Add operator<=> comparison to absl::Time and absl::Duration.

PiperOrigin-RevId: 648433954
Change-Id: I32e47a89685419ae8d37dfadb354cfaab2a35ae9

3 files changed, 148 insertions, 0 deletions

diff --git a/absl/time/duration_test.cc b/absl/time/duration_test.cc
index dcf7aad6..4c801a8d 100644
--- a/absl/time/duration_test.cc
+++ b/absl/time/duration_test.cc
@@ -19,6 +19,11 @@
 #include <array>
 #include <cfloat>
 #include <chrono>  // NOLINT(build/c++11)
+
+#ifdef __cpp_impl_three_way_comparison
+#include <compare>
+#endif  // __cpp_impl_three_way_comparison
+
 #include <cmath>
 #include <cstdint>
 #include <ctime>
@@ -431,6 +436,15 @@ TEST(Duration, InfinityComparison) {
   EXPECT_LT(-inf, any_dur);
   EXPECT_LT(-inf, inf);
   EXPECT_GT(inf, -inf);
+
+#ifdef __cpp_impl_three_way_comparison
+  EXPECT_EQ(inf <=> inf, std::strong_ordering::equal);
+  EXPECT_EQ(-inf <=> -inf, std::strong_ordering::equal);
+  EXPECT_EQ(-inf <=> inf, std::strong_ordering::less);
+  EXPECT_EQ(inf <=> -inf, std::strong_ordering::greater);
+  EXPECT_EQ(any_dur <=> inf, std::strong_ordering::less);
+  EXPECT_EQ(any_dur <=> -inf, std::strong_ordering::greater);
+#endif  // __cpp_impl_three_way_comparison
 }
 
 TEST(Duration, InfinityAddition) {
@@ -496,9 +510,20 @@ TEST(Duration, InfinitySubtraction) {
   // Interesting case
   absl::Duration almost_neg_inf = sec_min;
   EXPECT_LT(-inf, almost_neg_inf);
+
+#ifdef __cpp_impl_three_way_comparison
+  EXPECT_EQ(-inf <=> almost_neg_inf, std::strong_ordering::less);
+  EXPECT_EQ(almost_neg_inf <=> -inf, std::strong_ordering::greater);
+#endif  // __cpp_impl_three_way_comparison
+
   almost_neg_inf -= -absl::Nanoseconds(1);
   EXPECT_LT(-inf, almost_neg_inf);
 
+#ifdef __cpp_impl_three_way_comparison
+  EXPECT_EQ(-inf <=> almost_neg_inf, std::strong_ordering::less);
+  EXPECT_EQ(almost_neg_inf <=> -inf, std::strong_ordering::greater);
+#endif  // __cpp_impl_three_way_comparison
+
   // For reference: IEEE 754 behavior
   const double dbl_inf = std::numeric_limits<double>::infinity();
   EXPECT_TRUE(std::isnan(dbl_inf - dbl_inf));  // We return inf
@@ -857,6 +882,21 @@ TEST(Duration, Range) {
 
   EXPECT_LT(neg_full_range, full_range);
   EXPECT_EQ(neg_full_range, -full_range);
+
+#ifdef __cpp_impl_three_way_comparison
+  EXPECT_EQ(range_future <=> absl::InfiniteDuration(),
+            std::strong_ordering::less);
+  EXPECT_EQ(range_past <=> -absl::InfiniteDuration(),
+            std::strong_ordering::greater);
+  EXPECT_EQ(full_range <=> absl::ZeroDuration(),  //
+            std::strong_ordering::greater);
+  EXPECT_EQ(full_range <=> -absl::InfiniteDuration(),
+            std::strong_ordering::greater);
+  EXPECT_EQ(neg_full_range <=> -absl::InfiniteDuration(),
+            std::strong_ordering::greater);
+  EXPECT_EQ(neg_full_range <=> full_range, std::strong_ordering::less);
+  EXPECT_EQ(neg_full_range <=> -full_range, std::strong_ordering::equal);
+#endif  // __cpp_impl_three_way_comparison
 }
 
 TEST(Duration, RelationalOperators) {
@@ -880,6 +920,27 @@ TEST(Duration, RelationalOperators) {
 #undef TEST_REL_OPS
 }
 
