Flee
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226
Parsing/LookAheadReader.cs
Normal file
226
Parsing/LookAheadReader.cs
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namespace Flee.Parsing
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{
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// * A look-ahead character stream reader. This class provides the
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// * functionalities of a buffered line-number reader, but with the
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// * additional possibility of peeking an unlimited number of
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// * characters ahead. When looking further and further ahead in the
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// * character stream, the buffer is continously enlarged to contain
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// * all the required characters from the current position an
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// * onwards. This means that looking more characters ahead requires
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// * more memory, and thus becomes unviable in the end.
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internal class LookAheadReader : TextReader
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{
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private const int StreamBlockSize = 4096;
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private const int BufferBlockSize = 1024;
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private char[] _buffer = new char[StreamBlockSize];
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private int _pos;
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private int _length;
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private TextReader _input = null;
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private int _line = 1;
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private int _column = 1;
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public LookAheadReader(TextReader input) : base()
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{
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this._input = input;
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}
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public int LineNumber => _line;
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public int ColumnNumber => _column;
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public override int Read()
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{
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ReadAhead(1);
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if (_pos >= _length)
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{
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return -1;
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}
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else
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{
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UpdateLineColumnNumbers(1);
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return Convert.ToInt32(_buffer[System.Math.Max(System.Threading.Interlocked.Increment(ref _pos), _pos - 1)]);
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}
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}
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public override int Read(char[] cbuf, int off, int len)
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{
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ReadAhead(len);
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if (_pos >= _length)
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{
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return -1;
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}
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else
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{
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var count = _length - _pos;
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if (count > len)
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{
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count = len;
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}
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UpdateLineColumnNumbers(count);
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Array.Copy(_buffer, _pos, cbuf, off, count);
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_pos += count;
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return count;
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}
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}
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public string ReadString(int len)
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{
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ReadAhead(len);
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if (_pos >= _length)
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{
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return null;
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}
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else
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{
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var count = _length - _pos;
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if (count > len)
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{
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count = len;
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}
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UpdateLineColumnNumbers(count);
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var result = new string(_buffer, _pos, count);
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_pos += count;
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return result;
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}
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}
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public override int Peek()
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{
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return Peek(0);
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}
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public int Peek(int off)
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{
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ReadAhead(off + 1);
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if (_pos + off >= _length)
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{
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return -1;
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}
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else
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{
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return Convert.ToInt32(_buffer[_pos + off]);
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}
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}
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public string PeekString(int off, int len)
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{
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ReadAhead(off + len + 1);
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if (_pos + off >= _length)
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{
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return null;
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}
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else
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{
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var count = _length - (_pos + off);
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if (count > len)
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{
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count = len;
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}
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return new string(_buffer, _pos + off, count);
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}
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}
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public override void Close()
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{
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_buffer = null;
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_pos = 0;
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_length = 0;
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if (_input != null)
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{
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_input.Close();
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_input = null;
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}
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}
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private void ReadAhead(int offset)
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{
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int size = 0;
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int readSize = 0;
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// Check for end of stream or already read characters
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if (_input == null || _pos + offset < _length)
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{
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return;
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}
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// Remove old characters from buffer
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if (_pos > BufferBlockSize)
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{
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Array.Copy(_buffer, _pos, _buffer, 0, _length - _pos);
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_length -= _pos;
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_pos = 0;
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}
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// Calculate number of characters to read
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size = _pos + offset - _length + 1;
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if (size % StreamBlockSize != 0)
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{
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size = (size / StreamBlockSize) * StreamBlockSize;
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size += StreamBlockSize;
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}
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EnsureBufferCapacity(_length + size);
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// Read characters
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try
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{
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readSize = _input.Read(_buffer, _length, size);
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}
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catch (IOException e)
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{
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_input = null;
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throw;
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}
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// Append characters to buffer
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if (readSize > 0)
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{
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_length += readSize;
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}
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if (readSize < size)
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{
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try
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{
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_input.Close();
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}
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finally
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{
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_input = null;
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}
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}
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}
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private void EnsureBufferCapacity(int size)
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{
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char[] newbuf = null;
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if (_buffer.Length >= size)
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{
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return;
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}
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if (size % BufferBlockSize != 0)
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{
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size = (size / BufferBlockSize) * BufferBlockSize;
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size += BufferBlockSize;
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}
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newbuf = new char[size];
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Array.Copy(_buffer, 0, newbuf, 0, _length);
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_buffer = newbuf;
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}
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private void UpdateLineColumnNumbers(int offset)
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{
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for (int i = 0; i <= offset - 1; i++)
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{
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if (_buffer.Contains(_buffer[_pos + i]))
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{
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_line += 1;
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_column = 1;
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}
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else
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{
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_column += 1;
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}
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}
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}
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}
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}
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