Port ReadOnlyBitStream from Compression, add tests

SabreTools.IO.Test/ReadOnlyBitStreamTests.cs

@@ -0,0 +1,54 @@
+using System.IO;
+using SabreTools.IO.Streams;
+using Xunit;
+
+namespace SabreTools.IO.Test
+{
+    public class ReadOnlyBitStreamTests
+    {
+        [Fact]
+        public void DefaultConstructorTest()
+        {
+            var stream = new ReadOnlyBitStream(new MemoryStream());
+            Assert.Equal(0, stream.Length);
+            Assert.Equal(0, stream.Position);
+
+            stream = new ReadOnlyBitStream(new MemoryStream(new byte[16]));
+            Assert.Equal(16, stream.Length);
+            Assert.Equal(0, stream.Position);
+        }
+
+        [Fact]
+        public void ReadSingleBitTest()
+        {
+            byte[] data = [0b01010101];
+            var stream = new ReadOnlyBitStream(new MemoryStream(data));
+            byte? bit = stream.ReadBit();
+            Assert.NotNull(bit);
+            Assert.Equal((byte)0b00000001, bit);
+            Assert.Equal(1, stream.Position);
+        }
+
+        [Fact]
+        public void ReadBitsLSBTest()
+        {
+            byte[] data = [0b01010101, 0b01010101, 0b01010101, 0b01010101];
+            var stream = new ReadOnlyBitStream(new MemoryStream(data));
+            uint? bits = stream.ReadBitsLSB(4);
+            Assert.NotNull(bits);
+            Assert.Equal((byte)0b00000101, bits);
+            Assert.Equal(1, stream.Position);
+        }
+
+        [Fact]
+        public void ReadBitsMSBTest()
+        {
+            byte[] data = [0b01010101, 0b01010101, 0b01010101, 0b01010101];
+            var stream = new ReadOnlyBitStream(new MemoryStream(data));
+            uint? bits = stream.ReadBitsMSB(4);
+            Assert.NotNull(bits);
+            Assert.Equal((byte)0b00001010, bits);
+            Assert.Equal(1, stream.Position);
+        }
+    }
+}

