Move PRNG from BWE test framework to webrtc/test.

webrtc/test/random.cc

 /*
  *  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.
  */
 
-#include "webrtc/modules/remote_bitrate_estimator/test/random.h"
+#include "webrtc/test/random.h"
 
 #include <math.h>
 
+#include "webrtc/base/checks.h"
+
 namespace webrtc {
 
+namespace test {
+
 Random::Random(uint32_t seed) : a_(0x531FDB97 ^ seed), b_(0x6420ECA8 + seed) {
 }
 
 float Random::Rand() {
   const float kScale = 1.0f / 0xffffffff;
   float result = kScale * b_;
   a_ ^= b_;
   b_ += a_;
   return result;
 }
 
+int Random::Rand(int low, int high) {
+  RTC_DCHECK(low <= high);
+  float uniform = Rand() * (high - low + 1) + low;

[pbos-webrtc, 2015/10/19 13:33:01]

Then this one has off-by-one errors?

for Rand() = 1.0:

Rand(1, 2):

Rand() = 1.0 * (2 - 1 + 1) + 1 = 1.0 * 2 + 1 = 3.0.

Which gets rounded to 3.

[the sun, 2015/10/19 15:10:25]

Looks like that. Good catch!
https://codereview.webrtc.org/1412183002/

+  return static_cast<int>(uniform);
+}
+
 int Random::Gaussian(int mean, int standard_deviation) {
   // Creating a Normal distribution variable from two independent uniform
   // variables based on the Box-Muller transform, which is defined on the
   // interval (0, 1], hence the mask+add below.
   const double kPi = 3.14159265358979323846;
   const double kScale = 1.0 / 0x80000000ul;
   double u1 = kScale * ((a_ & 0x7ffffffful) + 1);
   double u2 = kScale * ((b_ & 0x7ffffffful) + 1);
   a_ ^= b_;
   b_ += a_;
   return static_cast<int>(
       mean + standard_deviation * sqrt(-2 * log(u1)) * cos(2 * kPi * u2));
 }
+
+int Random::Exponential(float lambda) {
+  float uniform = Rand();
+  return static_cast<int>(-log(uniform) / lambda);
+}
+}  // namespace test
 }  // namespace webrtc