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Diffstat (limited to '')
| -rw-r--r-- | contrib/zstd/zstd_compress_literals.c | 235 |
1 files changed, 235 insertions, 0 deletions
diff --git a/contrib/zstd/zstd_compress_literals.c b/contrib/zstd/zstd_compress_literals.c new file mode 100644 index 0000000..bfd4f11 --- /dev/null +++ b/contrib/zstd/zstd_compress_literals.c @@ -0,0 +1,235 @@ +/* + * Copyright (c) Meta Platforms, Inc. and affiliates. + * 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. + */ + + /*-************************************* + * Dependencies + ***************************************/ +#include "zstd_compress_literals.h" + + +/* ************************************************************** +* Debug Traces +****************************************************************/ +#if DEBUGLEVEL >= 2 + +static size_t showHexa(const void* src, size_t srcSize) +{ + const BYTE* const ip = (const BYTE*)src; + size_t u; + for (u=0; u<srcSize; u++) { + RAWLOG(5, " %02X", ip[u]); (void)ip; + } + RAWLOG(5, " \n"); + return srcSize; +} + +#endif + + +/* ************************************************************** +* Literals compression - special cases +****************************************************************/ +size_t ZSTD_noCompressLiterals (void* dst, size_t dstCapacity, const void* src, size_t srcSize) +{ + BYTE* const ostart = (BYTE*)dst; + U32 const flSize = 1 + (srcSize>31) + (srcSize>4095); + + DEBUGLOG(5, "ZSTD_noCompressLiterals: srcSize=%zu, dstCapacity=%zu", srcSize, dstCapacity); + + RETURN_ERROR_IF(srcSize + flSize > dstCapacity, dstSize_tooSmall, ""); + + switch(flSize) + { + case 1: /* 2 - 1 - 5 */ + ostart[0] = (BYTE)((U32)set_basic + (srcSize<<3)); + break; + case 2: /* 2 - 2 - 12 */ + MEM_writeLE16(ostart, (U16)((U32)set_basic + (1<<2) + (srcSize<<4))); + break; + case 3: /* 2 - 2 - 20 */ + MEM_writeLE32(ostart, (U32)((U32)set_basic + (3<<2) + (srcSize<<4))); + break; + default: /* not necessary : flSize is {1,2,3} */ + assert(0); + } + + ZSTD_memcpy(ostart + flSize, src, srcSize); + DEBUGLOG(5, "Raw (uncompressed) literals: %u -> %u", (U32)srcSize, (U32)(srcSize + flSize)); + return srcSize + flSize; +} + +static int allBytesIdentical(const void* src, size_t srcSize) +{ + assert(srcSize >= 1); + assert(src != NULL); + { const BYTE b = ((const BYTE*)src)[0]; + size_t p; + for (p=1; p<srcSize; p++) { + if (((const BYTE*)src)[p] != b) return 0; + } + return 1; + } +} + +size_t ZSTD_compressRleLiteralsBlock (void* dst, size_t dstCapacity, const void* src, size_t srcSize) +{ + BYTE* const ostart = (BYTE*)dst; + U32 const flSize = 1 + (srcSize>31) + (srcSize>4095); + + assert(dstCapacity >= 4); (void)dstCapacity; + assert(allBytesIdentical(src, srcSize)); + + switch(flSize) + { + case 1: /* 2 - 1 - 5 */ + ostart[0] = (BYTE)((U32)set_rle + (srcSize<<3)); + break; + case 2: /* 2 - 2 - 12 */ + MEM_writeLE16(ostart, (U16)((U32)set_rle + (1<<2) + (srcSize<<4))); + break; + case 3: /* 2 - 2 - 20 */ + MEM_writeLE32(ostart, (U32)((U32)set_rle + (3<<2) + (srcSize<<4))); + break; + default: /* not necessary : flSize is {1,2,3} */ + assert(0); + } + + ostart[flSize] = *(const BYTE*)src; + DEBUGLOG(5, "RLE : Repeated Literal (%02X: %u times) -> %u bytes encoded", ((const BYTE*)src)[0], (U32)srcSize, (U32)flSize + 1); + return flSize+1; +} + +/* ZSTD_minLiteralsToCompress() : + * returns minimal amount of literals + * for literal compression to even be attempted. + * Minimum is made tighter as compression strategy increases. + */ +static size_t +ZSTD_minLiteralsToCompress(ZSTD_strategy strategy, HUF_repeat huf_repeat) +{ + assert((int)strategy >= 0); + assert((int)strategy <= 9); + /* btultra2 : min 8 bytes; + * then 2x larger for each successive compression strategy + * max threshold 64 bytes */ + { int const shift = MIN(9-(int)strategy, 3); + size_t const mintc = (huf_repeat == HUF_repeat_valid) ? 