The Tor Browser: comparison js/src/v8/splay.js

comparison: js/src/v8/splay.js

js/src/v8/splay.js

changeset 0: 6474c204b198

equal deleted inserted replaced

--1:000000000000
+:ebbc1ddd8b12
+// Copyright 2009 the V8 project authors. 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.
+// This benchmark is based on a JavaScript log processing module used
+// by the V8 profiler to generate execution time profiles for runs of
+// JavaScript applications, and it effectively measures how fast the
+// JavaScript engine is at allocating nodes and reclaiming the memory
+// used for old nodes. Because of the way splay trees work, the engine
+// also has to deal with a lot of changes to the large tree object
+// graph.
+var Splay = new BenchmarkSuite('Splay', 81491, [
+new Benchmark("Splay", SplayRun, SplaySetup, SplayTearDown)
+]);
+// Configuration.
+var kSplayTreeSize = 8000;
+var kSplayTreeModifications = 80;
+var kSplayTreePayloadDepth = 5;
+var splayTree = null;
+function GeneratePayloadTree(depth, tag) {
+if (depth == 0) {
+return {
+array  : [ 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 ],
+string : 'String for key ' + tag + ' in leaf node'
+};
+} else {
+return {
+left:  GeneratePayloadTree(depth - 1, tag),
+right: GeneratePayloadTree(depth - 1, tag)
+};
+}
+}
+function GenerateKey() {
+// The benchmark framework guarantees that Math.random is
+// deterministic; see base.js.
+return Math.random();
+}
+function InsertNewNode() {
+// Insert new node with a unique key.
+var key;
+do {
+key = GenerateKey();
+} while (splayTree.find(key) != null);
+var payload = GeneratePayloadTree(kSplayTreePayloadDepth, String(key));
+splayTree.insert(key, payload);
+return key;
+}
+function SplaySetup() {
+splayTree = new SplayTree();
+for (var i = 0; i < kSplayTreeSize; i++) InsertNewNode();
+}
+function SplayTearDown() {
+// Allow the garbage collector to reclaim the memory
+// used by the splay tree no matter how we exit the
+// tear down function.
+var keys = splayTree.exportKeys();
+splayTree = null;
+// Verify that the splay tree has the right size.
+var length = keys.length;
+if (length != kSplayTreeSize) {
+throw new Error("Splay tree has wrong size");
+}
+// Verify that the splay tree has sorted, unique keys.
+for (var i = 0; i < length - 1; i++) {
+if (keys[i] >= keys[i + 1]) {
+throw new Error("Splay tree not sorted");
+}
+}
+}
+function SplayRun() {
+// Replace a few nodes in the splay tree.
+for (var i = 0; i < kSplayTreeModifications; i++) {
+var key = InsertNewNode();
+var greatest = splayTree.findGreatestLessThan(key);
+if (greatest == null) splayTree.remove(key);
+else splayTree.remove(greatest.key);
+}
+}
+/**
+* Constructs a Splay tree.  A splay tree is a self-balancing binary
+* search tree with the additional property that recently accessed
+* elements are quick to access again. It performs basic operations
+* such as insertion, look-up and removal in O(log(n)) amortized time.
+*
+* @constructor
+*/
+function SplayTree() {
+};
+/**
+* Pointer to the root node of the tree.
+*
+* @type {SplayTree.Node}
+* @private
+*/
+SplayTree.prototype.root_ = null;
+/**
+* @return {boolean} Whether the tree is empty.
+*/
+SplayTree.prototype.isEmpty = function() {
+return !this.root_;
+};
+/**
+* Inserts a node into the tree with the specified key and value if
+* the tree does not already contain a node with the specified key. If
+* the value is inserted, it becomes the root of the tree.
+*
+* @param {number} key Key to insert into the tree.
+* @param {*} value Value to insert into the tree.
+*/
+SplayTree.prototype.insert = function(key, value) {
+if (this.isEmpty()) {
+this.root_ = new SplayTree.Node(key, value);
+return;
+}
+// Splay on the key to move the last node on the search path for
+// the key to the root of the tree.
+this.splay_(key);
+if (this.root_.key == key) {
+return;
+}
+var node = new SplayTree.Node(key, value);
+if (key > this.root_.key) {
+node.left = this.root_;
+node.right = this.root_.right;
+this.root_.right = null;
+} else {
+node.right = this.root_;
+node.left = this.root_.left;
+this.root_.left = null;
+}
+this.root_ = node;
+};
+/**
+* Removes a node with the specified key from the tree if the tree
+* contains a node with this key. The removed node is returned. If the
+* key is not found, an exception is thrown.
+*
+* @param {number} key Key to find and remove from the tree.
+* @return {SplayTree.Node} The removed node.
+*/
+SplayTree.prototype.remove = function(key) {
+if (this.isEmpty()) {
