Improve Math.round(). Fix the bug in r4146. Further improve performance by ch...

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 5332 matching lines @@
   if (y == 0) {
       return Smi::FromInt(1);
   } else if (isnan(y) || ((x == 1 || x == -1) && isinf(y))) {
       return Heap::nan_value();
   } else {
       return Heap::AllocateHeapNumber(pow(x, y));
   }
 }
 
 
-static Object* Runtime_Math_round(Arguments args) {
+static Object* Runtime_RoundNumber(Arguments args) {
   NoHandleAllocation ha;
   ASSERT(args.length() == 1);
   Counters::math_round.Increment();
 
-  CONVERT_DOUBLE_CHECKED(x, args[0]);
-  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 (!args[0]->IsHeapNumber()) {
+    // Must be smi. Return the argument unchanged for all the other types
+    // to make fuzz-natives test happy.
+    return args[0];
+  }
+
+  HeapNumber* number = reinterpret_cast<HeapNumber*>(args[0]);
+
+  double value = number->value();
+  int exponent = number->get_exponent();
+  int sign = number->get_sign();
+
+  // We compare with kSmiValueSize - 3 because (2^30 - 0.1) has exponent 29 and
+  // should be rounded to 2^30, which is not smi.
+  if (!sign && exponent <= kSmiValueSize - 3) {
+    return Smi::FromInt(static_cast<int>(value + 0.5));
+  }
+
+  // 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 (exponent >= 52) {
+    return number;
+  }
+
+  if (sign && value >= -0.5) return Heap::minus_zero_value();
+
+  return Heap::NumberFromDouble(floor(value + 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 4029 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