Adds signed infinity to timestamps.

Negative infinity is useful in comparisons as it represents a value
guaranteed to be less than any other timestamp. This avoid using
Timestamp::ms(0) to represent such a value or having to use optional
for the special case of first time execution.

To avoid ambiguity, Timestamp::Infinity is renamed to PlusInfinity.

Bug: webrtc:9709
Change-Id: Ib2debff91036e94d1dc903ec0c6faae30febde4e
Reviewed-on: https://webrtc-review.googlesource.com/79440
Commit-Queue: Sebastian Jansson <srte@webrtc.org>
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#24556}
diff --git a/api/transport/network_types.cc b/api/transport/network_types.cc
index b4c09d4..48bdcab 100644
--- a/api/transport/network_types.cc
+++ b/api/transport/network_types.cc
@@ -48,7 +48,7 @@
 std::vector<PacketResult> TransportPacketsFeedback::LostWithSendInfo() const {
   std::vector<PacketResult> res;
   for (const PacketResult& fb : packet_feedbacks) {
-    if (fb.receive_time.IsInfinite() && fb.sent_packet.has_value()) {
+    if (fb.receive_time.IsPlusInfinity() && fb.sent_packet.has_value()) {
       res.push_back(fb);
     }
   }
diff --git a/api/transport/network_types.h b/api/transport/network_types.h
index e34bf0e..eee1de0 100644
--- a/api/transport/network_types.h
+++ b/api/transport/network_types.h
@@ -30,7 +30,7 @@
   StreamsConfig();
   StreamsConfig(const StreamsConfig&);
   ~StreamsConfig();
-  Timestamp at_time = Timestamp::Infinity();
+  Timestamp at_time = Timestamp::PlusInfinity();
   bool requests_alr_probing = false;
   absl::optional<double> pacing_factor;
   absl::optional<DataRate> min_pacing_rate;
@@ -42,7 +42,7 @@
   TargetRateConstraints();
   TargetRateConstraints(const TargetRateConstraints&);
   ~TargetRateConstraints();
-  Timestamp at_time = Timestamp::Infinity();
+  Timestamp at_time = Timestamp::PlusInfinity();
   absl::optional<DataRate> min_data_rate;
   absl::optional<DataRate> max_data_rate;
   // The initial bandwidth estimate to base target rate on. This should be used
@@ -53,7 +53,7 @@
 // Send side information
 
 struct NetworkAvailability {
-  Timestamp at_time = Timestamp::Infinity();
+  Timestamp at_time = Timestamp::PlusInfinity();
   bool network_available = false;
 };
 
@@ -61,7 +61,7 @@
   NetworkRouteChange();
   NetworkRouteChange(const NetworkRouteChange&);
   ~NetworkRouteChange();
-  Timestamp at_time = Timestamp::Infinity();
+  Timestamp at_time = Timestamp::PlusInfinity();
   // The TargetRateConstraints are set here so they can be changed synchronously
   // when network route changes.
   TargetRateConstraints constraints;
@@ -84,7 +84,7 @@
 };
 
 struct SentPacket {
-  Timestamp send_time = Timestamp::Infinity();
+  Timestamp send_time = Timestamp::PlusInfinity();
   DataSize size = DataSize::Zero();
   PacedPacketInfo pacing_info;
   // Transport independent sequence number, any tracked packet should have a
@@ -98,20 +98,20 @@
 // Transport level feedback
 
 struct RemoteBitrateReport {
-  Timestamp receive_time = Timestamp::Infinity();
+  Timestamp receive_time = Timestamp::PlusInfinity();
   DataRate bandwidth = DataRate::Infinity();
 };
 
 struct RoundTripTimeUpdate {
-  Timestamp receive_time = Timestamp::Infinity();
+  Timestamp receive_time = Timestamp::PlusInfinity();
   TimeDelta round_trip_time = TimeDelta::PlusInfinity();
   bool smoothed = false;
 };
 
 struct TransportLossReport {
-  Timestamp receive_time = Timestamp::Infinity();
-  Timestamp start_time = Timestamp::Infinity();
-  Timestamp end_time = Timestamp::Infinity();
+  Timestamp receive_time = Timestamp::PlusInfinity();
+  Timestamp start_time = Timestamp::PlusInfinity();
+  Timestamp end_time = Timestamp::PlusInfinity();
   uint64_t packets_lost_delta = 0;
   uint64_t packets_received_delta = 0;
 };
@@ -124,7 +124,7 @@
   ~PacketResult();
 
   absl::optional<SentPacket> sent_packet;
-  Timestamp receive_time = Timestamp::Infinity();
+  Timestamp receive_time = Timestamp::PlusInfinity();
 };
 
 struct TransportPacketsFeedback {
@@ -132,7 +132,7 @@
   TransportPacketsFeedback(const TransportPacketsFeedback& other);
   ~TransportPacketsFeedback();
 
