RtpToNtpEstimator:: Add a DCHECK to avoid div-by-0

webrtc/system_wrappers/source/rtp_to_ntp_estimator.cc

 /*
  *  Copyright (c) 2012 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/system_wrappers/include/rtp_to_ntp_estimator.h"
 
+#include "webrtc/rtc_base/checks.h"
 #include "webrtc/rtc_base/logging.h"
 #include "webrtc/system_wrappers/include/clock.h"
 
 namespace webrtc {
 namespace {
 // Number of RTCP SR reports to use to map between RTP and NTP.
 const size_t kNumRtcpReportsToUse = 2;
 
 // Calculates the RTP timestamp frequency from two pairs of NTP/RTP timestamps.
 bool CalculateFrequency(int64_t ntp_ms1,
@@ skipping 132 matching lines @@
   if (!params_.calculated || measurements_.empty())
     return false;
 
   uint32_t rtp_timestamp_old = measurements_.back().rtp_timestamp;
   int64_t rtp_timestamp_unwrapped;
   if (!CompensateForWrapAround(rtp_timestamp, rtp_timestamp_old,
                                &rtp_timestamp_unwrapped)) {
     return false;
   }
 
+  // params_.calculated should not be true unless params_.frequency_khz has been
+  // set to something non-zero.
+  RTC_DCHECK_NE(params_.frequency_khz, 0.0);

[kwiberg-webrtc, 2017/09/01 12:53:06]

Is it OK if the value is very, very close to zero?

   double rtp_ms =
       (static_cast<double>(rtp_timestamp_unwrapped) - params_.offset_ms) /
           params_.frequency_khz +
       0.5f;
 
   if (rtp_ms < 0)
     return false;
 
   *rtp_timestamp_ms = rtp_ms;
   return true;
@@ skipping 10 matching lines @@
     }
   } else if (static_cast<int32_t>(old_timestamp - new_timestamp) > 0) {
     // This difference should be less than -2^31 if we have had a backward wrap
     // around. Since it is cast to a int32_t, it should be positive.
     return -1;
   }
   return 0;
 }
 
 }  // namespace webrtc