Random.h

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/*
 * Copyright 2011-present Facebook, 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.
 */

#pragma once
#define FOLLY_RANDOM_H_

#include <array>
#include <cstdint>
#include <random>
#include <type_traits>

#include <folly/Portability.h>
#include <folly/Traits.h>
#include <folly/functional/Invoke.h>

#if FOLLY_HAVE_EXTRANDOM_SFMT19937
#include <ext/random>
#endif

namespace folly {

class ThreadLocalPRNG {
 public:
  using result_type = uint32_t;

  result_type operator()();

  static constexpr result_type min() {
    return std::numeric_limits<result_type>::min();
  }
  static constexpr result_type max() {
    return std::numeric_limits<result_type>::max();
  }
};

class Random {
 private:
  template <class RNG>
  using ValidRNG = typename std::
      enable_if<std::is_unsigned<invoke_result_t<RNG&>>::value, RNG>::type;

  template <class T>
  class SecureRNG {
   public:
    using result_type = typename std::enable_if<
        std::is_integral<T>::value && !std::is_same<T, bool>::value,
        T>::type;

    result_type operator()() {
      return Random::secureRandom<result_type>();
    }

    static constexpr result_type min() {
      return std::numeric_limits<result_type>::min();
    }

    static constexpr result_type max() {
      return std::numeric_limits<result_type>::max();
    }
  };

 public:
  // Default generator type.
#if FOLLY_HAVE_EXTRANDOM_SFMT19937
  typedef __gnu_cxx::sfmt19937 DefaultGenerator;
#else
  typedef std::mt19937 DefaultGenerator;
#endif

  static void secureRandom(void* data, size_t len);

  template <class T>
  static typename std::enable_if<
      std::is_integral<T>::value && !std::is_same<T, bool>::value,
      T>::type
  secureRandom() {
    T val;
    secureRandom(&val, sizeof(val));
    return val;
  }

  static uint32_t secureRand32() {
    return secureRandom<uint32_t>();
  }

  static uint32_t secureRand32(uint32_t max) {
    SecureRNG<uint32_t> srng;
    return rand32(max, srng);
  }

  static uint32_t secureRand32(uint32_t min, uint32_t max) {
    SecureRNG<uint32_t> srng;
    return rand32(min, max, srng);
  }

  static uint64_t secureRand64() {
    return secureRandom<uint64_t>();
  }

  static uint64_t secureRand64(uint64_t max) {
    SecureRNG<uint64_t> srng;
    return rand64(max, srng);
  }

  static uint64_t secureRand64(uint64_t min, uint64_t max) {
    SecureRNG<uint64_t> srng;
    return rand64(min, max, srng);
  }

  static bool secureOneIn(uint32_t n) {
    SecureRNG<uint32_t> srng;
    return rand32(0, n, srng) == 0;
  }

  static double secureRandDouble01() {
    SecureRNG<uint64_t> srng;
    return randDouble01(srng);
  }

  static double secureRandDouble(double min, double max) {
    SecureRNG<uint64_t> srng;
    return randDouble(min, max, srng);
  }

  template <class RNG = DefaultGenerator, class /* EnableIf */ = ValidRNG<RNG>>
  static void seed(RNG& rng);

  template <class RNG = DefaultGenerator, class /* EnableIf */ = ValidRNG<RNG>>
  static RNG create();

  static uint32_t rand32() {
    return rand32(ThreadLocalPRNG());
  }

  template <class RNG, class /* EnableIf */ = ValidRNG<RNG>>
  static uint32_t rand32(RNG&& rng) {
    return rng();
  }

  static uint32_t rand32(uint32_t max) {
    return rand32(0, max, ThreadLocalPRNG());
  }

  template <class RNG = ThreadLocalPRNG, class /* EnableIf */ = ValidRNG<RNG>>
  static uint32_t rand32(uint32_t max, RNG&& rng) {
    return rand32(0, max, rng);
  }

  static uint32_t rand32(uint32_t min, uint32_t max) {
    return rand32(min, max, ThreadLocalPRNG());
  }

  template <class RNG = ThreadLocalPRNG, class /* EnableIf */ = ValidRNG<RNG>>
  static uint32_t rand32(uint32_t min, uint32_t max, RNG&& rng) {
    if (min == max) {
      return 0;
    }
    return std::uniform_int_distribution<uint32_t>(min, max - 1)(rng);
  }

  static uint64_t rand64() {
    return rand64(ThreadLocalPRNG());
  }

  template <class RNG = ThreadLocalPRNG, class /* EnableIf */ = ValidRNG<RNG>>
  static uint64_t rand64(RNG&& rng) {
    return ((uint64_t)rng() << 32) | rng();
  }

  static uint64_t rand64(uint64_t max) {
    return rand64(0, max, ThreadLocalPRNG());
  }

  template <class RNG = ThreadLocalPRNG, class /* EnableIf */ = ValidRNG<RNG>>
  static uint64_t rand64(uint64_t max, RNG&& rng) {
    return rand64(0, max, rng);
  }

  static uint64_t rand64(uint64_t min, uint64_t max) {
    return rand64(min, max, ThreadLocalPRNG());
  }

  template <class RNG = ThreadLocalPRNG, class /* EnableIf */ = ValidRNG<RNG>>
  static uint64_t rand64(uint64_t min, uint64_t max, RNG&& rng) {
    if (min == max) {
      return 0;
    }
    return std::uniform_int_distribution<uint64_t>(min, max - 1)(rng);
  }

  static bool oneIn(uint32_t n) {
    return oneIn(n, ThreadLocalPRNG());
  }

  template <class RNG = ThreadLocalPRNG, class /* EnableIf */ = ValidRNG<RNG>>
  static bool oneIn(uint32_t n, RNG&& rng) {
    if (n == 0) {
      return false;
    }
    return rand32(0, n, rng) == 0;
  }

  static double randDouble01() {
    return randDouble01(ThreadLocalPRNG());
  }

  template <class RNG = ThreadLocalPRNG, class /* EnableIf */ = ValidRNG<RNG>>
  static double randDouble01(RNG&& rng) {
    return std::generate_canonical<double, std::numeric_limits<double>::digits>(
        rng);
  }

  static double randDouble(double min, double max) {
    return randDouble(min, max, ThreadLocalPRNG());
  }

  template <class RNG = ThreadLocalPRNG, class /* EnableIf */ = ValidRNG<RNG>>
  static double randDouble(double min, double max, RNG&& rng) {
    if (std::fabs(max - min) < std::numeric_limits<double>::epsilon()) {
      return 0;
    }
    return std::uniform_real_distribution<double>(min, max)(rng);
  }
};

/*
 * Return a good seed for a random number generator.
 * Note that this is a legacy function, as it returns a 32-bit value, which
 * is too small to be useful as a "real" RNG seed. Use the functions in class
 * Random instead.
 */
inline uint32_t randomNumberSeed() {
  return Random::rand32();
}

} // namespace folly

#include <folly/Random-inl.h>