[typedarrays] Move %TypedArray%.prototype.slice to C++

src/elements.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/elements.h"
 
 #include "src/arguments.h"
 #include "src/conversions.h"
 #include "src/factory.h"
 #include "src/isolate-inl.h"
@@ skipping 682 matching lines @@
                    uint32_t unshift_size) final {
     return Subclass::UnshiftImpl(receiver, args, unshift_size);
   }
 
   static uint32_t UnshiftImpl(Handle<JSArray> receiver, Arguments* args,
                               uint32_t unshift_size) {
     UNREACHABLE();
     return 0;
   }
 
-  Handle<JSArray> Slice(Handle<JSObject> receiver, uint32_t start,
-                        uint32_t end) final {
+  Handle<JSObject> Slice(Handle<JSObject> receiver, uint32_t start,
+                         uint32_t end) final {
     return Subclass::SliceImpl(receiver, start, end);
   }
 
-  static Handle<JSArray> SliceImpl(Handle<JSObject> receiver,
-                                   uint32_t start, uint32_t end) {
+  Handle<JSObject> Slice(Handle<JSObject> receiver, uint32_t start,
+                         uint32_t end, Handle<JSObject> result) final {
+    return Subclass::SliceWithResultImpl(receiver, start, end, result);
+  }
+
+  static Handle<JSObject> SliceImpl(Handle<JSObject> receiver, uint32_t start,
+                                    uint32_t end) {
     UNREACHABLE();
-    return Handle<JSArray>();
+    return Handle<JSObject>();
+  }
+
+  static Handle<JSObject> SliceWithResultImpl(Handle<JSObject> receiver,
+                                              uint32_t start, uint32_t end,
+                                              Handle<JSObject> result) {
+    return Subclass::SliceImpl(receiver, start, end);

[Camillo Bruni, 2017/03/27 08:59:01]

This should be UNREACHABLE(); since it is not possible to perform the raw slice
operation of a non-typed array receiver and result (22.2.4.6 TypedArrayCreate
prevents this).

[Choongwoo Han, 2017/03/27 12:36:33]

Done.

   }
 
   Handle<JSArray> Splice(Handle<JSArray> receiver, uint32_t start,
                          uint32_t delete_count, Arguments* args,
                          uint32_t add_count) final {
     return Subclass::SpliceImpl(receiver, start, delete_count, args, add_count);
   }
 
   static Handle<JSArray> SpliceImpl(Handle<JSArray> receiver,
                                     uint32_t start, uint32_t delete_count,
@@ skipping 1320 matching lines @@
                                   AT_END);
   }
 
   static uint32_t UnshiftImpl(Handle<JSArray> receiver,
                               Arguments* args, uint32_t unshift_size) {
     Handle<FixedArrayBase> backing_store(receiver->elements());
     return Subclass::AddArguments(receiver, backing_store, args, unshift_size,
                                   AT_START);
   }
 
-  static Handle<JSArray> SliceImpl(Handle<JSObject> receiver,
-                                   uint32_t start, uint32_t end) {
+  static Handle<JSObject> SliceImpl(Handle<JSObject> receiver, uint32_t start,
+                                    uint32_t end) {
     Isolate* isolate = receiver->GetIsolate();
     Handle<FixedArrayBase> backing_store(receiver->elements(), isolate);
     int result_len = end < start ? 0u : end - start;
     Handle<JSArray> result_array = isolate->factory()->NewJSArray(
         KindTraits::Kind, result_len, result_len);
     DisallowHeapAllocation no_gc;
     Subclass::CopyElementsImpl(*backing_store, start, result_array->elements(),
                                KindTraits::Kind, 0, kPackedSizeNotKnown,
                                result_len);
     Subclass::TryTransitionResultArrayToPacked(result_array);
@@ skipping 981 matching lines @@
     DCHECK(!WasNeutered(receiver));
 
