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rocksdb/util/compression.h

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// Copyright (c) 2011-present, Facebook, Inc. All rights reserved.
// This source code is licensed under both the GPLv2 (found in the
// COPYING file in the root directory) and Apache 2.0 License
// (found in the LICENSE.Apache file in the root directory).
//
// Copyright (c) 2011 The LevelDB Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file. See the AUTHORS file for names of contributors.
//
#pragma once
#include <algorithm>
#include <limits>
#include <string>
#include "rocksdb/options.h"
#include "util/coding.h"
#ifdef SNAPPY
#include <snappy.h>
#endif
#ifdef ZLIB
#include <zlib.h>
#endif
#ifdef BZIP2
#include <bzlib.h>
#endif
#if defined(LZ4)
#include <lz4.h>
#include <lz4hc.h>
#endif
#if defined(ZSTD)
#include <zstd.h>
#if ZSTD_VERSION_NUMBER >= 800 // v0.8.0+
#include <zdict.h>
#endif // ZSTD_VERSION_NUMBER >= 800
#endif // ZSTD
#if defined(XPRESS)
#include "port/xpress.h"
#endif
namespace rocksdb {
inline bool Snappy_Supported() {
#ifdef SNAPPY
return true;
#else
return false;
#endif
}
inline bool Zlib_Supported() {
#ifdef ZLIB
return true;
#else
return false;
#endif
}
inline bool BZip2_Supported() {
#ifdef BZIP2
return true;
#else
return false;
#endif
}
inline bool LZ4_Supported() {
#ifdef LZ4
return true;
#else
return false;
#endif
}
inline bool XPRESS_Supported() {
#ifdef XPRESS
return true;
#else
return false;
#endif
}
inline bool ZSTD_Supported() {
#ifdef ZSTD
// ZSTD format is finalized since version 0.8.0.
return (ZSTD_versionNumber() >= 800);
#else
return false;
#endif
}
inline bool ZSTDNotFinal_Supported() {
#ifdef ZSTD
return true;
#else
return false;
#endif
}
inline bool CompressionTypeSupported(CompressionType compression_type) {
switch (compression_type) {
case kNoCompression:
return true;
case kSnappyCompression:
return Snappy_Supported();
case kZlibCompression:
return Zlib_Supported();
case kBZip2Compression:
return BZip2_Supported();
case kLZ4Compression:
return LZ4_Supported();
case kLZ4HCCompression:
return LZ4_Supported();
case kXpressCompression:
return XPRESS_Supported();
case kZSTDNotFinalCompression:
return ZSTDNotFinal_Supported();
case kZSTD:
return ZSTD_Supported();
default:
assert(false);
return false;
}
}
inline std::string CompressionTypeToString(CompressionType compression_type) {
switch (compression_type) {
case kNoCompression:
return "NoCompression";
case kSnappyCompression:
return "Snappy";
case kZlibCompression:
return "Zlib";
case kBZip2Compression:
return "BZip2";
case kLZ4Compression:
return "LZ4";
case kLZ4HCCompression:
return "LZ4HC";
case kXpressCompression:
return "Xpress";
case kZSTD:
return "ZSTD";
case kZSTDNotFinalCompression:
return "ZSTDNotFinal";
default:
assert(false);
return "";
}
}
// compress_format_version can have two values:
// 1 -- decompressed sizes for BZip2 and Zlib are not included in the compressed
// block. Also, decompressed sizes for LZ4 are encoded in platform-dependent
// way.
// 2 -- Zlib, BZip2 and LZ4 encode decompressed size as Varint32 just before the
// start of compressed block. Snappy format is the same as version 1.
inline bool Snappy_Compress(const CompressionOptions& /*opts*/,
const char* input, size_t length,
::std::string* output) {
#ifdef SNAPPY
output->resize(snappy::MaxCompressedLength(length));
size_t outlen;
snappy::RawCompress(input, length, &(*output)[0], &outlen);
output->resize(outlen);
return true;
#else
return false;
#endif
}
inline bool Snappy_GetUncompressedLength(const char* input, size_t length,
size_t* result) {
#ifdef SNAPPY
return snappy::GetUncompressedLength(input, length, result);
#else
return false;
#endif
}
inline bool Snappy_Uncompress(const char* input, size_t length,
char* output) {
#ifdef SNAPPY
return snappy::RawUncompress(input, length, output);
#else
return false;
#endif
}
namespace compression {
// returns size
inline size_t PutDecompressedSizeInfo(std::string* output, uint32_t length) {
PutVarint32(output, length);
return output->size();
}
inline bool GetDecompressedSizeInfo(const char** input_data,
size_t* input_length,
uint32_t* output_len) {
auto new_input_data =
GetVarint32Ptr(*input_data, *input_data + *input_length, output_len);
if (new_input_data == nullptr) {
return false;
}
*input_length -= (new_input_data - *input_data);
*input_data = new_input_data;
return true;
}
} // namespace compression
// compress_format_version == 1 -- decompressed size is not included in the
// block header
// compress_format_version == 2 -- decompressed size is included in the block
// header in varint32 format
// @param compression_dict Data for presetting the compression library's
// dictionary.
