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/*
* Copyright (c) 2017 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_NUMERICS_MOVING_MAX_COUNTER_H_
#define RTC_BASE_NUMERICS_MOVING_MAX_COUNTER_H_
#include <stdint.h>
#include <deque>
#include <limits>
#include <optional>
#include <utility>
#include "rtc_base/checks.h"
namespace rtc {
// Implements moving max: can add samples to it and calculate maximum over some
// fixed moving window.
//
// Window size is configured at constructor.
// Samples can be added with `Add()` and max over current window is returned by
// `MovingMax`. `current_time_ms` in successive calls to Add and MovingMax
// should never decrease as if it's a wallclock time.
template <class T>
class MovingMaxCounter {
public:
explicit MovingMaxCounter(int64_t window_length_ms);
MovingMaxCounter(const MovingMaxCounter&) = delete;
MovingMaxCounter& operator=(const MovingMaxCounter&) = delete;
// Advances the current time, and adds a new sample. The new current time must
// be at least as large as the old current time.
void Add(const T& sample, int64_t current_time_ms);
// Advances the current time, and returns the maximum sample in the time
// window ending at the current time. The new current time must be at least as
// large as the old current time.
std::optional<T> Max(int64_t current_time_ms);
void Reset();
private:
// Throws out obsolete samples.
void RollWindow(int64_t new_time_ms);
const int64_t window_length_ms_;
// This deque stores (timestamp, sample) pairs in chronological order; new
// pairs are only ever added at the end. However, because they can't affect
// the Max() calculation, pairs older than window_length_ms_ are discarded,
// and if an older pair has a sample that's smaller than that of a younger
// pair, the older pair is discarded. As a result, the sequence of timestamps
// is strictly increasing, and the sequence of samples is strictly decreasing.
std::deque<std::pair<int64_t, T>> samples_;
#if RTC_DCHECK_IS_ON
int64_t last_call_time_ms_ = std::numeric_limits<int64_t>::min();
#endif
};
template <class T>
MovingMaxCounter<T>::MovingMaxCounter(int64_t window_length_ms)
: window_length_ms_(window_length_ms) {}
template <class T>
void MovingMaxCounter<T>::Add(const T& sample, int64_t current_time_ms) {
RollWindow(current_time_ms);
// Remove samples that will never be maximum in any window: newly added sample
// will always be in all windows the previous samples are. Thus, smaller or
// equal samples could be removed. This will maintain the invariant - deque
// contains strictly decreasing sequence of values.
while (!samples_.empty() && samples_.back().second <= sample) {
samples_.pop_back();
}
// Add the new sample but only if there's no existing sample at the same time.
// Due to checks above, the already existing element will be larger, so the
// new sample will never be the maximum in any window.
if (samples_.empty() || samples_.back().first < current_time_ms) {
samples_.emplace_back(std::make_pair(current_time_ms, sample));
}
}
template <class T>
std::optional<T> MovingMaxCounter<T>::Max(int64_t current_time_ms) {
RollWindow(current_time_ms);
std::optional<T> res;
if (!samples_.empty()) {
res.emplace(samples_.front().second);
}
return res;
}
template <class T>
void MovingMaxCounter<T>::Reset() {
samples_.clear();
}
template <class T>
void MovingMaxCounter<T>::RollWindow(int64_t new_time_ms) {
#if RTC_DCHECK_IS_ON
RTC_DCHECK_GE(new_time_ms, last_call_time_ms_);
last_call_time_ms_ = new_time_ms;
#endif
const int64_t window_begin_ms = new_time_ms - window_length_ms_;
auto it = samples_.begin();
while (it != samples_.end() && it->first < window_begin_ms) {
++it;
}
samples_.erase(samples_.begin(), it);
}
} // namespace rtc
#endif // RTC_BASE_NUMERICS_MOVING_MAX_COUNTER_H_