Change to use local Random object instead of global rand() in the RtcEventLog unit 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/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 double kScale = 1.0f / (static_cast<uint64_t>(1) << 32);
   double result = kScale * b_;
   a_ ^= b_;
   b_ += a_;
   return static_cast<float>(result);
 }

[stefan-webrtc, 2015/10/22 09:41:22]

Should this be implemented using Uniform() instead?

[the sun, 2015/10/22 12:30:38]

Maybe the a_ ^= b_; b_ += a_; part could be put in an internal helper uint32_t
Next()?

However, I'm fine duplicating the code as well. Your call.

[terelius, 2015/10/26 18:18:41]

Using Uniform(MAX_INT) would give the exact same result as the current code, but
requires 64-bit arithmetic. I think it is better to keep it as it is for now.

[terelius, 2015/10/26 18:18:41]

Considering it is only 2 simple lines I think it is fine to duplicate them here.
When I rewrite the PRNG to use an xorshift* algorithm I'll make sure to add a
helper function to advance the state though.

 
-int Random::Rand(int low, int high) {
+uint32_t Random::Uniform(uint32_t t) {
+  uint64_t result = t;
+  result = b_ * (result + 1);
+  result = result >> 32;

[the sun, 2015/10/22 12:30:38]

Nice!

+  a_ ^= b_;
+  b_ += a_;
+  return result;
+}
+
+uint32_t Random::Uniform(uint32_t low, uint32_t high) {
   RTC_DCHECK(low <= high);
-  float uniform = Rand() * (high - low + 1) + low;
-  return static_cast<int>(uniform);
+  return Uniform(high - low) + low;
 }
 
 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