1 files changed, 69 insertions, 0 deletions
diff --git a/library/cpp/yt/coding/unittests/bit_io_ut.cpp b/library/cpp/yt/coding/unittests/bit_io_ut.cpp
new file mode 100644
index 00000000000..5d61b166f0a
--- /dev/null
+++ b/library/cpp/yt/coding/unittests/bit_io_ut.cpp
@@ -0,0 +1,69 @@
+#include <library/cpp/testing/gtest/gtest.h>
+
+#include <library/cpp/yt/coding/bit_io.h>
+
+#include <utility>
+#include <vector>
+
+namespace NYT {
+namespace {
+
+////////////////////////////////////////////////////////////////////////////////
+
+TEST(TBitIOTest, RoundTrip)
+{
+    std::vector<std::pair<ui32, int>> items = {
+        {0, 0}, {1, 1}, {0, 1}, {5, 3}, {0, 8}, {255, 8}, {12345, 14},
+        {0, 32}, {0xffffffffu, 32}, {0x12345, 17}, {7, 3}, {1u << 30, 31},
+    };
+    std::vector<char> buffer(256, 0);
+
+    TBitWriter writer(buffer.data());
+    for (auto [value, width] : items) {
+        writer.WriteBits(value, width);
+    }
+    writer.Finish();
+
+    TBitReader reader(buffer.data());
+    for (auto [value, width] : items) {
+        EXPECT_EQ(reader.ReadBits(width), value) << "width=" << width;
+    }
+}
+
+TEST(TBitIOTest, ZeroWidthIsNoop)
+{
+    std::vector<char> buffer(16, 0);
+    TBitWriter writer(buffer.data());
+    writer.WriteBits(0, 0);
+    writer.WriteBits(1, 1);
+    writer.WriteBits(0, 0);
+    char* end = writer.Finish();
+    EXPECT_EQ(end - buffer.data(), 1);  // a single bit occupies one byte
+
+    TBitReader reader(buffer.data());
+    EXPECT_EQ(reader.ReadBits(0), 0u);
+    EXPECT_EQ(reader.ReadBits(1), 1u);
+    EXPECT_EQ(reader.ReadBits(0), 0u);
+}
+
+TEST(TBitIOTest, FlushBoundary)
+{
+    // Many 17-bit writes repeatedly cross the internal 32-bit flush boundary.
+    constexpr int Count = 1000;
+    std::vector<char> buffer(Count * 3 + 16, 0);
+    TBitWriter writer(buffer.data());
+    for (int i = 0; i < Count; ++i) {
+        writer.WriteBits(static_cast<ui32>(i) & 0x1ffff, 17);
+    }
+    writer.Finish();
+
+    TBitReader reader(buffer.data());
+    for (int i = 0; i < Count; ++i) {
+        EXPECT_EQ(reader.ReadBits(17), static_cast<ui32>(i) & 0x1ffff) << "i=" << i;
+    }
+}
+
+////////////////////////////////////////////////////////////////////////////////
+
+} // namespace
+} // namespace NYT