mirror of
https://github.com/facebook/rocksdb.git
synced 2024-11-26 16:30:56 +00:00
31da5e34c1
Summary: Based on https://github.com/facebook/rocksdb/issues/6648 (CLA Signed), but heavily modified / extended: * Implicit capture of this via [=] deprecated in C++20, and [=,this] not standard before C++20 -> now using explicit capture lists * Implicit copy operator deprecated in gcc 9 -> add explicit '= default' definition * std::random_shuffle deprecated in C++17 and removed in C++20 -> migrated to a replacement in RocksDB random.h API * Add the ability to build with different std version though -DCMAKE_CXX_STANDARD=11/14/17/20 on the cmake command line * Minimal rebuild flag of MSVC is deprecated and is forbidden with /std:c++latest (C++20) * Added MSVC 2019 C++11 & MSVC 2019 C++20 in AppVeyor * Added GCC 9 C++11 & GCC9 C++20 in Travis Pull Request resolved: https://github.com/facebook/rocksdb/pull/6697 Test Plan: make check and CI Reviewed By: cheng-chang Differential Revision: D21020318 Pulled By: pdillinger fbshipit-source-id: 12311be5dbd8675a0e2c817f7ec50fa11c18ab91
84 lines
3 KiB
C++
84 lines
3 KiB
C++
// 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.
|
|
|
|
#include "util/hash.h"
|
|
#include <string.h>
|
|
#include "port/lang.h"
|
|
#include "util/coding.h"
|
|
#include "util/xxhash.h"
|
|
|
|
namespace ROCKSDB_NAMESPACE {
|
|
|
|
uint32_t Hash(const char* data, size_t n, uint32_t seed) {
|
|
// MurmurHash1 - fast but mediocre quality
|
|
// https://github.com/aappleby/smhasher/wiki/MurmurHash1
|
|
//
|
|
const uint32_t m = 0xc6a4a793;
|
|
const uint32_t r = 24;
|
|
const char* limit = data + n;
|
|
uint32_t h = static_cast<uint32_t>(seed ^ (n * m));
|
|
|
|
// Pick up four bytes at a time
|
|
while (data + 4 <= limit) {
|
|
uint32_t w = DecodeFixed32(data);
|
|
data += 4;
|
|
h += w;
|
|
h *= m;
|
|
h ^= (h >> 16);
|
|
}
|
|
|
|
// Pick up remaining bytes
|
|
switch (limit - data) {
|
|
// Note: The original hash implementation used data[i] << shift, which
|
|
// promotes the char to int and then performs the shift. If the char is
|
|
// negative, the shift is undefined behavior in C++. The hash algorithm is
|
|
// part of the format definition, so we cannot change it; to obtain the same
|
|
// behavior in a legal way we just cast to uint32_t, which will do
|
|
// sign-extension. To guarantee compatibility with architectures where chars
|
|
// are unsigned we first cast the char to int8_t.
|
|
case 3:
|
|
h += static_cast<uint32_t>(static_cast<int8_t>(data[2])) << 16;
|
|
FALLTHROUGH_INTENDED;
|
|
case 2:
|
|
h += static_cast<uint32_t>(static_cast<int8_t>(data[1])) << 8;
|
|
FALLTHROUGH_INTENDED;
|
|
case 1:
|
|
h += static_cast<uint32_t>(static_cast<int8_t>(data[0]));
|
|
h *= m;
|
|
h ^= (h >> r);
|
|
break;
|
|
}
|
|
return h;
|
|
}
|
|
|
|
// We are standardizing on a preview release of XXH3, because that's
|
|
// the best available at time of standardizing.
|
|
//
|
|
// In testing (mostly Intel Skylake), this hash function is much more
|
|
// thorough than Hash32 and is almost universally faster. Hash() only
|
|
// seems faster when passing runtime-sized keys of the same small size
|
|
// (less than about 24 bytes) thousands of times in a row; this seems
|
|
// to allow the branch predictor to work some magic. XXH3's speed is
|
|
// much less dependent on branch prediction.
|
|
//
|
|
// Hashing with a prefix extractor is potentially a common case of
|
|
// hashing objects of small, predictable size. We could consider
|
|
// bundling hash functions specialized for particular lengths with
|
|
// the prefix extractors.
|
|
uint64_t Hash64(const char* data, size_t n, uint64_t seed) {
|
|
return XXH3p_64bits_withSeed(data, n, seed);
|
|
}
|
|
|
|
uint64_t Hash64(const char* data, size_t n) {
|
|
// Same as seed = 0
|
|
return XXH3p_64bits(data, n);
|
|
}
|
|
|
|
} // namespace ROCKSDB_NAMESPACE
|