6 : (size_t)8 << shift; + DEBUGLOG(7, "minLiteralsToCompress = %zu", mintc); + return mintc; + } +} + +size_t ZSTD_compressLiterals ( + void* dst, size_t dstCapacity, + const void* src, size_t srcSize, + void* entropyWorkspace, size_t entropyWorkspaceSize, + const ZSTD_hufCTables_t* prevHuf, + ZSTD_hufCTables_t* nextHuf, + ZSTD_strategy strategy, + int disableLiteralCompression, + int suspectUncompressible, + int bmi2) +{ + size_t const lhSize = 3 + (srcSize >= 1 KB) + (srcSize >= 16 KB); + BYTE* const ostart = (BYTE*)dst; + U32 singleStream = srcSize < 256; + symbolEncodingType_e hType = set_compressed; + size_t cLitSize; + + DEBUGLOG(5,"ZSTD_compressLiterals (disableLiteralCompression=%i, srcSize=%u, dstCapacity=%zu)", + disableLiteralCompression, (U32)srcSize, dstCapacity); + + DEBUGLOG(6, "Completed literals listing (%zu bytes)", showHexa(src, srcSize)); + + /* Prepare nextEntropy assuming reusing the existing table */ + ZSTD_memcpy(nextHuf, prevHuf, sizeof(*prevHuf)); + + if (disableLiteralCompression) + return ZSTD_noCompressLiterals(dst, dstCapacity, src, srcSize); + + /* if too small, don't even attempt compression (speed opt) */ + if (srcSize < ZSTD_minLiteralsToCompress(strategy, prevHuf->repeatMode)) + return ZSTD_noCompressLiterals(dst, dstCapacity, src, srcSize); + + RETURN_ERROR_IF(dstCapacity < lhSize+1, dstSize_tooSmall, "not enough space for compression"); + { HUF_repeat repeat = prevHuf->repeatMode; + int const flags = 0 + | (bmi2 ? HUF_flags_bmi2 : 0) + | (strategy < ZSTD_lazy && srcSize <= 1024 ? HUF_flags_preferRepeat : 0) + | (strategy >= HUF_OPTIMAL_DEPTH_THRESHOLD ? HUF_flags_optimalDepth : 0) + | (suspectUncompressible ? HUF_flags_suspectUncompressible : 0); + + typedef size_t (*huf_compress_f)(void*, size_t, const void*, size_t, unsigned, unsigned, void*, size_t, HUF_CElt*, HUF_repeat*, int); + huf_compress_f huf_compress; + if (repeat == HUF_repeat_valid && lhSize == 3) singleStream = 1; + huf_compress = singleStream ? HUF_compress1X_repeat : HUF_compress4X_repeat; + cLitSize = huf_compress(ostart+lhSize, dstCapacity-lhSize, + src, srcSize, + HUF_SYMBOLVALUE_MAX, LitHufLog, + entropyWorkspace, entropyWorkspaceSize, + (HUF_CElt*)nextHuf->CTable, + &repeat, flags); + DEBUGLOG(5, "%zu literals compressed into %zu bytes (before header)", srcSize, cLitSize); + if (repeat != HUF_repeat_none) { + /* reused the existing table */ + DEBUGLOG(5, "reusing statistics from previous huffman block"); + hType = set_repeat; + } + } + + { size_t const minGain = ZSTD_minGain(srcSize, strategy); + if ((cLitSize==0) || (cLitSize >= srcSize - minGain) || ERR_isError(cLitSize)) { + ZSTD_memcpy(nextHuf, prevHuf, sizeof(*prevHuf)); + return ZSTD_noCompressLiterals(dst, dstCapacity, src, srcSize); + } } + if (cLitSize==1) { + /* A return value of 1 signals that the alphabet consists of a single symbol. + * However, in some rare circumstances, it could be the compressed size (a single byte). + * For that outcome to have a chance to happen, it's necessary that `srcSize < 8`. + * (it's also necessary to not generate statistics). + * Therefore, in such a case, actively check that all bytes are identical. */ + if ((srcSize >= 8) || allBytesIdentical(src, srcSize)) { + ZSTD_memcpy(nextHuf, prevHuf, sizeof(*prevHuf)); + return ZSTD_compressRleLiteralsBlock(dst, dstCapacity, src, srcSize); + } } + + if (hType == set_compressed) { + /* using a newly constructed table */ + nextHuf->repeatMode = HUF_repeat_check; + } + + /* Build header */ + switch(lhSize) + { + case 3: /* 2 - 2 - 10 - 10 */ + if (!singleStream) assert(srcSize >= MIN_LITERALS_FOR_4_STREAMS); + { U32 const lhc = hType + ((U32)(!singleStream) << 2) + ((U32)srcSize<<4) + ((U32)cLitSize<<14); + MEM_writeLE24(ostart, lhc); + break; + } + case 4: /* 2 - 2 - 14 - 14 */ + assert(srcSize >= MIN_LITERALS_FOR_4_STREAMS); + { U32 const lhc = hType + (2 << 2) + ((U32)srcSize<<4) + ((U32)cLitSize<<18); + MEM_writeLE32(ostart, lhc); + break; + } + case 5: /* 2 - 2 - 18 - 18 */ + assert(srcSize >= MIN_LITERALS_FOR_4_STREAMS); + { U32 const lhc = hType + (3 << 2) + ((U32)srcSize<<4) + ((U32)cLitSize<<22); + MEM_writeLE32(ostart, lhc); + ostart[4] = (BYTE)(cLitSize >> 10); + break; + } + default: /* not possible : lhSize is {3,4,5} */ + assert(0); + } + DEBUGLOG(5, "Compressed literals: %u -> %u", (U32)srcSize, (U32)(lhSize+cLitSize)); + return lhSize+cLitSize; +} |