inline bool Zlib_Compress(const CompressionOptions& opts,
uint32_t compress_format_version, const char* input,
size_t length, ::std::string* output,
const Slice& compression_dict = Slice()) {
#ifdef ZLIB
if (length > std::numeric_limits<uint32_t>::max()) {
// Can't compress more than 4GB
return false;
}
size_t output_header_len = 0;
if (compress_format_version == 2) {
output_header_len = compression::PutDecompressedSizeInfo(
output, static_cast<uint32_t>(length));
}
// Resize output to be the plain data length.
// This may not be big enough if the compression actually expands data.
output->resize(output_header_len + length);
// The memLevel parameter specifies how much memory should be allocated for
// the internal compression state.
// memLevel=1 uses minimum memory but is slow and reduces compression ratio.
// memLevel=9 uses maximum memory for optimal speed.
// The default value is 8. See zconf.h for more details.
static const int memLevel = 8;
z_stream _stream;
memset(&_stream, 0, sizeof(z_stream));
int st = deflateInit2(&_stream, opts.level, Z_DEFLATED, opts.window_bits,
memLevel, opts.strategy);
if (st != Z_OK) {
return false;
}
if (compression_dict.size()) {
// Initialize the compression library's dictionary
st = deflateSetDictionary(
&_stream, reinterpret_cast<const Bytef*>(compression_dict.data()),
static_cast<unsigned int>(compression_dict.size()));
if (st != Z_OK) {
deflateEnd(&_stream);
return false;
}
}
// Compress the input, and put compressed data in output.
_stream.next_in = (Bytef *)input;
_stream.avail_in = static_cast<unsigned int>(length);
// Initialize the output size.
_stream.avail_out = static_cast<unsigned int>(length);
_stream.next_out = reinterpret_cast<Bytef*>(&(*output)[output_header_len]);
bool compressed = false;
st = deflate(&_stream, Z_FINISH);
if (st == Z_STREAM_END) {
compressed = true;
output->resize(output->size() - _stream.avail_out);
}
// The only return value we really care about is Z_STREAM_END.
// Z_OK means insufficient output space. This means the compression is
// bigger than decompressed size. Just fail the compression in that case.
deflateEnd(&_stream);
return compressed;
#else
return false;
#endif
}
// compress_format_version == 1 -- decompressed size is not included in the
// block header
// compress_format_version == 2 -- decompressed size is included in the block
// header in varint32 format
// @param compression_dict Data for presetting the compression library's
// dictionary.
inline char* Zlib_Uncompress(const char* input_data, size_t input_length,
int* decompress_size,
uint32_t compress_format_version,
const Slice& compression_dict = Slice(),
int windowBits = -14) {
#ifdef ZLIB
uint32_t output_len = 0;
if (compress_format_version == 2) {
if (!compression::GetDecompressedSizeInfo(&input_data, &input_length,
&output_len)) {
return nullptr;
}
} else {
// Assume the decompressed data size will 5x of compressed size, but round
// to the page size
size_t proposed_output_len = ((input_length * 5) & (~(4096 - 1))) + 4096;
output_len = static_cast<uint32_t>(
std::min(proposed_output_len,
static_cast<size_t>(std::numeric_limits<uint32_t>::max())));
}
z_stream _stream;
memset(&_stream, 0, sizeof(z_stream));
// For raw inflate, the windowBits should be -8..-15.
