tor-browser

splay.js (11557B)

---

// 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, 2739514], [
 new Benchmark("Splay", true, false, 1400,
   SplayRun, SplaySetup, SplayTearDown, SplayRMS)
]);


// Configuration.
var kSplayTreeSize = 8000;
var kSplayTreeModifications = 80;
var kSplayTreePayloadDepth = 5;

var splayTree = null;
var splaySampleTimeStart = 0.0;

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();
}

var splaySamples = 0;
var splaySumOfSquaredPauses = 0;

function SplayRMS() {
 return Math.round(Math.sqrt(splaySumOfSquaredPauses / splaySamples) * 10000);
}

function SplayUpdateStats(time) {
 var pause = time - splaySampleTimeStart;
 splaySampleTimeStart = time;
 splaySamples++;
 splaySumOfSquaredPauses += pause * pause;
}

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() {
 // Check if the platform has the performance.now high resolution timer.
 // If not, throw exception and quit.
 if (!performance.now) {
   throw "PerformanceNowUnsupported";
 }

 splayTree = new SplayTree();
 splaySampleTimeStart = performance.now()
 for (var i = 0; i < kSplayTreeSize; i++) {
   InsertNewNode();
   if ((i+1) % 20 == 19) {
     SplayUpdateStats(performance.now());
   }
 }
}


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;

 splaySamples = 0;
 splaySumOfSquaredPauses = 0;

 // 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);
 }
 SplayUpdateStats(performance.now());
}


/**
* 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;
 }
};