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diff --git a/util/histogram.h b/util/histogram.h
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+++ b/util/histogram.h
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+// Copyright (c) 2011 The LevelDB Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file. See the AUTHORS file for names of contributors.
+
+#ifndef STORAGE_LEVELDB_UTIL_HISTOGRAM_H_
+#define STORAGE_LEVELDB_UTIL_HISTOGRAM_H_
+
+#include <string>
+
+namespace leveldb {
+
+class Histogram {
+ public:
+  Histogram() { }
+  ~Histogram() { }
+
+  void Clear();
+  void Add(double value);
+  void Merge(const Histogram& other);
+
+  std::string ToString() const;
+
+ private:
+  double min_;
+  double max_;
+  double num_;
+  double sum_;
+  double sum_squares_;
+
+  enum { kNumBuckets = 154 };
+  static const double kBucketLimit[kNumBuckets];
+  double buckets_[kNumBuckets];
+
+  double Median() const;
+  double Percentile(double p) const;
+  double Average() const;
+  double StandardDeviation() const;
+};
+
+}  // namespace leveldb
+
+#endif  // STORAGE_LEVELDB_UTIL_HISTOGRAM_H_