Testing using a TypedArray to emulate memory

arv · Nov 6, 2013 · 9b812c5 · 9b812c5
1 parent 77f0ef1
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diff --git a/experiments/typed-array-backing-test.html b/experiments/typed-array-backing-test.html
@@ -0,0 +1,37 @@
+<!doctype html>
+<script src="typed-array-backing.js"></script>
+<script>
+
+var p, c, c2;
+
+if (typeof Node_set_firstChild !== 'undefined') {
+
+  p = new Node;  // 1
+  c = new Node;  // 7
+  // var c2 = new Node;  // 13
+
+  // Emulate memory
+  Node_set_firstChild(1, 7);
+  Node_set_firstChild(7, 13);
+
+  console.assert(c.firstChild instanceof Node);
+
+} else {
+  p = document.createElement('p');
+  c = p.appendChild(document.createElement('p'));
+  c2 = c.appendChild(document.createElement('p'));
+}
+
+function test() {
+  p.firstChild === c
+  c2 = c.firstChild
+  c2.firstChild === null;
+}
+
+console.profile('firstChild');
+for (var i = 0; i < 1e7; i++) {
+  test();
+}
+console.profileEnd('firstChild');
+
+</script>
diff --git a/experiments/typed-array-backing.js b/experiments/typed-array-backing.js
@@ -0,0 +1,66 @@
+(function() {
+  'use strict';
+
+  var MEMORY = new Uint32Array(1024);
+  var BUFFER = MEMORY.buffer;
+  var handles = [0];
+
+  var ptr = 1;  // Keep 0 for null
+
+  function allocate(size) {
+    // Uint32Array.BYTES_PER_ELEMENT
+    var obj = new Uint32Array(BUFFER, ptr * 4, size);
+    var index = handles.length;
+    MEMORY[ptr] = index;
+    handles[index] = obj;
+    ptr += size;
+    return obj;
+  }
+
+  function Node_wrap(address) {
+    var obj = new Uint32Array(BUFFER, address * 4, NODE_SIZE);
+    obj.__proto__ = $Node_prototype;
+    return obj;
+  }
+
+  var HANDLE_OFFSET = 0
+  var PARENT_NODE_OFFSET = 1;
+  var FIRST_CHILD_OFFSET = 2;
+  var LAST_CHILD_OFFSET = 3;
+  var NEXT_SIBLING_OFFSET = 4;
+  var PREVIOUS_SIBLING_OFFSET = 5;
+  var NODE_SIZE = 6;
+
+  function Node_set_firstChild(parentAddress, childAddress) {
+    MEMORY[parentAddress + FIRST_CHILD_OFFSET] = childAddress;
+  }
+
+  function $Node() {
+    var self = allocate(NODE_SIZE);
+    self.__proto__ = $Node_prototype;
+    return self;
+  }
+
+  var $Node_prototype = $Node.prototype = {
+    get firstChild() {
+      // Type check. See instance-type-check.js
+      var address = this[2];  // FIRST_CHILD_OFFSET
+      if (!address)
+        return null;
+      var handleIndex = MEMORY[address];
+      if (handleIndex !== 0)
+        return handles[handleIndex];
+      var object = Node_wrap(address);
+      var handleIndex = handles.length;
+      handles[handleIndex] = object;
+      MEMORY[address] = handleIndex;
+      return object;
+    }
+  };
+
+  window.Node = $Node;
+
+  window.Node_set_firstChild = Node_set_firstChild;
+
+
+})();