Use offset and count to request slices of lists, maps, and typed_data.

runtime/vm/object.cc

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/object.h"
 
 #include "include/dart_api.h"
 #include "platform/assert.h"
 #include "vm/assembler.h"
 #include "vm/cpu.h"
@@ skipping 20025 matching lines @@
 
 void Array::PrintJSONImpl(JSONStream* stream, bool ref) const {
   JSONObject jsobj(stream);
   PrintSharedInstanceJSON(&jsobj, ref);
   jsobj.AddProperty("kind", "List");
   jsobj.AddServiceId(*this);
   jsobj.AddProperty("length", Length());
   if (ref) {
     return;
   }
+  intptr_t offset;
+  intptr_t count;
+  stream->ComputeOffsetAndCount(Length(), &offset, &count);
+  if (offset > 0) {
+    jsobj.AddProperty("offset", offset);
+  }
+  if (count < Length()) {
+    jsobj.AddProperty("count", count);
+  }
+  intptr_t limit = offset + count;
+  ASSERT(limit <= Length());
   {
     JSONArray jsarr(&jsobj, "elements");
     Object& element = Object::Handle();
-    for (intptr_t index = 0; index < Length(); index++) {
+    for (intptr_t index = offset; index < limit; index++) {
       element = At(index);
       jsarr.AddValue(element);
     }
   }
 }
 
 
 RawArray* Array::Grow(const Array& source,
                       intptr_t new_length,
                       Heap::Space space) {
@@ skipping 214 matching lines @@
 void GrowableObjectArray::PrintJSONImpl(JSONStream* stream,
                                         bool ref) const {
   JSONObject jsobj(stream);
   PrintSharedInstanceJSON(&jsobj, ref);
   jsobj.AddProperty("kind", "List");
   jsobj.AddServiceId(*this);
   jsobj.AddProperty("length", Length());
   if (ref) {
     return;
   }
+  intptr_t offset;
+  intptr_t count;
+  stream->ComputeOffsetAndCount(Length(), &offset, &count);
+  if (offset > 0) {
+    jsobj.AddProperty("offset", offset);
+  }
+  if (count < Length()) {
+    jsobj.AddProperty("count", count);
+  }
+  intptr_t limit = offset + count;
+  ASSERT(limit <= Length());
   {
     JSONArray jsarr(&jsobj, "elements");
     Object& element = Object::Handle();
-    for (intptr_t index = 0; index < Length(); index++) {
+    for (intptr_t index = offset; index < limit; index++) {
       element = At(index);
       jsarr.AddValue(element);
     }
   }
 }
 
 
 // Equivalent to Dart's operator "==" and hashCode.
 class DefaultHashTraits {
  public:
@@ skipping 82 matching lines @@
 
 void LinkedHashMap::PrintJSONImpl(JSONStream* stream, bool ref) const {
   JSONObject jsobj(stream);
   PrintSharedInstanceJSON(&jsobj, ref);
   jsobj.AddProperty("kind", "Map");
   jsobj.AddServiceId(*this);
   jsobj.AddProperty("length", Length());
   if (ref) {
     return;
   }
+  intptr_t offset;
+  intptr_t count;
+  stream->ComputeOffsetAndCount(Length(), &offset, &count);
+  if (offset > 0) {
+    jsobj.AddProperty("offset", offset);
+  }
+  if (count < Length()) {
+    jsobj.AddProperty("count", count);
+  }
+  intptr_t limit = offset + count;
+  ASSERT(limit <= Length());
   {
     JSONArray jsarr(&jsobj, "associations");
     Object& object = Object::Handle();
     LinkedHashMap::Iterator iterator(*this);
-    while (iterator.MoveNext()) {
-      JSONObject jsassoc(&jsarr);
-      object = iterator.CurrentKey();
-      jsassoc.AddProperty("key", object);
-      object = iterator.CurrentValue();
-      jsassoc.AddProperty("value", object);
+    int i = 0;
+    while (iterator.MoveNext() && i < limit) {
+      if (i >= offset) {
+        JSONObject jsassoc(&jsarr);
+        object = iterator.CurrentKey();
+        jsassoc.AddProperty("key", object);
+        object = iterator.CurrentValue();
+        jsassoc.AddProperty("value", object);
+      }
+      i++;
     }
   }
 }
 
