Avoid convertion to double when it is not needed.

src/runtime.cc

 // Copyright 2012 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 839 matching lines @@
 
   holder->set_buffer(*buffer);
   holder->set_byte_offset(*byte_offset_object);
   holder->set_byte_length(*byte_length_object);
 
   size_t byte_offset = NumberToSize(isolate, *byte_offset_object);
   size_t byte_length = NumberToSize(isolate, *byte_length_object);
   ASSERT(byte_length % elementSize == 0);
   size_t length = byte_length / elementSize;
 
-  Handle<Object> length_obj =
-      isolate->factory()->NewNumber(static_cast<double>(length));
-  holder->set_length(*length_obj);
+  if (Smi::IsValid(static_cast<intptr_t>(length))) {

[rossberg, 2013/05/14 14:00:45]

I think this should be refactored into a function Factory::NewNumberFromIntptr

+    holder->set_length(Smi::FromIntptr(length));
+  } else {
+    Handle<Object> length_obj=
+        isolate->factory()->NewNumber(static_cast<double>(length));
+    holder->set_length(*length_obj);
+  }
+
   Handle<ExternalArray> elements =
       isolate->factory()->NewExternalArray(
           static_cast<int>(length), arrayType,
           static_cast<uint8_t*>(buffer->backing_store()) + byte_offset);
   Handle<Map> map =
       isolate->factory()->GetElementsTransitionMap(holder, elementsKind);
   holder->set_map(*map);
   holder->set_elements(*elements);
   return isolate->heap()->undefined_value();
 }
@@ skipping 12634 matching lines @@
     // Handle last resort GC and make sure to allow future allocations
     // to grow the heap without causing GCs (if possible).
     isolate->counters()->gc_last_resort_from_js()->Increment();
     isolate->heap()->CollectAllGarbage(Heap::kNoGCFlags,
                                        "Runtime::PerformGC");
   }
 }
 
 
 } }  // namespace v8::internal