Introduce new API to expose external string resource regardless of encoding.

include/v8.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 1000 matching lines @@
   V8EXPORT bool Value() const;
   static inline Handle<Boolean> New(bool value);
 };
 
 
 /**
  * A JavaScript string value (ECMA-262, 4.3.17).
  */
 class String : public Primitive {
  public:
+  enum Encoding {
+    UNKNOWN_ENCODING = 0x1,
+    TWO_BYTE_ENCODING = 0x0,
+    ASCII_ENCODING = 0x4
+  };
   /**
    * Returns the number of characters in this string.
    */
   V8EXPORT int Length() const;
 
   /**
    * Returns the number of bytes in the UTF-8 encoded
    * representation of this string.
    */
   V8EXPORT int Utf8Length() const;
@@ skipping 143 matching lines @@
     virtual ~ExternalAsciiStringResource() {}
     /** The string data from the underlying buffer.*/
     virtual const char* data() const = 0;
     /** The number of ASCII characters in the string.*/
     virtual size_t length() const = 0;
    protected:
     ExternalAsciiStringResource() {}
   };
 
   /**
+   * If the string is an external string, return the ExternalStringResourceBase
+   * regardless of the encoding, otherwise return NULL.  The encoding of the
+   * string is returned in type_out.
+   */
+  inline ExternalStringResourceBase* GetExternalStringResourceBase(
+      Encoding* encoding_out) const;
+
+  /**
    * Get the ExternalStringResource for an external string.  Returns
    * NULL if IsExternal() doesn't return true.
    */
   inline ExternalStringResource* GetExternalStringResource() const;
 
   /**
    * Get the ExternalAsciiStringResource for an external ASCII string.
    * Returns NULL if IsExternalAscii() doesn't return true.
    */
   V8EXPORT const ExternalAsciiStringResource* GetExternalAsciiStringResource()
@@ skipping 25 matching lines @@
   V8EXPORT static Local<String> Concat(Handle<String> left,
                                        Handle<String> right);
 
   /**
    * Creates a new external string using the data defined in the given
    * resource. When the external string is no longer live on V8's heap the
    * resource will be disposed by calling its Dispose method. The caller of
    * this function should not otherwise delete or modify the resource. Neither
    * should the underlying buffer be deallocated or modified except through the
    * destructor of the external string resource.
+   * The optional encoding argument provides a hint on whether scanning for
+   * ASCII content is necessary.

[drcarney, 2012/09/12 11:27:09]

Looks like this comment accidentally slipped in.

[Yang, 2012/09/12 11:28:50]

Done.

    */
   V8EXPORT static Local<String> NewExternal(ExternalStringResource* resource);
 
   /**
    * Associate an external string resource with this string by transforming it
    * in place so that existing references to this string in the JavaScript heap
    * will use the external string resource. The external string resource's
    * character contents need to be equivalent to this string.
    * Returns true if the string has been changed to be an external string.
    * The string is not modified if the operation fails. See NewExternal for
@@ skipping 97 matching lines @@
    private:
     uint16_t* str_;
     int length_;
 
     // Disallow copying and assigning.
     Value(const Value&);
     void operator=(const Value&);
   };
 
  private:
+  V8EXPORT void VerifyExternalStringResourceBase(ExternalStringResourceBase* v,
+                                                 Encoding encoding_out) const;
   V8EXPORT void VerifyExternalStringResource(ExternalStringResource* val) const;
   V8EXPORT static void CheckCast(v8::Value* obj);
 };
 
 
 /**
  * A JavaScript number value (ECMA-262, 4.3.20)
  */
 class Number : public Primitive {
  public:
@@ skipping 2670 matching lines @@
   // These values match non-compiler-dependent values defined within
   // the implementation of v8.
   static const int kHeapObjectMapOffset = 0;
   static const int kMapInstanceTypeOffset = 1 * kApiPointerSize + kApiIntSize;
   static const int kStringResourceOffset = 3 * kApiPointerSize;
 
   static const int kOddballKindOffset = 3 * kApiPointerSize;
   static const int kForeignAddressOffset = kApiPointerSize;
   static const int kJSObjectHeaderSize = 3 * kApiPointerSize;
   static const int kFullStringRepresentationMask = 0x07;
+  static const int kStringEncodingMask = 0x4;
   static const int kExternalTwoByteRepresentationTag = 0x02;
+  static const int kExternalAsciiRepresentationTag = 0x06;
 
   static const int kIsolateStateOffset = 0;
   static const int kIsolateEmbedderDataOffset = 1 * kApiPointerSize;
   static const int kIsolateRootsOffset = 3 * kApiPointerSize;
   static const int kUndefinedValueRootIndex = 5;
   static const int kNullValueRootIndex = 7;
   static const int kTrueValueRootIndex = 8;
   static const int kFalseValueRootIndex = 9;
   static const int kEmptySymbolRootIndex = 116;
 
@@ skipping 334 matching lines @@
   } else {
     result = NULL;
   }
 #ifdef V8_ENABLE_CHECKS
   VerifyExternalStringResource(result);
 #endif
   return result;
 }
 
 
+String::ExternalStringResourceBase* String::GetExternalStringResourceBase(
+    String::Encoding* encoding_out) 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;
+  *encoding_out = static_cast<Encoding>(type & I::kStringEncodingMask);
+  ExternalStringResourceBase* resource = NULL;
+  if (type == I::kExternalAsciiRepresentationTag ||
+      type == I::kExternalTwoByteRepresentationTag) {
+    void* value = I::ReadField<void*>(obj, I::kStringResourceOffset);
+    resource = static_cast<ExternalStringResourceBase*>(value);
+  }
+#ifdef V8_ENABLE_CHECKS
+    VerifyExternalStringResourceBase(resource, *encoding_out);
+#endif
+  return resource;
+}
+
+
 bool Value::IsUndefined() const {
 #ifdef V8_ENABLE_CHECKS
   return FullIsUndefined();
 #else
   return QuickIsUndefined();
 #endif
 }
 
 bool Value::QuickIsUndefined() const {
   typedef internal::Object O;
@@ skipping 209 matching lines @@
 
 
 }  // namespace v8
 
 
 #undef V8EXPORT
 #undef TYPE_CHECK
 
 
 #endif  // V8_H_