[vm] Change TypedData_getUint64 native method to silently cast values

runtime/vm/object.cc

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/object.h"
 
 #include "include/dart_api.h"
 #include "platform/assert.h"
 #include "vm/assembler.h"
 #include "vm/become.h"
@@ skipping 18137 matching lines @@
 
 RawInteger* Integer::New(int64_t value, Heap::Space space) {
   const bool is_smi = Smi::IsValid(value);
   if (is_smi) {
     return Smi::New(static_cast<intptr_t>(value));
   }
   return Mint::New(value, space);
 }
 
 RawInteger* Integer::NewFromUint64(uint64_t value, Heap::Space space) {
-  if (value > static_cast<uint64_t>(Mint::kMaxValue)) {
-    if (FLAG_limit_ints_to_64_bits) {
-      // Out of range.
-      return Integer::null();
-    } else {
-      return Bigint::NewFromUint64(value, space);
-    }
+  if (!FLAG_limit_ints_to_64_bits &&
+      (value > static_cast<uint64_t>(Mint::kMaxValue))) {
+    return Bigint::NewFromUint64(value, space);
+  }
+  return Integer::New(static_cast<int64_t>(value), space);
+}
+
+bool Integer::IsValidUint64(uint64_t value) {
+  if (FLAG_limit_ints_to_64_bits) {
+    return (value <= static_cast<uint64_t>(Mint::kMaxValue));
   } else {
-    return Integer::New(value, space);

[siva, 2017/07/31 21:46:08]

why is it not ok to just change this to 
  return Integer::New(static_cast<int64_t>(value), space);

and not have this new function IsValidUint64 ... and drop the changes in
Dart_NewIntegerFromUint64

[alexmarkov, 2017/07/31 23:58:12]

Integer::NewFromUint64 is called from 2 places: Dart_NewIntegerFromUint64 and
TypedData_getUint64. The latter requires silent wrap-around, so range checking
is moved to Dart_NewIntegerFromUint64.

As per our discussion, I'm going to rename Integer::IsValidUint64 in order to
improve readability in the follow-up CL:
https://codereview.chromium.org/2992783002/

+    return true;
   }
 }
 
 bool Integer::Equals(const Instance& other) const {
   // Integer is an abstract class.
   UNREACHABLE();
   return false;
 }
 
 bool Integer::IsZero() const {
@@ skipping 4356 matching lines @@
   }
   return UserTag::null();
 }
 
 const char* UserTag::ToCString() const {
   const String& tag_label = String::Handle(label());
   return tag_label.ToCString();
 }
 
 }  // namespace dart