Change VM's string-buffer patch to use a Uin16Array as backing buffer.

runtime/lib/string.cc

 // Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/bootstrap_natives.h"
 
 #include "vm/exceptions.h"
 #include "vm/native_entry.h"
 #include "vm/object.h"
 #include "vm/symbols.h"
@@ skipping 31 matching lines @@
       }
     }
     utf32_array[i] = value;
   }
   if (is_one_byte_string) {
     return OneByteString::New(utf32_array, array_len, Heap::kNew);
   }
   return TwoByteString::New(utf16_len, utf32_array, array_len, Heap::kNew);
 }
 
-

[srdjan, 2013/03/05 16:02:21]

Why remove the line?

[Lasse Reichstein Nielsen, 2013/03/05 16:56:56]

That was where I originally had the new method. Guess I cut one line too many
when moving it below. Will restore.

 DEFINE_NATIVE_ENTRY(StringBase_substringUnchecked, 3) {
   const String& receiver = String::CheckedHandle(arguments->NativeArgAt(0));
   GET_NON_NULL_NATIVE_ARGUMENT(Smi, start_obj, arguments->NativeArgAt(1));
   GET_NON_NULL_NATIVE_ARGUMENT(Smi, end_obj, arguments->NativeArgAt(2));
 
   intptr_t start = start_obj.Value();
   intptr_t end = end_obj.Value();
   return String::SubString(receiver, start, (end - start));
 }
 
@@ skipping 127 matching lines @@
     elem ^= strings.At(i);
     if (!elem.IsString()) {
       const Array& args = Array::Handle(Array::New(1));
       args.SetAt(0, elem);
       Exceptions::ThrowByType(Exceptions::kArgument, args);
     }
   }
   return String::ConcatAll(strings);
 }
 
+DEFINE_NATIVE_ENTRY(StringBuffer_createStringFromUint16Array, 2) {

[srdjan, 2013/03/05 16:02:21]

Check if you can create OneByteString instead of TwoByteString. The former are
much faster than the later ate the moment, and use much less memory.

[Lasse Reichstein Nielsen, 2013/03/05 16:56:56]

Will do.

+  GET_NON_NULL_NATIVE_ARGUMENT(Uint16Array, a, arguments->NativeArgAt(0));
+  GET_NON_NULL_NATIVE_ARGUMENT(Smi, smiLength, arguments->NativeArgAt(1));
+  intptr_t array_len = a.Length();
+  int32_t length = smiLength.Value();
+  if (length < 0 || length > array_len) {

[srdjan, 2013/03/05 16:02:21]

Add parenthesis (length < 0) || (length > array_len)

[Lasse Reichstein Nielsen, 2013/03/05 16:56:56]

Will do.

+    const Array& args = Array::Handle(Array::New(1));
+    args.SetAt(0, smiLength);
+    Exceptions::ThrowByType(Exceptions::kRange, args);
+  }
+  // TODO(lrn): Pass parameter saying whether the data is Latin1, and
+  // use OneByteString::New in that case.
+  const String& result = String::Handle(TwoByteString::New(length, Heap::kNew));
+  NoGCScope no_gc;
+  uint16_t* data_position = reinterpret_cast<uint16_t*>(
+      reinterpret_cast<char*>(a.raw()) +
+      Uint16Array::data_offset() - kHeapObjectTag);
+  String::Copy(result, 0, data_position, length);
+  return result.raw();
+}
+
 }  // namespace dart