1 files changed, 63 insertions, 0 deletions
diff --git a/library/cpp/yt/coding/bit_io.h b/library/cpp/yt/coding/bit_io.h
new file mode 100644
index 00000000000..18900d69f85
--- /dev/null
+++ b/library/cpp/yt/coding/bit_io.h
@@ -0,0 +1,63 @@
+#pragma once
+
+#include <util/system/types.h>
+
+namespace NYT {
+
+////////////////////////////////////////////////////////////////////////////////
+
+//! MSB-first bit writer over a caller-owned buffer.
+/*!
+ *  Bits are flushed to the buffer in 4-byte chunks, so the buffer must have room
+ *  for up to 3 bytes beyond the last logically-written byte before #Finish is
+ *  called.
+ */
+class TBitWriter
+{
+public:
+    explicit TBitWriter(char* ptr);
+
+    //! Appends the #width low bits of #value. Requires 0 <= #width <= 32 and
+    //! #value < 2^#width (for #width == 32 any value is accepted).
+    void WriteBits(ui32 value, int width);
+
+    //! Pads the last partial byte with zero low bits and returns the
+    //! one-past-end pointer.
+    char* Finish();
+
+private:
+    char* Ptr_;
+    ui64 Accumulator_ = 0;
+    int BitCount_ = 0;
+};
+
+//! MSB-first bit reader.
+/*!
+ *  Reads bits written by #TBitWriter. Assumes up to 8 bytes past the logical end
+ *  of the stream are safe to read.
+ */
+class TBitReader
+{
+public:
+    explicit TBitReader(const char* ptr);
+
+    //! Reads and returns #width bits (0 <= #width <= 32).
+    ui32 ReadBits(int width);
+
+    //! Returns the one-past-end pointer; the (< 8) buffered sub-byte bits, which
+    //! are the writer's zero padding, are dropped.
+    const char* Finish();
+
+private:
+    const ui8* Ptr_;
+    ui64 Accumulator_ = 0;
+    int BitCount_ = 0;
+};
+
+////////////////////////////////////////////////////////////////////////////////
+
+} // namespace NYT
+
+#define BIT_IO_INL_H_
+#include "bit_io-inl.h"
+#undef BIT_IO_INL_H_