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diff --git a/toolkit/components/places/ClusterLib.js b/toolkit/components/places/ClusterLib.js
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+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+/**
+ * Class that can run the hierarchical clustering algorithm with the given
+ * parameters.
+ *
+ * @param distance
+ *        Function that should return the distance between two items.
+ *        Defaults to clusterlib.euclidean_distance.
+ * @param merge
+ *        Function that should take in two items and return a merged one.
+ *        Defaults to clusterlib.average_linkage.
+ * @param threshold
+ *        The maximum distance between two items for which their clusters
+ *        can be merged.
+ */
+function HierarchicalClustering(distance, merge, threshold) {
+  this.distance = distance || clusterlib.euclidean_distance;
+  this.merge = merge || clusterlib.average_linkage;
+  this.threshold = threshold == undefined ? Infinity : threshold;
+}
+
+HierarchicalClustering.prototype = {
+  /**
+   * Run the hierarchical clustering algorithm on the given items to produce
+   * a final set of clusters.  Uses the parameters set in the constructor.
+   *
+   * @param items
+   *        An array of "things" to cluster - this is the domain-specific
+   *        collection you're trying to cluster (colors, points, etc.)
+   * @param snapshotGap
+   *        How many iterations of the clustering algorithm to wait between
+   *        calling the snapshotCallback
+   * @param snapshotCallback
+   *        If provided, will be called as clusters are merged to let you view
+   *        the progress of the algorithm.  Passed the current array of
+   *        clusters, cached distances, and cached closest clusters.
+   *
+   * @return An array of merged clusters.  The represented item can be
+   *         found in the "item" property of the cluster.
+   */
+  cluster: function HC_cluster(items, snapshotGap, snapshotCallback) {
+    // array of all remaining clusters
+    let clusters = [];
+    // 2D matrix of distances between each pair of clusters, indexed by key
+    let distances = [];
+    // closest cluster key for each cluster, indexed by key
+    let neighbors = [];
+    // an array of all clusters, but indexed by key
+    let clustersByKey = [];
+
+    // set up clusters from the initial items array
+    for (let index = 0; index < items.length; index++) {
+      let cluster = {
+        // the item this cluster represents
+        item: items[index],
+        // a unique key for this cluster, stays constant unless merged itself
+        key: index,
+        // index of cluster in clusters array, can change during any merge
+        index: index,
+        // how many clusters have been merged into this one
+        size: 1
+      };
+      clusters[index] = cluster;
+      clustersByKey[index] = cluster;
+      distances[index] = [];
+      neighbors[index] = 0;
+    }
+
+    // initialize distance matrix and cached neighbors
+    for (let i = 0; i < clusters.length; i++) {
+      for (let j = 0; j <= i; j++) {
+        var dist = (i == j) ? Infinity :
+          this.distance(clusters[i].item, clusters[j].item);
+        distances[i][j] = dist;
+        distances[j][i] = dist;
+
+        if (dist < distances[i][neighbors[i]]) {
+          neighbors[i] = j;
+        }
+      }
+    }
+
+    // merge the next two closest clusters until none of them are close enough
+    let next = null, i = 0;
+    for (; next = this.closestClusters(clusters, distances, neighbors); i++) {
+      if (snapshotCallback && (i % snapshotGap) == 0) {
+        snapshotCallback(clusters);
+      }
+      this.mergeClusters(clusters, distances, neighbors, clustersByKey,
+                         clustersByKey[next[0]], clustersByKey[next[1]]);
+    }
+    return clusters;
+  },
+
+  /**
+   * Once we decide to merge two clusters in the cluster method, actually
+   * merge them.  Alters the given state of the algorithm.
