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596a35acca
25511b7 Merge branch 'master' of github.com:rescrv/HyperLevelDB into hyperdb ed01020 Make "source" universal 3784d92 Ignore the static file 507319b Don't package with snappy 3e2cc8b Tolerate -fno-rtti 4dcdd6e Drop revision down to 1.0.dev 2542163 Drop all but the latest kept for garbage reasons 9c270b7 Update .gitignore 5331878 Add upack script adc2a7a Explicitly add -lpthread for Ubuntu 7b57bbd Strip NULL chars passed to LiveBackup e3b87e7 Add write-buffer-size option to benchmark 2f11087 Followup to snappy support with -DSNAPPY af503da Improve efficiency of ReplayIterator; fix a bug 33c1f0c Add snappy support ce1cacf Fix a race in ReplayIterator 5c4679b Fix a bug in the replay_iterator ca332bd Fix sort algorithm used for compaction boundaries. d9ec544 make checK b83a9cd Fix a deadlock in the ReplayIterator dtor 273547b Fix a double-delete in ReplayIterator 3377c7a Add "all" to set of special timestamps 387f43a Timestamp comparison and validation. f9a6eb1 make distcheck 9a4d0b7 Add a ReplayIterator. 1d53869 Conditionally enable read-driven compaction. f6fa561 16% end-to-end performance improvement from the skiplist 28ffd32 Merge remote-tracking branch 'upstream/master' a58de73 Revert "Remove read-driven compactions." e19fc0c Fix upstream issue 200 748539c LevelDB 1.13 78b7812 Add install instructions to README e47a48e Make benchmark dir variable 820a096 Update distributed files. 486ca7f Live backup of LevelDB instances 6579884 Put a reference counter on log_/logfile_ 3075253 Update internal benchmark. 2a6b0bd Make the Version a parameter of PickCompaction 5bd76dc Release leveldb 1.12 git-subtree-dir: src/hyperleveldb git-subtree-split: 25511b7a9101b0bafb57349d2194ba80ccbf7bc3
65 lines
2.1 KiB
C++
65 lines
2.1 KiB
C++
// 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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#ifndef STORAGE_HYPERLEVELDB_UTIL_RANDOM_H_
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#define STORAGE_HYPERLEVELDB_UTIL_RANDOM_H_
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#include <stdint.h>
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namespace hyperleveldb {
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// A very simple random number generator. Not especially good at
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// generating truly random bits, but good enough for our needs in this
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// package.
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class Random {
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private:
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uint32_t seed_;
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public:
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explicit Random(uint32_t s) : seed_(s & 0x7fffffffu) {
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// Avoid bad seeds.
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if (seed_ == 0 || seed_ == 2147483647L) {
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seed_ = 1;
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}
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}
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uint32_t Next() {
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static const uint32_t M = 2147483647L; // 2^31-1
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static const uint64_t A = 16807; // bits 14, 8, 7, 5, 2, 1, 0
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// We are computing
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// seed_ = (seed_ * A) % M, where M = 2^31-1
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//
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// seed_ must not be zero or M, or else all subsequent computed values
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// will be zero or M respectively. For all other values, seed_ will end
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// up cycling through every number in [1,M-1]
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uint64_t product = seed_ * A;
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// Compute (product % M) using the fact that ((x << 31) % M) == x.
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seed_ = static_cast<uint32_t>((product >> 31) + (product & M));
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// The first reduction may overflow by 1 bit, so we may need to
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// repeat. mod == M is not possible; using > allows the faster
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// sign-bit-based test.
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if (seed_ > M) {
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seed_ -= M;
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}
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return seed_;
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}
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// Returns a uniformly distributed value in the range [0..n-1]
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// REQUIRES: n > 0
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uint32_t Uniform(int n) { return Next() % n; }
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// Randomly returns true ~"1/n" of the time, and false otherwise.
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// REQUIRES: n > 0
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bool OneIn(int n) { return (Next() % n) == 0; }
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// Skewed: pick "base" uniformly from range [0,max_log] and then
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// return "base" random bits. The effect is to pick a number in the
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// range [0,2^max_log-1] with exponential bias towards smaller numbers.
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uint32_t Skewed(int max_log) {
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return Uniform(1 << Uniform(max_log + 1));
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}
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};
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} // namespace hyperleveldb
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#endif // STORAGE_HYPERLEVELDB_UTIL_RANDOM_H_
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