b90d283911
This reverts commit f2556b4ffe.
Reason for revert: absl::BitGen has issues seeding on Windows10 Chromium render process. https://ci.chromium.org/ui/p/chromium/builders/webrtc.fyi/WebRTC%20Chromium%20FYI%20Win10%20Tester/18543/test-results
Original change's description:
> Use absl::BitGen to generate Random's seed
>
> This adds a default constructor to Random which uses absl::BitGet to
> generate its own seed. This allows us to replace places where the
> current time was used to set a seed.
>
> Bug: webrtc:441137274
> Change-Id: I5afeca99b2fee5e5a2a0b31043ee0c81c00af5cc
> Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/408005
> Commit-Queue: Evan Shrubsole <eshr@webrtc.org>
> Auto-Submit: Evan Shrubsole <eshr@webrtc.org>
> Reviewed-by: Harald Alvestrand <hta@webrtc.org>
> Reviewed-by: Tomas Gunnarsson <tommi@webrtc.org>
> Cr-Commit-Position: refs/heads/main@{#45588}
Bug: webrtc:441137274
Change-Id: I7acb39e56cfb119742a2b36f053abd1a43781417
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/408903
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Commit-Queue: Evan Shrubsole <eshr@webrtc.org>
Reviewed-by: Harald Alvestrand <hta@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#45619}
90 lines
2.8 KiB
C++
90 lines
2.8 KiB
C++
/*
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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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#include "rtc_base/random.h"
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#include <cmath>
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#include <cstdint>
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#include <numbers>
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#include "rtc_base/checks.h"
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#include "rtc_base/numerics/safe_conversions.h"
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namespace webrtc {
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Random::Random(uint64_t seed) {
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RTC_DCHECK(seed != 0x0ull);
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state_ = seed;
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}
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uint32_t Random::Rand(uint32_t t) {
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// Casting the output to 32 bits will give an almost uniform number.
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// Pr[x=0] = (2^32-1) / (2^64-1)
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// Pr[x=k] = 2^32 / (2^64-1) for k!=0
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// Uniform would be Pr[x=k] = 2^32 / 2^64 for all 32-bit integers k.
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uint32_t x = NextOutput();
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// If x / 2^32 is uniform on [0,1), then x / 2^32 * (t+1) is uniform on
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// the interval [0,t+1), so the integer part is uniform on [0,t].
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uint64_t result = x * (static_cast<uint64_t>(t) + 1);
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result >>= 32;
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return result;
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}
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uint32_t Random::Rand(uint32_t low, uint32_t high) {
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RTC_DCHECK(low <= high);
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return Rand(high - low) + low;
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}
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int32_t Random::Rand(int32_t low, int32_t high) {
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RTC_DCHECK(low <= high);
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const int64_t low_i64{low};
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return dchecked_cast<int32_t>(Rand(dchecked_cast<uint32_t>(high - low_i64)) +
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low_i64);
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}
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template <>
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float Random::Rand<float>() {
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double result = NextOutput() - 1;
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result = result / static_cast<double>(0xFFFFFFFFFFFFFFFFull);
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return static_cast<float>(result);
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}
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template <>
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double Random::Rand<double>() {
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double result = NextOutput() - 1;
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result = result / static_cast<double>(0xFFFFFFFFFFFFFFFFull);
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return result;
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}
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template <>
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bool Random::Rand<bool>() {
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return Rand(0, 1) == 1;
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}
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double Random::Gaussian(double mean, double standard_deviation) {
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// Creating a Normal distribution variable from two independent uniform
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// variables based on the Box-Muller transform, which is defined on the
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// interval (0, 1]. Note that we rely on NextOutput to generate integers
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// in the range [1, 2^64-1]. Normally this behavior is a bit frustrating,
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// but here it is exactly what we need.
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const double kPi = std::numbers::pi;
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double u1 = static_cast<double>(NextOutput()) /
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static_cast<double>(0xFFFFFFFFFFFFFFFFull);
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double u2 = static_cast<double>(NextOutput()) /
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static_cast<double>(0xFFFFFFFFFFFFFFFFull);
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return mean + standard_deviation * sqrt(-2 * log(u1)) * cos(2 * kPi * u2);
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}
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double Random::Exponential(double lambda) {
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double uniform = Rand<double>();
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return -log(uniform) / lambda;
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}
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} // namespace webrtc
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