GBA LZ decompression function in C#

LZ77Decompress.cs

/// <summary>
/// Decompresses LZ77-compressed data from the given input stream.
/// </summary>
/// <param name="input">The input stream to read from.</param>
/// <returns>The decompressed data.</returns>
public static MemoryStream Decompress(Stream input) {
	BinaryReader reader = new BinaryReader(input);

	// Check LZ77 type.
	if (reader.ReadByte() != 0x10)
		throw new ArgumentException("Input stream does not contain LZ77-compressed data.", "input");

	// Read the size.
	int size = reader.ReadUInt16() | (reader.ReadByte() << 16);

	// Create output stream.
	MemoryStream output = new MemoryStream(size);

	// Begin decompression.
	while (output.Length < size) {
		// Load flags for the next 8 blocks.
		int flagByte = reader.ReadByte();

		// Process the next 8 blocks.
		for (int i = 0; i < 8; i++) {
			// Check if the block is compressed.
			if ((flagByte & (0x80 >> i)) == 0) {
				// Uncompressed block; copy single byte.
				output.WriteByte(reader.ReadByte());
			} else {
				// Compressed block; read block.
				ushort block = reader.ReadUInt16();
				// Get byte count.
				int count = ((block >> 4) & 0xF) + 3;
				// Get displacement.
				int disp = ((block & 0xF) << 8) | ((block >> 8) & 0xFF);

				// Save current position and copying position.
				long outPos = output.Position;
				long copyPos = output.Position - disp - 1;

				// Copy all bytes.
				for (int j = 0; j < count; j++) {
					// Read byte to be copied.
					output.Position = copyPos++;
					byte b = (byte)output.ReadByte();

					// Write byte to be copied.
					output.Position = outPos++;
					output.WriteByte(b);
				}
			}

			// If all data has been decompressed, stop.
			if (output.Length >= size) {
				break;
			}
		}
	}

	output.Position = 0;
	return output;
}