Refactored fast external string resource getter.

include/v8.h

Index: include/v8.h
diff --git a/include/v8.h b/include/v8.h
index ddde388cd4f27c970c29e351333b06cd94b5c026..6d0eec8f2ca3ca29707a5137557c08a3c2a0ff59 100644
--- a/include/v8.h
+++ b/include/v8.h
@@ -1018,6 +1018,8 @@ class Boolean : public Primitive {
  */
 class String : public Primitive {
  public:
+  static const int kExternalAsciiStringType = 0x06;
+  static const int kExternalTwoByteStringType = 0x02;
   /**
    * Returns the number of characters in this string.
    */
@@ -1181,6 +1183,15 @@ class String : public Primitive {
   };
 
   /**
+   * Get any type of external string resource.
+   * Returns 0 if there is no external string and does not modify resource or
+   * returns either kExternalAsciiStringType or kExternalTwoByteStringType and
+   * sets the resource pointer.
+   */
+  inline int GetExternalStringResourceBase(
+      ExternalStringResourceBase*& resource) const;
+
+  /**
    * Get the ExternalStringResource for an external string.  Returns
    * NULL if IsExternal() doesn't return true.
    */
@@ -1343,6 +1354,8 @@ class String : public Primitive {
   };
 
  private:
+  V8EXPORT void VerifyExternalStringResourceBase(ExternalStringResourceBase* v,
+                                                 int type) const;
   V8EXPORT void VerifyExternalStringResource(ExternalStringResource* val) const;
   V8EXPORT static void CheckCast(v8::Value* obj);
 };
@@ -4034,6 +4047,7 @@ class Internals {
   static const int kJSObjectHeaderSize = 3 * kApiPointerSize;
   static const int kFullStringRepresentationMask = 0x07;
   static const int kExternalTwoByteRepresentationTag = 0x02;
+  static const int kExternalAsciiRepresentationTag = 0x06;
 
   static const int kIsolateStateOffset = 0;
   static const int kIsolateEmbedderDataOffset = 1 * kApiPointerSize;
@@ -4387,6 +4401,27 @@ String::ExternalStringResource* String::GetExternalStringResource() const {
   return result;
 }
 
+int String::GetExternalStringResourceBase(
+    String::ExternalStringResourceBase*& resource) const {
+  typedef internal::Object O;
+  typedef internal::Internals I;
+  O* obj = *reinterpret_cast<O**>(const_cast<String*>(this));
+  int type = I::GetInstanceType(obj) & I::kFullStringRepresentationMask;
+  if (type == I::kExternalAsciiRepresentationTag
+      || type == I::kExternalTwoByteRepresentationTag) {
+    void* value = I::ReadField<void*>(obj, I::kStringResourceOffset);
+    resource = static_cast<String::ExternalStringResourceBase*>(value);
+#ifdef V8_ENABLE_CHECKS
+    VerifyExternalStringResourceBase(resource, type);
+#endif
+    return type;
+  } else {
+#ifdef V8_ENABLE_CHECKS
+    VerifyExternalStringResourceBase(NULL, 0);
+#endif
+    return 0;
+  }
+}
 
 bool Value::IsUndefined() const {
 #ifdef V8_ENABLE_CHECKS