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+/*
+ *
+ * Copyright 2015, Google Inc.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ *     * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *     * Redistributions in binary form must reproduce the above
+ * copyright notice, this list of conditions and the following disclaimer
+ * in the documentation and/or other materials provided with the
+ * distribution.
+ *     * Neither the name of Google Inc. nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ */
+
+/**
+ * Histogram module. Exports the Histogram class
+ * @module
+ */
+
+'use strict';
+
+/**
+ * Histogram class. Collects data and exposes a histogram and other statistics.
+ * This data structure is taken directly from src/core/support/histogram.c, but
+ * pared down to the statistics needed for client stats in
+ * test/proto/benchmarks/stats.proto.
+ * @constructor
+ * @param {number} resolution The histogram's bucket resolution. Must be positive
+ * @param {number} max_possible The maximum allowed value. Must be greater than 1
+ */
+function Histogram(resolution, max_possible) {
+  this.resolution = resolution;
+  this.max_possible = max_possible;
+
+  this.sum = 0;
+  this.sum_of_squares = 0;
+  this.multiplier = 1 + resolution;
+  this.count = 0;
+  this.min_seen = max_possible;
+  this.max_seen = 0;
+  this.buckets = [];
+  for (var i = 0; i < this.bucketFor(max_possible) + 1; i++) {
+    this.buckets[i] = 0;
+  }
+}
+
+/**
+ * Get the bucket index for a given value.
+ * @param {number} value The value to check
+ * @return {number} The bucket index
+ */
+Histogram.prototype.bucketFor = function(value) {
+  return Math.floor(Math.log(value) / Math.log(this.multiplier));
+};
+
+/**
+ * Get the minimum value for a given bucket index
+ * @param {number} The bucket index to check
+ * @return {number} The minimum value for that bucket
+ */
+Histogram.prototype.bucketStart = function(index) {
+  return Math.pow(this.multiplier, index);
+};
+
+/**
+ * Add a value to the histogram. This updates all statistics with the new
+ * value. Those statistics should not be modified except with this function
+ * @param {number} value The value to add
+ */
+Histogram.prototype.add = function(value) {
+  // Ensure value is a number
+  value = +value;
+  this.sum += value;
+  this.sum_of_squares += value * value;
+  this.count++;
+  if (value < this.min_seen) {
+    this.min_seen = value;
+  }
+  if (value > this.max_seen) {
+    this.max_seen = value;
+  }
+  this.buckets[this.bucketFor(value)]++;
+};
+
+/**
+ * Get the mean of all added values
+ * @return {number} The mean
+ */
+Histogram.prototype.mean = function() {
+  return this.sum / this.count;
+};
+
+/**
+ * Get the variance of all added values. Used to calulate the standard deviation
+ * @return {number} The variance
+ */
+Histogram.prototype.variance = function() {
+  if (this.count == 0) {
+    return 0;
+  }
+  return (this.sum_of_squares * this.count - this.sum * this.sum) /
+      (this.count * this.count);
+};
+
+/**
+ * Get the standard deviation of all added values
+ * @return {number} The standard deviation
+ */
+Histogram.prototype.stddev = function() {
+  return Math.sqrt(this.variance);
+};
+
+/**
+ * Get the maximum among all added values
+ * @return {number} The maximum
+ */
+Histogram.prototype.maximum = function() {
+  return this.max_seen;
+};
+
+/**
+ * Get the minimum among all added values
+ * @return {number} The minimum
+ */
+Histogram.prototype.minimum = function() {
+  return this.min_seen;
+};
+
+/**
+ * Get the number of all added values
+ * @return {number} The count
+ */
+Histogram.prototype.getCount = function() {
+  return this.count;
+};
+
+/**
+ * Get the sum of all added values
+ * @return {number} The sum
+ */
+Histogram.prototype.getSum = function() {
+  return this.sum;
+};
+
+/**
+ * Get the sum of squares of all added values
+ * @return {number} The sum of squares
+ */
+Histogram.prototype.sumOfSquares = function() {
+  return this.sum_of_squares;
+};
+
+/**
+ * Get the raw histogram as a list of bucket sizes
+ * @return {Array.<number>} The buckets
+ */
+Histogram.prototype.getContents = function() {
+  return this.buckets;
+};
+
+module.exports = Histogram;