-  Timestamp feedback_time = Timestamp::Infinity();
+  Timestamp feedback_time = Timestamp::PlusInfinity();
   DataSize data_in_flight = DataSize::Zero();
   DataSize prior_in_flight = DataSize::Zero();
   std::vector<PacketResult> packet_feedbacks;
@@ -145,7 +145,7 @@
 // Network estimation
 
 struct NetworkEstimate {
-  Timestamp at_time = Timestamp::Infinity();
+  Timestamp at_time = Timestamp::PlusInfinity();
   DataRate bandwidth = DataRate::Infinity();
   TimeDelta round_trip_time = TimeDelta::PlusInfinity();
   TimeDelta bwe_period = TimeDelta::PlusInfinity();
@@ -156,7 +156,7 @@
 // Network control
 
 struct PacerConfig {
-  Timestamp at_time = Timestamp::Infinity();
+  Timestamp at_time = Timestamp::PlusInfinity();
   // Pacer should send at most data_window data over time_window duration.
   DataSize data_window = DataSize::Infinity();
   TimeDelta time_window = TimeDelta::PlusInfinity();
@@ -167,14 +167,14 @@
 };
 
 struct ProbeClusterConfig {
-  Timestamp at_time = Timestamp::Infinity();
+  Timestamp at_time = Timestamp::PlusInfinity();
   DataRate target_data_rate = DataRate::Zero();
   TimeDelta target_duration = TimeDelta::Zero();
   int32_t target_probe_count = 0;
 };
 
 struct TargetTransferRate {
-  Timestamp at_time = Timestamp::Infinity();
+  Timestamp at_time = Timestamp::PlusInfinity();
   // The estimate on which the target rate is based on.
   NetworkEstimate network_estimate;
   DataRate target_rate = DataRate::Zero();
@@ -195,7 +195,7 @@
 
 // Process control
 struct ProcessInterval {
-  Timestamp at_time = Timestamp::Infinity();
+  Timestamp at_time = Timestamp::PlusInfinity();
 };
 }  // namespace webrtc
 
diff --git a/api/units/time_delta_unittest.cc b/api/units/time_delta_unittest.cc
index e5906bf..bf8bbce 100644
--- a/api/units/time_delta_unittest.cc
+++ b/api/units/time_delta_unittest.cc
@@ -74,6 +74,12 @@
   EXPECT_TRUE(TimeDelta::ms(-kValue).IsFinite());
   EXPECT_TRUE(TimeDelta::ms(kValue).IsFinite());
   EXPECT_TRUE(TimeDelta::Zero().IsFinite());
+
+  EXPECT_TRUE(TimeDelta::PlusInfinity().IsPlusInfinity());
+  EXPECT_FALSE(TimeDelta::MinusInfinity().IsPlusInfinity());
+
+  EXPECT_TRUE(TimeDelta::MinusInfinity().IsMinusInfinity());
+  EXPECT_FALSE(TimeDelta::PlusInfinity().IsMinusInfinity());
 }
 
 TEST(TimeDeltaTest, ComparisonOperators) {
diff --git a/api/units/timestamp.h b/api/units/timestamp.h
index d7e6a8d..0298f5d 100644
--- a/api/units/timestamp.h
+++ b/api/units/timestamp.h
@@ -36,9 +36,12 @@
 class Timestamp {
  public:
   Timestamp() = delete;
-  static constexpr Timestamp Infinity() {
+  static constexpr Timestamp PlusInfinity() {
     return Timestamp(timestamp_impl::kPlusInfinityVal);
   }
+  static constexpr Timestamp MinusInfinity() {
+    return Timestamp(timestamp_impl::kMinusInfinityVal);
+  }
   template <int64_t seconds>
   static constexpr Timestamp Seconds() {
     static_assert(seconds >= 0, "");
@@ -103,7 +106,9 @@
                 nullptr>
   static Timestamp us(T microseconds) {
     if (microseconds == std::numeric_limits<double>::infinity()) {
-      return Infinity();
+      return PlusInfinity();
+    } else if (microseconds == -std::numeric_limits<double>::infinity()) {
+      return MinusInfinity();
     } else {
       RTC_DCHECK(!std::isnan(microseconds));
       RTC_DCHECK_GE(microseconds, 0);
@@ -141,7 +146,10 @@
   template <typename T>
   constexpr typename std::enable_if<std::is_floating_point<T>::value, T>::type
   us() const {
-    return IsInfinite() ? std::numeric_limits<T>::infinity() : microseconds_;
+    return IsPlusInfinity()
+               ? std::numeric_limits<T>::infinity()
+               : IsMinusInfinity() ? -std::numeric_limits<T>::infinity()
+                                   : microseconds_;
   }
 
   constexpr int64_t seconds_or(int64_t fallback_value) const {
@@ -154,25 +162,53 @@
     return IsFinite() ? microseconds_ : fallback_value;
   }
 
