folly/folly/Random.h

/*
 * Copyright (c) Meta Platforms, Inc. and affiliates.
 *
 * 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.
 */

//
// Docs: https://fburl.com/fbvref_random
//

#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>
#include <folly/lang/Bits.h>

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

namespace folly {

namespace detail {

#if FOLLY_HAVE_EXTRANDOM_SFMT19937
using DefaultGenerator = __gnu_cxx::sfmt19937;
#else
DefaultGenerator;
#endif

} // namespace detail

/**
 * A PRNG with one instance per thread. This PRNG uses a mersenne twister random
 * number generator and is seeded from /dev/urandom. It should not be used for
 * anything which requires security, only for statistical randomness.
 */
class ThreadLocalPRNG { … };

class Random { … };

/*
 * 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() { … }

} // namespace folly

#include <folly/Random-inl.h>