YugabyteDB (2.13.1.0-b60, 21121d69985fbf76aa6958d8f04a9bfa936293b5)

//  Copyright (c) 2011-present, 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.

//

// The following only applies to changes made to this file as part of YugaByte development.

//

// Portions Copyright (c) YugaByte, Inc.

//

// Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except

// in compliance with the License.  You may obtain a copy of the License at

//

// http://www.apache.org/licenses/LICENSE-2.0

//

// Unless required by applicable law or agreed to in writing, software distributed under the License

// is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express

// or implied.  See the License for the specific language governing permissions and limitations

// under the License.

//

// 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.

#ifndef YB_ROCKSDB_UTIL_RANDOM_H

#define YB_ROCKSDB_UTIL_RANDOM_H

#include <stdint.h>

#include <random>

#include "yb/util/slice.h"

namespace rocksdb {

// 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)1.53M
 : 
1834
; }

 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_;

  }

  // 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 (Next() % 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(1 << Uniform(max_log + 1));

  }

  // Returns a Random instance for use by the current thread without

  // additional locking

  static Random* GetTLSInstance();

};

// A simple 64bit 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(1 << Uniform(max_log + 1));

  }

};

// Store in *dst a random string of length "len" and return a Slice that

// references the generated data.

Slice RandomString(Random* rnd, int len, std::string* dst);

inline std::string RandomString(Random* rnd, int len) {

  std::string r;

  RandomString(rnd, len, &r);

  return r;

}

// Store in *dst a string of length "len" that will compress to

// "N*compressed_fraction" bytes and return a Slice that references

// the generated data.

Slice CompressibleString(Random* rnd, double compressed_fraction, int len, std::string* dst);

}  // namespace rocksdb

#endif // YB_ROCKSDB_UTIL_RANDOM_H