Add missing overflow handling to base::RandInt().

base/rand_util.cc

 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "base/rand_util.h"
 
 #include <math.h>
 #include <stdint.h>
 
 #include <algorithm>
 #include <limits>
 
 #include "base/basictypes.h"
 #include "base/logging.h"
 #include "base/strings/string_util.h"
 
 namespace base {
 
 int RandInt(int min, int max) {
   DCHECK_LE(min, max);
 
   uint64 range = static_cast<uint64>(max) - min + 1;
-  int result = min + static_cast<int>(base::RandGenerator(range));
+  // |range| is at most UINT_MAX + 1, so the result of RandGenerator(range)
+  // is at most UINT_MAX.  Hence it's safe to cast it from uint64 to int64.
+  int result =
+      static_cast<int>(min + static_cast<int64>(base::RandGenerator(range)));

[Lei Zhang, 2015/10/29 16:38:15]

int64_t, and fix line 22 as well?

[Nico, 2015/10/29 16:46:45]

Done.

   DCHECK_GE(result, min);
   DCHECK_LE(result, max);
   return result;
 }
 
 double RandDouble() {
   return BitsToOpenEndedUnitInterval(base::RandUint64());
 }
 
 double BitsToOpenEndedUnitInterval(uint64 bits) {
@@ skipping 29 matching lines @@
 }
 
 std::string RandBytesAsString(size_t length) {
   DCHECK_GT(length, 0u);
   std::string result;
   RandBytes(WriteInto(&result, length + 1), length);
   return result;
 }
 
 }  // namespace base