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

src/runtime.cc

Index: src/runtime.cc
===================================================================
--- src/runtime.cc	(revision 4138)
+++ src/runtime.cc	(working copy)
@@ -5323,12 +5323,21 @@
   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));
 }