// If windowBits is bigger than zero, it will use either zlib
// header or gzip header. Adding 32 to it will do automatic detection.
int st = inflateInit2(&_stream,
windowBits > 0 ? windowBits + 32 : windowBits);
if (st != Z_OK) {
return nullptr;
}
if (compression_dict.size()) {
// Initialize the compression library's dictionary
st = inflateSetDictionary(
&_stream, reinterpret_cast<const Bytef*>(compression_dict.data()),
static_cast<unsigned int>(compression_dict.size()));
if (st != Z_OK) {
return nullptr;
}
}
_stream.next_in = (Bytef *)input_data;
_stream.avail_in = static_cast<unsigned int>(input_length);
char* output = new char[output_len];
_stream.next_out = (Bytef *)output;
_stream.avail_out = static_cast<unsigned int>(output_len);
bool done = false;
while (!done) {
st = inflate(&_stream, Z_SYNC_FLUSH);
switch (st) {
case Z_STREAM_END:
done = true;
break;
case Z_OK: {
// No output space. Increase the output space by 20%.
// We should never run out of output space if
// compress_format_version == 2
assert(compress_format_version != 2);
size_t old_sz = output_len;
uint32_t output_len_delta = output_len/5;
output_len += output_len_delta < 10 ? 10 : output_len_delta;
char* tmp = new char[output_len];
memcpy(tmp, output, old_sz);
delete[] output;
output = tmp;
// Set more output.
_stream.next_out = (Bytef *)(output + old_sz);
_stream.avail_out = static_cast<unsigned int>(output_len - old_sz);
break;
}
case Z_BUF_ERROR:
default:
delete[] output;
inflateEnd(&_stream);
return nullptr;
}
}
// If we encoded decompressed block size, we should have no bytes left
assert(compress_format_version != 2 || _stream.avail_out == 0);
*decompress_size = static_cast<int>(output_len - _stream.avail_out);
inflateEnd(&_stream);
return output;
#else
return nullptr;
#endif
}
// compress_format_version == 1 -- decompressed size is not included in the
// block header
// compress_format_version == 2 -- decompressed size is included in the block
// header in varint32 format
inline bool BZip2_Compress(const CompressionOptions& /*opts*/,
uint32_t compress_format_version, const char* input,
size_t length, ::std::string* output) {
#ifdef BZIP2
if (length > std::numeric_limits<uint32_t>::max()) {
// Can't compress more than 4GB
return false;
}
size_t output_header_len = 0;
if (compress_format_version == 2) {
output_header_len = compression::PutDecompressedSizeInfo(
output, static_cast<uint32_t>(length));
}
// Resize output to be the plain data length.
// This may not be big enough if the compression actually expands data.
output->resize(output_header_len + length);
bz_stream _stream;
memset(&_stream, 0, sizeof(bz_stream));
// Block size 1 is 100K.
// 0 is for silent.
// 30 is the default workFactor
int st = BZ2_bzCompressInit(&_stream, 1, 0, 30);
if (st != BZ_OK) {
return false;
}
// Compress the input, and put compressed data in output.
_stream.next_in = (char *)input;
_stream.avail_in = static_cast<unsigned int>(length);
// Initialize the output size.
_stream.avail_out = static_cast<unsigned int>(length);
_stream.next_out = reinterpret_cast<char*>(&(*output)[output_header_len]);
bool compressed = false;
st = BZ2_bzCompress(&_stream, BZ_FINISH);
if (st == BZ_STREAM_END) {
compressed = true;
output->resize(output->size() - _stream.avail_out);
}
// The only return value we really care about is BZ_STREAM_END.
// BZ_FINISH_OK means insufficient output space. This means the compression
// is bigger than decompressed size. Just fail the compression in that case.
BZ2_bzCompressEnd(&_stream);
return compressed;
#else
return false;
#endif
}
// compress_format_version == 1 -- decompressed size is not included in the
// block header
// compress_format_version == 2 -- decompressed size is included in the block
// header in varint32 format
inline char* BZip2_Uncompress(const char* input_data, size_t input_length,
int* decompress_size,
uint32_t compress_format_version) {
#ifdef BZIP2
uint32_t output_len = 0;
if (compress_format_version == 2) {
if (!compression::GetDecompressedSizeInfo(&input_data, &input_length,
&output_len)) {
return nullptr;
}
} else {
// Assume the decompressed data size will 5x of compressed size, but round
// to the next page size
size_t proposed_output_len = ((input_length * 5) & (~(4096 - 1))) + 4096;
output_len = static_cast<uint32_t>(
std::min(proposed_output_len,
static_cast<size_t>(std::numeric_limits<uint32_t>::max())));
}
bz_stream _stream;
memset(&_stream, 0, sizeof(bz_stream));
int st = BZ2_bzDecompressInit(&_stream, 0, 0);
if (st != BZ_OK) {
return nullptr;
}
_stream.next_in = (char *)input_data;
_stream.avail_in = static_cast<unsigned int>(input_length);
char* output = new char[output_len];
_stream.next_out = (char *)output;
_stream.avail_out = static_cast<unsigned int>(output_len);
bool done = false;
while (!done) {
st = BZ2_bzDecompress(&_stream);
switch (st) {
case BZ_STREAM_END:
done = true;
break;
case BZ_OK: {
// No output space. Increase the output space by 20%.
