rocksdb/util/dynamic_bloom.h

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// Copyright (c) 2013, Facebook, Inc. All rights reserved.
// This source code is licensed under the BSD-style license found in the
// LICENSE file in the root directory of this source tree. An additional grant
// of patent rights can be found in the PATENTS file in the same directory.
#pragma once
#include <atomic>
#include <memory>
namespace rocksdb {
class Slice;
class DynamicBloom {
public:
// total_bits: fixed total bits for the bloom
// hash_func: customized hash function
// num_probes: number of hash probes for a single key
DynamicBloom(uint32_t total_bits,
uint32_t (*hash_func)(const Slice& key),
uint32_t num_probes = 6);
explicit DynamicBloom(uint32_t total_bits, uint32_t num_probes = 6);
// Assuming single threaded access to this function.
void Add(const Slice& key);
// Assuming single threaded access to this function.
void AddHash(uint32_t hash);
// Multithreaded access to this function is OK
bool MayContain(const Slice& key);
// Multithreaded access to this function is OK
bool MayContainHash(uint32_t hash);
private:
uint32_t (*hash_func_)(const Slice& key);
const uint32_t kTotalBits;
const uint32_t kNumProbes;
std::unique_ptr<unsigned char[]> data_;
};
inline void DynamicBloom::Add(const Slice& key) { AddHash(hash_func_(key)); }
inline bool DynamicBloom::MayContain(const Slice& key) {
return (MayContainHash(hash_func_(key)));
}
inline bool DynamicBloom::MayContainHash(uint32_t h) {
const uint32_t delta = (h >> 17) | (h << 15); // Rotate right 17 bits
for (uint32_t i = 0; i < kNumProbes; i++) {
const uint32_t bitpos = h % kTotalBits;
if (((data_[bitpos / 8]) & (1 << (bitpos % 8))) == 0) {
return false;
}
h += delta;
}
return true;
}
inline void DynamicBloom::AddHash(uint32_t h) {
const uint32_t delta = (h >> 17) | (h << 15); // Rotate right 17 bits
for (uint32_t i = 0; i < kNumProbes; i++) {
const uint32_t bitpos = h % kTotalBits;
data_[bitpos / 8] |= (1 << (bitpos % 8));
h += delta;
}
}
} // rocksdb