BitStreamReader.cs

using System;
using System.IO;
using System.Text;



namespace Brc;
public class BitStreamReader(Stream stream) : IDisposable
{
	private byte bitIndex = 8;
	private byte currentByte;
	private readonly Stream stream = stream;
	private bool ReadBit(out bool bit)
	{
		if (bitIndex == 8 || bitIndex == 0)
		{
			int b = stream.ReadByte();
			if (b < 0)
			{
				bit = false;
				return false;
			}
			currentByte = (byte)b;
			bitIndex = 0;
		}
		bit = (currentByte & 1 << bitIndex) > 0;
		bitIndex++;
		return true;
	}
	public bool ReadByte(out byte result)
	{
		int newbyte = stream.ReadByte();
		if (newbyte < 0)
		{
			result = 0;
			return false;
		}
		if (bitIndex == 8 || bitIndex == 0)
		{
			result = (byte)newbyte;
			currentByte = (byte)newbyte;
			return true;
		}
		result = (byte)(currentByte >> bitIndex | newbyte << 8 - bitIndex);
		currentByte = (byte)newbyte;
		return true;
	}
	public bool ReadBytes(int count, out byte[] result)
	{
		byte[] bytes = [];
		while (count > 0)
		{
			if (ReadByte(out byte b))
				bytes = [.. bytes, b];
			else
			{
				result = [.. bytes];
				return false;
			}
			count--;
		}
		result = [.. bytes];
		return true;
	}
	public bool Read(byte bitwidth, out ulong value)
	{
		value = 0;
		int index = 0;
		if (bitwidth > 64)
			throw new ArgumentException("The bitwidth must less than or equal to 64.", nameof(value));
		if (bitwidth > 0)
			while (bitwidth > 8)
			{
				if (ReadByte(out byte b))
					value |= (ulong)b << index++ * 8;
				else
					return false;
				bitwidth -= 8;
			}
		if (bitwidth > 0)
			if (Read(bitwidth, out byte b))
				value |= (ulong)b << index * 8;
			else
				return false;
		return true;
	}
	public bool Read(byte bitwidth, out uint value)
	{
		value = 0;
		int index = 0;
		if (bitwidth > 32)
			throw new ArgumentException("The bitwidth must less than or equal to 32.", nameof(value));
		if (bitwidth > 0)
			while (bitwidth > 8)
			{
				if (ReadByte(out byte b))
					value |= (uint)b << index++ * 8;
				else
					return false;
				bitwidth -= 8;
			}
		if (bitwidth > 0)
			if (Read(bitwidth, out byte b))
				value |= (uint)b << index * 8;
			else
				return false;
		return true;
	}
	public bool Read(byte bitwidth, out ushort value)
	{
		if (bitwidth > 16)
			throw new ArgumentException("The bitwidth must less than or equal to 16.", nameof(value));
		value = 0;
		int index = 0;
		if (bitwidth > 0)
			while (bitwidth > 8)
			{
				if (ReadByte(out byte b))
					value |= (ushort)(b << index++ * 8);
				else
					return false;
				bitwidth -= 8;
			}
		if (bitwidth > 0)
			if (Read(bitwidth, out byte b))
				value |= (ushort)(b << index * 8);
			else
				return false;
		return true;
	}
	public bool Read(byte bitwidth, out byte value)
	{
		if (bitwidth > 8)
			throw new ArgumentException("The bitwidth must less than or equal to 8.", nameof(value));
		value = 0;
		if (bitwidth > 0)
		{
			if (bitwidth + bitIndex > 8)
			{
				value = (byte)(currentByte >> bitIndex);
				int newbyte = stream.ReadByte();
				if (newbyte < 0)
					return false;
				currentByte = (byte)newbyte;
				int bitsFromNext = bitwidth + bitIndex - 8;
				byte mask = (byte)((1 << bitsFromNext) - 1);
				value |= (byte)((currentByte & mask) << (8 - bitIndex));
