Faster WriteUtf8 for medium size strings?

src/objects.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 6067 matching lines @@
     if (shape.representation_tag() == kSeqStringTag) {
       start = SeqTwoByteString::cast(string)->GetChars();
     } else {
       start = ExternalTwoByteString::cast(string)->GetChars();
     }
     return FlatContent(Vector<const uc16>(start + offset, length));
   }
 }
 
 
+int String::RecursivelySerializeToUtf8(char* buffer, int start, int end) {
+  if (IsAsciiRepresentation()) {
+    WriteToFlat(this, buffer, start, end);
+    return end - start;
+  }
+  switch (StringShape(this).representation_tag()) {
+    case kExternalStringTag: {
+      const uc16* data =
+          ExternalTwoByteString::cast(this)->GetChars();
+      char* current = buffer;
+      for (int i = start; i < end; i++) {
+        uc16 character = data[i];
+        current +=
+            unibrow::Utf8::Encode(current, character);
+      }
+      return current - buffer;
+    }
+    case kSeqStringTag: {
+      const uc16* data =
+          SeqTwoByteString::cast(this)->GetChars();
+      char* current = buffer;
+      for (int i = start; i < end; i++) {
+        uc16 character = data[i];
+        current +=
+            unibrow::Utf8::Encode(current, character);
+      }
+      return current - buffer;
+    }
+    case kConsStringTag: {
+      ConsString* cons_string = ConsString::cast(this);
+      String* first = cons_string->first();
+      int boundary = first->length();
+      if (start >= boundary) {
+        // Only need RHS.
+        return cons_string->second()->RecursivelySerializeToUtf8(
+            buffer, start - boundary, end - boundary);

[piscisaureus, 2012/03/01 14:21:18]

`start - boundary` does not look correct to me. If this function is invoked
recursively `start` would often be 0.

[piscisaureus, 2012/03/01 14:54:28]

Never mind, this is correct.

+      } else if (end <= boundary) {
+        // Only need LHS.
+        return first->RecursivelySerializeToUtf8(
+            buffer, start - boundary, end - boundary);

[piscisaureus, 2012/03/01 14:21:18]

sic

[piscisaureus, 2012/03/01 14:54:28]

This should read:
`return first->RecursivelySerializeToUtf8(buffer, start, boundary);`

+      } else {
+        int utf8_bytes = first->RecursivelySerializeToUtf8(
+            buffer, start, boundary);
+        return utf8_bytes +
+            cons_string->second()->RecursivelySerializeToUtf8(
+            buffer + utf8_bytes, 0, end - boundary);
+      }
+    }
+    case kSlicedStringTag: {
+      SlicedString* slice = SlicedString::cast(this);
+      unsigned offset = slice->offset();
+      return slice->parent()->RecursivelySerializeToUtf8(
+          buffer, start + offset, end + offset);
+    }
+  }
+  UNREACHABLE();
+  return 0;
+}
+
+
 SmartArrayPointer<char> String::ToCString(AllowNullsFlag allow_nulls,
                                           RobustnessFlag robust_flag,
                                           int offset,
                                           int length,
                                           int* length_return) {
   if (robust_flag == ROBUST_STRING_TRAVERSAL && !LooksValid()) {
     return SmartArrayPointer<char>(NULL);
   }
   Heap* heap = GetHeap();
 
@@ skipping 7071 matching lines @@
   if (break_point_objects()->IsUndefined()) return 0;
   // Single break point.
   if (!break_point_objects()->IsFixedArray()) return 1;
   // Multiple break points.
   return FixedArray::cast(break_point_objects())->length();
 }
 #endif  // ENABLE_DEBUGGER_SUPPORT
 
 
 } }  // namespace v8::internal