+
+#ifdef __cpp_impl_three_way_comparison
+
+TEST(Duration, SpaceshipOperators) {
+#define TEST_REL_OPS(UNIT)               \
+  static_assert(UNIT(2) <=> UNIT(2) == std::strong_ordering::equal, ""); \
+  static_assert(UNIT(1) <=> UNIT(2) == std::strong_ordering::less, ""); \
+  static_assert(UNIT(3) <=> UNIT(2) == std::strong_ordering::greater, "");
+
+  TEST_REL_OPS(absl::Nanoseconds);
+  TEST_REL_OPS(absl::Microseconds);
+  TEST_REL_OPS(absl::Milliseconds);
+  TEST_REL_OPS(absl::Seconds);
+  TEST_REL_OPS(absl::Minutes);
+  TEST_REL_OPS(absl::Hours);
+
+#undef TEST_REL_OPS
+}
+
+#endif  // __cpp_impl_three_way_comparison
+
 TEST(Duration, Addition) {
 #define TEST_ADD_OPS(UNIT)                  \
   do {                                      \
diff --git a/absl/time/time.h b/absl/time/time.h
index d367ace2..f133c2d2 100644
--- a/absl/time/time.h
+++ b/absl/time/time.h
@@ -75,15 +75,22 @@
 struct timeval;
 #endif
 #include <chrono>  // NOLINT(build/c++11)
+
+#ifdef __cpp_impl_three_way_comparison
+#include <compare>
+#endif  // __cpp_impl_three_way_comparison
+
 #include <cmath>
 #include <cstdint>
 #include <ctime>
 #include <limits>
 #include <ostream>
+#include <ratio>  // NOLINT(build/c++11)
 #include <string>
 #include <type_traits>
 #include <utility>
 
+#include "absl/base/attributes.h"
 #include "absl/base/config.h"
 #include "absl/base/macros.h"
 #include "absl/strings/string_view.h"
@@ -305,6 +312,14 @@ class Duration {
 };
 
 // Relational Operators
+
+#ifdef __cpp_impl_three_way_comparison
+
+ABSL_ATTRIBUTE_CONST_FUNCTION constexpr std::strong_ordering operator<=>(
+    Duration lhs, Duration rhs);
+
+#endif  // __cpp_impl_three_way_comparison
+
 ABSL_ATTRIBUTE_CONST_FUNCTION constexpr bool operator<(Duration lhs,
                                                        Duration rhs);
 ABSL_ATTRIBUTE_CONST_FUNCTION constexpr bool operator>(Duration lhs,
@@ -837,6 +852,11 @@ class Time {
  private:
   friend constexpr Time time_internal::FromUnixDuration(Duration d);
   friend constexpr Duration time_internal::ToUnixDuration(Time t);
+
+#ifdef __cpp_impl_three_way_comparison
+  friend constexpr std::strong_ordering operator<=>(Time lhs, Time rhs);
+#endif  // __cpp_impl_three_way_comparison
+
   friend constexpr bool operator<(Time lhs, Time rhs);
   friend constexpr bool operator==(Time lhs, Time rhs);
   friend Duration operator-(Time lhs, Time rhs);
@@ -848,6 +868,15 @@ class Time {
 };
 
 // Relational Operators
+#ifdef __cpp_impl_three_way_comparison
+
+ABSL_ATTRIBUTE_CONST_FUNCTION constexpr std::strong_ordering operator<=>(
+    Time lhs, Time rhs) {
+  return lhs.rep_ <=> rhs.rep_;
+}
+
+#endif  // __cpp_impl_three_way_comparison
+
 ABSL_ATTRIBUTE_CONST_FUNCTION constexpr bool operator<(Time lhs, Time rhs) {
   return lhs.rep_ < rhs.rep_;
 }
@@ -1723,6 +1752,25 @@ ABSL_ATTRIBUTE_CONST_FUNCTION constexpr bool operator<(Duration lhs,
              : time_internal::GetRepLo(lhs) < time_internal::GetRepLo(rhs);
 }
 