// We should never run out of output space if
// compress_format_version == 2
assert(compress_format_version != 2);
uint32_t old_sz = output_len;
output_len = output_len * 1.2;
char* tmp = new char[output_len];
memcpy(tmp, output, old_sz);
delete[] output;
output = tmp;
// Set more output.
_stream.next_out = (char *)(output + old_sz);
_stream.avail_out = static_cast<unsigned int>(output_len - old_sz);
break;
}
default:
delete[] output;
BZ2_bzDecompressEnd(&_stream);
return nullptr;
}
}
// If we encoded decompressed block size, we should have no bytes left
assert(compress_format_version != 2 || _stream.avail_out == 0);
*decompress_size = static_cast<int>(output_len - _stream.avail_out);
BZ2_bzDecompressEnd(&_stream);
return output;
#else
return nullptr;
#endif
}
// compress_format_version == 1 -- decompressed size is included in the
// block header using memcpy, which makes database non-portable)
// compress_format_version == 2 -- decompressed size is included in the block
// header in varint32 format
// @param compression_dict Data for presetting the compression library's
// dictionary.
inline bool LZ4_Compress(const CompressionOptions& /*opts*/,
uint32_t compress_format_version, const char* input,
size_t length, ::std::string* output,
const Slice compression_dict = Slice()) {
#ifdef LZ4
if (length > std::numeric_limits<uint32_t>::max()) {
// Can't compress more than 4GB
return false;
}
size_t output_header_len = 0;
if (compress_format_version == 2) {
// new encoding, using varint32 to store size information
output_header_len = compression::PutDecompressedSizeInfo(
output, static_cast<uint32_t>(length));
} else {
// legacy encoding, which is not really portable (depends on big/little
// endianness)
output_header_len = 8;
output->resize(output_header_len);
char* p = const_cast<char*>(output->c_str());
memcpy(p, &length, sizeof(length));
}
int compress_bound = LZ4_compressBound(static_cast<int>(length));
output->resize(static_cast<size_t>(output_header_len + compress_bound));
int outlen;
#if LZ4_VERSION_NUMBER >= 10400 // r124+
LZ4_stream_t* stream = LZ4_createStream();
if (compression_dict.size()) {
LZ4_loadDict(stream, compression_dict.data(),
static_cast<int>(compression_dict.size()));
}
#if LZ4_VERSION_NUMBER >= 10700 // r129+
outlen = LZ4_compress_fast_continue(
stream, input, &(*output)[output_header_len], static_cast<int>(length),
compress_bound, 1);
#else // up to r128
outlen = LZ4_compress_limitedOutput_continue(
stream, input, &(*output)[output_header_len], static_cast<int>(length),
compress_bound);
#endif
LZ4_freeStream(stream);
#else // up to r123
outlen = LZ4_compress_limitedOutput(input, &(*output)[output_header_len],
static_cast<int>(length), compress_bound);
#endif // LZ4_VERSION_NUMBER >= 10400
if (outlen == 0) {
return false;
}
output->resize(static_cast<size_t>(output_header_len + outlen));
return true;
#else // LZ4
return false;
#endif
}
// compress_format_version == 1 -- decompressed size is included in the
// block header using memcpy, which makes database non-portable)
// compress_format_version == 2 -- decompressed size is included in the block
// header in varint32 format
// @param compression_dict Data for presetting the compression library's
// dictionary.