+throw Error('Key not found: ' + key);
+}
+this.splay_(key);
+if (this.root_.key != key) {
+throw Error('Key not found: ' + key);
+}
+var removed = this.root_;
+if (!this.root_.left) {
+this.root_ = this.root_.right;
+} else {
+var right = this.root_.right;
+this.root_ = this.root_.left;
+// Splay to make sure that the new root has an empty right child.
+this.splay_(key);
+// Insert the original right child as the right child of the new
+// root.
+this.root_.right = right;
+}
+return removed;
+};
+/**
+* Returns the node having the specified key or null if the tree doesn't contain
+* a node with the specified key.
+*
+* @param {number} key Key to find in the tree.
+* @return {SplayTree.Node} Node having the specified key.
+*/
+SplayTree.prototype.find = function(key) {
+if (this.isEmpty()) {
+return null;
+}
+this.splay_(key);
+return this.root_.key == key ? this.root_ : null;
+};
+/**
+* @return {SplayTree.Node} Node having the maximum key value.
+*/
+SplayTree.prototype.findMax = function(opt_startNode) {
+if (this.isEmpty()) {
+return null;
+}
+var current = opt_startNode || this.root_;
+while (current.right) {
+current = current.right;
+}
+return current;
+};
+/**
+* @return {SplayTree.Node} Node having the maximum key value that
+*     is less than the specified key value.
+*/
+SplayTree.prototype.findGreatestLessThan = function(key) {
+if (this.isEmpty()) {
+return null;
+}
+// Splay on the key to move the node with the given key or the last
+// node on the search path to the top of the tree.
+this.splay_(key);
+// Now the result is either the root node or the greatest node in
+// the left subtree.
+if (this.root_.key < key) {
+return this.root_;
+} else if (this.root_.left) {
+return this.findMax(this.root_.left);
+} else {
+return null;
+}
+};
+/**
+* @return {Array<*>} An array containing all the keys of tree's nodes.
+*/
+SplayTree.prototype.exportKeys = function() {
+var result = [];
+if (!this.isEmpty()) {
+this.root_.traverse_(function(node) { result.push(node.key); });
+}
+return result;
+};
+/**
+* Perform the splay operation for the given key. Moves the node with
+* the given key to the top of the tree.  If no node has the given
+* key, the last node on the search path is moved to the top of the
+* tree. This is the simplified top-down splaying algorithm from:
+* "Self-adjusting Binary Search Trees" by Sleator and Tarjan
+*
+* @param {number} key Key to splay the tree on.
+* @private
+*/
+SplayTree.prototype.splay_ = function(key) {
+if (this.isEmpty()) {
+return;
+}
+// Create a dummy node.  The use of the dummy node is a bit
+// counter-intuitive: The right child of the dummy node will hold
+// the L tree of the algorithm.  The left child of the dummy node
+// will hold the R tree of the algorithm.  Using a dummy node, left
+// and right will always be nodes and we avoid special cases.
+var dummy, left, right;
+dummy = left = right = new SplayTree.Node(null, null);
+var current = this.root_;
+while (true) {
+if (key < current.key) {
+if (!current.left) {
+break;
+}
+if (key < current.left.key) {
+// Rotate right.
+var tmp = current.left;
+current.left = tmp.right;
+tmp.right = current;
+current = tmp;
+if (!current.left) {
+break;
+}
+}
+// Link right.
+right.left = current;
+right = current;
+current = current.left;
+} else if (key > current.key) {
+if (!current.right) {
+break;
+}
+if (key > current.right.key) {
+// Rotate left.
+var tmp = current.right;
+current.right = tmp.left;
+tmp.left = current;
+current = tmp;
+if (!current.right) {
+break;
+}
+}
+// Link left.
+left.right = current;
+left = current;
+current = current.right;
+} else {
+break;
+}
+}
+// Assemble.
+left.right = current.left;
+right.left = current.right;
+current.left = dummy.right;
+current.right = dummy.left;
+this.root_ = current;
+};
+/**
+* Constructs a Splay tree node.
+*
+* @param {number} key Key.
+* @param {*} value Value.
+*/
+SplayTree.Node = function(key, value) {
+this.key = key;
+this.value = value;
+};
+/**
+* @type {SplayTree.Node}
+*/
+SplayTree.Node.prototype.left = null;
+/**
+* @type {SplayTree.Node}
+*/
+SplayTree.Node.prototype.right = null;
+/**
+* Performs an ordered traversal of the subtree starting at
+* this SplayTree.Node.
+*
+* @param {function(SplayTree.Node)} f Visitor function.
+* @private
+*/
+SplayTree.Node.prototype.traverse_ = function(f) {
+var current = this;
+while (current) {
+var left = current.left;
+if (left) left.traverse_(f);
+f(current);
+current = current.right;
+}
+};