fork of https://github.com/oxigraph/rocksdb and https://github.com/facebook/rocksdb for nextgraph and oxigraph
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60 lines
2.0 KiB
60 lines
2.0 KiB
// Copyright (c) 2011-present, Facebook, Inc. All rights reserved.
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// This source code is licensed under both the GPLv2 (found in the
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// COPYING file in the root directory) and Apache 2.0 License
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// (found in the LICENSE.Apache file in the root directory).
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//
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// Copyright (c) 2011 The LevelDB Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file. See the AUTHORS file for names of contributors.
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//
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// Simple hash function used for internal data structures
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#pragma once
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#include <stddef.h>
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#include <stdint.h>
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#include "rocksdb/slice.h"
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#include "util/murmurhash.h"
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namespace rocksdb {
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// Non-persistent hash. Only used for in-memory data structure
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// The hash results are applicable to change.
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extern uint64_t NPHash64(const char* data, size_t n, uint32_t seed);
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extern uint32_t Hash(const char* data, size_t n, uint32_t seed);
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inline uint32_t BloomHash(const Slice& key) {
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return Hash(key.data(), key.size(), 0xbc9f1d34);
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}
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inline uint64_t GetSliceNPHash64(const Slice& s) {
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return NPHash64(s.data(), s.size(), 0);
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}
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inline uint32_t GetSliceHash(const Slice& s) {
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return Hash(s.data(), s.size(), 397);
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}
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inline uint64_t NPHash64(const char* data, size_t n, uint32_t seed) {
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// Right now murmurhash2B is used. It should able to be freely
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// changed to a better hash, without worrying about backward
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// compatibility issue.
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return MURMUR_HASH(data, static_cast<int>(n),
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static_cast<unsigned int>(seed));
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}
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// std::hash compatible interface.
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struct SliceHasher {
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uint32_t operator()(const Slice& s) const { return GetSliceHash(s); }
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};
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// An alternative to % for mapping a hash value to an arbitrary range. See
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// https://github.com/lemire/fastrange and
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// https://github.com/pdillinger/wormhashing/blob/2c4035a4462194bf15f3e9fc180c27c513335225/bloom_simulation_tests/foo.cc#L57
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inline uint32_t fastrange32(uint32_t a, uint32_t h) {
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uint64_t product = static_cast<uint64_t>(a) * h;
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return static_cast<uint32_t>(product >> 32);
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}
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} // namespace rocksdb
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