Move ArrayBuffer.prototype.slice implementation to C++

src/builtins/builtins-arraybuffer.cc

Index: src/builtins/builtins-arraybuffer.cc
diff --git a/src/builtins/builtins-arraybuffer.cc b/src/builtins/builtins-arraybuffer.cc
index e82c3850afabbb54b174badbfeaff1c42a7d6da7..535e2c77acda987f7696e2cd3c95e5aaf7893e4c 100644
--- a/src/builtins/builtins-arraybuffer.cc
+++ b/src/builtins/builtins-arraybuffer.cc
@@ -11,6 +11,15 @@
 namespace v8 {
 namespace internal {
 
+#define CHECK_IS_NOT_SHARED_ARRAY_BUFFER(name, method)                      \
+  if (name->is_shared()) {                                                  \
+    THROW_NEW_ERROR_RETURN_FAILURE(                                         \
+        isolate,                                                            \
+        NewTypeError(MessageTemplate::kIncompatibleMethodReceiver,          \
+                     isolate->factory()->NewStringFromAsciiChecked(method), \
+                     name));                                                \
+  }
+
 // -----------------------------------------------------------------------------
 // ES6 section 21.1 ArrayBuffer Objects
 
@@ -63,17 +72,10 @@ BUILTIN(ArrayBufferConstructor_ConstructStub) {
 
 // ES6 section 24.1.4.1 get ArrayBuffer.prototype.byteLength
 BUILTIN(ArrayBufferPrototypeGetByteLength) {
+  const char* const kMethodName = "get ArrayBuffer.prototype.byteLength";
   HandleScope scope(isolate);
-  CHECK_RECEIVER(JSArrayBuffer, array_buffer,
-                 "get ArrayBuffer.prototype.byteLength");
-
-  if (array_buffer->is_shared()) {
-    THROW_NEW_ERROR_RETURN_FAILURE(
-        isolate, NewTypeError(MessageTemplate::kIncompatibleMethodReceiver,
-                              isolate->factory()->NewStringFromAsciiChecked(
-                                  "get ArrayBuffer.prototype.byteLength"),
-                              args.receiver()));
-  }
+  CHECK_RECEIVER(JSArrayBuffer, array_buffer, kMethodName);
+  CHECK_IS_NOT_SHARED_ARRAY_BUFFER(array_buffer, kMethodName);
   // TODO(franzih): According to the ES6 spec, we should throw a TypeError
   // here if the JSArrayBuffer is detached.
   return array_buffer->byte_length();
@@ -87,5 +89,152 @@ BUILTIN(ArrayBufferIsView) {
   return isolate->heap()->ToBoolean(arg->IsJSArrayBufferView());
 }
 
+// ES6 section 24.1.4.3 ArrayBuffer.prototype.slice ( start, end )

[Dan Ehrenberg, 2017/02/17 09:18:19]

Optional nit: As long as you're updating the cross-references, could you follow
the newer convention of referring to section anchors, which are more stable?
Here, the comment might read as

// ES #sec-arraybuffer.prototype.slice
// ArrayBuffer.prototype.slice ( start, end )

[binji, 2017/02/17 18:59:27]

Done.

