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/* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
 * JFlex 1.5                                                               *
 * Copyright (C) 1998-2009  Gerwin Klein                     *
 * All rights reserved.                                                    *
 *                                                                         *
 * License: BSD                                                            *
 *                                                                         *
 * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * */
package jflex;

/**
 * Enumerates the states of a StateSet.
 *
 * @author Gerwin Klein
 * @version JFlex 1.5, $Revision: 586 $, $Date: 2010-03-07 19:59:36 +1100 (Sun, 07 Mar 2010) $
 */
final public class StateSetEnumerator {

  private final static boolean DEBUG = false;

  private int index;
  private int offset;
  private long mask;

  private long [] bits;
  
  /**
   * creates a new StateSetEnumerator that is not yet associated
   * with a StateSet. hasMoreElements() and nextElement() will 
   * throw NullPointerException when used before reset()
   */  
  public StateSetEnumerator() {
  }

  public StateSetEnumerator(StateSet states) {
    reset(states);
  }

  public void reset(StateSet states) {
    bits    = states.bits;
    index   = 0;
    offset  = 0;
    mask    = 1;
    while (index < bits.length && bits[index] == 0) 
      index++;

    if (index >= bits.length) return;
        
    while (offset <= StateSet.MASK && ((bits[index] & mask) == 0)) {
      mask<<= 1;
      offset++;
    }    
  }

  private void advance() {
    
    if (DEBUG) Out.dump("Advancing, at start, index = "+index+", offset = "+offset); //$NON-NLS-1$ //$NON-NLS-2$

    // cache fields in local variable for faster access
    int  _index   = this.index;
    int  _offset  = this.offset;
    long _mask    = this.mask;
    long [] _bits = this.bits;

    long bi = _bits[_index];

    do {
      _offset++;
      _mask<<= 1;
    } while (_offset <= StateSet.MASK && ((bi & _mask) == 0));

    if (_offset > StateSet.MASK) {
      int length = _bits.length;

      do 
        _index++;
      while (_index < length && _bits[_index] == 0);
        
      if (_index >= length) {
        this.index = length; // indicates "no more elements"
        return;
      }        

      _offset = 0;
      _mask = 1;
      bi = _bits[_index];

      // terminates, because bi != 0
      while ((bi & _mask) == 0) {
        _mask<<= 1;
        _offset++;
      }
    }

    // write back cached values
    this.index  = _index;
    this.mask   = _mask;
    this.offset = _offset;
  }

  public boolean hasMoreElements() {
    if (DEBUG) Out.dump("hasMoreElements, index = "+index+", offset = "+offset); //$NON-NLS-1$ //$NON-NLS-2$
    return index < bits.length;
  }

  public int nextElement() {
    if (DEBUG) Out.dump("nextElement, index = "+index+", offset = "+offset); //$NON-NLS-1$ //$NON-NLS-2$
    int x = (index << StateSet.BITS) + offset;
    advance();
    return x;
  }

}