Templatize percentile_filter.h and move it to base/analytics.

BUG=None

Review-Url: https://codereview.webrtc.org/2529063002
Cr-Commit-Position: refs/heads/master@{#15334}

webrtc/base/BUILD.gn

@@ -340,6 +340,10 @@ rtc_static_library("rtc_analytics") {
   sources = [
     "analytics/exp_filter.cc",
     "analytics/exp_filter.h",
+    "analytics/percentile_filter.h",
+  ]
+  deps = [
+    ":rtc_base_approved",
   ]
 }
 

webrtc/base/analytics/percentile_filter.h

@@ -0,0 +1,113 @@
+/*
+ *  Copyright (c) 2016 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 WEBRTC_BASE_ANALYTICS_PERCENTILE_FILTER_H_
+#define WEBRTC_BASE_ANALYTICS_PERCENTILE_FILTER_H_
+
+#include <stdint.h>
+
+#include <iterator>
+#include <set>
+
+#include "webrtc/base/checks.h"
+
+namespace webrtc {
+
+// Class to efficiently get the percentile value from a group of observations.
+// The percentile is the value below which a given percentage of the
+// observations fall.
+template <typename T>
+class PercentileFilter {
+ public:
+  // Construct filter. |percentile| should be between 0 and 1.
+  explicit PercentileFilter(float percentile);
+
+  // Insert one observation. The complexity of this operation is logarithmic in
+  // the size of the container.
+  void Insert(const T& value);
+
+  // Remove one observation. The complexity of this operation is logarithmic in
+  // the size of the container.
+  void Erase(const T& value);
+
+  // Get the percentile value. The complexity of this operation is constant.
+  T GetPercentileValue() const;
+
+ private:
+  // Update iterator and index to point at target percentile value.
+  void UpdatePercentileIterator();
+
+  const float percentile_;
+  std::multiset<T> set_;
+  // Maintain iterator and index of current target percentile value.
+  typename std::multiset<T>::iterator percentile_it_;
+  int64_t percentile_index_;
+};
+
+template <typename T>
+PercentileFilter<T>::PercentileFilter(float percentile)
+    : percentile_(percentile),
+      percentile_it_(set_.begin()),
+      percentile_index_(0) {
+  RTC_CHECK_GE(percentile, 0.0f);
+  RTC_CHECK_LE(percentile, 1.0f);
+}
+
+template <typename T>
+void PercentileFilter<T>::Insert(const T& value) {
+  // Insert element at the upper bound.
+  set_.insert(value);
+  if (set_.size() == 1u) {
+    // First element inserted - initialize percentile iterator and index.
+    percentile_it_ = set_.begin();
+    percentile_index_ = 0;
+  } else if (value < *percentile_it_) {
+    // If new element is before us, increment |percentile_index_|.
+    ++percentile_index_;
+  }
+  UpdatePercentileIterator();
+}
+
+template <typename T>
+void PercentileFilter<T>::Erase(const T& value) {
+  typename std::multiset<T>::const_iterator it = set_.lower_bound(value);
+  // Ignore erase operation if the element is not present in the current set.
+  if (it == set_.end() || *it != value)
+    return;
+  if (it == percentile_it_) {
+    // If same iterator, update to the following element. Index is not
+    // affected.
+    percentile_it_ = set_.erase(it);
+  } else {
+    set_.erase(it);
+    // If erased element was before us, decrement |percentile_index_|.
+    if (value <= *percentile_it_)
+      --percentile_index_;
+  }
+  UpdatePercentileIterator();
+}
+
+template <typename T>
+void PercentileFilter<T>::UpdatePercentileIterator() {
+  if (set_.empty())
+    return;
+  const int64_t index = static_cast<int64_t>(percentile_ * (set_.size() - 1));
+  std::advance(percentile_it_, index - percentile_index_);
+  percentile_index_ = index;
+}
+
+template <typename T>
+T PercentileFilter<T>::GetPercentileValue() const {
+  return set_.empty() ? 0 : *percentile_it_;
+}
+
+}  // namespace webrtc
+
+#endif  // WEBRTC_BASE_ANALYTICS_PERCENTILE_FILTER_H_

