Implement external strings.

runtime/vm/object.h

Index: runtime/vm/object.h
diff --git a/runtime/vm/object.h b/runtime/vm/object.h
index 7c815a806451a0549741d3f722e71e7363b2e710..c2d45b08b1a934ead373dc9c77400b71e6482c5b 100644
--- a/runtime/vm/object.h
+++ b/runtime/vm/object.h
@@ -2355,6 +2355,10 @@ class String : public Instance {
   // 32bit Smi representation for the hash code on all architectures.
   static const intptr_t kHashBits = 30;
 
+  static const intptr_t kOneByteChar = 1;
+  static const intptr_t kTwoByteChar = 2;
+  static const intptr_t kFourByteChar = 4;
+
   intptr_t Length() const { return Smi::Value(raw_ptr()->length_); }
   static intptr_t length_offset() { return OFFSET_OF(RawString, length_); }
 
@@ -2367,6 +2371,8 @@ class String : public Instance {
 
   virtual int32_t CharAt(intptr_t index) const;
 
+  virtual intptr_t CharSize() const;
+
   bool Equals(const String& str, intptr_t begin_index, intptr_t len) const;
   bool Equals(const char* str) const;
   bool Equals(const uint8_t* characters, intptr_t len) const;
@@ -2395,6 +2401,19 @@ class String : public Instance {
                         Heap::Space space = Heap::kNew);
   static RawString* New(const String& str, Heap::Space space = Heap::kNew);
 
+  static RawString* NewExternal(const uint8_t* characters,
+                                intptr_t len,
+                                void* peer,
+                                Heap::Space = Heap::kNew);
+  static RawString* NewExternal(const uint16_t* characters,
+                                intptr_t len,
+                                void* peer,
+                                Heap::Space = Heap::kNew);
+  static RawString* NewExternal(const uint32_t* characters,
+                                intptr_t len,
+                                void* peer,
+                                Heap::Space = Heap::kNew);
+
   static void Copy(const String& dst,
                    intptr_t dst_offset,
                    const uint8_t* characters,
@@ -2472,6 +2491,10 @@ class OneByteString : public String {
     return *CharAddr(index);
   }
 
+  virtual intptr_t CharSize() const {
+    return kOneByteChar;
+  }
+
   static intptr_t InstanceSize() {
     ASSERT(sizeof(RawOneByteString) == OFFSET_OF(RawOneByteString, data_));
     return 0;
@@ -2502,11 +2525,6 @@ class OneByteString : public String {
                                      intptr_t len,
                                      Heap::Space space);
 
-  static RawString* SubString(const OneByteString& str,
-                              intptr_t begin_index,
-                              intptr_t length,
-                              Heap::Space space);
-
   static RawOneByteString* Transform(int32_t (*mapping)(int32_t ch),
                                      const String& str,
                                      Heap::Space space);
@@ -2530,6 +2548,10 @@ class TwoByteString : public String {
     return *CharAddr(index);
   }
 
+  virtual intptr_t CharSize() const {
+    return kTwoByteChar;
+  }
+
   static intptr_t InstanceSize() {
     ASSERT(sizeof(RawTwoByteString) == OFFSET_OF(RawTwoByteString, data_));
     return 0;
@@ -2557,11 +2579,6 @@ class TwoByteString : public String {
                                      intptr_t len,
                                      Heap::Space space);
 
-  static RawString* SubString(const TwoByteString& str,
-                              intptr_t begin_index,
-                              intptr_t length,
-                              Heap::Space space);
-
   static RawTwoByteString* Transform(int32_t (*mapping)(int32_t ch),
                                      const String& str,
                                      Heap::Space space);
@@ -2584,6 +2601,10 @@ class FourByteString : public String {
     return *CharAddr(index);
   }
 
+  virtual intptr_t CharSize() const {
+    return kFourByteChar;
+  }
+
   static intptr_t InstanceSize() {
     ASSERT(sizeof(RawFourByteString) == OFFSET_OF(RawFourByteString, data_));
     return 0;
@@ -2608,11 +2629,6 @@ class FourByteString : public String {
                                       intptr_t len,
                                       Heap::Space space);
 
