[typedarrays] Implement %TypedArray%.prototype.reverse in C++

src/elements.cc

Index: src/elements.cc
diff --git a/src/elements.cc b/src/elements.cc
index f0b1605e9f443e2f3b5eba823bbc954779acad68..b9a171752c74d6804061952917184688545c896b 100644
--- a/src/elements.cc
+++ b/src/elements.cc
@@ -1233,6 +1233,12 @@ class ElementsAccessorBase : public ElementsAccessor {
     return Subclass::LastIndexOfValueImpl(isolate, receiver, value, start_from);
   }
 
+  static void ReverseImpl(Handle<JSObject> receiver) { UNREACHABLE(); }
+
+  void Reverse(Handle<JSObject> receiver) final {
+    Subclass::ReverseImpl(receiver);
+  }
+
   static uint32_t GetIndexForEntryImpl(FixedArrayBase* backing_store,
                                        uint32_t entry) {
     return entry;
@@ -2970,6 +2976,23 @@ class TypedElementsAccessor
     } while (k-- != 0);
     return Just<int64_t>(-1);
   }
+
+  static void ReverseImpl(Handle<JSObject> receiver) {
+    DisallowHeapAllocation no_gc;
+    DCHECK(!WasNeutered(*receiver));
+
+    BackingStore* elements = BackingStore::cast(receiver->elements());
+
+    uint32_t len = elements->length();
+    if (len == 0) return;
+
+    for (uint32_t i = 0, j = len - 1; i < j; i++, j--) {
+      ctype element_i = elements->get_scalar(i);
+      ctype element_j = elements->get_scalar(j);
+      elements->set(i, element_j);
+      elements->set(j, element_i);
+    }

[rongjie, 2017/03/19 06:47:52]

Why not try to use std::reverse on elements->DataPtr() instead? A win for both
correctness and performance.

[Choongwoo Han, 2017/03/19 09:30:31]

Done.

+  }
 };
 
 #define FIXED_ELEMENTS_ACCESSOR(Type, type, TYPE, ctype, size) \