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

webrtc/base/ipaddress.cc

 /*
  *  Copyright 2004 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.
  */
 
@@ skipping 394 matching lines @@
     }
   }
   if (word_to_count == 0) {
     return bits;
   }
 
   // Public domain bit-twiddling hack from:
   // http://graphics.stanford.edu/~seander/bithacks.html
   // Counts the trailing 0s in the word.
   unsigned int zeroes = 32;
-  word_to_count &= -static_cast<int32_t>(word_to_count);
+  // This could also be written word_to_count &= -word_to_count, but
+  // MSVC emits warning C4146 when negating an unsigned number.
+  word_to_count &= ~word_to_count + 1;  // Isolate lowest set bit.
   if (word_to_count) zeroes--;
   if (word_to_count & 0x0000FFFF) zeroes -= 16;
   if (word_to_count & 0x00FF00FF) zeroes -= 8;
   if (word_to_count & 0x0F0F0F0F) zeroes -= 4;
   if (word_to_count & 0x33333333) zeroes -= 2;
   if (word_to_count & 0x55555555) zeroes -= 1;
 
   return bits + (32 - zeroes);
 }
 
@@ skipping 89 matching lines @@
 IPAddress GetAnyIP(int family) {
   if (family == AF_INET) {
     return rtc::IPAddress(INADDR_ANY);
   }
   if (family == AF_INET6) {
     return rtc::IPAddress(in6addr_any);
   }
   return rtc::IPAddress();
 }
 
-}  // Namespace rtc
+}  // namespace rtc