The Tor Browser: js/src/v8/splay.js@6474c204b198 (annotated)

js/src/v8/splay.js@6474c204b198 (annotated)

js/src/v8/splay.js

Wed, 31 Dec 2014 06:09:35 +0100

author: Michael Schloh von Bennewitz <michael@schloh.com>
date: Wed, 31 Dec 2014 06:09:35 +0100
changeset 0: 6474c204b198
permissions: -rw-r--r--

Cloned upstream origin tor-browser at tor-browser-31.3.0esr-4.5-1-build1
revision ID fc1c9ff7c1b2defdbc039f12214767608f46423f for hacking purpose.

 // 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;
   }
 };