Add `operator<=>` support to `absl::int128` and `absl::uint128`

PiperOrigin-RevId: 626080616
Change-Id: If434be2371c1e28f9fd0133f411596bdc38bd222

1 files changed, 31 insertions, 0 deletions

diff --git a/absl/numeric/int128.h b/absl/numeric/int128.h
index a17d0e1b..562d5e58 100644
--- a/absl/numeric/int128.h
+++ b/absl/numeric/int128.h
@@ -38,6 +38,7 @@
 #include "absl/base/config.h"
 #include "absl/base/macros.h"
 #include "absl/base/port.h"
+#include "absl/types/compare.h"
 
 #if defined(_MSC_VER)
 // In very old versions of MSVC and when the /Zc:wchar_t flag is off, wchar_t is
@@ -819,6 +820,36 @@ constexpr bool operator<=(uint128 lhs, uint128 rhs) { return !(rhs < lhs); }
 
 constexpr bool operator>=(uint128 lhs, uint128 rhs) { return !(lhs < rhs); }
 
+#ifdef __cpp_impl_three_way_comparison
+constexpr absl::strong_ordering operator<=>(uint128 lhs, uint128 rhs) {
+#if defined(ABSL_HAVE_INTRINSIC_INT128)
+  if (auto lhs_128 = static_cast<unsigned __int128>(lhs),
+      rhs_128 = static_cast<unsigned __int128>(rhs);
+      lhs_128 < rhs_128) {
+    return absl::strong_ordering::less;
+  } else if (lhs_128 > rhs_128) {
+    return absl::strong_ordering::greater;
+  } else {
+    return absl::strong_ordering::equal;
+  }
+#else
+  if (uint64_t lhs_high = Uint128High64(lhs), rhs_high = Uint128High64(rhs);
+      lhs_high < rhs_high) {
+    return absl::strong_ordering::less;
+  } else if (lhs_high > rhs_high) {
+    return absl::strong_ordering::greater;
+  } else if (uint64_t lhs_low = Uint128Low64(lhs), rhs_low = Uint128Low64(rhs);
+             lhs_low < rhs_low) {
+    return absl::strong_ordering::less;
+  } else if (lhs_low > rhs_low) {
+    return absl::strong_ordering::greater;
+  } else {
+    return absl::strong_ordering::equal;
+  }
+#endif
+}
+#endif
+
 // Unary operators.
 
 constexpr inline uint128 operator+(uint128 val) { return val; }