Line data    Source code

       1             : /*
       2             :  *  Copyright (c) 2016 The WebRTC project authors. All Rights Reserved.
       3             :  *
       4             :  *  Use of this source code is governed by a BSD-style license
       5             :  *  that can be found in the LICENSE file in the root of the source
       6             :  *  tree. An additional intellectual property rights grant can be found
       7             :  *  in the file PATENTS.  All contributing project authors may
       8             :  *  be found in the AUTHORS file in the root of the source tree.
       9             :  */
      10             : 
      11             : #ifndef WEBRTC_MODULES_VIDEO_CODING_SEQUENCE_NUMBER_UTIL_H_
      12             : #define WEBRTC_MODULES_VIDEO_CODING_SEQUENCE_NUMBER_UTIL_H_
      13             : 
      14             : #include <limits>
      15             : #include <type_traits>
      16             : 
      17             : #include "webrtc/base/mod_ops.h"
      18             : 
      19             : namespace webrtc {
      20             : 
      21             : // Test if the sequence number |a| is ahead or at sequence number |b|.
      22             : //
      23             : // If |M| is an even number and the two sequence numbers are at max distance
      24             : // from each other, then the sequence number with the highest value is
      25             : // considered to be ahead.
      26             : template <typename T, T M>
      27           0 : inline bool AheadOrAt(T a, T b) {
      28             :   static_assert(std::is_unsigned<T>::value,
      29             :                 "Type must be an unsigned integer.");
      30           0 :   const T maxDist = M / 2;
      31           0 :   if (!(M & 1) && MinDiff<T, M>(a, b) == maxDist)
      32           0 :     return b < a;
      33           0 :   return ForwardDiff<T, M>(b, a) <= maxDist;
      34             : }
      35             : 
      36             : template <typename T>
      37           0 : inline bool AheadOrAt(T a, T b) {
      38             :   static_assert(std::is_unsigned<T>::value,
      39             :                 "Type must be an unsigned integer.");
      40           0 :   const T maxDist = std::numeric_limits<T>::max() / 2 + T(1);
      41           0 :   if (a - b == maxDist)
      42           0 :     return b < a;
      43           0 :   return ForwardDiff(b, a) < maxDist;
      44             : }
      45             : 
      46             : // Test if the sequence number |a| is ahead of sequence number |b|.
      47             : //
      48             : // If |M| is an even number and the two sequence numbers are at max distance
      49             : // from each other, then the sequence number with the highest value is
      50             : // considered to be ahead.
      51             : template <typename T, T M>
      52           0 : inline bool AheadOf(T a, T b) {
      53             :   static_assert(std::is_unsigned<T>::value,
      54             :                 "Type must be an unsigned integer.");
      55           0 :   return a != b && AheadOrAt<T, M>(a, b);
      56             : }
      57             : 
      58             : template <typename T>
      59           0 : inline bool AheadOf(T a, T b) {
      60             :   static_assert(std::is_unsigned<T>::value,
      61             :                 "Type must be an unsigned integer.");
      62           0 :   return a != b && AheadOrAt(a, b);
      63             : }
      64             : 
      65             : namespace internal {
      66             : 
      67             : template <typename T, typename M>
      68             : struct SeqNumComp;
      69             : 
      70             : template <typename T, T M>
      71             : struct SeqNumComp<T, std::integral_constant<T, M>> {
      72           0 :   bool operator()(T a, T b) const { return AheadOf<T, M>(a, b); }
      73             : };
      74             : 
      75             : template <typename T>
      76             : struct SeqNumComp<T, std::integral_constant<T, T(0)>> {
      77           0 :   bool operator()(T a, T b) const { return AheadOf<T>(a, b); }
      78             : };
      79             : 
      80             : }  // namespace internal
      81             : 
      82             : // Comparator used to compare sequence numbers in a continuous fashion.
      83             : //
      84             : // WARNING! If used to sort sequence numbers of length M then the interval
      85             : //          covered by the sequence numbers may not be larger than floor(M/2).
      86             : template <typename T, T M = 0>
      87             : struct AscendingSeqNumComp
      88             :     : private internal::SeqNumComp<T, std::integral_constant<T, M>> {
      89             :   bool operator()(T a, T b) const {
      90             :     return internal::SeqNumComp<T, std::integral_constant<T, M>>::operator()(a,
      91             :                                                                              b);
      92             :   }
      93             : };
      94             : 
      95             : // Comparator used to compare sequence numbers in a continuous fashion.
      96             : //
      97             : // WARNING! If used to sort sequence numbers of length M then the interval
      98             : //          covered by the sequence numbers may not be larger than floor(M/2).
      99             : template <typename T, T M = 0>
     100             : struct DescendingSeqNumComp
     101             :     : private internal::SeqNumComp<T, std::integral_constant<T, M>> {
     102           0 :   bool operator()(T a, T b) const {
     103           0 :     return internal::SeqNumComp<T, std::integral_constant<T, M>>::operator()(b,
     104           0 :                                                                              a);
     105             :   }
     106             : };
     107             : 
     108             : }  // namespace webrtc
     109             : 
     110             : #endif  // WEBRTC_MODULES_VIDEO_CODING_SEQUENCE_NUMBER_UTIL_H_