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));
+  uint64_t range = static_cast<uint64_t>(max) - min + 1;
+  // |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_t to int64_t.
+  int result =
+      static_cast<int>(min + static_cast<int64_t>(base::RandGenerator(range)));
   DCHECK_GE(result, min);
   DCHECK_LE(result, max);
   return result;
 }
 
 double RandDouble() {
   return BitsToOpenEndedUnitInterval(base::RandUint64());
 }
 
-double BitsToOpenEndedUnitInterval(uint64 bits) {
+double BitsToOpenEndedUnitInterval(uint64_t bits) {
   // We try to get maximum precision by masking out as many bits as will fit
   // in the target type's mantissa, and raising it to an appropriate power to
   // produce output in the range [0, 1).  For IEEE 754 doubles, the mantissa
   // is expected to accommodate 53 bits.
 
   COMPILE_ASSERT(std::numeric_limits<double>::radix == 2, otherwise_use_scalbn);
   static const int kBits = std::numeric_limits<double>::digits;
-  uint64 random_bits = bits & ((UINT64_C(1) << kBits) - 1);
+  uint64_t random_bits = bits & ((UINT64_C(1) << kBits) - 1);
   double result = ldexp(static_cast<double>(random_bits), -1 * kBits);
   DCHECK_GE(result, 0.0);
   DCHECK_LT(result, 1.0);
   return result;
 }
 
-uint64 RandGenerator(uint64 range) {
+uint64_t RandGenerator(uint64_t range) {
   DCHECK_GT(range, 0u);
   // We must discard random results above this number, as they would
   // make the random generator non-uniform (consider e.g. if
   // MAX_UINT64 was 7 and |range| was 5, then a result of 1 would be twice
   // as likely as a result of 3 or 4).
-  uint64 max_acceptable_value =
-      (std::numeric_limits<uint64>::max() / range) * range - 1;
+  uint64_t max_acceptable_value =
+      (std::numeric_limits<uint64_t>::max() / range) * range - 1;
 
-  uint64 value;
+  uint64_t value;
   do {
     value = base::RandUint64();
   } while (value > max_acceptable_value);
 
   return value % range;
 }
 
 std::string RandBytesAsString(size_t length) {
   DCHECK_GT(length, 0u);
   std::string result;
   RandBytes(WriteInto(&result, length + 1), length);
   return result;
 }
 
 }  // namespace base