Harden NumberToSize against overflows.

src/v8conversions.h

 // Copyright 2011 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 42 matching lines @@
                       double empty_string_val = 0);
 
 // Converts a string into an integer.
 double StringToInt(UnicodeCache* unicode_cache, String* str, int radix);
 
 // Converts a number into size_t.
 inline size_t NumberToSize(Isolate* isolate,
                            Object* number) {
   SealHandleScope shs(isolate);
   if (number->IsSmi()) {
+    int value = Smi::cast(number)->value();
+    CHECK(value >= 0

[Jakob Kummerow, 2013/11/14 10:17:48]

Not that it makes a big difference, but it's sufficient to:

CHECK(value >= 0);
ASSERT(static_cast<unsigned>(value) <= std::numeric_limits<size_t>::max());

or even:

STATIC_ASSERT(Smi::kMaxValue <= std::numeric_limits<size_t>::max());

if that numeric_limits call is static assert capable.

[Dmitry Lomov (no reviews), 2013/11/14 10:22:58]

Great suggestion, this is by far the commonest case so shaving a couple cycles
here is useful.

+        && static_cast<unsigned>(value) <= std::numeric_limits<size_t>::max());
     return Smi::cast(number)->value();
   } else {
     ASSERT(number->IsHeapNumber());
     double value = HeapNumber::cast(number)->value();
+    CHECK(value >= 0 &&
+        value <= std::numeric_limits<size_t>::max());

[Jakob Kummerow, 2013/11/14 10:17:48]

nit: I'd align "value" with "value".

     return static_cast<size_t>(value);
   }
 }
 
 } }  // namespace v8::internal
 
 #endif  // V8_V8CONVERSIONS_H_