modules/rtp_rtcp/source/time_util.cc

/*
 *  Copyright (c) 2016 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 "modules/rtp_rtcp/source/time_util.h"

#include <algorithm>

namespace webrtc {
namespace {
// TODO(danilchap): Make generic, optimize and move to base.
inline int64_t DivideRoundToNearest(int64_t x, uint32_t y) {
  // Caller ensure x is positive by converting unsigned value into it.
  // So this Divide doesn't need to handle negative argument case.
  return (x + y / 2) / y;
}
}  // namespace

int64_t CompactNtpRttToMs(uint32_t compact_ntp_interval) {
  // Interval to convert expected to be positive, e.g. rtt or delay.
  // Because interval can be derived from non-monotonic ntp clock,
  // it might become negative that is indistinguishable from very large values.
  // Since very large rtt/delay are less likely than non-monotonic ntp clock,
  // those values consider to be negative and convert to minimum value of 1ms.
  if (compact_ntp_interval > 0x80000000)
    return 1;
  // Convert to 64bit value to avoid multiplication overflow.
  int64_t value = static_cast<int64_t>(compact_ntp_interval);
  // To convert to milliseconds need to divide by 2^16 to get seconds,
  // then multiply by 1000 to get milliseconds. To avoid float operations,
  // multiplication and division swapped.
  int64_t ms = DivideRoundToNearest(value * 1000, 1 << 16);
  // Rtt value 0 considered too good to be true and increases to 1.
  return std::max<int64_t>(ms, 1);
}
}  // namespace webrtc