inline char* LZ4_Uncompress(const char* input_data, size_t input_length,
int* decompress_size,
uint32_t compress_format_version,
const Slice& compression_dict = Slice()) {
#ifdef LZ4
uint32_t output_len = 0;
if (compress_format_version == 2) {
// new encoding, using varint32 to store size information
if (!compression::GetDecompressedSizeInfo(&input_data, &input_length,
&output_len)) {
return nullptr;
}
} else {
// legacy encoding, which is not really portable (depends on big/little
// endianness)
if (input_length < 8) {
return nullptr;
}
memcpy(&output_len, input_data, sizeof(output_len));
input_length -= 8;
input_data += 8;
}
char* output = new char[output_len];
#if LZ4_VERSION_NUMBER >= 10400 // r124+
LZ4_streamDecode_t* stream = LZ4_createStreamDecode();
if (compression_dict.size()) {
LZ4_setStreamDecode(stream, compression_dict.data(),
static_cast<int>(compression_dict.size()));
}
*decompress_size = LZ4_decompress_safe_continue(
stream, input_data, output, static_cast<int>(input_length),
static_cast<int>(output_len));
LZ4_freeStreamDecode(stream);
#else // up to r123
*decompress_size =
LZ4_decompress_safe(input_data, output, static_cast<int>(input_length),
static_cast<int>(output_len));
#endif // LZ4_VERSION_NUMBER >= 10400
if (*decompress_size < 0) {
delete[] output;
return nullptr;
}
assert(*decompress_size == static_cast<int>(output_len));
return output;
#else // LZ4
return nullptr;
#endif
}
// compress_format_version == 1 -- decompressed size is included in the
// block header using memcpy, which makes database non-portable)
// compress_format_version == 2 -- decompressed size is included in the block
// header in varint32 format
// @param compression_dict Data for presetting the compression library's
// dictionary.
inline bool LZ4HC_Compress(const CompressionOptions& opts,
uint32_t compress_format_version, const char* input,
size_t length, ::std::string* output,
const Slice& compression_dict = Slice()) {
#ifdef LZ4
if (length > std::numeric_limits<uint32_t>::max()) {
// Can't compress more than 4GB
return false;
}
size_t output_header_len = 0;
if (compress_format_version == 2) {
// new encoding, using varint32 to store size information
output_header_len = compression::PutDecompressedSizeInfo(
output, static_cast<uint32_t>(length));
} else {
// legacy encoding, which is not really portable (depends on big/little
// endianness)
output_header_len = 8;
output->resize(output_header_len);
char* p = const_cast<char*>(output->c_str());
memcpy(p, &length, sizeof(length));
}
int compress_bound = LZ4_compressBound(static_cast<int>(length));
output->resize(static_cast<size_t>(output_header_len + compress_bound));
int outlen;
#if LZ4_VERSION_NUMBER >= 10400 // r124+
LZ4_streamHC_t* stream = LZ4_createStreamHC();
LZ4_resetStreamHC(stream, opts.level);
const char* compression_dict_data =
compression_dict.size() > 0 ? compression_dict.data() : nullptr;
size_t compression_dict_size = compression_dict.size();
LZ4_loadDictHC(stream, compression_dict_data,
static_cast<int>(compression_dict_size));
#if LZ4_VERSION_NUMBER >= 10700 // r129+
outlen =
LZ4_compress_HC_continue(stream, input, &(*output)[output_header_len],
static_cast<int>(length), compress_bound);
#else // r124-r128
outlen = LZ4_compressHC_limitedOutput_continue(
stream, input, &(*output)[output_header_len], static_cast<int>(length),
compress_bound);
#endif // LZ4_VERSION_NUMBER >= 10700
LZ4_freeStreamHC(stream);
#elif LZ4_VERSION_MAJOR // r113-r123
outlen = LZ4_compressHC2_limitedOutput(input, &(*output)[output_header_len],
static_cast<int>(length),
compress_bound, opts.level);
#else // up to r112
outlen =
LZ4_compressHC_limitedOutput(input, &(*output)[output_header_len],
static_cast<int>(length), compress_bound);
#endif // LZ4_VERSION_NUMBER >= 10400
if (outlen == 0) {
return false;
}
output->resize(static_cast<size_t>(output_header_len + outlen));
return true;
#else // LZ4
return false;
#endif
}
#ifdef XPRESS
inline bool XPRESS_Compress(const char* input, size_t length,
std::string* output) {
return port::xpress::Compress(input, length, output);
}
#else
inline bool XPRESS_Compress(const char* /*input*/, size_t /*length*/,
std::string* /*output*/) {
return false;
}
#endif
#ifdef XPRESS
inline char* XPRESS_Uncompress(const char* input_data,
size_t input_length,
int* decompress_size) {
return port::xpress::Decompress(input_data, input_length, decompress_size);
}
#else
inline char* XPRESS_Uncompress(const char* /*input_data*/,
size_t /*input_length*/,
int* /*decompress_size*/) {
return nullptr;
}
#endif
// @param compression_dict Data for presetting the compression library's
// dictionary.
