_detected, ""); match = dictEnd + (match - prefixStart); if (match + sequence.matchLength <= dictEnd) { memmove(oLitEnd, match, sequence.matchLength); return sequenceLength; } /* span extDict & currentPrefixSegment */ { size_t const length1 = dictEnd - match; memmove(oLitEnd, match, length1); op = oLitEnd + length1; sequence.matchLength -= length1; match = prefixStart; } } /* Match within prefix of 1 or more bytes */ assert(op <= oMatchEnd); assert(oMatchEnd <= oend_w); assert(match >= prefixStart); assert(sequence.matchLength >= 1); /* Nearly all offsets are >= WILDCOPY_VECLEN bytes, which means we can use wildcopy * without overlap checking. */ if (LIKELY(sequence.offset >= WILDCOPY_VECLEN)) { /* We bet on a full wildcopy for matches, since we expect matches to be * longer than literals (in general). In silesia, ~10% of matches are longer * than 16 bytes. */ ZSTD_wildcopy(op, match, (ptrdiff_t)sequence.matchLength, ZSTD_no_overlap); return sequenceLength; } assert(sequence.offset < WILDCOPY_VECLEN); /* Copy 8 bytes and spread the offset to be >= 8. */ ZSTD_overlapCopy8(&op, &match, sequence.offset); /* If the match length is > 8 bytes, then continue with the wildcopy. */ if (sequence.matchLength > 8) { assert(op < oMatchEnd); ZSTD_wildcopy(op, match, (ptrdiff_t)sequence.matchLength-8, ZSTD_overlap_src_before_dst); } return sequenceLength; } static void ZSTD_initFseState(ZSTD_fseState* DStatePtr, BIT_DStream_t* bitD, const ZSTD_seqSymbol* dt) { const void* ptr = dt; const ZSTD_seqSymbol_header* const DTableH = (const ZSTD_seqSymbol_header*)ptr; DStatePtr->state = BIT_readBits(bitD, DTableH->tableLog); DEBUGLOG(6, "ZSTD_initFseState : val=%u using %u bits", (U32)DStatePtr->state, DTableH->tableLog); BIT_reloadDStream(bitD); DStatePtr->table = dt + 1; } FORCE_INLINE_TEMPLATE void ZSTD_updateFseState(ZSTD_fseState* DStatePtr, BIT_DStream_t* bitD) { ZSTD_seqSymbol const DInfo = DStatePtr->table[DStatePtr->state]; U32 const nbBits = DInfo.nbBits; size_t const lowBits = BIT_readBits(bitD, nbBits); DStatePtr->state = DInfo.nextState + lowBits; } FORCE_INLINE_TEMPLATE void ZSTD_updateFseStateWithDInfo(ZSTD_fseState* DStatePtr, BIT_DStream_t* bitD, ZSTD_seqSymbol const DInfo) { U32 const nbBits = DInfo.nbBits; size_t const lowBits = BIT_readBits(bitD, nbBits); DStatePtr->state = DInfo.nextState + lowBits; } /* We need to add at most (ZSTD_WINDOWLOG_MAX_32 - 1) bits to read the maximum * offset bits. But we can only read at most (STREAM_ACCUMULATOR_MIN_32 - 1) * bits before reloading. This value is the maximum number of bytes we read * after reloading when we are decoding long offsets. */ #define LONG_OFFSETS_MAX_EXTRA_BITS_32 \ (ZSTD_WINDOWLOG_MAX_32 > STREAM_ACCUMULATOR_MIN_32 \ ? ZSTD_WINDOWLOG_MAX_32 - STREAM_ACCUMULATOR_MIN_32 \ : 0) typedef enum { ZSTD_lo_isRegularOffset, ZSTD_lo_isLongOffset=1 } ZSTD_longOffset_e; typedef enum { ZSTD_p_noPrefetch=0, ZSTD_p_prefetch=1 } ZSTD_prefetch_e; FORCE_INLINE_TEMPLATE seq_t