webrtc / src / 291cd8fac37a2efa026713d198d653bc083881db / . / webrtc / 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 "webrtc/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 |