Adding upstream version 18.2.2.upstream/18.2.2

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 190 insertions, 0 deletions

diff --git a/src/rocksdb/util/random.h b/src/rocksdb/util/random.h
new file mode 100644
index 000000000..8923bdc4f
--- /dev/null
+++ b/src/rocksdb/util/random.h
@@ -0,0 +1,190 @@
+//  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 <stdint.h>
+
+#include <algorithm>
+#include <random>
+
+#include "rocksdb/rocksdb_namespace.h"
+
+namespace ROCKSDB_NAMESPACE {
+
+// A very simple random number generator.  Not especially good at
+// generating truly random bits, but good enough for our needs in this
+// package.
+class Random {
+ private:
+  enum : uint32_t {
+    M = 2147483647L  // 2^31-1
+  };
+  enum : uint64_t {
+    A = 16807  // bits 14, 8, 7, 5, 2, 1, 0
+  };
+
+  uint32_t seed_;
+
+  static uint32_t GoodSeed(uint32_t s) { return (s & M) != 0 ? (s & M) : 1; }
+
+ public:
+  // This is the largest value that can be returned from Next()
+  enum : uint32_t { kMaxNext = M };
+
+  explicit Random(uint32_t s) : seed_(GoodSeed(s)) {}
+
+  void Reset(uint32_t s) { seed_ = GoodSeed(s); }
+
+  uint32_t Next() {
+    // We are computing
+    //       seed_ = (seed_ * A) % M,    where M = 2^31-1
+    //
+    // seed_ must not be zero or M, or else all subsequent computed values
+    // will be zero or M respectively.  For all other values, seed_ will end
+    // up cycling through every number in [1,M-1]
+    uint64_t product = seed_ * A;
+
+    // Compute (product % M) using the fact that ((x << 31) % M) == x.
+    seed_ = static_cast<uint32_t>((product >> 31) + (product & M));
+    // The first reduction may overflow by 1 bit, so we may need to
+    // repeat.  mod == M is not possible; using > allows the faster
+    // sign-bit-based test.
+    if (seed_ > M) {
+      seed_ -= M;
+    }
+    return seed_;
+  }
+
+  uint64_t Next64() { return (uint64_t{Next()} << 32) | Next(); }
+
+  // Returns a uniformly distributed value in the range [0..n-1]
+  // REQUIRES: n > 0
+  uint32_t Uniform(int n) { return Next() % n; }
+
+  // Randomly returns true ~"1/n" of the time, and false otherwise.
+  // REQUIRES: n > 0
+  bool OneIn(int n) { return Uniform(n) == 0; }
+
+  // "Optional" one-in-n, where 0 or negative always returns false
+  // (may or may not consume a random value)
+  bool OneInOpt(int n) { return n > 0 && OneIn(n); }
+
+  // Returns random bool that is true for the given percentage of
+  // calls on average. Zero or less is always false and 100 or more
+  // is always true (may or may not consume a random value)
+  bool PercentTrue(int percentage) {
+    return static_cast<int>(Uniform(100)) < percentage;
+  }
+
+  // Skewed: pick "base" uniformly from range [0,max_log] and then
+  // return "base" random bits.  The effect is to pick a number in the
+  // range [0,2^max_log-1] with exponential bias towards smaller numbers.
+  uint32_t Skewed(int max_log) { return Uniform(1 << Uniform(max_log + 1)); }
+
+  // Returns a random string of length "len"
+  std::string RandomString(int len);
+
+  // Generates a random string of len bytes using human-readable characters
+  std::string HumanReadableString(int len);
+
+  // Generates a random binary data
+  std::string RandomBinaryString(int len);
+
+  // Returns a Random instance for use by the current thread without
+  // additional locking
+  static Random* GetTLSInstance();
+};
+
+// A good 32-bit random number generator based on std::mt19937.
+// This exists in part to avoid compiler variance in warning about coercing
+// uint_fast32_t from mt19937 to uint32_t.
+class Random32 {
+ private:
+  std::mt19937 generator_;
+
+ public:
+  explicit Random32(uint32_t s) : generator_(s) {}
+
+  // Generates the next random number
+  uint32_t Next() { return static_cast<uint32_t>(generator_()); }
+
+  // Returns a uniformly distributed value in the range [0..n-1]
+  // REQUIRES: n > 0
+  uint32_t Uniform(uint32_t n) {
+    return static_cast<uint32_t>(
+        std::uniform_int_distribution<std::mt19937::result_type>(
+            0, n - 1)(generator_));
+  }
+
+  // Returns an *almost* uniformly distributed value in the range [0..n-1].
+  // Much faster than Uniform().
+  // REQUIRES: n > 0
+  uint32_t Uniformish(uint32_t n) {
+    // fastrange (without the header)
+    return static_cast<uint32_t>((uint64_t(generator_()) * uint64_t(n)) >> 32);
+  }
+
+  // Randomly returns true ~"1/n" of the time, and false otherwise.
+  // REQUIRES: n > 0
+  bool OneIn(uint32_t n) { return Uniform(n) == 0; }
+
+  // Skewed: pick "base" uniformly from range [0,max_log] and then
+  // return "base" random bits.  The effect is to pick a number in the
+  // range [0,2^max_log-1] with exponential bias towards smaller numbers.
+  uint32_t Skewed(int max_log) {
+    return Uniform(uint32_t{1} << Uniform(max_log + 1));
+  }
+
+  // Reset the seed of the generator to the given value
+  void Seed(uint32_t new_seed) { generator_.seed(new_seed); }
+};
+
+// A good 64-bit random number generator based on std::mt19937_64
+class Random64 {
+ private:
+  std::mt19937_64 generator_;
+
+ public:
+  explicit Random64(uint64_t s) : generator_(s) {}
+
+  // Generates the next random number
+  uint64_t Next() { return generator_(); }
+
+  // Returns a uniformly distributed value in the range [0..n-1]
+  // REQUIRES: n > 0
+  uint64_t Uniform(uint64_t n) {
+    return std::uniform_int_distribution<uint64_t>(0, n - 1)(generator_);
+  }
+
+  // Randomly returns true ~"1/n" of the time, and false otherwise.
+  // REQUIRES: n > 0
+  bool OneIn(uint64_t n) { return Uniform(n) == 0; }
+
+  // Skewed: pick "base" uniformly from range [0,max_log] and then
+  // return "base" random bits.  The effect is to pick a number in the
+  // range [0,2^max_log-1] with exponential bias towards smaller numbers.
+  uint64_t Skewed(int max_log) {
+    return Uniform(uint64_t(1) << Uniform(max_log + 1));
+  }
+};
+
+// A seeded replacement for removed std::random_shuffle
+template <class RandomIt>
+void RandomShuffle(RandomIt first, RandomIt last, uint32_t seed) {
+  std::mt19937 rng(seed);
+  std::shuffle(first, last, rng);
+}
+
+// A replacement for removed std::random_shuffle
+template <class RandomIt>
+void RandomShuffle(RandomIt first, RandomIt last) {
+  RandomShuffle(first, last, std::random_device{}());
+}
+
+}  // namespace ROCKSDB_NAMESPACE