inline bool ZSTD_Compress(const CompressionOptions& opts, const char* input,
size_t length, ::std::string* output,
const Slice& compression_dict = Slice()) {
#ifdef ZSTD
if (length > std::numeric_limits<uint32_t>::max()) {
// Can't compress more than 4GB
return false;
}
size_t output_header_len = compression::PutDecompressedSizeInfo(
output, static_cast<uint32_t>(length));
size_t compressBound = ZSTD_compressBound(length);
output->resize(static_cast<size_t>(output_header_len + compressBound));
size_t outlen;
#if ZSTD_VERSION_NUMBER >= 500 // v0.5.0+
ZSTD_CCtx* context = ZSTD_createCCtx();
outlen = ZSTD_compress_usingDict(
context, &(*output)[output_header_len], compressBound, input, length,
compression_dict.data(), compression_dict.size(), opts.level);
ZSTD_freeCCtx(context);
#else // up to v0.4.x
outlen = ZSTD_compress(&(*output)[output_header_len], compressBound, input,
length, opts.level);
#endif // ZSTD_VERSION_NUMBER >= 500
if (outlen == 0) {
return false;
}
output->resize(output_header_len + outlen);
return true;
#else // ZSTD
return false;
#endif
}
// @param compression_dict Data for presetting the compression library's
// dictionary.
inline char* ZSTD_Uncompress(const char* input_data, size_t input_length,
int* decompress_size,
const Slice& compression_dict = Slice()) {
#ifdef ZSTD
uint32_t output_len = 0;
if (!compression::GetDecompressedSizeInfo(&input_data, &input_length,
&output_len)) {
return nullptr;
}
char* output = new char[output_len];
size_t actual_output_length;
#if ZSTD_VERSION_NUMBER >= 500 // v0.5.0+
ZSTD_DCtx* context = ZSTD_createDCtx();
actual_output_length = ZSTD_decompress_usingDict(
context, output, output_len, input_data, input_length,
compression_dict.data(), compression_dict.size());
ZSTD_freeDCtx(context);
#else // up to v0.4.x
actual_output_length =
ZSTD_decompress(output, output_len, input_data, input_length);
#endif // ZSTD_VERSION_NUMBER >= 500
assert(actual_output_length == output_len);
*decompress_size = static_cast<int>(actual_output_length);
return output;
#else // ZSTD
return nullptr;
#endif
}
inline std::string ZSTD_TrainDictionary(const std::string& samples,
const std::vector<size_t>& sample_lens,
size_t max_dict_bytes) {
// Dictionary trainer is available since v0.6.1, but ZSTD was marked stable
// only since v0.8.0. For now we enable the feature in stable versions only.
#if ZSTD_VERSION_NUMBER >= 800 // v0.8.0+
std::string dict_data(max_dict_bytes, '\0');
size_t dict_len = ZDICT_trainFromBuffer(
&dict_data[0], max_dict_bytes, &samples[0], &sample_lens[0],
static_cast<unsigned>(sample_lens.size()));
if (ZDICT_isError(dict_len)) {
return "";
}
assert(dict_len <= max_dict_bytes);
dict_data.resize(dict_len);
return dict_data;
#else // up to v0.7.x
assert(false);
return "";
#endif // ZSTD_VERSION_NUMBER >= 800
}
inline std::string ZSTD_TrainDictionary(const std::string& samples,
size_t sample_len_shift,
size_t max_dict_bytes) {
// Dictionary trainer is available since v0.6.1, but ZSTD was marked stable
// only since v0.8.0. For now we enable the feature in stable versions only.
#if ZSTD_VERSION_NUMBER >= 800 // v0.8.0+
// skips potential partial sample at the end of "samples"
size_t num_samples = samples.size() >> sample_len_shift;
std::vector<size_t> sample_lens(num_samples, size_t(1) << sample_len_shift);
return ZSTD_TrainDictionary(samples, sample_lens, max_dict_bytes);
#else // up to v0.7.x
assert(false);
return "";
#endif // ZSTD_VERSION_NUMBER >= 800
}
} // namespace rocksdb