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stefanc62642c2015-07-07 04:20:34 -07001/*
2 * Copyright (c) 2015 The WebRTC project authors. All Rights Reserved.
3 *
4 * Use of this source code is governed by a BSD-style license
5 * that can be found in the LICENSE file in the root of the source
6 * tree. An additional intellectual property rights grant can be found
7 * in the file PATENTS. All contributing project authors may
8 * be found in the AUTHORS file in the root of the source tree.
9 */
10
Mirko Bonadei92ea95e2017-09-15 06:47:31 +020011#ifndef RTC_BASE_RANDOM_H_
12#define RTC_BASE_RANDOM_H_
stefanc62642c2015-07-07 04:20:34 -070013
Yves Gerey988cc082018-10-23 12:03:01 +020014#include <stdint.h>
Henrik Kjellanderec78f1c2017-06-29 07:52:50 +020015#include <limits>
terelius56b11282015-11-06 05:13:55 -080016
Mirko Bonadei92ea95e2017-09-15 06:47:31 +020017#include "rtc_base/checks.h"
Steve Anton10542f22019-01-11 09:11:00 -080018#include "rtc_base/constructor_magic.h"
Henrik Kjellanderec78f1c2017-06-29 07:52:50 +020019
20namespace webrtc {
21
22class Random {
23 public:
24 // TODO(tommi): Change this so that the seed can be initialized internally,
25 // e.g. by offering two ways of constructing or offer a static method that
26 // returns a seed that's suitable for initialization.
27 // The problem now is that callers are calling clock_->TimeInMicroseconds()
28 // which calls TickTime::Now().Ticks(), which can return a very low value on
29 // Mac and can result in a seed of 0 after conversion to microseconds.
30 // Besides the quality of the random seed being poor, this also requires
31 // the client to take on extra dependencies to generate a seed.
32 // If we go for a static seed generator in Random, we can use something from
kjellandere96c45b2017-06-30 10:45:21 -070033 // webrtc/rtc_base and make sure that it works the same way across platforms.
Henrik Kjellanderec78f1c2017-06-29 07:52:50 +020034 // See also discussion here: https://codereview.webrtc.org/1623543002/
35 explicit Random(uint64_t seed);
36
37 // Return pseudo-random integer of the specified type.
38 // We need to limit the size to 32 bits to keep the output close to uniform.
39 template <typename T>
40 T Rand() {
41 static_assert(std::numeric_limits<T>::is_integer &&
42 std::numeric_limits<T>::radix == 2 &&
43 std::numeric_limits<T>::digits <= 32,
44 "Rand is only supported for built-in integer types that are "
45 "32 bits or smaller.");
46 return static_cast<T>(NextOutput());
47 }
48
49 // Uniformly distributed pseudo-random number in the interval [0, t].
50 uint32_t Rand(uint32_t t);
51
52 // Uniformly distributed pseudo-random number in the interval [low, high].
53 uint32_t Rand(uint32_t low, uint32_t high);
54
55 // Uniformly distributed pseudo-random number in the interval [low, high].
56 int32_t Rand(int32_t low, int32_t high);
57
58 // Normal Distribution.
59 double Gaussian(double mean, double standard_deviation);
60
61 // Exponential Distribution.
62 double Exponential(double lambda);
63
64 private:
65 // Outputs a nonzero 64-bit random number.
66 uint64_t NextOutput() {
67 state_ ^= state_ >> 12;
68 state_ ^= state_ << 25;
69 state_ ^= state_ >> 27;
70 RTC_DCHECK(state_ != 0x0ULL);
71 return state_ * 2685821657736338717ull;
72 }
73
74 uint64_t state_;
75
76 RTC_DISALLOW_IMPLICIT_CONSTRUCTORS(Random);
77};
78
79// Return pseudo-random number in the interval [0.0, 1.0).
80template <>
81float Random::Rand<float>();
82
83// Return pseudo-random number in the interval [0.0, 1.0).
84template <>
85double Random::Rand<double>();
86
87// Return pseudo-random boolean value.
88template <>
89bool Random::Rand<bool>();
90
91} // namespace webrtc
stefanc62642c2015-07-07 04:20:34 -070092
Mirko Bonadei92ea95e2017-09-15 06:47:31 +020093#endif // RTC_BASE_RANDOM_H_