NQE: Add more statistics to ObservationBuffer class

net/nqe/observation_buffer.h

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef NET_NQE_OBSERVATION_BUFFER_H_
 #define NET_NQE_OBSERVATION_BUFFER_H_
 
 #include <float.h>
 
 #include <algorithm>
@@ skipping 104 matching lines @@
 
     // Computation may reach here due to floating point errors. This may happen
     // if |percentile| was 100 (or close to 100), and |desired_weight| was
     // slightly larger than |total_weight| (due to floating point errors).
     // In this case, we return the highest |value| among all observations.
     // This is same as value of the last observation in the sorted vector.
     *result = weighted_observations.at(weighted_observations.size() - 1).value;
     return true;
   }
 
+  // Returns true iff the weighted average of the observations in this

[Not at Google. Contact bengr, 2016/10/12 22:09:52]

Can you clarify why weighted average might not be available. I am guessing that:
// Returns false if all of the |observations_| are in
|disallowed_observation_sources|.

Same for below.

[tbansal1, 2016/10/12 22:45:01]

Done.

+  // buffer is available. Sets |result| to the computed weighted average value
+  // among all observations since |begin_timestamp|. If the value is
+  // unavailable, false is returned and |result| is not modified. |result| must
+  // not be null.
+  bool GetWeightedAverage(const base::TimeTicks begin_timestamp,
+                          const std::vector<NetworkQualityObservationSource>&
+                              disallowed_observation_sources,
+                          ValueType* result) const {
+    DCHECK(result);
+    DCHECK_GE(Capacity(), Size());
+
+    // Stores WeightedObservation in increasing order of value.
+    std::vector<WeightedObservation<ValueType>> weighted_observations;
+
+    // Total weight of all observations in |weighted_observations|.
+    double total_weight = 0.0;
+
+    ComputeWeightedObservations(begin_timestamp, weighted_observations,
+                                &total_weight, disallowed_observation_sources);
+    if (weighted_observations.empty())
+      return false;
+
+    DCHECK_LT(0.0, total_weight);
+
+    // |weighted_observations| may have a smaller size than |observations_|
+    // since the former contains only the observations later than
+    // |begin_timestamp|.
+    DCHECK_GE(observations_.size(), weighted_observations.size());
+
+    // Weighted average is the sum of observations times their respective
+    // weight, divided by the sum of weights of all observations.
+    double total_weight_times_value = 0.0;
+    for (const auto& weighted_observation : weighted_observations) {
+      total_weight_times_value +=
+          (weighted_observation.weight *
+           ConvertValueTypeToDouble(weighted_observation.value));
+    }
+
+    ConvertDoubleToValueType(total_weight_times_value / total_weight, result);
+    return true;
+  }
+
+  // Returns true iff the unweighted average of the observations in this buffer
+  // is available. Sets |result| to the computed unweighted average value among
+  // all observations since |begin_timestamp|. If the value is unavailable,
+  // false is returned and |result| is not modified. |result| must not be null.
+  bool GetUnweightedAverage(const base::TimeTicks begin_timestamp,
+                            const std::vector<NetworkQualityObservationSource>&
+                                disallowed_observation_sources,
+                            ValueType* result) const {
+    DCHECK(result);
+    DCHECK_GE(Capacity(), Size());
+
+    // Stores WeightedObservation in increasing order of value.
+    std::vector<WeightedObservation<ValueType>> weighted_observations;
+
+    // Total weight of all observations in |weighted_observations|.
+    double total_weight = 0.0;
+
+    ComputeWeightedObservations(begin_timestamp, weighted_observations,
+                                &total_weight, disallowed_observation_sources);
+    if (weighted_observations.empty())
+      return false;
+
+    // |weighted_observations| may have a smaller size than |observations_|
+    // since the former contains only the observations later than
+    // |begin_timestamp|.
+    DCHECK_GE(observations_.size(), weighted_observations.size());
+
+    // Unweighted average is the sum of all observations divided by the number
+    // of observations.
+    double total_value = 0.0;
+    for (const auto& weighted_observation : weighted_observations)
+      total_value += ConvertValueTypeToDouble(weighted_observation.value);
+
+    ConvertDoubleToValueType(total_value / weighted_observations.size(),
+                             result);
+    return true;
+  }
+
   void SetTickClockForTesting(std::unique_ptr<base::TickClock> tick_clock) {
     tick_clock_ = std::move(tick_clock);
   }
 
  private:
   // Maximum number of observations that can be held in the ObservationBuffer.
   static const size_t kMaximumObservationsBufferSize = 300;
 
+  // Convert different ValueTypes to double to make it possible to perform
+  // arithmetic operations on them.
+  double ConvertValueTypeToDouble(base::TimeDelta input) const {
+    return input.InMilliseconds();
+  }
+  double ConvertValueTypeToDouble(int32_t input) const { return input; }
+
+  // Convert double to different ValueTypes.
+  void ConvertDoubleToValueType(double input, base::TimeDelta* output) const {
+    *output = base::TimeDelta::FromMilliseconds(input);
+  }
+  void ConvertDoubleToValueType(double input, int32_t* output) const {
+    *output = input;
+  }
+
   // Computes the weighted observations and stores them in
   // |weighted_observations| sorted by ascending |WeightedObservation.value|.
   // Only the observations with timestamp later than |begin_timestamp| are
   // considered. Also, sets |total_weight| to the total weight of all
   // observations. Should be called only when there is at least one
   // observation in the buffer.
   void ComputeWeightedObservations(
       const base::TimeTicks& begin_timestamp,
       std::vector<WeightedObservation<ValueType>>& weighted_observations,
       double* total_weight,
@@ skipping 46 matching lines @@
   DISALLOW_COPY_AND_ASSIGN(ObservationBuffer);
 };
 
 }  // namespace internal
 
 }  // namespace nqe
 
 }  // namespace net
 
 #endif  // NET_NQE_OBSERVATION_BUFFER_H_