Speed up typed array constructors.

src/typedarray.js

 // Copyright 2013 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
@@ skipping 31 matching lines @@
 FUNCTION(4, Int16Array, 2)
 FUNCTION(5, Uint32Array, 4)
 FUNCTION(6, Int32Array, 4)
 FUNCTION(7, Float32Array, 4)
 FUNCTION(8, Float64Array, 8)
 FUNCTION(9, Uint8ClampedArray, 1)
 endmacro
 
 macro TYPED_ARRAY_CONSTRUCTOR(ARRAY_ID, NAME, ELEMENT_SIZE)
   function NAMEConstructByArrayBuffer(obj, buffer, byteOffset, length) {
-    var offset = ToPositiveInteger(byteOffset, "invalid_typed_array_length")
+    var bufferByteLength = buffer.byteLength;
+    var offset;
+    if (IS_UNDEFINED(byteOffset)) {
+      offset = 0;
+    } else {
+      offset = ToPositiveInteger(byteOffset, "invalid_typed_array_length");
 
-    if (offset % ELEMENT_SIZE !== 0) {
-      throw MakeRangeError("invalid_typed_array_alignment",
-          "start offset", "NAME", ELEMENT_SIZE);
-    }
-    var bufferByteLength = buffer.byteLength;
-    if (offset > bufferByteLength) {
-      throw MakeRangeError("invalid_typed_array_offset");
+      if (offset % ELEMENT_SIZE !== 0) {
+        throw MakeRangeError("invalid_typed_array_alignment",
+            "start offset", "NAME", ELEMENT_SIZE);
+      }
+      if (offset > bufferByteLength) {
+        throw MakeRangeError("invalid_typed_array_offset");
+      }
     }
 
     var newByteLength;
     var newLength;
     if (IS_UNDEFINED(length)) {
       if (bufferByteLength % ELEMENT_SIZE !== 0) {
         throw MakeRangeError("invalid_typed_array_alignment",
           "byte length", "NAME", ELEMENT_SIZE);
       }
       newByteLength = bufferByteLength - offset;
       newLength = newByteLength / ELEMENT_SIZE;
     } else {
       var newLength = ToPositiveInteger(length, "invalid_typed_array_length");
       newByteLength = newLength * ELEMENT_SIZE;
     }
     if (offset + newByteLength > bufferByteLength) {
       throw MakeRangeError("invalid_typed_array_length");
     }
     %TypedArrayInitialize(obj, ARRAY_ID, buffer, offset, newByteLength);
   }
 
   function NAMEConstructByLength(obj, length) {
-    var l = ToPositiveInteger(length, "invalid_typed_array_length");
+    var l = IS_UNDEFINED(length) ?
+      0 : ToPositiveInteger(length, "invalid_typed_array_length");
     var byteLength = l * ELEMENT_SIZE;
     var buffer = new $ArrayBuffer(byteLength);
     %TypedArrayInitialize(obj, ARRAY_ID, buffer, 0, byteLength);
   }
 
   function NAMEConstructByArrayLike(obj, arrayLike) {
     var length = arrayLike.length;
     var l = ToPositiveInteger(length, "invalid_typed_array_length");
     if(!%TypedArrayInitializeFromArrayLike(obj, ARRAY_ID, arrayLike, l)) {
       for (var i = 0; i < l; i++) {
@@ skipping 200 matching lines @@
 // --------------------------- DataView -----------------------------
 
 var $DataView = global.DataView;
 
 function DataViewConstructor(buffer, byteOffset, byteLength) { // length = 3
   if (%_IsConstructCall()) {
     if (!IS_ARRAYBUFFER(buffer)) {
       throw MakeTypeError('data_view_not_array_buffer', []);
     }
     var bufferByteLength = %ArrayBufferGetByteLength(buffer);
-    var offset = ToPositiveInteger(byteOffset, 'invalid_data_view_offset');
+    var offset = IS_UNDEFINED(byteOffset) ?
+      0 : ToPositiveInteger(byteOffset, 'invalid_data_view_offset');

[Yang, 2013/11/07 10:14:11]

I think we use 4 space indent after linebreak. I see you got 2 space indent
somewhere else too, so I guess it's your choice.

     if (offset > bufferByteLength) {
       throw MakeRangeError('invalid_data_view_offset');
     }
     var length = IS_UNDEFINED(byteLength) ?
       bufferByteLength - offset : TO_INTEGER(byteLength);
     if (length < 0 || offset + length > bufferByteLength) {
       throw new MakeRangeError('invalid_data_view_length');
     }
     %DataViewInitialize(this, buffer, offset, length);
   } else {
@@ skipping 280 matching lines @@
 
       "getFloat32", DataViewGetFloat32,
       "setFloat32", DataViewSetFloat32,
 
       "getFloat64", DataViewGetFloat64,
       "setFloat64", DataViewSetFloat64
   ));
 }
 
 SetupDataView();