+
+#ifdef __cpp_impl_three_way_comparison
+
+ABSL_ATTRIBUTE_CONST_FUNCTION constexpr std::strong_ordering operator<=>(
+    Duration lhs, Duration rhs) {
+  const int64_t lhs_hi = time_internal::GetRepHi(lhs);
+  const int64_t rhs_hi = time_internal::GetRepHi(rhs);
+  if (auto c = lhs_hi <=> rhs_hi; c != std::strong_ordering::equal) {
+    return c;
+  }
+  const uint32_t lhs_lo = time_internal::GetRepLo(lhs);
+  const uint32_t rhs_lo = time_internal::GetRepLo(rhs);
+  return (lhs_hi == (std::numeric_limits<int64_t>::min)())
+             ? (lhs_lo + 1) <=> (rhs_lo + 1)
+             : lhs_lo <=> rhs_lo;
+}
+
+#endif  // __cpp_impl_three_way_comparison
+
 ABSL_ATTRIBUTE_CONST_FUNCTION constexpr bool operator==(Duration lhs,
                                                         Duration rhs) {
   return time_internal::GetRepHi(lhs) == time_internal::GetRepHi(rhs) &&
diff --git a/absl/time/time_test.cc b/absl/time/time_test.cc
index 052d8806..71f54d64 100644
--- a/absl/time/time_test.cc
+++ b/absl/time/time_test.cc
@@ -24,6 +24,11 @@
 #endif
 
 #include <chrono>  // NOLINT(build/c++11)
+
+#ifdef __cpp_impl_three_way_comparison
+#include <compare>
+#endif  // __cpp_impl_three_way_comparison
+
 #include <cstring>
 #include <ctime>
 #include <iomanip>
@@ -207,6 +212,22 @@ TEST(Time, RelationalOperators) {
   static_assert(t3 >= t2, "");
   static_assert(t1 >= t1, "");
   static_assert(t3 >= t1, "");
+
+#ifdef __cpp_impl_three_way_comparison
+
+  static_assert((t1 <=> t1) == std::strong_ordering::equal, "");
+  static_assert((t2 <=> t2) == std::strong_ordering::equal, "");
+  static_assert((t3 <=> t3) == std::strong_ordering::equal, "");
+
+  static_assert((t1 <=> t2) == std::strong_ordering::less, "");
+  static_assert((t2 <=> t3) == std::strong_ordering::less, "");
+  static_assert((t1 <=> t3) == std::strong_ordering::less, "");
+
+  static_assert((t2 <=> t1) == std::strong_ordering::greater, "");
+  static_assert((t3 <=> t2) == std::strong_ordering::greater, "");
+  static_assert((t3 <=> t1) == std::strong_ordering::greater, "");
+
+#endif  // __cpp_impl_three_way_comparison
 }
 
 TEST(Time, Infinity) {
@@ -218,6 +239,15 @@ TEST(Time, Infinity) {
   static_assert(ipast < ifuture, "");
   static_assert(ifuture > ipast, "");
 
+#ifdef __cpp_impl_three_way_comparison
+
+  static_assert((ifuture <=> ifuture) == std::strong_ordering::equal, "");
+  static_assert((ipast <=> ipast) == std::strong_ordering::equal, "");
+  static_assert((ipast <=> ifuture) == std::strong_ordering::less, "");
+  static_assert((ifuture <=> ipast) == std::strong_ordering::greater, "");
+
+#endif  // __cpp_impl_three_way_comparison
+
   // Arithmetic saturates
   EXPECT_EQ(ifuture, ifuture + absl::Seconds(1));
   EXPECT_EQ(ifuture, ifuture - absl::Seconds(1));
@@ -233,6 +263,15 @@ TEST(Time, Infinity) {
   static_assert(t < ifuture, "");
   static_assert(t > ipast, "");
 
+#ifdef __cpp_impl_three_way_comparison
+
+  static_assert((t <=> ifuture) == std::strong_ordering::less, "");
+  static_assert((t <=> ipast) == std::strong_ordering::greater, "");
+  static_assert((ipast <=> t) == std::strong_ordering::less, "");
+  static_assert((ifuture <=> t) == std::strong_ordering::greater, "");
+
+#endif  // __cpp_impl_three_way_comparison
+
   EXPECT_EQ(ifuture, t + absl::InfiniteDuration());
   EXPECT_EQ(ipast, t - absl::InfiniteDuration());
 }