+BUILTIN(ArrayBufferPrototypeSlice) {
+  const char* const kMethodName = "ArrayBuffer.prototype.slice";
+  HandleScope scope(isolate);
+  Handle<Object> start = args.at(1);
+  Handle<Object> end = args.atOrUndefined(isolate, 2);
+
+  // 2. If Type(O) is not Object, throw a TypeError exception.
+  // 3. If O does not have an [[ArrayBufferData]] internal slot, throw a
+  //    TypeError exception.
+  CHECK_RECEIVER(JSArrayBuffer, array_buffer, kMethodName);
+  // 4. If IsSharedArrayBuffer(O) is true, throw a TypeError exception.
+  CHECK_IS_NOT_SHARED_ARRAY_BUFFER(array_buffer, kMethodName);
+
+  // 5. If IsDetachedBuffer(buffer) is true, throw a TypeError exception.
+  if (array_buffer->was_neutered()) {
+    THROW_NEW_ERROR_RETURN_FAILURE(
+        isolate, NewTypeError(MessageTemplate::kDetachedOperation,
+                              isolate->factory()->NewStringFromAsciiChecked(
+                                  kMethodName)));
+  }
+
+  // 6. Let len be O.[[ArrayBufferByteLength]].
+  double const len = array_buffer->byte_length()->Number();
+
+  // 7. Let relativeStart be ? ToInteger(start).
+  Handle<Object> relative_start;
+  ASSIGN_RETURN_FAILURE_ON_EXCEPTION(isolate, relative_start,
+                                     Object::ToInteger(isolate, start));
+
+  // 8. If relativeStart < 0, let first be max((len + relativeStart), 0); else
+  //    let first be min(relativeStart, len).
+  double const first = (relative_start->Number() < 0)
+                           ? Max(len + relative_start->Number(), 0.0)
+                           : Min(relative_start->Number(), len);
+  Handle<Object> first_obj = isolate->factory()->NewNumber(first);
+
+  // 9. If end is undefined, let relativeEnd be len; else let relativeEnd be ?
+  //    ToInteger(end).
+  double relative_end;
+  if (end->IsUndefined(isolate)) {
+    relative_end = len;
+  } else {
+    Handle<Object> relative_end_obj;
+    ASSIGN_RETURN_FAILURE_ON_EXCEPTION(isolate, relative_end_obj,
+                                       Object::ToInteger(isolate, end));
+    relative_end = relative_end_obj->Number();
+  }
+
+  // 10. If relativeEnd < 0, let final be max((len + relativeEnd), 0); else let
+  //     final be min(relativeEnd, len).
+  double const final_ = (relative_end < 0) ? Max(len + relative_end, 0.0)
+                                           : Min(relative_end, len);
+
+  // 11. Let newLen be max(final-first, 0).
+  double const new_len = Max(final_ - first, 0.0);
+  Handle<Object> new_len_obj = isolate->factory()->NewNumber(new_len);
+
+  // 12. Let ctor be ? SpeciesConstructor(O, %ArrayBuffer%).
+  Handle<JSFunction> arraybuffer_fun = isolate->array_buffer_fun();
+  Handle<Object> ctor;
+  ASSIGN_RETURN_FAILURE_ON_EXCEPTION(
+      isolate, ctor,
+      Object::SpeciesConstructor(
+          isolate, Handle<JSReceiver>::cast(args.receiver()), arraybuffer_fun));
+
+  // 13. Let new be ? Construct(ctor, newLen).
+  Handle<JSReceiver> new_;
+  {
+    const int argc = 1;
+
+    ScopedVector<Handle<Object>> argv(argc);
+    argv[0] = new_len_obj;
+
+    Handle<Object> new_obj;
+    ASSIGN_RETURN_FAILURE_ON_EXCEPTION(
+        isolate, new_obj,
+        Execution::New(Handle<JSFunction>::cast(ctor), argc, argv.start()));
+
+    new_ = Handle<JSReceiver>::cast(new_obj);
+  }
+
+  // 14. If new does not have an [[ArrayBufferData]] internal slot, throw a
+  //     TypeError exception.
+  if (!new_->IsJSArrayBuffer()) {
+    THROW_NEW_ERROR_RETURN_FAILURE(
+        isolate,
+        NewTypeError(MessageTemplate::kIncompatibleMethodReceiver,
+                     isolate->factory()->NewStringFromAsciiChecked(kMethodName),
+                     new_));
+  }
+
+  // 15. If IsSharedArrayBuffer(new) is true, throw a TypeError exception.
+  Handle<JSArrayBuffer> new_array_buffer = Handle<JSArrayBuffer>::cast(new_);
+  CHECK_IS_NOT_SHARED_ARRAY_BUFFER(new_array_buffer, kMethodName);
+
+  // 16. If IsDetachedBuffer(new) is true, throw a TypeError exception.
+  if (new_array_buffer->was_neutered()) {
+    THROW_NEW_ERROR_RETURN_FAILURE(
+        isolate, NewTypeError(MessageTemplate::kDetachedOperation,
+                              isolate->factory()->NewStringFromAsciiChecked(
+                                  kMethodName)));
+  }
+
+  // 17. If SameValue(new, O) is true, throw a TypeError exception.
+  if (new_->SameValue(*args.receiver())) {
+    THROW_NEW_ERROR_RETURN_FAILURE(
+        isolate, NewTypeError(MessageTemplate::kArrayBufferSpeciesThis));
+  }
+
+  // 18. If new.[[ArrayBufferByteLength]] < newLen, throw a TypeError exception.
+  if (new_array_buffer->byte_length()->Number() < new_len) {
+    THROW_NEW_ERROR_RETURN_FAILURE(
+        isolate, NewTypeError(MessageTemplate::kArrayBufferTooShort));
+  }
+
+  // 19. NOTE: Side-effects of the above steps may have detached O.
+  // 20. If IsDetachedBuffer(O) is true, throw a TypeError exception.
+  if (array_buffer->was_neutered()) {
+    THROW_NEW_ERROR_RETURN_FAILURE(
+        isolate, NewTypeError(MessageTemplate::kDetachedOperation,
+                              isolate->factory()->NewStringFromAsciiChecked(
+                                  kMethodName)));
+  }
+
+  // 21. Let fromBuf be O.[[ArrayBufferData]].
+  // 22. Let toBuf be new.[[ArrayBufferData]].
+  // 23. Perform CopyDataBlockBytes(toBuf, 0, fromBuf, first, newLen).
+  size_t first_size = 0, new_len_size = 0;
+  CHECK(TryNumberToSize(*first_obj, &first_size));
+  CHECK(TryNumberToSize(*new_len_obj, &new_len_size));
+  CHECK(NumberToSize(new_array_buffer->byte_length()) >= new_len_size);

[Dan Ehrenberg, 2017/02/17 09:18:19]

Should this last one be a DCHECK? Anyway, this (and the next comment) are not
very important, and it's reasonable to leave this code unchanged from the place
you took it from.

[binji, 2017/02/17 18:59:27]

Seems reasonable, done.

+
+  if (new_len_size != 0) {
+    size_t from_byte_length = NumberToSize(array_buffer->byte_length());
+    CHECK(first_size <= from_byte_length);
+    CHECK(from_byte_length - first_size >= new_len_size);

[Dan Ehrenberg, 2017/02/17 09:18:19]

DCHECKs?

[binji, 2017/02/17 18:59:27]

Done.

+    uint8_t* from_data =
+        reinterpret_cast<uint8_t*>(array_buffer->backing_store());
+    uint8_t* to_data =
+        reinterpret_cast<uint8_t*>(new_array_buffer->backing_store());
+    CopyBytes(to_data, from_data + first_size, new_len_size);
+  }
+
+  return *new_;
+}
+
 }  // namespace internal
 }  // namespace v8