rtt calculation handles time go backwards

webrtc/modules/rtp_rtcp/source/time_util_unittest.cc

 /*
  *  Copyright (c) 2015 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 "testing/gtest/include/gtest/gtest.h"
 
 namespace webrtc {
 
 TEST(TimeUtilTest, CompactNtp) {
   const uint32_t kNtpSec = 0x12345678;
   const uint32_t kNtpFrac = 0x23456789;
   const NtpTime kNtp(kNtpSec, kNtpFrac);
   const uint32_t kNtpMid = 0x56782345;
   EXPECT_EQ(kNtpMid, CompactNtp(kNtp));
 }
 
-TEST(TimeUtilTest, CompactNtpToMs) {
+TEST(TimeUtilTest, CompactNtpRttToMs) {
   const NtpTime ntp1(0x12345, 0x23456);
   const NtpTime ntp2(0x12654, 0x64335);
-  uint32_t ms_diff = ntp2.ToMs() - ntp1.ToMs();
+  int64_t ms_diff = ntp2.ToMs() - ntp1.ToMs();
   uint32_t ntp_diff = CompactNtp(ntp2) - CompactNtp(ntp1);
 
-  uint32_t ntp_to_ms_diff = CompactNtpIntervalToMs(ntp_diff);
+  int64_t ntp_to_ms_diff = CompactNtpRttToMs(ntp_diff);
 
   EXPECT_NEAR(ms_diff, ntp_to_ms_diff, 1);
 }
 
-TEST(TimeUtilTest, CompactNtpToMsWithWrap) {
+TEST(TimeUtilTest, CompactNtpRttToMsWithWrap) {
   const NtpTime ntp1(0x1ffff, 0x23456);
   const NtpTime ntp2(0x20000, 0x64335);
-  uint32_t ms_diff = ntp2.ToMs() - ntp1.ToMs();
+  int64_t ms_diff = ntp2.ToMs() - ntp1.ToMs();
 
   // While ntp2 > ntp1, there compact ntp presentation happen to be opposite.
   // That shouldn't be a problem as long as unsigned arithmetic is used.
   ASSERT_GT(ntp2.ToMs(), ntp1.ToMs());
   ASSERT_LT(CompactNtp(ntp2), CompactNtp(ntp1));
 
   uint32_t ntp_diff = CompactNtp(ntp2) - CompactNtp(ntp1);
-  uint32_t ntp_to_ms_diff = CompactNtpIntervalToMs(ntp_diff);
+  int64_t ntp_to_ms_diff = CompactNtpRttToMs(ntp_diff);
 
   EXPECT_NEAR(ms_diff, ntp_to_ms_diff, 1);
 }
 
-TEST(TimeUtilTest, CompactNtpToMsLarge) {
-  const NtpTime ntp1(0x10000, 0x23456);
-  const NtpTime ntp2(0x1ffff, 0x64335);
-  uint32_t ms_diff = ntp2.ToMs() - ntp1.ToMs();
-  // Ntp difference close to maximum of ~18 hours should convert correctly too.
-  ASSERT_GT(ms_diff, 18u * 3600 * 1000);
+TEST(TimeUtilTest, CompactNtpRttToMsLarge) {
+  const NtpTime ntp1(0x10000, 0x00006);
+  const NtpTime ntp2(0x17fff, 0xffff5);
+  int64_t ms_diff = ntp2.ToMs() - ntp1.ToMs();
+  // Ntp difference close to 2^15 seconds should convert correctly too.
+  ASSERT_NEAR(ms_diff, ((1 << 15) - 1) * 1000, 1);
   uint32_t ntp_diff = CompactNtp(ntp2) - CompactNtp(ntp1);
-  uint32_t ntp_to_ms_diff = CompactNtpIntervalToMs(ntp_diff);
+  int64_t ntp_to_ms_diff = CompactNtpRttToMs(ntp_diff);
 
   EXPECT_NEAR(ms_diff, ntp_to_ms_diff, 1);
 }
+
+TEST(TimeUtilTest, CompactNtpRttToMsNegative) {
+  const NtpTime ntp1(0x20000, 0x23456);
+  const NtpTime ntp2(0x1ffff, 0x64335);
+  int64_t ms_diff = ntp2.ToMs() - ntp1.ToMs();
+  ASSERT_GT(0, ms_diff);
+  // Ntp difference close to 2^16 seconds should be treated as negative.
+  uint32_t ntp_diff = CompactNtp(ntp2) - CompactNtp(ntp1);
+  int64_t ntp_to_ms_diff = CompactNtpRttToMs(ntp_diff);
+  EXPECT_EQ(1, ntp_to_ms_diff);
+}
 }  // namespace webrtc