Add a test to verify bit casting between signed and unsigned int128 works as expected
PiperOrigin-RevId: 684941948
Change-Id: I78a7ae6f4ec8f29e5bed414016eadf2ec95167a4
diff --git a/absl/numeric/int128_test.cc b/absl/numeric/int128_test.cc
index 3f16e05..0b59af8 100644
--- a/absl/numeric/int128_test.cc
+++ b/absl/numeric/int128_test.cc
@@ -22,6 +22,7 @@
#include <vector>
#include "gtest/gtest.h"
+#include "absl/base/casts.h"
#include "absl/base/internal/cycleclock.h"
#include "absl/hash/hash_testing.h"
#include "absl/meta/type_traits.h"
@@ -1282,4 +1283,50 @@
EXPECT_EQ(absl::Int128Max(), std::numeric_limits<absl::int128>::max());
}
+TEST(Int128, BitCastable) {
+ // NOTE: This test is not intended to be an example that demonstrate usages of
+ // `static_cast` and `std::bit_cast`, rather it is here simply to verify
+ // behavior. When deciding whether you should use `static_cast` or
+ // `std::bit_cast` when converting between `absl::int128` and `absl::uint128`,
+ // use your best judgement. As a rule of thumb, use the same cast that you
+ // would use when converting between the signed and unsigned counterparts of a
+ // builtin integral type.
+
+ // Verify bit casting between signed and unsigned works with regards to two's
+ // complement. This verifies we exhibit the same behavior as a theoretical
+ // builtin int128_t and uint128_t in C++20 onwards.
+ EXPECT_EQ(absl::bit_cast<absl::uint128>(absl::int128(-1)),
+ std::numeric_limits<absl::uint128>::max());
+ EXPECT_EQ(
+ absl::bit_cast<absl::int128>(std::numeric_limits<absl::uint128>::max()),
+ absl::int128(-1));
+ EXPECT_EQ(
+ absl::bit_cast<absl::uint128>(std::numeric_limits<absl::int128>::min()),
+ absl::uint128(1) << 127);
+ EXPECT_EQ(absl::bit_cast<absl::int128>(absl::uint128(1) << 127),
+ std::numeric_limits<absl::int128>::min());
+ EXPECT_EQ(
+ absl::bit_cast<absl::uint128>(std::numeric_limits<absl::int128>::max()),
+ (absl::uint128(1) << 127) - 1);
+ EXPECT_EQ(absl::bit_cast<absl::int128>((absl::uint128(1) << 127) - 1),
+ std::numeric_limits<absl::int128>::max());
+
+ // Also verify static casting has the same behavior as bit casting.
+ EXPECT_EQ(static_cast<absl::uint128>(absl::int128(-1)),
+ std::numeric_limits<absl::uint128>::max());
+ EXPECT_EQ(
+ static_cast<absl::int128>(std::numeric_limits<absl::uint128>::max()),
+ absl::int128(-1));
+ EXPECT_EQ(
+ static_cast<absl::uint128>(std::numeric_limits<absl::int128>::min()),
+ absl::uint128(1) << 127);
+ EXPECT_EQ(static_cast<absl::int128>(absl::uint128(1) << 127),
+ std::numeric_limits<absl::int128>::min());
+ EXPECT_EQ(
+ static_cast<absl::uint128>(std::numeric_limits<absl::int128>::max()),
+ (absl::uint128(1) << 127) - 1);
+ EXPECT_EQ(static_cast<absl::int128>((absl::uint128(1) << 127) - 1),
+ std::numeric_limits<absl::int128>::max());
+}
+
} // namespace
