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      1 /*
      2  * Copyright (C) 2013 The Android Open Source Project
      3  *
      4  * Licensed under the Apache License, Version 2.0 (the "License");
      5  * you may not use this file except in compliance with the License.
      6  * You may obtain a copy of the License at
      7  *
      8  *      http://www.apache.org/licenses/LICENSE-2.0
      9  *
     10  * Unless required by applicable law or agreed to in writing, software
     11  * distributed under the License is distributed on an "AS IS" BASIS,
     12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     13  * See the License for the specific language governing permissions and
     14  * limitations under the License.
     15  */
     16 #ifndef ART_RUNTIME_BASE_HISTOGRAM_H_
     17 #define ART_RUNTIME_BASE_HISTOGRAM_H_
     18 
     19 #include <vector>
     20 #include <string>
     21 
     22 #include "base/logging.h"
     23 
     24 namespace art {
     25 
     26 // Creates a data histogram  for a better understanding of statistical data.
     27 // Histogram analysis goes beyond simple mean and standard deviation to provide
     28 // percentiles values, describing where the $% of the input data lies.
     29 // Designed to be simple and used with timing logger in art.
     30 
     31 template <class Value> class Histogram {
     32   const double kAdjust;
     33   const size_t kInitialBucketCount;
     34 
     35  public:
     36   class CumulativeData {
     37     friend class Histogram<Value>;
     38     std::vector<uint64_t> freq_;
     39     std::vector<double> perc_;
     40   };
     41 
     42   // Used by the cumulative timing logger to search the histogram set using for an existing split
     43   // with the same name using CumulativeLogger::HistogramComparator.
     44   explicit Histogram(const char* name);
     45   // This is the expected constructor when creating new Histograms.
     46   Histogram(const char* name, Value initial_bucket_width, size_t max_buckets = 100);
     47   void AddValue(Value);
     48   void AdjustAndAddValue(Value);  // Add a value after dividing it by kAdjust.
     49   // Builds the cumulative distribution function from the frequency data.
     50   // Accumulative summation of frequencies.
     51   // cumulative_freq[i] = sum(frequency[j] : 0 < j < i )
     52   // Accumulative summation of percentiles; which is the frequency / SampleSize
     53   // cumulative_perc[i] = sum(frequency[j] / SampleSize : 0 < j < i )
     54   void CreateHistogram(CumulativeData* data) const;
     55   // Reset the cumulative values, next time CreateHistogram is called it will recreate the cache.
     56   void Reset();
     57   double Mean() const;
     58   double Variance() const;
     59   double Percentile(double per, const CumulativeData& data) const;
     60   void PrintConfidenceIntervals(std::ostream& os, double interval,
     61                                 const CumulativeData& data) const;
     62   void PrintBins(std::ostream& os, const CumulativeData& data) const;
     63   void DumpBins(std::ostream& os) const;
     64   Value GetRange(size_t bucket_idx) const;
     65   size_t GetBucketCount() const;
     66 
     67   uint64_t SampleSize() const {
     68     return sample_size_;
     69   }
     70 
     71   Value Sum() const {
     72     return sum_;
     73   }
     74 
     75   Value AdjustedSum() const {
     76     return sum_ * kAdjust;
     77   }
     78 
     79   Value Min() const {
     80     return min_value_added_;
     81   }
     82 
     83   Value Max() const {
     84     return max_value_added_;
     85   }
     86 
     87   const std::string& Name() const {
     88     return name_;
     89   }
     90 
     91  private:
     92   void Initialize();
     93   size_t FindBucket(Value val) const;
     94   void BucketiseValue(Value val);
     95   // Add more buckets to the histogram to fill in a new value that exceeded
     96   // the max_read_value_.
     97   void GrowBuckets(Value val);
     98   std::string name_;
     99   // Maximum number of buckets.
    100   const size_t max_buckets_;
    101   // Number of samples placed in histogram.
    102   size_t sample_size_;
    103   // Width of the bucket range. The lower the value is the more accurate
    104   // histogram percentiles are. Grows adaptively when we hit max buckets.
    105   Value bucket_width_;
    106   // How many occurrences of values fall within a bucket at index i where i covers the range
    107   // starting at  min_ + i * bucket_width_ with size bucket_size_.
    108   std::vector<uint32_t> frequency_;
    109   // Summation of all the elements inputed by the user.
    110   Value sum_;
    111   // Minimum value that can fit in the histogram. Fixed to zero for now.
    112   Value min_;
    113   // Maximum value that can fit in the histogram, grows adaptively.
    114   Value max_;
    115   // Summation of the values entered. Used to calculate variance.
    116   Value sum_of_squares_;
    117   // Maximum value entered in the histogram.
    118   Value min_value_added_;
    119   // Minimum value entered in the histogram.
    120   Value max_value_added_;
    121 
    122   DISALLOW_COPY_AND_ASSIGN(Histogram);
    123 };
    124 }  // namespace art
    125 
    126 #endif  // ART_RUNTIME_BASE_HISTOGRAM_H_
    127