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