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/*
* Copyright (c) 2015 The WebRTC project authors. All Rights Reserved.
*
* Use of this source code is governed by a BSD-style license
* that can be found in the LICENSE file in the root of the source
* tree. An additional intellectual property rights grant can be found
* in the file PATENTS. All contributing project authors may
* be found in the AUTHORS file in the root of the source tree.
*/
#ifndef RTC_BASE_RANDOM_H_
#define RTC_BASE_RANDOM_H_
#include <stdint.h>
#include <limits>
#include "rtc_base/checks.h"
namespace webrtc {
class Random {
public:
// TODO(tommi): Change this so that the seed can be initialized internally,
// e.g. by offering two ways of constructing or offer a static method that
// returns a seed that's suitable for initialization.
// The problem now is that callers are calling clock_->TimeInMicroseconds()
// which calls TickTime::Now().Ticks(), which can return a very low value on
// Mac and can result in a seed of 0 after conversion to microseconds.
// Besides the quality of the random seed being poor, this also requires
// the client to take on extra dependencies to generate a seed.
// If we go for a static seed generator in Random, we can use something from
// webrtc/rtc_base and make sure that it works the same way across platforms.
// See also discussion here: https://codereview.webrtc.org/1623543002/
explicit Random(uint64_t seed);
Random() = delete;
Random(const Random&) = delete;
Random& operator=(const Random&) = delete;
// Return pseudo-random integer of the specified type.
// We need to limit the size to 32 bits to keep the output close to uniform.
template <typename T>
T Rand() {
static_assert(std::numeric_limits<T>::is_integer &&
std::numeric_limits<T>::radix == 2 &&
std::numeric_limits<T>::digits <= 32,
"Rand is only supported for built-in integer types that are "
"32 bits or smaller.");
return static_cast<T>(NextOutput());
}
// Uniformly distributed pseudo-random number in the interval [0, t].
uint32_t Rand(uint32_t t);
// Uniformly distributed pseudo-random number in the interval [low, high].
uint32_t Rand(uint32_t low, uint32_t high);
// Uniformly distributed pseudo-random number in the interval [low, high].
int32_t Rand(int32_t low, int32_t high);
// Normal Distribution.
double Gaussian(double mean, double standard_deviation);
// Exponential Distribution.
double Exponential(double lambda);
private:
// Outputs a nonzero 64-bit random number using Xorshift algorithm.
// https://en.wikipedia.org/wiki/Xorshift
uint64_t NextOutput() {
state_ ^= state_ >> 12;
state_ ^= state_ << 25;
state_ ^= state_ >> 27;
RTC_DCHECK(state_ != 0x0ULL);
return state_ * 2685821657736338717ull;
}
uint64_t state_;
};
// Return pseudo-random number in the interval [0.0, 1.0).
template <>
float Random::Rand<float>();
// Return pseudo-random number in the interval [0.0, 1.0).
template <>
double Random::Rand<double>();
// Return pseudo-random boolean value.
template <>
bool Random::Rand<bool>();
} // namespace webrtc
#endif // RTC_BASE_RANDOM_H_
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