Add a special case in Math.round for a SMI result. Also change the implementa...

src/runtime.cc

 // Copyright 2006-2009 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 5305 matching lines @@
   } else {
       return Heap::AllocateHeapNumber(pow(x, y));
   }
 }
 
 
 static Object* Runtime_Math_round(Arguments args) {
   NoHandleAllocation ha;
   ASSERT(args.length() == 1);
   Counters::math_round.Increment();
+  CONVERT_DOUBLE_CHECKED(x, args[0]);
 
-  CONVERT_DOUBLE_CHECKED(x, args[0]);
+  if (x > 0 && x < Smi::kMaxValue) {
+    return Smi::FromInt(static_cast<int>(x + 0.5));
+  }
+
   if (signbit(x) && x >= -0.5) return Heap::minus_zero_value();
-  double integer = ceil(x);
-  if (integer - x > 0.5) { integer -= 1.0; }
-  return Heap::NumberFromDouble(integer);
+
+  // if the magnitude is big enough, there's no place for fraction part. If we
+  // try to add 0.5 to this number, 1.0 will be added instead.
+  if (x >= 9007199254740991.0 || x <= -9007199254740991.0) {
+    return Heap::NumberFromDouble(x);

[Erik Corry, 2010/03/15 20:11:34]

Seems like we could just return args[0] here and avoid creating a new HeapNumber
object.

+  }
+
+  return Heap::NumberFromDouble(floor(x + 0.5));
 }
 
 
 static Object* Runtime_Math_sin(Arguments args) {
   NoHandleAllocation ha;
   ASSERT(args.length() == 1);
   Counters::math_sin.Increment();
 
   CONVERT_DOUBLE_CHECKED(x, args[0]);
   return TranscendentalCache::Get(TranscendentalCache::SIN, x);
@@ skipping 3999 matching lines @@
   } else {
     // Handle last resort GC and make sure to allow future allocations
     // to grow the heap without causing GCs (if possible).
     Counters::gc_last_resort_from_js.Increment();
     Heap::CollectAllGarbage(false);
   }
 }
 
 
 } }  // namespace v8::internal