ZSTD_decodeSequence(seqState_t* seqState, const ZSTD_longOffset_e longOffsets, const ZSTD_prefetch_e prefetch) { seq_t seq; ZSTD_seqSymbol const llDInfo = seqState->stateLL.table[seqState->stateLL.state]; ZSTD_seqSymbol const mlDInfo = seqState->stateML.table[seqState->stateML.state]; ZSTD_seqSymbol const ofDInfo = seqState->stateOffb.table[seqState->stateOffb.state]; U32 const llBase = llDInfo.baseValue; U32 const mlBase = mlDInfo.baseValue; U32 const ofBase = ofDInfo.baseValue; BYTE const llBits = llDInfo.nbAdditionalBits; BYTE const mlBits = mlDInfo.nbAdditionalBits; BYTE const ofBits = ofDInfo.nbAdditionalBits; BYTE const totalBits = llBits+mlBits+ofBits; /* sequence */ { size_t offset; if (ofBits > 1) { ZSTD_STATIC_ASSERT(ZSTD_lo_isLongOffset == 1); ZSTD_STATIC_ASSERT(LONG_OFFSETS_MAX_EXTRA_BITS_32 == 5); assert(ofBits <= MaxOff); if (MEM_32bits() && longOffsets && (ofBits >= STREAM_ACCUMULATOR_MIN_32)) { U32 const extraBits = ofBits - MIN(ofBits, 32 - seqState->DStream.bitsConsumed); offset = ofBase + (BIT_readBitsFast(&seqState->DStream, ofBits - extraBits) << extraBits); BIT_reloadDStream(&seqState->DStream); if (extraBits) offset += BIT_readBitsFast(&seqState->DStream, extraBits); assert(extraBits <= LONG_OFFSETS_MAX_EXTRA_BITS_32); /* to avoid another reload */ } else { offset = ofBase + BIT_readBitsFast(&seqState->DStream, ofBits/*>0*/); /* <= (ZSTD_WINDOWLOG_MAX-1) bits */ if (MEM_32bits()) BIT_reloadDStream(&seqState->DStream); } seqState->prevOffset[2] = seqState->prevOffset[1]; seqState->prevOffset[1] = seqState->prevOffset[0]; seqState->prevOffset[0] = offset; } else { U32 const ll0 = (llBase == 0); if (LIKELY((ofBits == 0))) { if (LIKELY(!ll0)) offset = seqState->prevOffset[0]; else { offset = seqState->prevOffset[1]; seqState->prevOffset[1] = seqState->prevOffset[0]; seqState->prevOffset[0] = offset; } } else { offset = ofBase + ll0 + BIT_readBitsFast(&seqState->DStream, 1); { size_t temp = (offset==3) ? seqState->prevOffset[0] - 1 : seqState->prevOffset[offset]; temp += !temp; /* 0 is not valid; input is corrupted; force offset to 1 */ if (offset != 1) seqState->prevOffset[2] = seqState->prevOffset[1]; seqState->prevOffset[1] = seqState->prevOffset[0]; seqState->prevOffset[0] = offset = temp; } } } seq.offset = offset; } seq.matchLength = mlBase; if (mlBits > 0) seq.matchLength += BIT_readBitsFast(&seqState->DStream, mlBits/*>0*/); if (MEM_32bits() && (mlBits+llBits >= STREAM_ACCUMULATOR_MIN_32-LONG_OFFSETS_MAX_EXTRA_BITS_32)) BIT_reloadDStream(&seqState->DStream); if (MEM_64bits() && UNLIKELY(totalBits >= STREAM_ACCUMULATOR_MIN_64-(LLFSELog+MLFSELog+OffFSELog))) BIT_reloadDStream(&seqState->DStream); /* Ensure there are enough bits to read the rest of data in 64-bit mode. */ ZSTD_STATIC_ASSERT(16+LLFSELog+MLFSELog+OffFSELog < STREAM_ACCUMULATOR_MIN_64); seq.litLength = llBase; if (llBits > 0) seq.litLength += BIT_readBitsFast(&seqState->DStream, llBits/*>0*/); if (MEM_32bits()) BIT_reloadDStream(&seqState->DStream); DEBUGLOG(6, "seq: