236 lines
8.9 KiB
C
236 lines
8.9 KiB
C
/*
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* Copyright (c) Meta Platforms, Inc. and affiliates.
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* All rights reserved.
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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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/*-*************************************
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* Dependencies
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***************************************/
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#include "zstd_compress_literals.h"
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/* **************************************************************
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* Debug Traces
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****************************************************************/
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#if DEBUGLEVEL >= 2
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static size_t showHexa(const void* src, size_t srcSize)
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{
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const BYTE* const ip = (const BYTE*)src;
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size_t u;
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for (u=0; u<srcSize; u++) {
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RAWLOG(5, " %02X", ip[u]); (void)ip;
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}
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RAWLOG(5, " \n");
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return srcSize;
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}
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#endif
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/* **************************************************************
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* Literals compression - special cases
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****************************************************************/
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size_t ZSTD_noCompressLiterals (void* dst, size_t dstCapacity, const void* src, size_t srcSize)
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{
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BYTE* const ostart = (BYTE*)dst;
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U32 const flSize = 1 + (srcSize>31) + (srcSize>4095);
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DEBUGLOG(5, "ZSTD_noCompressLiterals: srcSize=%zu, dstCapacity=%zu", srcSize, dstCapacity);
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RETURN_ERROR_IF(srcSize + flSize > dstCapacity, dstSize_tooSmall, "");
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switch(flSize)
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{
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case 1: /* 2 - 1 - 5 */
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ostart[0] = (BYTE)((U32)set_basic + (srcSize<<3));
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break;
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case 2: /* 2 - 2 - 12 */
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MEM_writeLE16(ostart, (U16)((U32)set_basic + (1<<2) + (srcSize<<4)));
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break;
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case 3: /* 2 - 2 - 20 */
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MEM_writeLE32(ostart, (U32)((U32)set_basic + (3<<2) + (srcSize<<4)));
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break;
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default: /* not necessary : flSize is {1,2,3} */
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assert(0);
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}
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ZSTD_memcpy(ostart + flSize, src, srcSize);
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DEBUGLOG(5, "Raw (uncompressed) literals: %u -> %u", (U32)srcSize, (U32)(srcSize + flSize));
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return srcSize + flSize;
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}
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static int allBytesIdentical(const void* src, size_t srcSize)
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{
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assert(srcSize >= 1);
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assert(src != NULL);
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{ const BYTE b = ((const BYTE*)src)[0];
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size_t p;
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for (p=1; p<srcSize; p++) {
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if (((const BYTE*)src)[p] != b) return 0;
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}
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return 1;
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}
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}
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size_t ZSTD_compressRleLiteralsBlock (void* dst, size_t dstCapacity, const void* src, size_t srcSize)
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{
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BYTE* const ostart = (BYTE*)dst;
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U32 const flSize = 1 + (srcSize>31) + (srcSize>4095);
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assert(dstCapacity >= 4); (void)dstCapacity;
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assert(allBytesIdentical(src, srcSize));
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switch(flSize)
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{
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case 1: /* 2 - 1 - 5 */
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ostart[0] = (BYTE)((U32)set_rle + (srcSize<<3));
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break;
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case 2: /* 2 - 2 - 12 */
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MEM_writeLE16(ostart, (U16)((U32)set_rle + (1<<2) + (srcSize<<4)));
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break;
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case 3: /* 2 - 2 - 20 */
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MEM_writeLE32(ostart, (U32)((U32)set_rle + (3<<2) + (srcSize<<4)));
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break;
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default: /* not necessary : flSize is {1,2,3} */
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assert(0);
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}
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ostart[flSize] = *(const BYTE*)src;
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DEBUGLOG(5, "RLE : Repeated Literal (%02X: %u times) -> %u bytes encoded", ((const BYTE*)src)[0], (U32)srcSize, (U32)flSize + 1);
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return flSize+1;
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}
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/* ZSTD_minLiteralsToCompress() :
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* returns minimal amount of literals
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* for literal compression to even be attempted.
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* Minimum is made tighter as compression strategy increases.
