Encapsulate element handling into a class keyed on ElementsKind

src/elements.cc

+// Copyright 2011 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.
+
+#include "v8.h"
+
+#include "objects.h"
+#include "elements.h"
+
+namespace v8 {
+namespace internal {
+
+
+ElementsAccessor** ElementsAccessor::elements_accessors_;
+
+
+// Base class for element handler implementations. Contains the
+// the common logic for objects with different ElementsKinds.
+// Subclasses must specialize method for which the element
+// implementation differs from the base class implementation.
+//
+// This class is intended to be used in the following way:
+//
+//   class SomeElementsAccessor :
+//       public ElementsAccessorBase<SomeElementsAccessor,
+//                                   BackingStoreClass> {
+//     ...
+//   }
+//
+// This is an example of the Curiously Recurring Template Pattern (see
+// http://en.wikipedia.org/wiki/Curiously_recurring_template_pattern).  We use
+// CRTP to guarantee aggressive compile time optimizations (i.e.  inlining and
+// specialization of SomeElementsAccessor methods).
+template <typename ElementsAccessorSubclass, typename BackingStoreClass>
+class ElementsAccessorBase : public ElementsAccessor {
+ public:
+  ElementsAccessorBase() { }
+  virtual MaybeObject* GetWithReceiver(JSObject* obj,
+                                       Object* receiver,
+                                       uint32_t index) {
+    if (index < ElementsAccessorSubclass::GetLength(obj)) {
+      BackingStoreClass* backing_store =
+          ElementsAccessorSubclass::GetBackingStore(obj);
+      return backing_store->get(index);
+    }
+    return obj->GetHeap()->the_hole_value();
+  }
+
+ protected:
+  static BackingStoreClass* GetBackingStore(JSObject* obj) {
+    return BackingStoreClass::cast(obj->elements());
+  }
+
+  static uint32_t GetLength(JSObject* obj) {
+    return ElementsAccessorSubclass::GetBackingStore(obj)->length();
+  }
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(ElementsAccessorBase);
+};
+
+
+class FastElementsAccessor
+    : public ElementsAccessorBase<FastElementsAccessor, FixedArray> {
+};
+
+
+class FastDoubleElementsAccessor
+    : public ElementsAccessorBase<FastDoubleElementsAccessor,
+                                  FixedDoubleArray> {
+};
+
+
+// Super class for all external element arrays.
+template<typename ExternalElementsAccessorSubclass,
+         typename ExternalArray>
+class ExternalElementsAccessor
+    : public ElementsAccessorBase<ExternalElementsAccessorSubclass,
+                                  ExternalArray> {
+ public:
+  virtual MaybeObject* GetWithReceiver(JSObject* obj,
+                                       Object* receiver,
+                                       uint32_t index) {
+    if (index < ExternalElementsAccessorSubclass::GetLength(obj)) {
+      ExternalArray* backing_store =
+          ExternalElementsAccessorSubclass::GetBackingStore(obj);
+      return backing_store->get(index);
+    } else {
+      return obj->GetHeap()->undefined_value();
+    }
+  }
+};
+
+
+class ExternalByteElementsAccessor
+    : public ExternalElementsAccessor<ExternalByteElementsAccessor,
+                                      ExternalByteArray> {
+};
+
+
+class ExternalUnsignedByteElementsAccessor
+    : public ExternalElementsAccessor<ExternalUnsignedByteElementsAccessor,
+                                      ExternalUnsignedByteArray> {
+};
+
+
+class ExternalShortElementsAccessor
+    : public ExternalElementsAccessor<ExternalShortElementsAccessor,
+                                      ExternalShortArray> {
+};
+
+
+class ExternalUnsignedShortElementsAccessor
+    : public ExternalElementsAccessor<ExternalUnsignedShortElementsAccessor,
+                                      ExternalUnsignedShortArray> {
+};
+
+
+class ExternalIntElementsAccessor
+    : public ExternalElementsAccessor<ExternalIntElementsAccessor,
+                                      ExternalIntArray> {
+};
+
+
+class ExternalUnsignedIntElementsAccessor
+    : public ExternalElementsAccessor<ExternalUnsignedIntElementsAccessor,
+                                      ExternalUnsignedIntArray> {
+};
+
+
+class ExternalFloatElementsAccessor
+    : public ExternalElementsAccessor<ExternalFloatElementsAccessor,
+                                      ExternalFloatArray> {
+};
+
+
+class ExternalDoubleElementsAccessor
+    : public ExternalElementsAccessor<ExternalDoubleElementsAccessor,
+                                      ExternalDoubleArray> {
+};
+
+
