Speed up compares with characters ie single-character strings....

src/objects-inl.h

 // Copyright 2006-2008 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 132 matching lines @@
 
 bool Object::IsString() {
   return Object::IsHeapObject()
     && HeapObject::cast(this)->map()->instance_type() < FIRST_NONSTRING_TYPE;
 }
 
 
 bool Object::IsSymbol() {
   if (!this->IsHeapObject()) return false;
   uint32_t type = HeapObject::cast(this)->map()->instance_type();
-  return (type & (kIsNotStringMask | kIsSymbolMask)) ==
-         (kStringTag | kSymbolTag);
+  // Because the symbol tag is non-zero and no non-string types have the
+  // symbol bit set we can test for symbols with a very simple test
+  // operation.
+  ASSERT(kSymbolTag != 0);
+  ASSERT(kNotStringTag + kIsSymbolMask > LAST_TYPE);
+  return (type & kIsSymbolMask != 0);
 }
 
 
 bool Object::IsConsString() {
   if (!this->IsHeapObject()) return false;
   uint32_t type = HeapObject::cast(this)->map()->instance_type();
   return (type & (kIsNotStringMask | kStringRepresentationMask)) ==
          (kStringTag | kConsStringTag);
 }
 
@@ skipping 54 matching lines @@
 
 StringShape::StringShape(InstanceType t)
   : type_(static_cast<uint32_t>(t)) {
   set_valid();
   ASSERT((type_ & kIsNotStringMask) == kStringTag);
 }
 
 
 bool StringShape::IsSymbol() {
   ASSERT(valid());
-  return (type_ & kIsSymbolMask) == kSymbolTag;
+  ASSERT(kSymbolTag != 0);
+  return (type_ & kIsSymbolMask) != 0;
 }
 
 
 bool String::IsAsciiRepresentation() {
   uint32_t type = map()->instance_type();
   if ((type & kStringRepresentationMask) == kConsStringTag &&
       ConsString::cast(this)->second()->length() == 0) {
     return ConsString::cast(this)->first()->IsAsciiRepresentation();
   }
   return (type & kStringEncodingMask) == kAsciiStringTag;
@@ skipping 2790 matching lines @@
 #undef WRITE_INT_FIELD
 #undef READ_SHORT_FIELD
 #undef WRITE_SHORT_FIELD
 #undef READ_BYTE_FIELD
 #undef WRITE_BYTE_FIELD
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_OBJECTS_INL_H_