 
 RawFloat32x4* Float32x4::New(float v0, float v1, float v2, float v3,
                              Heap::Space space) {
   ASSERT(Isolate::Current()->object_store()->float32x4_class() !=
          Class::null());
   Float32x4& result = Float32x4::Handle();
@@ skipping 371 matching lines @@
   JSONObject jsobj(stream);
   PrintSharedInstanceJSON(&jsobj, ref);
   const Class& cls = Class::Handle(clazz());
   const String& kind = String::Handle(cls.UserVisibleName());
   jsobj.AddProperty("kind", kind.ToCString());
   jsobj.AddServiceId(*this);
   jsobj.AddProperty("length", Length());
   if (ref) {
     return;
   }
-
-  {
+  intptr_t offset;
+  intptr_t count;
+  stream->ComputeOffsetAndCount(Length(), &offset, &count);
+  if (offset > 0) {
+    jsobj.AddProperty("offset", offset);
+  }
+  if (count < Length()) {
+    jsobj.AddProperty("count", count);
+  }
+  if (count == 0) {
+    jsobj.AddProperty("bytes", "");
+  } else {
     NoSafepointScope no_safepoint;
     jsobj.AddPropertyBase64("bytes",
-                            reinterpret_cast<const uint8_t*>(DataAddr(0)),
-                            LengthInBytes());
+                            reinterpret_cast<const uint8_t*>(
+                                DataAddr(offset * ElementSizeInBytes())),
+                            count * ElementSizeInBytes());
   }
 }
 
 
 FinalizablePersistentHandle* ExternalTypedData::AddFinalizer(
     void* peer, Dart_WeakPersistentHandleFinalizer callback) const {
   return dart::AddFinalizer(*this, peer, callback);
 }
 
 
@@ skipping 25 matching lines @@
   JSONObject jsobj(stream);
   PrintSharedInstanceJSON(&jsobj, ref);
   const Class& cls = Class::Handle(clazz());
   const String& kind = String::Handle(cls.UserVisibleName());
   jsobj.AddProperty("kind", kind.ToCString());
   jsobj.AddServiceId(*this);
   jsobj.AddProperty("length", Length());
   if (ref) {
     return;
   }
-
-  {
+  intptr_t offset;
+  intptr_t count;
+  stream->ComputeOffsetAndCount(Length(), &offset, &count);
+  if (offset > 0) {
+    jsobj.AddProperty("offset", offset);
+  }
+  if (count < Length()) {
+    jsobj.AddProperty("count", count);
+  }
+  if (count == 0) {
+    jsobj.AddProperty("bytes", "");
+  } else {
     NoSafepointScope no_safepoint;
     jsobj.AddPropertyBase64("bytes",
-                            reinterpret_cast<const uint8_t*>(DataAddr(0)),
-                            LengthInBytes());
+                            reinterpret_cast<const uint8_t*>(
+                                DataAddr(offset * ElementSizeInBytes())),
+                            count * ElementSizeInBytes());
   }
 }
 
 
 RawCapability* Capability::New(uint64_t id, Heap::Space space) {
   Capability& result = Capability::Handle();
   {
     RawObject* raw = Object::Allocate(Capability::kClassId,
                                       Capability::InstanceSize(),
                                       space);
@@ skipping 666 matching lines @@
   return tag_label.ToCString();
 }
 
 
 void UserTag::PrintJSONImpl(JSONStream* stream, bool ref) const {
   Instance::PrintJSONImpl(stream, ref);
 }
 
 
 }  // namespace dart