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*/
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static size_t
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ZSTD_minLiteralsToCompress(ZSTD_strategy strategy, HUF_repeat huf_repeat)
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{
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assert((int)strategy >= 0);
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assert((int)strategy <= 9);
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/* btultra2 : min 8 bytes;
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* then 2x larger for each successive compression strategy
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* max threshold 64 bytes */
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{ int const shift = MIN(9-(int)strategy, 3);
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size_t const mintc = (huf_repeat == HUF_repeat_valid) ? 6 : (size_t)8 << shift;
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DEBUGLOG(7, "minLiteralsToCompress = %zu", mintc);
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return mintc;
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}
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}
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size_t ZSTD_compressLiterals (
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void* dst, size_t dstCapacity,
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const void* src, size_t srcSize,
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void* entropyWorkspace, size_t entropyWorkspaceSize,
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const ZSTD_hufCTables_t* prevHuf,
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ZSTD_hufCTables_t* nextHuf,
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ZSTD_strategy strategy,
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int disableLiteralCompression,
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int suspectUncompressible,
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int bmi2)
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{
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size_t const lhSize = 3 + (srcSize >= 1 KB) + (srcSize >= 16 KB);
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BYTE* const ostart = (BYTE*)dst;
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U32 singleStream = srcSize < 256;
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symbolEncodingType_e hType = set_compressed;
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size_t cLitSize;
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DEBUGLOG(5,"ZSTD_compressLiterals (disableLiteralCompression=%i, srcSize=%u, dstCapacity=%zu)",
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disableLiteralCompression, (U32)srcSize, dstCapacity);
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DEBUGLOG(6, "Completed literals listing (%zu bytes)", showHexa(src, srcSize));
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/* Prepare nextEntropy assuming reusing the existing table */
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ZSTD_memcpy(nextHuf, prevHuf, sizeof(*prevHuf));
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if (disableLiteralCompression)
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return ZSTD_noCompressLiterals(dst, dstCapacity, src, srcSize);
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/* if too small, don't even attempt compression (speed opt) */
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if (srcSize < ZSTD_minLiteralsToCompress(strategy, prevHuf->repeatMode))
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return ZSTD_noCompressLiterals(dst, dstCapacity, src, srcSize);
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RETURN_ERROR_IF(dstCapacity < lhSize+1, dstSize_tooSmall, "not enough space for compression");
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{ HUF_repeat repeat = prevHuf->repeatMode;
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int const flags = 0
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| (bmi2 ? HUF_flags_bmi2 : 0)
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| (strategy < ZSTD_lazy && srcSize <= 1024 ? HUF_flags_preferRepeat : 0)
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| (strategy >= HUF_OPTIMAL_DEPTH_THRESHOLD ? HUF_flags_optimalDepth : 0)
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| (suspectUncompressible ? HUF_flags_suspectUncompressible : 0);
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typedef size_t (*huf_compress_f)(void*, size_t, const void*, size_t, unsigned, unsigned, void*, size_t, HUF_CElt*, HUF_repeat*, int);
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huf_compress_f huf_compress;
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if (repeat == HUF_repeat_valid && lhSize == 3) singleStream = 1;
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huf_compress = singleStream ? HUF_compress1X_repeat : HUF_compress4X_repeat;
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cLitSize = huf_compress(ostart+lhSize, dstCapacity-lhSize,
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src, srcSize,
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HUF_SYMBOLVALUE_MAX, LitHufLog,
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entropyWorkspace, entropyWorkspaceSize,
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(HUF_CElt*)nextHuf->CTable,
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&repeat, flags);
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DEBUGLOG(5, "%zu literals compressed into %zu bytes (before header)", srcSize, cLitSize);
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if (repeat != HUF_repeat_none) {
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/* reused the existing table */
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DEBUGLOG(5, "reusing statistics from previous huffman block");
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hType = set_repeat;
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}
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}
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{ size_t const minGain = ZSTD_minGain(srcSize, strategy);
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if ((cLitSize==0) || (cLitSize >= srcSize - minGain) || ERR_isError(cLitSize)) {
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ZSTD_memcpy(nextHuf, prevHuf, sizeof(*prevHuf));
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return ZSTD_noCompressLiterals(dst, dstCapacity, src, srcSize);
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} }
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if (cLitSize==1) {
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/* A return value of 1 signals that the alphabet consists of a single symbol.
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* However, in some rare circumstances, it could be the compressed size (a single byte).
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* For that outcome to have a chance to happen, it's necessary that `srcSize < 8`.
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* (it's also necessary to not generate statistics).
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* Therefore, in such a case, actively check that all bytes are identical. */
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if ((srcSize >= 8) || allBytesIdentical(src, srcSize)) {
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ZSTD_memcpy(nextHuf, prevHuf, sizeof(*prevHuf));
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return ZSTD_compressRleLiteralsBlock(dst, dstCapacity, src, srcSize);
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} }
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if (hType == set_compressed) {
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/* using a newly constructed table */
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nextHuf->repeatMode = HUF_repeat_check;
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}
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/* Build header */
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switch(lhSize)
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{
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case 3: /* 2 - 2 - 10 - 10 */
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if (!singleStream) assert(srcSize >= MIN_LITERALS_FOR_4_STREAMS);
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{ U32 const lhc = hType + ((U32)(!singleStream) << 2) + ((U32)srcSize<<4) + ((U32)cLitSize<<14);
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MEM_writeLE24(ostart, lhc);
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break;
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}
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case 4: /* 2 - 2 - 14 - 14 */
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assert(srcSize >= MIN_LITERALS_FOR_4_STREAMS);
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{ U32 const lhc = hType + (2 << 2) + ((U32)srcSize<<4) + ((U32)cLitSize<<18);
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MEM_writeLE32(ostart, lhc);
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break;
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}
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case 5: /* 2 - 2 - 18 - 18 */
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assert(srcSize >= MIN_LITERALS_FOR_4_STREAMS);
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{ U32 const lhc = hType + (3 << 2) + ((U32)srcSize<<4) + ((U32)cLitSize<<22);
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MEM_writeLE32(ostart, lhc);
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ostart[4] = (BYTE)(cLitSize >> 10);
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break;
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}
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default: /* not possible : lhSize is {3,4,5} */
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assert(0);
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}
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DEBUGLOG(5, "Compressed literals: %u -> %u", (U32)srcSize, (U32)(lhSize+cLitSize));
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return lhSize+cLitSize;
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}
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