+   *
+   * @param clusters
+   *        The array of all remaining clusters
+   * @param distances
+   *        Cached distances between pairs of clusters
+   * @param neighbors
+   *        Cached closest clusters
+   * @param clustersByKey
+   *        Array of all clusters, indexed by key
+   * @param cluster1
+   *        First cluster to merge
+   * @param cluster2
+   *        Second cluster to merge
+   */
+  mergeClusters: function HC_mergeClus(clusters, distances, neighbors,
+                                       clustersByKey, cluster1, cluster2) {
+    let merged = { item: this.merge(cluster1.item, cluster2.item),
+                   left: cluster1,
+                   right: cluster2,
+                   key: cluster1.key,
+                   size: cluster1.size + cluster2.size };
+
+    clusters[cluster1.index] = merged;
+    clusters.splice(cluster2.index, 1);
+    clustersByKey[cluster1.key] = merged;
+
+    // update distances with new merged cluster
+    for (let i = 0; i < clusters.length; i++) {
+      var ci = clusters[i];
+      var dist;
+      if (cluster1.key == ci.key) {
+        dist = Infinity;
+      } else if (this.merge == clusterlib.single_linkage) {
+        dist = distances[cluster1.key][ci.key];
+        if (distances[cluster1.key][ci.key] >
+            distances[cluster2.key][ci.key]) {
+          dist = distances[cluster2.key][ci.key];
+        }
+      } else if (this.merge == clusterlib.complete_linkage) {
+        dist = distances[cluster1.key][ci.key];
+        if (distances[cluster1.key][ci.key] <
+            distances[cluster2.key][ci.key]) {
+          dist = distances[cluster2.key][ci.key];
+        }
+      } else if (this.merge == clusterlib.average_linkage) {
+        dist = (distances[cluster1.key][ci.key] * cluster1.size
+              + distances[cluster2.key][ci.key] * cluster2.size)
+              / (cluster1.size + cluster2.size);
+      } else {
+        dist = this.distance(ci.item, cluster1.item);
+      }
+
+      distances[cluster1.key][ci.key] = distances[ci.key][cluster1.key]
+                                      = dist;
+    }
+
+    // update cached neighbors
+    for (let i = 0; i < clusters.length; i++) {
+      var key1 = clusters[i].key;
+      if (neighbors[key1] == cluster1.key ||
+          neighbors[key1] == cluster2.key) {
+        let minKey = key1;
+        for (let j = 0; j < clusters.length; j++) {
+          var key2 = clusters[j].key;
+          if (distances[key1][key2] < distances[key1][minKey]) {
+            minKey = key2;
+          }
+        }
+        neighbors[key1] = minKey;
+      }
+      clusters[i].index = i;
+    }
+  },
+
+  /**
+   * Given the current state of the algorithm, return the keys of the two
+   * clusters that are closest to each other so we know which ones to merge
+   * next.
+   *
+   * @param clusters
+   *        The array of all remaining clusters
+   * @param distances
+   *        Cached distances between pairs of clusters
+   * @param neighbors
+   *        Cached closest clusters
+   *
+   * @return An array of two keys of clusters to merge, or null if there are
+   *         no more clusters close enough to merge
+   */
+  closestClusters: function HC_closestClus(clusters, distances, neighbors) {
+    let minKey = 0, minDist = Infinity;
+    for (let i = 0; i < clusters.length; i++) {
+      var key = clusters[i].key;
+      if (distances[key][neighbors[key]] < minDist) {
+        minKey = key;
+        minDist = distances[key][neighbors[key]];
+      }
+    }
+    if (minDist < this.threshold) {
+      return [minKey, neighbors[minKey]];
+    }
+    return null;
+  }
+};
+
+var clusterlib = {
+  hcluster: function hcluster(items, distance, merge, threshold, snapshotGap,
+                              snapshotCallback) {
+    return (new HierarchicalClustering(distance, merge, threshold))
+           .cluster(items, snapshotGap, snapshotCallback);
+  },
+
+  single_linkage: function single_linkage(cluster1, cluster2) {
+    return cluster1;
+  },
+
+  complete_linkage: function complete_linkage(cluster1, cluster2) {
+    return cluster1;
+  },
+
+  average_linkage: function average_linkage(cluster1, cluster2) {
+    return cluster1;
+  },
+
+  euclidean_distance: function euclidean_distance(v1, v2) {
+    let total = 0;
+    for (let i = 0; i < v1.length; i++) {
+      total += Math.pow(v2[i] - v1[i], 2);
+    }
+    return Math.sqrt(total);
+  },
+
+  manhattan_distance: function manhattan_distance(v1, v2) {
+    let total = 0;
+    for (let i = 0; i < v1.length; i++) {
+      total += Math.abs(v2[i] - v1[i]);
+    }
+    return total;
+  },
+
+  max_distance: function max_distance(v1, v2) {
+    let max = 0;
+    for (let i = 0; i < v1.length; i++) {
+      max = Math.max(max, Math.abs(v2[i] - v1[i]));
+    }
+    return max;
+  }
+};