diff options
Diffstat (limited to 'absl/hash/hash_test.cc')
-rw-r--r-- | absl/hash/hash_test.cc | 114 |
1 files changed, 112 insertions, 2 deletions
diff --git a/absl/hash/hash_test.cc b/absl/hash/hash_test.cc index 9a667ba703b4..61f7661f5912 100644 --- a/absl/hash/hash_test.cc +++ b/absl/hash/hash_test.cc @@ -274,8 +274,8 @@ TEST(HashValueTest, Strings) { const std::string small = "foo"; const std::string dup = "foofoo"; - const std::string large = "large"; - const std::string huge = std::string(5000, 'a'); + const std::string large = std::string(2048, 'x'); // multiple of chunk size + const std::string huge = std::string(5000, 'a'); // not a multiple EXPECT_TRUE(absl::VerifyTypeImplementsAbslHashCorrectly(std::make_tuple( std::string(), absl::string_view(), @@ -378,6 +378,116 @@ struct Private { } }; +// Test helper for combine_piecewise_buffer. It holds a string_view to the +// buffer-to-be-hashed. Its AbslHashValue specialization will split up its +// contents at the character offsets requested. +class PiecewiseHashTester { + public: + // Create a hash view of a buffer to be hashed contiguously. + explicit PiecewiseHashTester(absl::string_view buf) + : buf_(buf), piecewise_(false), split_locations_() {} + + // Create a hash view of a buffer to be hashed piecewise, with breaks at the + // given locations. + PiecewiseHashTester(absl::string_view buf, std::set<size_t> split_locations) + : buf_(buf), + piecewise_(true), + split_locations_(std::move(split_locations)) {} + + template <typename H> + friend H AbslHashValue(H h, const PiecewiseHashTester& p) { + if (!p.piecewise_) { + return H::combine_contiguous(std::move(h), p.buf_.data(), p.buf_.size()); + } + absl::hash_internal::PiecewiseCombiner combiner; + if (p.split_locations_.empty()) { + h = combiner.add_buffer(std::move(h), p.buf_.data(), p.buf_.size()); + return combiner.finalize(std::move(h)); + } + size_t begin = 0; + for (size_t next : p.split_locations_) { + absl::string_view chunk = p.buf_.substr(begin, next - begin); + h = combiner.add_buffer(std::move(h), chunk.data(), chunk.size()); + begin = next; + } + absl::string_view last_chunk = p.buf_.substr(begin); + if (!last_chunk.empty()) { + h = combiner.add_buffer(std::move(h), last_chunk.data(), + last_chunk.size()); + } + return combiner.finalize(std::move(h)); + } + + private: + absl::string_view buf_; + bool piecewise_; + std::set<size_t> split_locations_; +}; + +// Dummy object that hashes as two distinct contiguous buffers, "foo" followed +// by "bar" +struct DummyFooBar { + template <typename H> + friend H AbslHashValue(H h, const DummyFooBar&) { + const char* foo = "foo"; + const char* bar = "bar"; + h = H::combine_contiguous(std::move(h), foo, 3); + h = H::combine_contiguous(std::move(h), bar, 3); + return std::move(h); + } +}; + +TEST(HashValueTest, CombinePiecewiseBuffer) { + absl::Hash<PiecewiseHashTester> hash; + + // Check that hashing an empty buffer through the piecewise API works. + EXPECT_EQ(hash(PiecewiseHashTester("")), hash(PiecewiseHashTester("", {}))); + + // Similarly, small buffers should give consistent results + EXPECT_EQ(hash(PiecewiseHashTester("foobar")), + hash(PiecewiseHashTester("foobar", {}))); + EXPECT_EQ(hash(PiecewiseHashTester("foobar")), + hash(PiecewiseHashTester("foobar", {3}))); + + // But hashing "foobar" in pieces gives a different answer than hashing "foo" + // contiguously, then "bar" contiguously. + EXPECT_NE(hash(PiecewiseHashTester("foobar", {3})), + absl::Hash<DummyFooBar>()(DummyFooBar{})); + + // Test hashing a large buffer incrementally, broken up in several different + // ways. Arrange for breaks on and near the stride boundaries to look for + // off-by-one errors in the implementation. + // + // This test is run on a buffer that is a multiple of the stride size, and one + // that isn't. + for (size_t big_buffer_size : {1024 * 2 + 512, 1024 * 3}) { + SCOPED_TRACE(big_buffer_size); + std::string big_buffer; + for (int i = 0; i < big_buffer_size; ++i) { + // Arbitrary std::string + big_buffer.push_back(32 + (i * (i / 3)) % 64); + } + auto big_buffer_hash = hash(PiecewiseHashTester(big_buffer)); + + const int possible_breaks = 9; + size_t breaks[possible_breaks] = {1, 512, 1023, 1024, 1025, + 1536, 2047, 2048, 2049}; + for (unsigned test_mask = 0; test_mask < (1u << possible_breaks); + ++test_mask) { + SCOPED_TRACE(test_mask); + std::set<size_t> break_locations; + for (int j = 0; j < possible_breaks; ++j) { + if (test_mask & (1u << j)) { + break_locations.insert(breaks[j]); + } + } + EXPECT_EQ( + hash(PiecewiseHashTester(big_buffer, std::move(break_locations))), + big_buffer_hash); + } + } +} + TEST(HashValueTest, PrivateSanity) { // Sanity check that Private is working as the tests below expect it to work. EXPECT_TRUE(is_hashable<Private>::value); |