Faster WriteUtf8 for medium size strings?

src/api.cc

 // 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 3684 matching lines @@
 
 int String::WriteUtf8(char* buffer,
                       int capacity,
                       int* nchars_ref,
                       int options) const {
   i::Isolate* isolate = Utils::OpenHandle(this)->GetIsolate();
   if (IsDeadCheck(isolate, "v8::String::WriteUtf8()")) return 0;
   LOG_API(isolate, "String::WriteUtf8");
   ENTER_V8(isolate);
   i::Handle<i::String> str = Utils::OpenHandle(this);
+  int string_length = str->length();
   if (str->IsAsciiRepresentation()) {
     int len;
     if (capacity == -1) {
       capacity = str->length() + 1;
-      len = str->length();
+      len = string_length;
     } else {
       len = i::Min(capacity, str->length());
     }
     i::String::WriteToFlat(*str, buffer, 0, len);
     if (nchars_ref != NULL) *nchars_ref = len;
     if (!(options & NO_NULL_TERMINATION) && capacity > len) {
       buffer[len] = '\0';
       return len + 1;
     }
     return len;
   }
 
+  if (capacity == -1 || capacity >= string_length * 3) {
+    if (string_length < 100) {
+      int utf8_bytes =
+          str->RecursivelySerializeToUtf8(buffer, 0, string_length);
+      if ((options & NO_NULL_TERMINATION) == 0 &&
+          (capacity > utf8_bytes || capacity == -1)) {
+        buffer[utf8_bytes++] = '\0';
+      }
+      if (nchars_ref != NULL) *nchars_ref = string_length;
+      return utf8_bytes;
+    }
+  }
+
   i::StringInputBuffer& write_input_buffer = *isolate->write_input_buffer();
   isolate->string_tracker()->RecordWrite(str);
   if (options & HINT_MANY_WRITES_EXPECTED) {
     // Flatten the string for efficiency.  This applies whether we are
     // using StringInputBuffer or Get(i) to access the characters.
     FlattenString(str);
   }
   write_input_buffer.Reset(0, *str);
   int len = str->length();
   // Encode the first K - 3 bytes directly into the buffer since we
@@ skipping 2462 matching lines @@
 
 
 char* HandleScopeImplementer::Iterate(ObjectVisitor* v, char* storage) {
   HandleScopeImplementer* scope_implementer =
       reinterpret_cast<HandleScopeImplementer*>(storage);
   scope_implementer->IterateThis(v);
   return storage + ArchiveSpacePerThread();
 }
 
 } }  // namespace v8::internal