64 lines
2.0 KiB
C++
64 lines
2.0 KiB
C++
// Copyright 2014 Google Inc. All rights reserved.
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//
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file or at
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// https://developers.google.com/open-source/licenses/bsd
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#include "mpd/base/bandwidth_estimator.h"
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#include <cmath>
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#include <cstdlib>
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#include "base/logging.h"
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const int BandwidthEstimator::kUseAllBlocks = 0;
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BandwidthEstimator::BandwidthEstimator(int num_blocks)
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: num_blocks_for_estimation_(num_blocks),
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harmonic_mean_denominator_(0.0),
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num_blocks_added_(0) {}
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BandwidthEstimator::~BandwidthEstimator() {}
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void BandwidthEstimator::AddBlock(uint64 size, double duration) {
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DCHECK_GT(duration, 0.0);
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DCHECK_GT(size, 0u);
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if (num_blocks_for_estimation_ < 0 &&
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static_cast<int>(history_.size()) >= -1 * num_blocks_for_estimation_) {
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// Short circuiting the case where |num_blocks_for_estimation_| number of
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// blocks have been added already.
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return;
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}
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const int kBitsInByte = 8;
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const double bits_per_second_reciprocal = duration / (kBitsInByte * size);
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harmonic_mean_denominator_ += bits_per_second_reciprocal;
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if (num_blocks_for_estimation_ == kUseAllBlocks) {
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DCHECK_EQ(history_.size(), 0u);
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++num_blocks_added_;
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return;
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}
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history_.push_back(bits_per_second_reciprocal);
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if (num_blocks_for_estimation_ > 0 &&
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static_cast<int>(history_.size()) > num_blocks_for_estimation_) {
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harmonic_mean_denominator_ -= history_.front();
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history_.pop_front();
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}
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DCHECK_NE(num_blocks_for_estimation_, kUseAllBlocks);
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DCHECK_LE(static_cast<int>(history_.size()), abs(num_blocks_for_estimation_));
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DCHECK_EQ(num_blocks_added_, 0u);
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return;
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}
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uint64 BandwidthEstimator::Estimate() const {
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if (harmonic_mean_denominator_ == 0.0)
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return 0;
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const uint64 num_blocks = num_blocks_for_estimation_ == kUseAllBlocks
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? num_blocks_added_
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: history_.size();
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return static_cast<uint64>(ceil(num_blocks / harmonic_mean_denominator_));
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}
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