-  constexpr bool IsInfinite() const {
-    return microseconds_ == timestamp_impl::kPlusInfinityVal;
-  }
   constexpr bool IsFinite() const { return !IsInfinite(); }
+  constexpr bool IsInfinite() const {
+    return microseconds_ == timedelta_impl::kPlusInfinityVal ||
+           microseconds_ == timedelta_impl::kMinusInfinityVal;
+  }
+  constexpr bool IsPlusInfinity() const {
+    return microseconds_ == timedelta_impl::kPlusInfinityVal;
+  }
+  constexpr bool IsMinusInfinity() const {
+    return microseconds_ == timedelta_impl::kMinusInfinityVal;
+  }
+  Timestamp operator+(const TimeDelta& other) const {
+    if (IsPlusInfinity() || other.IsPlusInfinity()) {
+      RTC_DCHECK(!IsMinusInfinity());
+      RTC_DCHECK(!other.IsMinusInfinity());
+      return PlusInfinity();
+    } else if (IsMinusInfinity() || other.IsMinusInfinity()) {
+      RTC_DCHECK(!IsPlusInfinity());
+      RTC_DCHECK(!other.IsPlusInfinity());
+      return MinusInfinity();
+    }
+    return Timestamp::us(us() + other.us());
+  }
+  Timestamp operator-(const TimeDelta& other) const {
+    if (IsPlusInfinity() || other.IsMinusInfinity()) {
+      RTC_DCHECK(!IsMinusInfinity());
+      RTC_DCHECK(!other.IsPlusInfinity());
+      return PlusInfinity();
+    } else if (IsMinusInfinity() || other.IsPlusInfinity()) {
+      RTC_DCHECK(!IsPlusInfinity());
+      RTC_DCHECK(!other.IsMinusInfinity());
+      return MinusInfinity();
+    }
+    return Timestamp::us(us() - other.us());
+  }
   TimeDelta operator-(const Timestamp& other) const {
+    if (IsPlusInfinity() || other.IsMinusInfinity()) {
+      RTC_DCHECK(!IsMinusInfinity());
+      RTC_DCHECK(!other.IsPlusInfinity());
+      return TimeDelta::PlusInfinity();
+    } else if (IsMinusInfinity() || other.IsPlusInfinity()) {
+      RTC_DCHECK(!IsPlusInfinity());
+      RTC_DCHECK(!other.IsMinusInfinity());
+      return TimeDelta::MinusInfinity();
+    }
     return TimeDelta::us(us() - other.us());
   }
-  Timestamp operator-(const TimeDelta& delta) const {
-    RTC_DCHECK(!delta.IsPlusInfinity());
-    if (IsInfinite() || delta.IsMinusInfinity())
-      return Infinity();
-    return Timestamp::us(us() - delta.us());
-  }
-  Timestamp operator+(const TimeDelta& delta) const {
-    RTC_DCHECK(!delta.IsMinusInfinity());
-    if (IsInfinite() || delta.IsPlusInfinity())
-      return Infinity();
-    return Timestamp::us(us() + delta.us());
-  }
   Timestamp& operator-=(const TimeDelta& other) {
     *this = *this - other;
     return *this;
diff --git a/api/units/timestamp_unittest.cc b/api/units/timestamp_unittest.cc
index ff0c79e..6c2d1ee 100644
--- a/api/units/timestamp_unittest.cc
+++ b/api/units/timestamp_unittest.cc
@@ -15,7 +15,7 @@
 namespace test {
 TEST(TimestampTest, ConstExpr) {
   constexpr int64_t kValue = 12345;
-  constexpr Timestamp kTimestampInf = Timestamp::Infinity();
+  constexpr Timestamp kTimestampInf = Timestamp::PlusInfinity();
   static_assert(kTimestampInf.IsInfinite(), "");
   static_assert(kTimestampInf.ms_or(-1) == -1, "");
 
@@ -55,20 +55,28 @@
 TEST(TimestampTest, IdentityChecks) {
   const int64_t kValue = 3000;
 
-  EXPECT_TRUE(Timestamp::Infinity().IsInfinite());
+  EXPECT_TRUE(Timestamp::PlusInfinity().IsInfinite());
+  EXPECT_TRUE(Timestamp::MinusInfinity().IsInfinite());
   EXPECT_FALSE(Timestamp::ms(kValue).IsInfinite());
 
