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

base/rand_util.cc

Index: base/rand_util.cc
diff --git a/base/rand_util.cc b/base/rand_util.cc
index 931eb4e943e646e2f39e2848b33683247b5b4725..e12088e54344a9f0ba2de21d45a0cd467bd016df 100644
--- a/base/rand_util.cc
+++ b/base/rand_util.cc
@@ -10,7 +10,6 @@
 #include <algorithm>
 #include <limits>
 
-#include "base/basictypes.h"
 #include "base/logging.h"
 #include "base/strings/string_util.h"
 
@@ -19,8 +18,11 @@ 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;
@@ -30,7 +32,7 @@ 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
@@ -38,23 +40,23 @@ double BitsToOpenEndedUnitInterval(uint64 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);