litL=%u, matchL=%u, offset=%u", (U32)seq.litLength, (U32)seq.matchLength, (U32)seq.offset); if (prefetch == ZSTD_p_prefetch) { size_t const pos = seqState->pos + seq.litLength; const BYTE* const matchBase = (seq.offset > pos) ? seqState->dictEnd : seqState->prefixStart; seq.match = matchBase + pos - seq.offset; /* note : this operation can overflow when seq.offset is really too large, which can only happen when input is corrupted. * No consequence though : no memory access will occur, offset is only used for prefetching */ seqState->pos = pos + seq.matchLength; } /* ANS state update * gcc-9.0.0 does 2.5% worse with ZSTD_updateFseStateWithDInfo(). * clang-9.2.0 does 7% worse with ZSTD_updateFseState(). * Naturally it seems like ZSTD_updateFseStateWithDInfo() should be the * better option, so it is the default for other compilers. But, if you * measure that it is worse, please put up a pull request. */ { #if defined(__GNUC__) && !defined(__clang__) const int kUseUpdateFseState = 1; #else const int kUseUpdateFseState = 0; #endif if (kUseUpdateFseState) { ZSTD_updateFseState(&seqState->stateLL, &seqState->DStream); /* <= 9 bits */ ZSTD_updateFseState(&seqState->stateML, &seqState->DStream); /* <= 9 bits */ if (MEM_32bits()) BIT_reloadDStream(&seqState->DStream); /* <= 18 bits */ ZSTD_updateFseState(&seqState->stateOffb, &seqState->DStream); /* <= 8 bits */ } else { ZSTD_updateFseStateWithDInfo(&seqState->stateLL, &seqState->DStream, llDInfo); /* <= 9 bits */ ZSTD_updateFseStateWithDInfo(&seqState->stateML, &seqState->DStream, mlDInfo); /* <= 9 bits */ if (MEM_32bits()) BIT_reloadDStream(&seqState->DStream); /* <= 18 bits */ ZSTD_updateFseStateWithDInfo(&seqState->stateOffb, &seqState->DStream, ofDInfo); /* <= 8 bits */ } } return seq; } #ifndef ZSTD_FORCE_DECOMPRESS_SEQUENCES_LONG FORCE_INLINE_TEMPLATE size_t DONT_VECTORIZE ZSTD_decompressSequences_body( ZSTD_DCtx* dctx, void* dst, size_t maxDstSize, const void* seqStart, size_t seqSize, int nbSeq, const ZSTD_longOffset_e isLongOffset) { const BYTE* ip = (const BYTE*)seqStart; const BYTE* const iend = ip + seqSize; BYTE* const ostart = (BYTE* const)dst; BYTE* const oend = ostart + maxDstSize; BYTE* op = ostart; const BYTE* litPtr = dctx->litPtr; const BYTE* const litEnd = litPtr + dctx->litSize; const BYTE* const prefixStart = (const BYTE*) (dctx->prefixStart); const BYTE* const vBase = (const BYTE*) (dctx->virtualStart); const BYTE* const dictEnd = (const BYTE*) (dctx->dictEnd); DEBUGLOG(5, "ZSTD_decompressSequences_body"); /* Regen sequences */ if (nbSeq) { seqState_t seqState; size_t error = 0; dctx->fseEntropy = 1; { U32 i; for (i=0; ientropy.rep[i]; } RETURN_ERROR_IF( ERR_isError(BIT_initDStream(&seqState.DStream, ip, iend-ip)), corruption_detected, ""); ZSTD_initFseState(&seqState.stateLL, &seqState.DStream, dctx->LLTptr); ZSTD_initFseState(&seqState.stateOffb, &seqState.DStream, dctx->OFTptr); ZSTD_initFseState(&seqState.stateML, &seqState.DStream, dctx->MLTptr); assert(dst != NULL); ZSTD_STATIC_ASSERT( BIT_DStream_unfinished < BIT_DStream_completed && BIT_DStream_endOfBuffer < BIT_DStream_completed && BIT_DStream_completed < BIT_DStream_overflow); #if defined(__GNUC__) && defined(__x86_64__) /* Align the decompression loop to 32 + 16 bytes. * * zstd compiled with gcc-9 on an Intel i9-9900k shows 10% decompression * speed swings based on the alignment of the decompression loop. This * performance swing is caused by parts of the decompression loop falling * out of the DSB. The entire decompression loop should fit in the DSB, * when it can't we get much worse performance. You can measure if you've * hit the good case or the bad case with this perf command for some * compressed file test.zst: * * perf stat -e cycles -e instructions -e idq.all_dsb_cycles_any_uops \ * -e idq.all_mite_cycles_any_uops -- ./zstd -tq test.zst * * If you see most cycles served out of the MITE you've hit the bad case. * If you see most cycles served out of the DSB you've hit the good case. * If it is pretty even then you may be in an okay case. * * I've been able to reproduce this issue on the following CPUs: * - Kabylake: Macbook Pro (15-inch, 2019) 2.4 GHz Intel Core i9 * Use Instruments->Counters to get DSB/MITE cycles. * I never got performance swings, but I was able to * go from the good case of mostly DSB to half of the * cycles served from MITE. * - Coffeelake: Intel i9-9900k * * I haven't been able to reproduce the instability or DSB misses on any * of the following CPUS: * - Haswell * - Broadwell: Intel(R) Xeon(R) CPU E5-2680 v4 @ 2.40GH * - Skylake * * If you are seeing performance stability this script can help test. * It tests on 4 commits in zstd where I saw performance change. * * https://gist.github.com/terrelln/9889fc06a423fd5ca6e99351564473f4 */ __asm__(".p2align 5"); __asm__("nop"); __asm__(".p2align 4"); #endif for ( ; ; ) { seq_t const sequence = ZSTD_decodeSequence(&seqState, isLongOffset, ZSTD_p_noPrefetch); size_t const oneSeqSize = ZSTD_execSequence(op, oend, sequence, &litPtr, litEnd, prefixStart, vBase, dictEnd); DEBUGLOG(6, "regenerated sequence size : %u", (U32)oneSeqSize); BIT_reloadDStream(&(seqState.DStream)); /* gcc and clang both don't like early returns in this loop. * gcc doesn't like early breaks either. * Instead save an error and report it at the end. * When there is an error, don't increment op, so we don't * overwrite. */ if (UNLIKELY(ZSTD_isError(oneSeqSize))) error = oneSeqSize; else op += oneSeqSize; if (UNLIKELY(!--nbSeq)) break; } /* check if reached exact end */ DEBUGLOG(5, "ZSTD_decompressSequences_body: after decode loop, remaining nbSeq : %i", nbSeq); if (ZSTD_isError(error)) return error; RETURN_ERROR_IF(nbSeq, corruption_detected, ""); RETURN_ERROR_IF(BIT_reloadDStream(&seqState.DStream) < BIT_DStream_completed, corruption_detected, ""); /* save reps for next block */ { U32 i; for (i=0; ientropy.rep[i] = (U32)(seqState.prevOffset[i]); } } /* last literal segment */ { size_t const lastLLSize = litEnd - litPtr; RETURN_ERROR_IF(lastLLSize > (size_t)(oend-op), dstSize_tooSmall, ""); if (op != NULL) { memcpy(op, litPtr, lastLLSize); op += lastLLSize; } } return op-ostart; } static size_t ZSTD_decompressSequences_default(ZSTD_DCtx* dctx, void* dst, size_t maxDstSize, const void* seqStart, size_t seqSize, int nbSeq, const ZSTD_longOffset_e isLongOffset) { return ZSTD_decompressSequences_body(dctx, dst, maxDstSize, seqStart, seqSize, nbSeq, isLongOffset); } #endif /* ZSTD_FORCE_DECOMPRESS_SEQUENCES_LONG */ #ifndef ZSTD_FORCE_DECOMPRESS_SEQUENCES_SHORT FORCE_INLINE_TEMPLATE size_t ZSTD_decompressSequencesLong_body( ZSTD_DCtx* dctx, void* dst, size_t maxDstSize, const void* seqStart, size_t seqSize, int nbSeq, const ZSTD_longOffset_e isLongOffset) { const BYTE* ip = (const BYTE*)seqStart; const BYTE* const iend = ip + seqSize; BYTE* const ostart = (BYTE* const)dst; BYTE* const oend = ostart + maxDstSize; BYTE* op = ostart; const BYTE* litPtr = dctx->litPtr; const BYTE* const litEnd = litPtr + dctx->litSize; const BYTE* const prefixStart = (const BYTE*) (dctx->prefixStart); const BYTE* const dictStart = (const BYTE*) (dctx->virtualStart); const BYTE* const dictEnd = (const BYTE*) (dctx->dictEnd); /* Regen sequences */ if (nbSeq) { #define STORED_SEQS 4 #define STORED_SEQS_MASK (STORED_SEQS-1) #define ADVANCED_SEQS 4 seq_t sequences[STORED_SEQS]; int const seqAdvance = MIN(nbSeq, ADVANCED_SEQS); seqState_t seqState; int seqNb; dctx->fseEntropy = 1; { int i; for (i=0; ientropy.rep[i]; } seqState.prefixStart = prefixStart; seqState.pos = (size_t)(op-prefixStart); seqState.dictEnd = dictEnd; assert(dst != NULL); assert(iend >= ip); RETURN_ERROR_IF( ERR_isError(BIT_initDStream(&seqState.DStream, ip, iend-ip)), corruption_detected, ""); ZSTD_initFseState(&seqState.stateLL, &seqState.DStream, dctx->LLTptr); ZSTD_initFseState(&seqState.stateOffb, &seqState.DStream, dctx->OFTptr); ZSTD_initFseState(&seqState.stateML, &seqState.DStream, dctx->MLTptr); /* prepare in advance */ for (seqNb=0; (BIT_reloadDStream(&seqState.DStream) <= BIT_DStream_completed) && (seqNbentropy.rep[i] = (U32)(seqState.prevOffset[i]); } } /* last literal segment */ { size_t const lastLLSize = litEnd - litPtr; RETURN_ERROR_IF(lastLLSize > (size_t)(oend-op), dstSize_tooSmall, ""); if (op != NULL) { memcpy(op, litPtr, lastLLSize); op += lastLLSize; } } return op-ostart; } static size_t ZSTD_decompressSequencesLong_default(ZSTD_DCtx* dctx, void* dst, size_t maxDstSize, const void* seqStart, size_t seqSize, int nbSeq, const ZSTD_longOffset_e isLongOffset) { return ZSTD_decompressSequencesLong_body(dctx, dst, maxDstSize, seqStart, seqSize, nbSeq, isLongOffset); } #endif /* ZSTD_FORCE_DECOMPRESS_SEQUENCES_SHORT */ #if DYNAMIC_BMI2 #ifndef ZSTD_FORCE_DECOMPRESS_SEQUENCES_LONG static TARGET_ATTRIBUTE("bmi2") size_t DONT_VECTORIZE ZSTD_decompressSequences_bmi2(ZSTD_DCtx* dctx, void* dst, size_t maxDstSize, const void* seqStart, size_t seqSize, int nbSeq, const ZSTD_longOffset_e