X64: Convert smis to holding 32 bits of payload.

src/v8.cc

Index: src/v8.cc
diff --git a/src/v8.cc b/src/v8.cc
index 3f8e6cdeae055286b7014fbf13d36a1a8a1ee7b4..3c70ee96b0b57146ad44776c164b990911fc8a8b 100644
--- a/src/v8.cc
+++ b/src/v8.cc
@@ -178,11 +178,14 @@ bool V8::IdleNotification() {
   return Heap::IdleNotification();
 }
 
+static const uint32_t kRandomPositiveSmiMax = 0x3fffffff;
 
 Smi* V8::RandomPositiveSmi() {
   uint32_t random = Random();
-  ASSERT(IsPowerOf2(Smi::kMaxValue + 1));
-  return Smi::FromInt(random & Smi::kMaxValue);
+  ASSERT(static_cast<uint32_t>(Smi::kMaxValue) >= kRandomPositiveSmiMax);
+  // kRandomPositiveSmiMax must match the value being divided
+  // by in math.js.
+  return Smi::FromInt(random & kRandomPositiveSmiMax);
 }
 
 } }  // namespace v8::internal