-  static RawString* SubString(const FourByteString& str,
-                              intptr_t begin_index,
-                              intptr_t length,
-                              Heap::Space space);
-
   static RawFourByteString* Transform(int32_t (*mapping)(int32_t ch),
                                       const String& str,
                                       Heap::Space space);
@@ -2629,6 +2645,138 @@ class FourByteString : public String {
 };
 
 
+class ExternalOneByteString : public String {
+ public:
+  virtual int32_t CharAt(intptr_t index) const {
+    return *CharAddr(index);
+  }
+
+  virtual intptr_t CharSize() const {
+    return kOneByteChar;
+  }
+
+  void* Peer() const {
+    return raw_ptr()->peer_;
+  }
+
+  static intptr_t InstanceSize() {
+    return RoundedAllocationSize(sizeof(RawExternalOneByteString));
+  }
+
+  static RawExternalOneByteString* New(const uint8_t* characters,
+                                       intptr_t len,
+                                       void* peer,
+                                       Heap::Space space);
+
+ private:
+  uint8_t* CharAddr(intptr_t index) const {
+    // TODO(iposva): Determine if we should throw an exception here.
+    ASSERT((index >= 0) && (index < Length()));
+    return &raw_ptr()->data_[index];
+  }
+
+  void SetData(const uint8_t* characters) {
+    raw_ptr()->data_ = const_cast<uint8_t*>(characters);
+  }
+
+  void SetPeer(void* peer) {
+    raw_ptr()->peer_ = peer;
+  }
+
+  HEAP_OBJECT_IMPLEMENTATION(ExternalOneByteString, String);
+  friend class Class;
+  friend class String;
+};
+
+
+class ExternalTwoByteString : public String {
+ public:
+  virtual int32_t CharAt(intptr_t index) const {
+    return *CharAddr(index);
+  }
+
+  virtual intptr_t CharSize() const {
+    return kTwoByteChar;
+  }
+
+  static intptr_t InstanceSize() {
+    return RoundedAllocationSize(sizeof(RawExternalTwoByteString));
+  }
+
+  void* Peer() const {
+    return raw_ptr()->peer_;
+  }
+
+  static RawExternalTwoByteString* New(const uint16_t* characters,
+                                       intptr_t len,
+                                       void* peer,
+                                       Heap::Space space = Heap::kNew);
+
+ private:
+  uint16_t* CharAddr(intptr_t index) const {
+    // TODO(iposva): Determine if we should throw an exception here.
+    ASSERT((index >= 0) && (index < Length()));
+    return &raw_ptr()->data_[index];
+  }
+
+  void SetData(const uint16_t* characters) {
+    raw_ptr()->data_ = const_cast<uint16_t*>(characters);
+  }
+
+  void SetPeer(void* peer) {
+    raw_ptr()->peer_ = peer;
+  }
+
+  HEAP_OBJECT_IMPLEMENTATION(ExternalTwoByteString, String);
+  friend class Class;
+  friend class String;
+};
+
+
+class ExternalFourByteString : public String {
+ public:
+  virtual int32_t CharAt(intptr_t index) const {
+    return *CharAddr(index);
+  }
+
+  virtual intptr_t CharSize() const {
+    return kFourByteChar;
+  }
+
+  void* Peer() const {
+    return raw_ptr()->peer_;
+  }
+
+  static intptr_t InstanceSize() {
+    return RoundedAllocationSize(sizeof(RawExternalFourByteString));
+  }
+
+  static RawExternalFourByteString* New(const uint32_t* characters,
+                                        intptr_t len,
+                                        void* peer,
+                                        Heap::Space space = Heap::kNew);
+
+ private:
+  uint32_t* CharAddr(intptr_t index) const {
+    // TODO(iposva): Determine if we should throw an exception here.
+    ASSERT((index >= 0) && (index < Length()));
+    return &raw_ptr()->data_[index];
+  }
+
+  void SetData(const uint32_t* characters) {
+    raw_ptr()->data_ = const_cast<uint32_t*>(characters);
+  }
+
+  void SetPeer(void* peer) {
+    raw_ptr()->peer_ = peer;
+  }
+
+  HEAP_OBJECT_IMPLEMENTATION(ExternalFourByteString, String);
+  friend class Class;
+  friend class String;
+};
+
+
 class Bool : public Instance {
  public:
   bool value() const {