isLongOffset) { return ZSTD_decompressSequences_body(dctx, dst, maxDstSize, seqStart, seqSize, nbSeq, isLongOffset); } #endif /* ZSTD_FORCE_DECOMPRESS_SEQUENCES_LONG */ #ifndef ZSTD_FORCE_DECOMPRESS_SEQUENCES_SHORT static TARGET_ATTRIBUTE("bmi2") size_t ZSTD_decompressSequencesLong_bmi2(ZSTD_DCtx* dctx, void* dst, size_t maxDstSize, const void* seqStart, size_t seqSize, int nbSeq, const ZSTD_longOffset_e isLongOffset) { return ZSTD_decompressSequencesLong_body(dctx, dst, maxDstSize, seqStart, seqSize, nbSeq, isLongOffset); } #endif /* ZSTD_FORCE_DECOMPRESS_SEQUENCES_SHORT */ #endif /* DYNAMIC_BMI2 */ typedef size_t (*ZSTD_decompressSequences_t)( ZSTD_DCtx* dctx, void* dst, size_t maxDstSize, const void* seqStart, size_t seqSize, int nbSeq, const ZSTD_longOffset_e isLongOffset); #ifndef ZSTD_FORCE_DECOMPRESS_SEQUENCES_LONG static size_t ZSTD_decompressSequences(ZSTD_DCtx* dctx, void* dst, size_t maxDstSize, const void* seqStart, size_t seqSize, int nbSeq, const ZSTD_longOffset_e isLongOffset) { DEBUGLOG(5, "ZSTD_decompressSequences"); #if DYNAMIC_BMI2 if (dctx->bmi2) { return ZSTD_decompressSequences_bmi2(dctx, dst, maxDstSize, seqStart, seqSize, nbSeq, isLongOffset); } #endif return ZSTD_decompressSequences_default(dctx, dst, maxDstSize, seqStart, seqSize, nbSeq, isLongOffset); } #endif /* ZSTD_FORCE_DECOMPRESS_SEQUENCES_LONG */ #ifndef ZSTD_FORCE_DECOMPRESS_SEQUENCES_SHORT /* ZSTD_decompressSequencesLong() : * decompression function triggered when a minimum share of offsets is considered "long", * aka out of cache. * note : "long" definition seems overloaded here, sometimes meaning "wider than bitstream register", and sometimes meaning "farther than memory cache distance". * This function will try to mitigate main memory latency through the use of prefetching */ static size_t ZSTD_decompressSequencesLong(ZSTD_DCtx* dctx, void* dst, size_t maxDstSize, const void* seqStart, size_t seqSize, int nbSeq, const ZSTD_longOffset_e isLongOffset) { DEBUGLOG(5, "ZSTD_decompressSequencesLong"); #if DYNAMIC_BMI2 if (dctx->bmi2) { return ZSTD_decompressSequencesLong_bmi2(dctx, dst, maxDstSize, seqStart, seqSize, nbSeq, isLongOffset); } #endif return ZSTD_decompressSequencesLong_default(dctx, dst, maxDstSize, seqStart, seqSize, nbSeq, isLongOffset); } #endif /* ZSTD_FORCE_DECOMPRESS_SEQUENCES_SHORT */ #if !defined(ZSTD_FORCE_DECOMPRESS_SEQUENCES_SHORT) && \ !defined(ZSTD_FORCE_DECOMPRESS_SEQUENCES_LONG) /* ZSTD_getLongOffsetsShare() : * condition : offTable must be valid * @return : "share" of long offsets (arbitrarily defined as > (1<<23)) * compared to maximum possible of (1< 22) total += 1; } assert(tableLog <= OffFSELog); total <<= (OffFSELog - tableLog); /* scale to OffFSELog */ return total; } #endif size_t ZSTD_decompressBlock_internal(ZSTD_DCtx* dctx, void* dst, size_t dstCapacity, const void* src, size_t srcSize, const int frame) { /* blockType == blockCompressed */ const BYTE* ip = (const BYTE*)src; /* isLongOffset must be true if there