code: /**
   * Copyright (c) 2005, Regents of the University of California
   * All rights reserved.
   *
   * Redistribution and use in source and binary forms, with or without
   * modification, are permitted provided that the following conditions
   * are met:
   *
   * Redistributions of source code must retain the above copyright notice,
   * this list of conditions and the following disclaimer.
   *
   * Redistributions in binary form must reproduce the above copyright
   * notice, this list of conditions and the following disclaimer in the
   * documentation and/or other materials provided with the distribution.
   *
   * Neither the name of the University of California, Los Angeles nor the
   * names of its contributors may be used to endorse or promote products
   * derived from this software without specific prior written permission.
   *
   * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
   * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
   * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
   * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
   * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
   * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
   * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
   * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
   * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
   * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
   * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
   */
  
  package jintgen.gen.disassembler;
  
  import java.util.HashMap;
  import java.util.Map;
  
  /**
   * The <code>TreeFactorer</code> class implements a factoring algorithm that reduces
   * the size of a decoding tree and turns it into directed acyclic graph. It does this
   * by recursively rebuilding the tree and caching equivalent subtrees. The algorithm
   * guarantees that the new DAG that is created will be equivalent.
   *
   * @author Ben L. Titzer
   */
  public class TreeFactorer {
  
      final DTNode oldRoot;
      DTNode newRoot;
      final HashMap<Long, HashMap<DTNode, DTNode>> pathMap;
  
      public TreeFactorer(DTNode dt) {
          oldRoot = dt;
          pathMap = new HashMap<Long, HashMap<DTNode, DTNode>>();
      }
  
      /**
       * The <code>getNewTree()</code> method rebuilds the tree and returns a reference to the new
       * root.
       * @return a reference to the new root of the tree
       */
      public DTNode getNewTree() {
          if ( newRoot == null ) newRoot = rebuild(0, oldRoot);
          return newRoot;
      }
  
      private DTNode rebuild(long state, DTNode n) {
          long nstate = DGUtil.getBitStates(state, n);
          // rebuild each of the children
          HashMap<Integer, DTNode> nc = new HashMap<Integer, DTNode>();
          for ( Map.Entry<Integer, DTNode> e : n.getEdges() ) {
              int value = e.getKey();
              DTNode child = e.getValue();
              DTNode nchild = rebuild(nstate, child);
              nc.put(new Integer(value), nchild);
          }
  
          DTNode nn = n.shallowCopy(nc);
          DTNode prev = getPrevNode(state, nn);
          if ( prev != null ) return prev;
  
          // cache this node and (and its subgraph)
          addNewNode(state, nn);
          return nn;
      }
  
      private void addNewNode(long state, DTNode ndt) {
          HashMap<DTNode, DTNode> set = getTreeMap(state);
          set.put(ndt, ndt);
      }
  
      private HashMap<DTNode, DTNode> getTreeMap(long state) {
          HashMap<DTNode, DTNode> set = pathMap.get(state);
          if ( set == null ) {
              set = new HashMap<DTNode, DTNode>();
              pathMap.put(state, set);
          }
          return set;
      }
  
      private DTNode getPrevNode(long state, DTNode dt) {
          HashMap<DTNode, DTNode> set = getTreeMap(state);
          return set.get(dt);
      }
  }
  