Implement faster splitting with empty string as pattern. Add special native for computing substring…

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 33 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);
 }
 
 
 DEFINE_NATIVE_ENTRY(StringBase_substringUnchecked, 3) {
-  GET_NATIVE_ARGUMENT(String, receiver, arguments->NativeArgAt(0));
+  const String& receiver = String::CheckedHandle(arguments->NativeArgAt(0));
   GET_NATIVE_ARGUMENT(Smi, start_obj, arguments->NativeArgAt(1));
   GET_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));
 }
 
 
+DEFINE_NATIVE_ENTRY(OneByteString_substringUnchecked, 3) {
+  const String& receiver = String::CheckedHandle(arguments->NativeArgAt(0));
+  ASSERT(receiver.IsOneByteString());
+  GET_NATIVE_ARGUMENT(Smi, start_obj, arguments->NativeArgAt(1));
+  GET_NATIVE_ARGUMENT(Smi, end_obj, arguments->NativeArgAt(2));
+
+  const intptr_t start = start_obj.Value();
+  const intptr_t end = end_obj.Value();
+  return OneByteString::New(receiver, start, end - start, Heap::kNew);
+}
+
+
 DEFINE_NATIVE_ENTRY(String_getHashCode, 1) {
   const String& receiver = String::CheckedHandle(arguments->NativeArgAt(0));
   intptr_t hash_val = receiver.Hash();
   ASSERT(hash_val > 0);
   ASSERT(Smi::IsValid(hash_val));
   return Smi::New(hash_val);
 }
 
 
 DEFINE_NATIVE_ENTRY(String_getLength, 1) {
@@ skipping 73 matching lines @@
     if (!elem.IsString()) {
       GrowableArray<const Object*> args;
       args.Add(&elem);
       Exceptions::ThrowByType(Exceptions::kArgument, args);
     }
   }
   return String::ConcatAll(strings);
 }
 
 }  // namespace dart