     BackingStore* elements = BackingStore::cast(receiver->elements());
 
     uint32_t len = elements->length();
     if (len == 0) return;
 
     ctype* data = static_cast<ctype*>(elements->DataPtr());
     std::reverse(data, data + len);
   }
+
+  static Handle<JSObject> SliceWithResultImpl(Handle<JSObject> receiver,
+                                              uint32_t start, uint32_t end,
+                                              Handle<JSObject> result) {
+    Isolate* isolate = receiver->GetIsolate();
+    DCHECK(!WasNeutered(*receiver));
+    DCHECK(result->IsJSTypedArray());
+    DCHECK(!WasNeutered(*result));
+    DCHECK_LE(start, end);
+
+    Handle<JSTypedArray> array = Handle<JSTypedArray>::cast(receiver);
+    Handle<JSTypedArray> result_array = Handle<JSTypedArray>::cast(result);
+    DCHECK_LE(end, array->length_value());
+
+    // Fast path for the same type result array
+    if (result_array->type() == array->type()) {
+      int64_t element_size = array->element_size();
+      int64_t count = std::max<int64_t>(end - start, 0);
+
+      DisallowHeapAllocation no_gc;
+      BackingStore* src_elements = BackingStore::cast(receiver->elements());
+      BackingStore* result_elements =
+          BackingStore::cast(result_array->elements());
+
+      DCHECK_LE(count, result_elements->length());
+
+      uint8_t* src = static_cast<uint8_t*>(src_elements->DataPtr());
+      uint8_t* result = static_cast<uint8_t*>(result_elements->DataPtr());
+      std::memcpy(result, src + start * element_size, count * element_size);
+      return result_array;
+    }
+
+    // If the types of the two typed arrays are different, properly convert
+    // elements
+    Handle<BackingStore> from(BackingStore::cast(array->elements()), isolate);
+    ElementsAccessor* result_accessor = result_array->GetElementsAccessor();
+    for (uint32_t k = start; k < end; k++) {

[Camillo Bruni, 2017/03/27 08:59:01]

nit: please use "i" as iteration index.

[Choongwoo Han, 2017/03/27 12:36:33]

Done.

+      Handle<Object> elem = AccessorClass::GetImpl(isolate, *from, k);
+      result_accessor->Set(result_array, k, *elem);
+    }
+    return result_array;
+  }
 };
 
 #define FIXED_ELEMENTS_ACCESSOR(Type, type, TYPE, ctype, size) \
   typedef TypedElementsAccessor<TYPE##_ELEMENTS, ctype>        \
       Fixed##Type##ElementsAccessor;
 
 TYPED_ARRAYS(FIXED_ELEMENTS_ACCESSOR)
 #undef FIXED_ELEMENTS_ACCESSOR
 
 template <typename Subclass, typename ArgumentsAccessor, typename KindTraits>
@@ skipping 417 matching lines @@
             FastSloppyArgumentsElementsAccessor,
             FastHoleyObjectElementsAccessor,
             ElementsKindTraits<FAST_SLOPPY_ARGUMENTS_ELEMENTS> >(name) {}
 
   static Handle<FixedArray> GetArguments(Isolate* isolate,
                                          FixedArrayBase* backing_store) {
     FixedArray* parameter_map = FixedArray::cast(backing_store);
     return Handle<FixedArray>(FixedArray::cast(parameter_map->get(1)), isolate);
   }
 
-  static Handle<JSArray> SliceImpl(Handle<JSObject> receiver, uint32_t start,
-                                   uint32_t end) {
+  static Handle<JSObject> SliceImpl(Handle<JSObject> receiver, uint32_t start,
+                                    uint32_t end) {
     Isolate* isolate = receiver->GetIsolate();
     uint32_t result_len = end < start ? 0u : end - start;
     Handle<JSArray> result_array = isolate->factory()->NewJSArray(
         FAST_HOLEY_ELEMENTS, result_len, result_len);
     DisallowHeapAllocation no_gc;
     FixedArray* elements = FixedArray::cast(result_array->elements());
     FixedArray* parameters = FixedArray::cast(receiver->elements());
     uint32_t insertion_index = 0;
     for (uint32_t i = start; i < end; i++) {
       uint32_t entry = GetEntryForIndexImpl(isolate, *receiver, parameters, i,
@@ skipping 496 matching lines @@
     insertion_index += len;
   }
 
   DCHECK_EQ(insertion_index, result_len);
   return result_array;
 }
 
 ElementsAccessor** ElementsAccessor::elements_accessors_ = NULL;
 }  // namespace internal
 }  // namespace v8