SabreTools.IO/Streams/ReadOnlyBitStream.cs

@@ -0,0 +1,238 @@
+using System;
+using System.IO;
+
+namespace SabreTools.IO.Streams
+{
+    /// <summary>
+    /// Wrapper to allow reading bits from a source stream
+    /// </summary>
+    public class ReadOnlyBitStream
+    {
+        /// <inheritdoc cref="Stream.Position"/>
+        public long Position => _source.Position;
+
+        /// <inheritdoc cref="Stream.Length"/>
+        public long Length => _source.Length;
+
+        /// <summary>
+        /// Original stream source
+        /// </summary>
+        private readonly Stream _source;
+
+        /// <summary>
+        /// Last read byte value from the stream
+        /// </summary>
+        private byte? _bitBuffer;
+
+        /// <summary>
+        /// Index in the byte of the current bit
+        /// </summary>
+        private int _bitIndex;
+
+        /// <summary>
+        /// Create a new BitStream from a source Stream
+        /// </summary>
+        public ReadOnlyBitStream(Stream source)
+        {
+            _source = source;
+            _bitBuffer = null;
+            _bitIndex = 0;
+
+            // Verify the stream
+            if (!source.CanRead || !source.CanSeek)
+                throw new ArgumentException($"{nameof(source)} needs to be readable and seekable");
+        }
+
+        /// <summary>
+        /// Discard the current cached byte
+        /// </summary>
+        public void Discard()
+        {
+            _bitBuffer = null;
+            _bitIndex = 0;
+        }
+
+        /// <summary>
+        /// Read a single bit, if possible
+        /// </summary>
+        /// <returns>The next bit encoded in a byte, null on error or end of stream</returns>
+        public byte? ReadBit()
+        {
+            // If we reached the end of the stream
+            if (_source.Position >= _source.Length)
+                return null;
+
+            // If we don't have a value cached
+            if (_bitBuffer == null)
+            {
+                // Read the next byte, if possible
+                _bitBuffer = ReadSourceByte();
+                if (_bitBuffer == null)
+                    return null;
+
+                // Reset the bit index
+                _bitIndex = 0;
+            }
+
+            // Get the value by bit-shifting
+            int value = _bitBuffer.Value & 0x01;
+            _bitBuffer = (byte?)(_bitBuffer >> 1);
+            _bitIndex++;
+
+            // Reset the byte if we're at the end
+            if (_bitIndex >= 8)
+                Discard();
+
+            return (byte)value;
+        }
+
+        /// <summary>
+        /// Read a multiple bits in LSB, if possible
+        /// </summary>
+        /// <returns>The next bits encoded in a UInt32, null on error or end of stream</returns>
+        public uint? ReadBitsLSB(int bits)
+        {
+            uint value = 0;
+            for (int i = 0; i < bits; i++)
+            {
+                // Read the next bit
+                byte? bitValue = ReadBit();
+                if (bitValue == null)
+                    return null;
+
+                // Add the bit shifted by the current index
+                value += (uint)(bitValue.Value << i);
+            }
+
+            return value;
+        }
+
+        /// <summary>
+        /// Read a multiple bits in MSB, if possible
+        /// </summary>
+        /// <returns>The next bits encoded in a UInt32, null on error or end of stream</returns>
+        public uint? ReadBitsMSB(int bits)
+        {
+            uint value = 0;
+            for (int i = 0; i < bits; i++)
+            {
+                // Read the next bit
+                byte? bitValue = ReadBit();
+                if (bitValue == null)
+                    return null;
+
+                // Add the bit shifted by the current index
+                value = (value << 1) + bitValue.Value;
+            }
+
+            return value;
+        }
+
+        /// <summary>
+        /// Read a byte, if possible
+        /// </summary>
+        /// <returns>The next byte, null on error or end of stream</returns>
+        /// <remarks>Assumes the stream is byte-aligned</remarks>
+        public byte? ReadByte()
+        {
+            try
+            {
+                Discard();
+                return _source.ReadByteValue();
+            }
+            catch
+            {
+                return null;
+            }
+        }
+
+        /// <summary>
+        /// Read a UInt16, if possible
+        /// </summary>
+        /// <returns>The next UInt16, null on error or end of stream</returns>
+        /// <remarks>Assumes the stream is byte-aligned</remarks>
+        public ushort? ReadUInt16()
+        {
+            try
+            {
+                Discard();
+                return _source.ReadUInt16();
+            }
+            catch
+            {
+                return null;
+            }
+        }
+
+        /// <summary>
+        /// Read a UInt32, if possible
+        /// </summary>
+        /// <returns>The next UInt32, null on error or end of stream</returns>
+        /// <remarks>Assumes the stream is byte-aligned</remarks>
+        public uint? ReadUInt32()
+        {
+            try
+            {
+                Discard();
+                return _source.ReadUInt32();
+            }
+            catch
+            {
+                return null;
+            }
+        }
+
+        /// <summary>
+        /// Read a UInt64, if possible
+        /// </summary>
+        /// <returns>The next UInt64, null on error or end of stream</returns>
+        /// <remarks>Assumes the stream is byte-aligned</remarks>
+        public ulong? ReadUInt64()
+        {
+            try
+            {
+                Discard();
+                return _source.ReadUInt64();
+            }
+            catch
+            {
+                return null;
+            }
+        }
+
+        /// <summary>
+        /// Read <paramref name="bytes"/> bytes, if possible
+        /// </summary>
+        /// <param name="bytes">Number of bytes to read</param>
+        /// <returns>The next <paramref name="bytes"/> bytes, null on error or end of stream</returns>
+        /// <remarks>Assumes the stream is byte-aligned</remarks>
+        public byte[]? ReadBytes(int bytes)
+        {
+            try
+            {
+                Discard();
+                return _source.ReadBytes(bytes);
+            }
+            catch
+            {
+                return null;
+            }
+        }
+
+        /// <summary>
+        /// Read a single byte from the underlying stream, if possible
+        /// </summary>
+        /// <returns>The next full byte from the stream, null on error or end of stream</returns>
+        private byte? ReadSourceByte()
+        {
+            try
+            {
+                return _source.ReadByteValue();
+            }
+            catch
+            {
+                return null;
+            }
+        }
+    }
+}