Move UBSan warnings from a blacklist to the source

webrtc/rtc_base/random.cc

 /*
  *  Copyright (c) 2015 The WebRTC project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 #include "webrtc/rtc_base/random.h"
 
 #include <math.h>
 
 #include "webrtc/rtc_base/checks.h"
+#include "webrtc/rtc_base/safe_conversions.h"
 
 namespace webrtc {
 
 Random::Random(uint64_t seed) {
   RTC_DCHECK(seed != 0x0ull);
   state_ = seed;
 }
 
 uint32_t Random::Rand(uint32_t t) {
   // Casting the output to 32 bits will give an almost uniform number.
   // Pr[x=0] = (2^32-1) / (2^64-1)
   // Pr[x=k] = 2^32 / (2^64-1) for k!=0
   // Uniform would be Pr[x=k] = 2^32 / 2^64 for all 32-bit integers k.
   uint32_t x = NextOutput();
   // If x / 2^32 is uniform on [0,1), then x / 2^32 * (t+1) is uniform on
   // the interval [0,t+1), so the integer part is uniform on [0,t].
   uint64_t result = x * (static_cast<uint64_t>(t) + 1);
   result >>= 32;
   return result;
 }
 
 uint32_t Random::Rand(uint32_t low, uint32_t high) {
   RTC_DCHECK(low <= high);
   return Rand(high - low) + low;
 }
 
 int32_t Random::Rand(int32_t low, int32_t high) {
   RTC_DCHECK(low <= high);
-  // We rely on subtraction (and addition) to be the same for signed and
-  // unsigned numbers in two-complement representation. Thus, although
-  // high - low might be negative as an int, it is the correct difference
-  // when interpreted as an unsigned.
-  return Rand(high - low) + low;
+  const int64_t low_i64{low};
+  return rtc::dchecked_cast<int32_t>(
+      Rand(rtc::dchecked_cast<uint32_t>(high - low_i64)) + low_i64);
 }
 
 template <>
 float Random::Rand<float>() {
   double result = NextOutput() - 1;
   result = result / 0xFFFFFFFFFFFFFFFEull;
   return static_cast<float>(result);
 }
 
 template <>
@@ skipping 19 matching lines @@
   double u2 = static_cast<double>(NextOutput()) / 0xFFFFFFFFFFFFFFFFull;
   return mean + standard_deviation * sqrt(-2 * log(u1)) * cos(2 * kPi * u2);
 }
 
 double Random::Exponential(double lambda) {
   double uniform = Rand<double>();
   return -log(uniform) / lambda;
 }
 
 }  // namespace webrtc