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// 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_BASE_PERCENTILE_ESTIMATOR_H_
#define NET_BASE_PERCENTILE_ESTIMATOR_H_
#include "base/callback.h"
#include "base/macros.h"
#include "net/base/net_export.h"
namespace net {
// This class estimates statistical percentiles (e.g. 10%l, 50%l) for
// integer distributions presented in stream form. These estimates
// adjust automatically when the stream distribution changes.
// TODO(rdsmith): Expand the class to maintain floating point
// estimates rather than integer estimates, when there's a use case
// for that that deserves the extra complexity and pitfalls of
// floating point arithmetic.
class NET_EXPORT PercentileEstimator {
public:
using RandomNumberCallback = base::Callback<int(void)>;
static const int kMedianPercentile = 50;
// |percentile| is a number between 0 and 100 indicating what percentile
// should be estimated (e.g. 50 would be a median estimate).
// |initial_estimate| is the value the class is seeded with; in other
// words, if AddSample() is never called,
// |CurrentEstimate() == initial_estimate|.
PercentileEstimator(int percentile, int initial_estimate);
~PercentileEstimator();
int current_estimate() const { return current_estimate_; }
void AddSample(int sample);
// Specify a callback that will generate a "random" number
// in the range [0,99] on each call. Used so that tests can
// rely on reproducible behavior.
void SetRandomNumberGeneratorForTesting(
RandomNumberCallback generator_callback);
private:
const int percentile_;
bool sign_positive_;
int current_estimate_;
int current_step_;
RandomNumberCallback generator_callback_;
DISALLOW_COPY_AND_ASSIGN(PercentileEstimator);
};
} // namespace net
#endif // NET_BASE_PERCENTILE_ESTIMATOR_H_
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