Bump to WebRTC M120 release

Some API deprecation -- ExperimentalAgc and ExperimentalNs are gone.
We're continuing to carry iSAC even though it's gone upstream, but maybe
we'll want to drop that soon.

webrtc/rtc_base/random.h

@@ -0,0 +1,96 @@
+/*
+ *  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_