Fix some signed overflow errors causing undefined behavior (in theory).

webrtc/base/random_unittest.cc

Index: webrtc/base/random_unittest.cc
diff --git a/webrtc/base/random_unittest.cc b/webrtc/base/random_unittest.cc
index 3b47a00806eb0fc29ae0e43568df0f8b19fde960..ae1a0a2f5122004399404afa7ea316f7c8a52c8c 100644
--- a/webrtc/base/random_unittest.cc
+++ b/webrtc/base/random_unittest.cc
@@ -14,6 +14,7 @@
 #include <vector>
 
 #include "testing/gtest/include/gtest/gtest.h"
+#include "webrtc/base/mathutils.h"  // unsigned difference
 #include "webrtc/base/random.h"
 
 namespace webrtc {
@@ -118,7 +119,7 @@ void BucketTestSignedInterval(unsigned int bucket_count,
 
   ASSERT_GE(high, low);
   ASSERT_GE(bucket_count, 2u);
-  uint32_t interval = static_cast<uint32_t>(high - low + 1);
+  uint32_t interval = unsigned_difference<int32_t>(high, low) + 1;
   uint32_t numbers_per_bucket;
   if (interval == 0) {
     // The computation high - low + 1 should be 2^32 but overflowed
@@ -134,7 +135,7 @@ void BucketTestSignedInterval(unsigned int bucket_count,
     int32_t sample = prng->Rand(low, high);
     EXPECT_LE(low, sample);
     EXPECT_GE(high, sample);
-    buckets[static_cast<uint32_t>(sample - low) / numbers_per_bucket]++;
+    buckets[unsigned_difference<int32_t>(sample, low) / numbers_per_bucket]++;
   }
 
   for (unsigned int i = 0; i < bucket_count; i++) {
@@ -158,7 +159,7 @@ void BucketTestUnsignedInterval(unsigned int bucket_count,
 
   ASSERT_GE(high, low);
   ASSERT_GE(bucket_count, 2u);
-  uint32_t interval = static_cast<uint32_t>(high - low + 1);
+  uint32_t interval = high - low + 1;
   uint32_t numbers_per_bucket;
   if (interval == 0) {
     // The computation high - low + 1 should be 2^32 but overflowed
@@ -174,7 +175,7 @@ void BucketTestUnsignedInterval(unsigned int bucket_count,
     uint32_t sample = prng->Rand(low, high);
     EXPECT_LE(low, sample);
     EXPECT_GE(high, sample);
-    buckets[static_cast<uint32_t>(sample - low) / numbers_per_bucket]++;
+    buckets[(sample - low) / numbers_per_bucket]++;
   }
 
   for (unsigned int i = 0; i < bucket_count; i++) {