webrtc/base/analytics/percentile_filter_unittest.cc

@@ -0,0 +1,135 @@
+/*
+ *  Copyright 2016 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 <algorithm>
+#include <climits>
+
+#include "webrtc/base/analytics/percentile_filter.h"
+#include "webrtc/base/constructormagic.h"
+#include "webrtc/test/gtest.h"
+
+namespace webrtc {
+
+class PercentileFilterTest : public ::testing::TestWithParam<float> {
+ public:
+  PercentileFilterTest() : filter_(GetParam()) {
+    // Make sure the tests are deterministic by seeding with a constant.
+    srand(42);
+  }
+
+ protected:
+  PercentileFilter<int64_t> filter_;
+
+ private:
+  RTC_DISALLOW_COPY_AND_ASSIGN(PercentileFilterTest);
+};
+
+INSTANTIATE_TEST_CASE_P(PercentileFilterTests,
+                        PercentileFilterTest,
+                        ::testing::Values(0.0f, 0.1f, 0.5f, 0.9f, 1.0f));
+
+TEST(PercentileFilterTest, MinFilter) {
+  PercentileFilter<int64_t> filter(0.0f);
+  filter.Insert(4);
+  EXPECT_EQ(4, filter.GetPercentileValue());
+  filter.Insert(3);
+  EXPECT_EQ(3, filter.GetPercentileValue());
+}
+
+TEST(PercentileFilterTest, MaxFilter) {
+  PercentileFilter<int64_t> filter(1.0f);
+  filter.Insert(3);
+  EXPECT_EQ(3, filter.GetPercentileValue());
+  filter.Insert(4);
+  EXPECT_EQ(4, filter.GetPercentileValue());
+}
+
+TEST(PercentileFilterTest, MedianFilterDouble) {
+  PercentileFilter<double> filter(0.5f);
+  filter.Insert(2.71828);
+  filter.Insert(3.14159);
+  filter.Insert(1.41421);
+  EXPECT_EQ(2.71828, filter.GetPercentileValue());
+}
+
+TEST(PercentileFilterTest, MedianFilterInt) {
+  PercentileFilter<int> filter(0.5f);
+  filter.Insert(INT_MIN);
+  filter.Insert(1);
+  filter.Insert(2);
+  EXPECT_EQ(1, filter.GetPercentileValue());
+  filter.Insert(INT_MAX);
+  filter.Erase(INT_MIN);
+  EXPECT_EQ(2, filter.GetPercentileValue());
+}
+
+TEST(PercentileFilterTest, MedianFilterUnsigned) {
+  PercentileFilter<unsigned> filter(0.5f);
+  filter.Insert(UINT_MAX);
+  filter.Insert(2u);
+  filter.Insert(1u);
+  EXPECT_EQ(2u, filter.GetPercentileValue());
+  filter.Insert(0u);
+  filter.Erase(UINT_MAX);
+  EXPECT_EQ(1u, filter.GetPercentileValue());
+}
+
+TEST_P(PercentileFilterTest, EmptyFilter) {
+  EXPECT_EQ(0, filter_.GetPercentileValue());
+  filter_.Insert(3);
+  filter_.Erase(3);
+  EXPECT_EQ(0, filter_.GetPercentileValue());
+}
+
+TEST_P(PercentileFilterTest, EraseNonExistingElement) {
+  filter_.Erase(3);
+  EXPECT_EQ(0, filter_.GetPercentileValue());
+  filter_.Insert(4);
+  filter_.Erase(3);
+  EXPECT_EQ(4, filter_.GetPercentileValue());
+}
+
+TEST_P(PercentileFilterTest, DuplicateElements) {
+  filter_.Insert(3);
+  filter_.Insert(3);
+  filter_.Erase(3);
+  EXPECT_EQ(3, filter_.GetPercentileValue());
+}
+
+TEST_P(PercentileFilterTest, InsertAndEraseTenValuesInRandomOrder) {
+  int64_t zero_to_nine[10] = {0, 1, 2, 3, 4, 5, 6, 7, 8, 9};
+  // The percentile value of the ten values above.
+  const int64_t expected_value = static_cast<int64_t>(GetParam() * 9);
+
+  // Insert two sets of |zero_to_nine| in random order.
+  for (int i = 0; i < 2; ++i) {
+    std::random_shuffle(zero_to_nine, zero_to_nine + 10);
+    for (int64_t value : zero_to_nine)
+      filter_.Insert(value);
+    // After inserting a full set of |zero_to_nine|, the percentile should
+    // stay constant.
+    EXPECT_EQ(expected_value, filter_.GetPercentileValue());
+  }
+
+  // Insert and erase sets of |zero_to_nine| in random order a few times.
+  for (int i = 0; i < 3; ++i) {
+    std::random_shuffle(zero_to_nine, zero_to_nine + 10);
+    for (int64_t value : zero_to_nine)
+      filter_.Erase(value);
+    EXPECT_EQ(expected_value, filter_.GetPercentileValue());
+
+    std::random_shuffle(zero_to_nine, zero_to_nine + 10);
+    for (int64_t value : zero_to_nine)
+      filter_.Insert(value);
+    EXPECT_EQ(expected_value, filter_.GetPercentileValue());
+  }
+}
+
+}  // namespace webrtc