Make rtc::TimestampWrapAroundHandler handle backwards wrapping

webrtc/base/timeutils.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 175 matching lines @@
     if (later <= earlier) {
       return -static_cast<long>(earlier - later);
     } else {
       return -static_cast<long>(earlier + (UINT32_MAX - later) + 1);
     }
   }
 #endif
 }
 
 TimestampWrapAroundHandler::TimestampWrapAroundHandler()
-    : last_ts_(0), num_wrap_(0) {}
+    : last_ts_(0), num_wrap_(-1) {}
 
 int64_t TimestampWrapAroundHandler::Unwrap(uint32_t ts) {
+  if (num_wrap_ == -1) {
+    last_ts_ = ts;
+    num_wrap_ = 0;
+    return ts;
+  }
+
   if (ts < last_ts_) {
-    if (last_ts_ > 0xf0000000 && ts < 0x0fffffff) {
+    if (last_ts_ >= 0xf0000000 && ts < 0x0fffffff)
       ++num_wrap_;
-    }
+  } else if ((ts - last_ts_) > 0xf0000000) {
+    // Backwards wrap. Unwrap with last wrap count and don't update last_ts_.
+    return ts + ((num_wrap_ - 1) << 32);
   }
+
   last_ts_ = ts;
-  int64_t unwrapped_ts = ts + (num_wrap_ << 32);
-  return unwrapped_ts;
+  return ts + (num_wrap_ << 32);
 }
 
 int64_t TmToSeconds(const std::tm& tm) {
   static short int mdays[12] = {31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};
   static short int cumul_mdays[12] = {0,   31,  59,  90,  120, 151,
                                       181, 212, 243, 273, 304, 334};
   int year = tm.tm_year + 1900;
   int month = tm.tm_mon;
   int day = tm.tm_mday - 1;  // Make 0-based like the rest.
   int hour = tm.tm_hour;
@@ skipping 27 matching lines @@
   if (expiry_in_leap_year && month <= 2 - 1) // |month| is zero based.
     day -= 1;
 
   // Combine all variables into seconds from 1970-01-01 00:00 (except |month|
   // which was accumulated into |day| above).
   return (((static_cast<int64_t>
             (year - 1970) * 365 + day) * 24 + hour) * 60 + min) * 60 + sec;
 }
 
 } // namespace rtc