[typedarrays] move %TypedArray%.prototype.copyWithin to C++

src/builtins/builtins-typedarray.cc

Index: src/builtins/builtins-typedarray.cc
diff --git a/src/builtins/builtins-typedarray.cc b/src/builtins/builtins-typedarray.cc
index e394df4e7abfe2d357dc6dc2fbeb649010996243..f91dfccd4a719cad91c824ce841016fca8527121 100644
--- a/src/builtins/builtins-typedarray.cc
+++ b/src/builtins/builtins-typedarray.cc
@@ -167,5 +167,86 @@ void Builtins::Generate_TypedArrayPrototypeKeys(
       state, "%TypedArray%.prototype.keys()");
 }
 
+namespace {
+
+MaybeHandle<JSTypedArray> ValiadateTypedArray(Isolate* isolate,
+                                              Handle<Object> receiver,
+                                              const char* method_name) {
+  if (V8_UNLIKELY(!receiver->IsJSTypedArray())) {
+    const MessageTemplate::Template message = MessageTemplate::kNotTypedArray;
+    THROW_NEW_ERROR(isolate, NewTypeError(message), JSTypedArray);
+  }
+
+  Handle<JSTypedArray> array = Handle<JSTypedArray>::cast(receiver);
+  if (V8_UNLIKELY(array->WasNeutered())) {
+    const MessageTemplate::Template message = MessageTemplate::kNotTypedArray;
+    Handle<String> operation =
+        isolate->factory()->NewStringFromAsciiChecked(method_name);
+    THROW_NEW_ERROR(isolate, NewTypeError(message, operation), JSTypedArray);
+  }
+
+  return array;
+}
+}  // namespace
+
+BUILTIN(TypedArrayPrototypeCopyWithin) {
+  HandleScope scope(isolate);
+
+  Handle<JSTypedArray> array;
+  const char* method = "%TypedArray%.prototype.copyWithin";
+  ASSIGN_RETURN_FAILURE_ON_EXCEPTION(
+      isolate, array, ValiadateTypedArray(isolate, args.receiver(), method));
+
+  int64_t len = array->length_value();
+  int64_t to = 0;
+  int64_t from = 0;
+  int64_t final = len;
+
+  if (V8_LIKELY(args.length() > 1)) {
+    Handle<Object> target_int;
+    ASSIGN_RETURN_FAILURE_ON_EXCEPTION(
+        isolate, target_int, Object::ToInteger(isolate, args.at<Object>(1)));
+    int64_t relative = static_cast<int64_t>(target_int->Number());

[Benedikt Meurer, 2017/02/06 14:35:23]

I think this is wrong for infinities (also below). You probably need to do the
comparisons on doubles. Please also add a test for this.

[Camillo Bruni, 2017/02/06 14:43:35]

nit: only if you feel motivated ;) could you add a Object::ToInt64 (check
Object::ToUint32) which has a nicely inlineable fast-path for smi lengths and
thus avoids an uncessary and costly double conversion.

[caitp, 2017/02/06 14:44:40]

That's a good point, didn't realize ToInteger() kept non-finite numbers. Dan: it
seems like there isn't any test262 coverage for this point

[caitp, 2017/02/06 14:57:12]

Because of the issue with -Infiity/+Infinity, we'd need it to be like
`ToInt64Clamped()` to restrict -Infinity to 0, and +Infinity to be the length
value.

Does that seem reasonable? It could be a helper function specific to
builtins-typedarray.cc

[caitp, 2017/02/06 16:27:53]

Tests added, and I've tried to add a new helper for this as suggested by cbruni,
but it's a bit awkward in some ways.

What about something like

```
Maybe<int64_t> result = Object::ToInteger(isolate, input, &flags);
if (flags & ToIntegerFlags::kFinite) {
  // Do the max(relativeXXX + len, len) stuff ...
} else {
  to = (flags & ToIntegerFlags::kNegative) ? 0 : len;
}
```

Or, alternatively, just using doubles the whole way as originally suggested.

+
+    to = relative < 0 ? std::max<int64_t>(relative + len, 0)
+                      : std::min<int64_t>(relative, len);
+
+    if (args.length() > 2) {
+      Handle<Object> start;
+      Handle<Object> end;
+      ASSIGN_RETURN_FAILURE_ON_EXCEPTION(
+          isolate, start, Object::ToInteger(isolate, args.at<Object>(2)));
+      relative = static_cast<int64_t>(start->Number());

[Camillo Bruni, 2017/02/06 14:43:35]

ditto.

+      from = relative < 0 ? std::max<int64_t>(relative + len, 0)
+                          : std::min<int64_t>(relative, len);
+
+      end = args.atOrUndefined(isolate, 3);
+      if (!end->IsUndefined(isolate)) {
+        ASSIGN_RETURN_FAILURE_ON_EXCEPTION(isolate, end,
+                                           Object::ToInteger(isolate, end));
+        relative = static_cast<int64_t>(end->Number());

[Camillo Bruni, 2017/02/06 14:43:35]

ditto.

+
+        final = relative < 0 ? std::max<int64_t>(relative + len, 0)
+                             : std::min<int64_t>(relative, len);
+      }
+    }
+  }
+
+  int64_t count = std::min<int64_t>(final - from, len - to);
+  if (count <= 0) return *array;
+
+  Handle<FixedTypedArrayBase> elements(
+      FixedTypedArrayBase::cast(array->elements()));
+  size_t element_size = array->element_size();
+  to = to * element_size;
+  from = from * element_size;
+  count = count * element_size;
+
+  uint8_t* data = static_cast<uint8_t*>(elements->DataPtr());
+  std::memmove(data + to, data + from, count);
+
+  return *array;
+}
+
 }  // namespace internal
 }  // namespace v8