are long offsets. * Offsets are long if they are larger than 2^STREAM_ACCUMULATOR_MIN. * We don't expect that to be the case in 64-bit mode. * In block mode, window size is not known, so we have to be conservative. * (note: but it could be evaluated from current-lowLimit) */ ZSTD_longOffset_e const isLongOffset = (ZSTD_longOffset_e)(MEM_32bits() && (!frame || (dctx->fParams.windowSize > (1ULL << STREAM_ACCUMULATOR_MIN)))); DEBUGLOG(5, "ZSTD_decompressBlock_internal (size : %u)", (U32)srcSize); RETURN_ERROR_IF(srcSize >= ZSTD_BLOCKSIZE_MAX, srcSize_wrong, ""); /* Decode literals section */ { size_t const litCSize = ZSTD_decodeLiteralsBlock(dctx, src, srcSize); DEBUGLOG(5, "ZSTD_decodeLiteralsBlock : %u", (U32)litCSize); if (ZSTD_isError(litCSize)) return litCSize; ip += litCSize; srcSize -= litCSize; } /* Build Decoding Tables */ { /* These macros control at build-time which decompressor implementation * we use. If neither is defined, we do some inspection and dispatch at * runtime. */ #if !defined(ZSTD_FORCE_DECOMPRESS_SEQUENCES_SHORT) && \ !defined(ZSTD_FORCE_DECOMPRESS_SEQUENCES_LONG) int usePrefetchDecoder = dctx->ddictIsCold; #endif int nbSeq; size_t const seqHSize = ZSTD_decodeSeqHeaders(dctx, &nbSeq, ip, srcSize); if (ZSTD_isError(seqHSize)) return seqHSize; ip += seqHSize; srcSize -= seqHSize; RETURN_ERROR_IF(dst == NULL && nbSeq > 0, dstSize_tooSmall, "NULL not handled"); #if !defined(ZSTD_FORCE_DECOMPRESS_SEQUENCES_SHORT) && \ !defined(ZSTD_FORCE_DECOMPRESS_SEQUENCES_LONG) if ( !usePrefetchDecoder && (!frame || (dctx->fParams.windowSize > (1<<24))) && (nbSeq>ADVANCED_SEQS) ) { /* could probably use a larger nbSeq limit */ U32 const shareLongOffsets = ZSTD_getLongOffsetsShare(dctx->OFTptr); U32 const minShare = MEM_64bits() ? 7 : 20; /* heuristic values, correspond to 2.73% and 7.81% */ usePrefetchDecoder = (shareLongOffsets >= minShare); } #endif dctx->ddictIsCold = 0; #if !defined(ZSTD_FORCE_DECOMPRESS_SEQUENCES_SHORT) && \ !defined(ZSTD_FORCE_DECOMPRESS_SEQUENCES_LONG) if (usePrefetchDecoder) #endif #ifndef ZSTD_FORCE_DECOMPRESS_SEQUENCES_SHORT return ZSTD_decompressSequencesLong(dctx, dst, dstCapacity, ip, srcSize, nbSeq, isLongOffset); #endif #ifndef ZSTD_FORCE_DECOMPRESS_SEQUENCES_LONG /* else */ return ZSTD_decompressSequences(dctx, dst, dstCapacity, ip, srcSize, nbSeq, isLongOffset); #endif } } void ZSTD_checkContinuity(ZSTD_DCtx* dctx, const void* dst) { if (dst != dctx->previousDstEnd) { /* not contiguous */ dctx->dictEnd = dctx->previousDstEnd; dctx->virtualStart = (const char*)dst - ((const char*)(dctx->previousDstEnd) - (const char*)(dctx->prefixStart)); dctx->prefixStart = dst; dctx->previousDstEnd = dst; } } size_t ZSTD_decompressBlock(ZSTD_DCtx* dctx, void* dst, size_t dstCapacity, const void* src, size_t srcSize) { size_t dSize; ZSTD_checkContinuity(dctx, dst); dSize = ZSTD_decompressBlock_internal(dctx, dst, dstCapacity, src, srcSize, /* frame */ 0); dctx->previousDstEnd = (char*)dst + dSize; return dSize; }