+class PixelElementsAccessor
+    : public ExternalElementsAccessor<PixelElementsAccessor,
+                                      ExternalPixelArray> {
+};
+
+
+class DictionaryElementsAccessor
+    : public ElementsAccessorBase<DictionaryElementsAccessor,
+                                  NumberDictionary> {
+ public:
+  static MaybeObject* GetNumberDictionaryElement(
+      JSObject* obj,
+      Object* receiver,
+      NumberDictionary* backing_store,
+      uint32_t index) {
+    int entry = backing_store->FindEntry(index);
+    if (entry != NumberDictionary::kNotFound) {
+      Object* element = backing_store->ValueAt(entry);
+      PropertyDetails details = backing_store->DetailsAt(entry);
+      if (details.type() == CALLBACKS) {
+        return obj->GetElementWithCallback(receiver,
+                                           element,
+                                           index,
+                                           obj);
+      } else {
+        return element;
+      }
+    }
+    return obj->GetHeap()->the_hole_value();
+  }
+
+  virtual MaybeObject* GetWithReceiver(JSObject* obj,
+                                       Object* receiver,
+                                       uint32_t index) {
+    return GetNumberDictionaryElement(obj,
+                                      receiver,
+                                      obj->element_dictionary(),
+                                      index);
+  }
+};
+
+
+class NonStrictArgumentsElementsAccessor
+    : public ElementsAccessorBase<NonStrictArgumentsElementsAccessor,
+                                  FixedArray> {
+ public:
+  virtual MaybeObject* GetWithReceiver(JSObject* obj,
+                                       Object* receiver,
+                                       uint32_t index) {
+    FixedArray* parameter_map = GetBackingStore(obj);
+    uint32_t length = parameter_map->length();
+    Object* probe =
+        (index < length - 2) ? parameter_map->get(index + 2) : NULL;
+    if (probe != NULL && !probe->IsTheHole()) {
+      Context* context = Context::cast(parameter_map->get(0));
+      int context_index = Smi::cast(probe)->value();
+      ASSERT(!context->get(context_index)->IsTheHole());
+      return context->get(context_index);
+    } else {
+      // Object is not mapped, defer to the arguments.
+      FixedArray* arguments = FixedArray::cast(parameter_map->get(1));
+      if (arguments->IsDictionary()) {
+        return DictionaryElementsAccessor::GetNumberDictionaryElement(
+            obj,
+            receiver,
+            NumberDictionary::cast(arguments),
+            index);
+      } else if (index < static_cast<uint32_t>(arguments->length())) {
+        return arguments->get(index);
+      }
+    }
+    return obj->GetHeap()->the_hole_value();
+  }
+};
+
+
+void ElementsAccessor::InitializeOncePerProcess() {
+  static struct ConcreteElementsAccessors {
+    FastElementsAccessor fast_elements_handler;
+    FastDoubleElementsAccessor fast_double_elements_handler;
+    DictionaryElementsAccessor dictionary_elements_handler;
+    NonStrictArgumentsElementsAccessor non_strict_arguments_elements_handler;
+    ExternalByteElementsAccessor byte_elements_handler;
+    ExternalUnsignedByteElementsAccessor unsigned_byte_elements_handler;
+    ExternalShortElementsAccessor short_elements_handler;
+    ExternalUnsignedShortElementsAccessor unsigned_short_elements_handler;
+    ExternalIntElementsAccessor int_elements_handler;
+    ExternalUnsignedIntElementsAccessor unsigned_int_elements_handler;
+    ExternalFloatElementsAccessor float_elements_handler;
+    ExternalDoubleElementsAccessor double_elements_handler;
+    PixelElementsAccessor pixel_elements_handler;
+  } element_accessors;
+
+  static ElementsAccessor* accessor_array[] = {
+    &element_accessors.fast_elements_handler,
+    &element_accessors.fast_double_elements_handler,
+    &element_accessors.dictionary_elements_handler,
+    &element_accessors.non_strict_arguments_elements_handler,
+    &element_accessors.byte_elements_handler,
+    &element_accessors.unsigned_byte_elements_handler,
+    &element_accessors.short_elements_handler,
+    &element_accessors.unsigned_short_elements_handler,
+    &element_accessors.int_elements_handler,
+    &element_accessors.unsigned_int_elements_handler,
+    &element_accessors.float_elements_handler,
+    &element_accessors.double_elements_handler,
+    &element_accessors.pixel_elements_handler
+  };
+
+  elements_accessors_ = accessor_array;
+}
+
+
+} }  // namespace v8::internal