Optionally use 31-bits SMI value for 64-bit system

include/v8.h

 // Copyright 2012 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 5347 matching lines @@
   }
   V8_INLINE(static internal::Object* IntToSmi(int value)) {
     return internal::IntToSmi<kSmiShiftSize>(value);
   }
   V8_INLINE(static bool IsValidSmi(intptr_t value)) {
     // To be representable as a long smi, the value must be a 32-bit integer.
     return (value == static_cast<int32_t>(value));
   }
 };
 
+#if V8_USE_31_BIT_SMI_VALUE
+typedef SmiTagging<4> PlatformSmiTagging;
+#else
 typedef SmiTagging<kApiPointerSize> PlatformSmiTagging;
+#endif
 const int kSmiShiftSize = PlatformSmiTagging::kSmiShiftSize;
 const int kSmiValueSize = PlatformSmiTagging::kSmiValueSize;
 
 /**
  * This class exports constants and functionality from within v8 that
  * is necessary to implement inline functions in the v8 api.  Don't
  * depend on functions and constants defined here.
  */
 class Internals {
  public:
@@ skipping 1102 matching lines @@
 
 
 }  // namespace v8
 
 
 #undef V8EXPORT
 #undef TYPE_CHECK
 
 
 #endif  // V8_H_