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Buffer.hpp

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/*==========================================================================
 * Copyright (c) 2004 University of Massachusetts.  All Rights Reserved.
 *
 * Use of the Lemur Toolkit for Language Modeling and Information Retrieval
 * is subject to the terms of the software license set forth in the LICENSE
 * file included with this software, and also available at
 * http://www.lemurproject.org/license.html
 *
 *==========================================================================
*/


//
// Buffer
//
// 14 May 2004 -- tds
//

#ifndef INDRI_BUFFER_HPP
#define INDRI_BUFFER_HPP

#include <assert.h>
#include "lemur-compat.hpp"

class Buffer {
private:
  char* _buffer;
  size_t _size;
  size_t _position;

public:
  Buffer() :
    _buffer(0),
    _size(0),
    _position(0)
  {
  }

  ~Buffer() {
    free( _buffer );
  }

  size_t size() const {
    return _size;
  }

  size_t position() const {
    return _position;
  }

  void clear() {
    _position = 0;
  }

  char* front() {
    return _buffer;
  }

  char* write( size_t length ) {
    grow( _position + length );
    char* spot = _buffer + _position;
    _position += length;
    return spot;
  }

  void unwrite( size_t length ) {
    assert( length <= _position );
    _position -= length;
  }
  
  void grow( size_t newSize ) {
    if( newSize > _size ) {
      if( newSize < 1024*1024 ) {
        // find next larger power of two, up to one megabyte
        size_t powSize;
        for( powSize = 64; powSize < newSize; powSize *= 2 )
          ;
        newSize = powSize;
      } else {
        // round to nearest megabyte
        newSize = (newSize + 1024*1024) & ~(1024*1024-1);
      }

      char* newBuffer = (char*) malloc( newSize );
      memcpy( newBuffer, _buffer, _position );
      free( _buffer );
      _buffer = newBuffer;
      _size = newSize;
    }
  }

  void grow() {
    if( _size == 0 )
      grow(64);
    else
      grow(_size*2);
  }

  void remove( size_t start ) {
    memmove( _buffer, _buffer + start, _position - start );
    _position -= start;
  }

  void detach() {
    _size = 0;
    _buffer = 0;
  }
};

#endif // INDRI_BUFFER_HPP

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