OutputWindow.cs

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namespace System.IO.Compression;
 
internal sealed class OutputWindow
{
    private readonly byte[] _window = new byte[262144];
 
    private int _end;
 
    private int _bytesUsed;
 
    public int FreeBytes => 262144 - _bytesUsed;
 
    internal void ClearBytesUsed()
    {
        _bytesUsed = 0;
    }
 
    public void Write(byte b)
    {
        _window[_end++] = b;
        _end &= 262143;
        _bytesUsed++;
    }
 
    public void WriteLengthDistance(int length, int distance)
    {
        _bytesUsed += length;
        int num = (_end - distance) & 0x3FFFF;
        int num2 = 262144 - length;
        if (num <= num2 && _end < num2)
        {
            if (length <= distance)
            {
                Array.Copy(_window, num, _window, _end, length);
                _end += length;
            }
            else
            {
                while (length-- > 0)
                {
                    _window[_end++] = _window[num++];
                }
            }
        }
        else
        {
            while (length-- > 0)
            {
                _window[_end++] = _window[num++];
                _end &= 262143;
                num &= 0x3FFFF;
            }
        }
    }
 
    public int CopyFrom(InputBuffer input, int length)
    {
        length = Math.Min(Math.Min(length, 262144 - _bytesUsed), input.AvailableBytes);
        int num = 262144 - _end;
        int num2;
        if (length > num)
        {
            num2 = input.CopyTo(_window, _end, num);
            if (num2 == num)
            {
                num2 += input.CopyTo(_window, 0, length - num);
            }
        }
        else
        {
            num2 = input.CopyTo(_window, _end, length);
        }
        _end = (_end + num2) & 0x3FFFF;
        _bytesUsed += num2;
        return num2;
    }
 
    public int CopyTo(Span<byte> output)
    {
        int num;
        if (output.Length > _bytesUsed)
        {
            num = _end;
            output = output.Slice(0, _bytesUsed);
        }
        else
        {
            num = (_end - _bytesUsed + output.Length) & 0x3FFFF;
        }
        int length = output.Length;
        int num2 = output.Length - num;
        if (num2 > 0)
        {
            _window.AsSpan(262144 - num2, num2).CopyTo(output);
            output = output.Slice(num2, num);
        }
        _window.AsSpan(num - output.Length, output.Length).CopyTo(output);
        _bytesUsed -= length;
        return length;
    }
}