-  EXPECT_FALSE(Timestamp::Infinity().IsFinite());
+  EXPECT_FALSE(Timestamp::PlusInfinity().IsFinite());
+  EXPECT_FALSE(Timestamp::MinusInfinity().IsFinite());
   EXPECT_TRUE(Timestamp::ms(kValue).IsFinite());
+
+  EXPECT_TRUE(Timestamp::PlusInfinity().IsPlusInfinity());
+  EXPECT_FALSE(Timestamp::MinusInfinity().IsPlusInfinity());
+
+  EXPECT_TRUE(Timestamp::MinusInfinity().IsMinusInfinity());
+  EXPECT_FALSE(Timestamp::PlusInfinity().IsMinusInfinity());
 }
 
 TEST(TimestampTest, ComparisonOperators) {
   const int64_t kSmall = 450;
   const int64_t kLarge = 451;
 
-  EXPECT_EQ(Timestamp::Infinity(), Timestamp::Infinity());
-  EXPECT_GE(Timestamp::Infinity(), Timestamp::Infinity());
-  EXPECT_GT(Timestamp::Infinity(), Timestamp::ms(kLarge));
+  EXPECT_EQ(Timestamp::PlusInfinity(), Timestamp::PlusInfinity());
+  EXPECT_GE(Timestamp::PlusInfinity(), Timestamp::PlusInfinity());
+  EXPECT_GT(Timestamp::PlusInfinity(), Timestamp::ms(kLarge));
   EXPECT_EQ(Timestamp::ms(kSmall), Timestamp::ms(kSmall));
   EXPECT_LE(Timestamp::ms(kSmall), Timestamp::ms(kSmall));
   EXPECT_GE(Timestamp::ms(kSmall), Timestamp::ms(kSmall));
@@ -102,14 +110,21 @@
   EXPECT_EQ(Timestamp::us(kMicrosDouble).us(), kMicros);
 
   const double kPlusInfinity = std::numeric_limits<double>::infinity();
+  const double kMinusInfinity = -kPlusInfinity;
 
-  EXPECT_EQ(Timestamp::Infinity().seconds<double>(), kPlusInfinity);
-  EXPECT_EQ(Timestamp::Infinity().ms<double>(), kPlusInfinity);
-  EXPECT_EQ(Timestamp::Infinity().us<double>(), kPlusInfinity);
+  EXPECT_EQ(Timestamp::PlusInfinity().seconds<double>(), kPlusInfinity);
+  EXPECT_EQ(Timestamp::MinusInfinity().seconds<double>(), kMinusInfinity);
+  EXPECT_EQ(Timestamp::PlusInfinity().ms<double>(), kPlusInfinity);
+  EXPECT_EQ(Timestamp::MinusInfinity().ms<double>(), kMinusInfinity);
+  EXPECT_EQ(Timestamp::PlusInfinity().us<double>(), kPlusInfinity);
+  EXPECT_EQ(Timestamp::MinusInfinity().us<double>(), kMinusInfinity);
 
-  EXPECT_TRUE(Timestamp::seconds(kPlusInfinity).IsInfinite());
-  EXPECT_TRUE(Timestamp::ms(kPlusInfinity).IsInfinite());
-  EXPECT_TRUE(Timestamp::us(kPlusInfinity).IsInfinite());
+  EXPECT_TRUE(Timestamp::seconds(kPlusInfinity).IsPlusInfinity());
+  EXPECT_TRUE(Timestamp::seconds(kMinusInfinity).IsMinusInfinity());
+  EXPECT_TRUE(Timestamp::ms(kPlusInfinity).IsPlusInfinity());
+  EXPECT_TRUE(Timestamp::ms(kMinusInfinity).IsMinusInfinity());
+  EXPECT_TRUE(Timestamp::us(kPlusInfinity).IsPlusInfinity());
+  EXPECT_TRUE(Timestamp::us(kMinusInfinity).IsMinusInfinity());
 }
 
 TEST(UnitConversionTest, TimestampAndTimeDeltaMath) {
@@ -135,8 +150,8 @@
   const int64_t kValue = 267;
   const Timestamp finite_time = Timestamp::ms(kValue);
   const TimeDelta finite_delta = TimeDelta::ms(kValue);
-  EXPECT_TRUE((Timestamp::Infinity() + finite_delta).IsInfinite());
-  EXPECT_TRUE((Timestamp::Infinity() - finite_delta).IsInfinite());
+  EXPECT_TRUE((Timestamp::PlusInfinity() + finite_delta).IsInfinite());
+  EXPECT_TRUE((Timestamp::PlusInfinity() - finite_delta).IsInfinite());
   EXPECT_TRUE((finite_time + TimeDelta::PlusInfinity()).IsInfinite());
   EXPECT_TRUE((finite_time - TimeDelta::MinusInfinity()).IsInfinite());
 }