Changes imported from Abseil "staging" branch:

  - c01cbbc23470f60e54aa28f88faa49df17d26c9c Add constexpr function for max uint128 to replace global ... by Alex Strelnikov <strel@google.com>
  - 07491549940e51fb6a0c8aad0ce101cb2830ee8e fix __GNUC__ typo in ABSL_ATTRIBUTE_RETURNS_NONNULL test by Abseil Team <absl-team@google.com>
  - 1bc29bafa53c387b0e097856cffb2fb9ce56c331 Remove redundant uint128 function cast expressions. by Alex Strelnikov <strel@google.com>
  - e3dddbd7be9e85e1bac77648af35ddccdba4500e Add ABSL_ATTRIBUTE_RETURNS_NONNULL macro. by Chris Kennelly <ckennelly@google.com>

GitOrigin-RevId: c01cbbc23470f60e54aa28f88faa49df17d26c9c
Change-Id: I7a5f608f58fb53bf013cdf56018f5b39842427fc

3 files changed, 38 insertions, 25 deletions

diff --git a/absl/base/attributes.h b/absl/base/attributes.h
index 02bb030f5e5a..4e1fc8b550d1 100644
--- a/absl/base/attributes.h
+++ b/absl/base/attributes.h
@@ -281,6 +281,18 @@
 #define ABSL_ATTRIBUTE_NO_SANITIZE_CFI
 #endif
 
+// ABSL_ATTRIBUTE_RETURNS_NONNULL
+//
+// Tells the compiler that a particular function never returns a null pointer.
+#if ABSL_HAVE_ATTRIBUTE(returns_nonnull) || \
+    (defined(__GNUC__) && \
+     (__GNUC__ > 5 || (__GNUC__ == 4 && __GNUC_MINOR__ >= 9)) && \
+     !defined(__clang__))
+#define ABSL_ATTRIBUTE_RETURNS_NONNULL __attribute__((returns_nonnull))
+#else
+#define ABSL_ATTRIBUTE_RETURNS_NONNULL
+#endif
+
 // ABSL_HAVE_ATTRIBUTE_SECTION
 //
 // Indicates whether labeled sections are supported. Labeled sections are not
diff --git a/absl/numeric/int128.h b/absl/numeric/int128.h
index a204ac4d9c3f..bd1b553ab2dc 100644
--- a/absl/numeric/int128.h
+++ b/absl/numeric/int128.h
@@ -71,8 +71,8 @@ namespace absl {
 //
 // Example:
 //
-//     float y = absl::kuint128max;  // Error. uint128 cannot be implicitly
-//                                   // converted to float.
+//     float y = absl::Uint128Max();  // Error. uint128 cannot be implicitly
+//                                    // converted to float.
 //
 //     absl::uint128 v;
 //     absl::uint64_t i = v;                         // Error
@@ -177,6 +177,11 @@ class alignas(16) uint128 {
   //   absl::uint128 big = absl::MakeUint128(1, 0);
   friend constexpr uint128 MakeUint128(uint64_t high, uint64_t low);
 
+  // Uint128Max()
+  //
+  // Returns the highest value for a 128-bit unsigned integer.
+  friend constexpr uint128 Uint128Max();
+
  private:
   constexpr uint128(uint64_t high, uint64_t low);
 
@@ -195,6 +200,9 @@ class alignas(16) uint128 {
 #endif  // byte order
 };
 
+// Prefer to use the constexpr `Uint128Max()`.
+//
+// TODO(absl-team) deprecate kuint128max once migration tool is released.
 extern const uint128 kuint128max;
 
 // allow uint128 to be logged
@@ -212,6 +220,11 @@ constexpr uint128 MakeUint128(uint64_t high, uint64_t low) {
   return uint128(high, low);
 }
 
+constexpr uint128 Uint128Max() {
+  return uint128(std::numeric_limits<uint64_t>::max(),
+                 std::numeric_limits<uint64_t>::max());
+}
+
 // Assignment from integer types.
 
 inline uint128& uint128::operator=(int v) { return *this = uint128(v); }
@@ -251,33 +264,19 @@ inline uint128& uint128::operator=(unsigned __int128 v) {
 
 // Shift and arithmetic operators.
 
-inline uint128 operator<<(uint128 lhs, int amount) {
-  return uint128(lhs) <<= amount;
-}
+inline uint128 operator<<(uint128 lhs, int amount) { return lhs <<= amount; }
 
-inline uint128 operator>>(uint128 lhs, int amount) {
-  return uint128(lhs) >>= amount;
-}
+inline uint128 operator>>(uint128 lhs, int amount) { return lhs >>= amount; }
 
-inline uint128 operator+(uint128 lhs, uint128 rhs) {
-  return uint128(lhs) += rhs;
-}
+inline uint128 operator+(uint128 lhs, uint128 rhs) { return lhs += rhs; }
 
-inline uint128 operator-(uint128 lhs, uint128 rhs) {
-  return uint128(lhs) -= rhs;
-}
+inline uint128 operator-(uint128 lhs, uint128 rhs) { return lhs -= rhs; }
 
-inline uint128 operator*(uint128 lhs, uint128 rhs) {
-  return uint128(lhs) *= rhs;
-}
+inline uint128 operator*(uint128 lhs, uint128 rhs) { return lhs *= rhs; }
 
-inline uint128 operator/(uint128 lhs, uint128 rhs) {
-  return uint128(lhs) /= rhs;
-}
+inline uint128 operator/(uint128 lhs, uint128 rhs) { return lhs /= rhs; }
 
-inline uint128 operator%(uint128 lhs, uint128 rhs) {
-  return uint128(lhs) %= rhs;
-}
+inline uint128 operator%(uint128 lhs, uint128 rhs) { return lhs %= rhs; }
 
 constexpr uint64_t Uint128Low64(uint128 v) { return v.lo_; }
 
diff --git a/absl/numeric/int128_test.cc b/absl/numeric/int128_test.cc
index d674cb125f5e..79bcca907ae9 100644
--- a/absl/numeric/int128_test.cc
+++ b/absl/numeric/int128_test.cc
@@ -110,7 +110,7 @@ TEST(Uint128, AllTests) {
   absl::uint128 big = absl::MakeUint128(2000, 2);
   absl::uint128 big_minus_one = absl::MakeUint128(2000, 1);
   absl::uint128 bigger = absl::MakeUint128(2001, 1);
-  absl::uint128 biggest = absl::kuint128max;
+  absl::uint128 biggest = absl::Uint128Max();
   absl::uint128 high_low = absl::MakeUint128(1, 0);
   absl::uint128 low_high =
       absl::MakeUint128(0, std::numeric_limits<uint64_t>::max());
@@ -227,8 +227,10 @@ TEST(Uint128, AllTests) {
 
   EXPECT_EQ(big, -(-big));
   EXPECT_EQ(two, -((-one) - 1));
-  EXPECT_EQ(absl::kuint128max, -one);
+  EXPECT_EQ(absl::Uint128Max(), -one);
   EXPECT_EQ(zero, -zero);
+
+  EXPECT_EQ(absl::Uint128Max(), absl::kuint128max);
 }
 
 TEST(Uint128, ConversionTests) {