				bitIndex = (byte)bitsFromNext;
			}
			else
			{
				value = (byte)(currentByte >> bitIndex & ~(0xFF << bitwidth));
				bitIndex += bitwidth;
			}
		}
		return true;
	}
	public bool Read(int bitwidth, out byte[] value)
	{
		if (bitwidth <= 0)
		{
			value = [];
			return true;
		}
		if (ReadBytes(bitwidth / 8, out value))
		{
			if (bitwidth % 8 != 0)
			{
				Read((byte)(bitwidth % 8), out byte b);
				value = [.. value, b];
			}
			return true;
		}
		return false;
	}
	public bool Read(out bool value)
	{
		return ReadBit(out value);
	}
	public bool Read(out byte value) => ReadByte(out value);
	public bool Read(out ushort value)
	{
		if (ReadBytes(2, out byte[] bytes))
		{
			value = BitConverter.ToUInt16(bytes,0);
			return true;
		}
		value = 0;
		return false;
	}
	public bool Read(out short value)
	{
		if (ReadBytes(2, out byte[] bytes))
		{
			value = BitConverter.ToInt16(bytes, 0);
			return true;
		}
		value = 0;
		return false;
	}
	public bool Read(out uint value)
	{
		if (ReadBytes(4, out byte[] bytes))
		{
			value = BitConverter.ToUInt32(bytes, 0);
			return true;
		}
		value = 0;
		return false;
	}
	public bool Read(out int value)
	{
		if (ReadBytes(4, out byte[] bytes))
		{
			value = BitConverter.ToInt32(bytes, 0);
			return true;
		}
		value = 0;
		return false;
	}
	public bool Read(out ulong value)
	{
		if (ReadBytes(8, out byte[] bytes))
		{
			value = BitConverter.ToUInt64(bytes, 0);
			return true;
		}
		value = 0;
		return false;
	}
	public bool Read(out long value)
	{
		if (ReadBytes(8, out byte[] bytes))
		{
			value = BitConverter.ToInt64(bytes, 0);
			return true;
		}
		value = 0;
		return false;
	}
	public bool Read(out char value)
	{
		if (ReadBit(out bool bit))
		{
			if (bit && ReadBit(out bit))
			{
				if (bit)
				{
					if (Read(Shared.stages[2], out ushort c2))
					{
						value = (char)c2;
						return true;
					}
				}
				if (Read(Shared.stages[1], out ushort c1))
				{
					value = (char)c1;
					return true;
				}
			}
			if (Read(Shared.stages[0], out ushort c0))
			{
				value = (char)c0;
				return true;
			}
		}
		value = '\0';
		return false;
	}
	public bool Read(out string value)
	{
		value = string.Empty;
		StringBuilder sb = new();
		while (Read(7, out byte length))
		{
			Read(out bool isUnicode);
			for (byte i = 0; i < length; i++)
				if (isUnicode && Read(out char u))
					sb.Append(u);
				else if (Read(7, out byte c))
					sb.Append((char)c);
				else
					return false;
			if (length != 255)
				break;
		}
		value = sb.ToString();
		return true;
	}
	public bool Read(out float value)
	{
		if (ReadBytes(4, out byte[] bytes))
		{
			value = BitConverter.ToSingle(bytes,0);
			return true;
		}
		value = 0;
		return false;
	}
	public bool Read(out double value)
	{
		if (ReadBytes(8, out byte[] bytes))
		{
			value = BitConverter.ToDouble(bytes, 0);
			return true;
		}
		value = 0;
		return false;
	}
	public bool Read<TEnum>(out TEnum value) where TEnum : struct, Enum
	{
		byte length = Shared.GetBitWidth<TEnum>();
		if (Read(length, out ulong index))
		{
			value = (TEnum)Enum.ToObject(typeof(TEnum), index);
			return true;
		}
		value = default;
		return false;
	}
	public void Dispose()
	{
		GC.SuppressFinalize(this);
	}
}