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| 1 // Copyright 2016 The Chromium Authors. All rights reserved. |
| 2 // Use of this source code is governed by a BSD-style license that can be |
| 3 // found in the LICENSE file. |
| 4 |
| 5 #ifndef NET_BASE_PERCENTILE_ESTIMATOR_H_ |
| 6 #define NET_BASE_PERCENTILE_ESTIMATOR_H_ |
| 7 |
| 8 #include "base/callback.h" |
| 9 #include "base/macros.h" |
| 10 #include "net/base/net_export.h" |
| 11 |
| 12 namespace net { |
| 13 |
| 14 // This class estimates statistical percentiles (e.g. 10%l, 50%l) for |
| 15 // integer distributions presented in stream form. These estimates |
| 16 // adjust automatically when the stream distribution changes. |
| 17 // TODO(rdsmith): Expand the class to maintain floating point |
| 18 // estimates rather than integer estimates, when there's a use case |
| 19 // for that that deserves the extra complexity and pitfalls of |
| 20 // floating point arithmetic. |
| 21 class NET_EXPORT PercentileEstimator { |
| 22 public: |
| 23 using RandomNumberCallback = base::Callback<int(void)>; |
| 24 |
| 25 static const int kMedianPercentile = 50; |
| 26 |
| 27 // |percentile| is a number between 0 and 100 indicating what percentile |
| 28 // should be estimated (e.g. 50 would be a median estimate). |
| 29 // |initial_estimate| is the value the class is seeded with; in other |
| 30 // words, if AddSample() is never called, |
| 31 // |CurrentEstimate() == initial_estimate|. |
| 32 PercentileEstimator(int percentile, int initial_estimate); |
| 33 |
| 34 ~PercentileEstimator(); |
| 35 |
| 36 int current_estimate() const { return current_estimate_; } |
| 37 void AddSample(int sample); |
| 38 |
| 39 // Specify a callback that will generate a "random" number |
| 40 // in the range [0,99] on each call. Used so that tests can |
| 41 // rely on reproducible behavior. |
| 42 void SetRandomNumberGeneratorForTesting( |
| 43 RandomNumberCallback generator_callback); |
| 44 |
| 45 private: |
| 46 const int percentile_; |
| 47 |
| 48 bool sign_positive_; |
| 49 int current_estimate_; |
| 50 int current_step_; |
| 51 |
| 52 RandomNumberCallback generator_callback_; |
| 53 |
| 54 DISALLOW_COPY_AND_ASSIGN(PercentileEstimator); |
| 55 }; |
| 56 |
| 57 } // namespace net |
| 58 |
| 59 #endif // NET_BASE_PERCENTILE_ESTIMATOR_H_ |
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