lucene/analysis/stempel/src/java/org/egothor/stemmer/Lift.java

/*
                   Egothor Software License version 1.00
                   Copyright (C) 1997-2004 Leo Galambos.
                Copyright (C) 2002-2004 "Egothor developers"
                     on behalf of the Egothor Project.
                            All rights reserved.

  This  software  is  copyrighted  by  the "Egothor developers". If this
  license applies to a single file or document, the "Egothor developers"
  are the people or entities mentioned as copyright holders in that file
  or  document.  If  this  license  applies  to the Egothor project as a
  whole,  the  copyright holders are the people or entities mentioned in
  the  file CREDITS. This file can be found in the same location as this
  license in the distribution.

  Redistribution  and  use  in  source and binary forms, with or without
  modification, are permitted provided that the following conditions are
  met:
   1. Redistributions  of  source  code  must retain the above copyright
      notice, the list of contributors, this list of conditions, and the
      following disclaimer.
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      notice, the list of contributors, this list of conditions, and the
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   3. The name "Egothor" must not be used to endorse or promote products
      derived  from  this software without prior written permission. For
      written permission, please contact Leo.G@seznam.cz
   4. Products  derived  from this software may not be called "Egothor",
      nor  may  "Egothor"  appear  in  their name, without prior written
      permission from Leo.G@seznam.cz.

  In addition, we request that you include in the end-user documentation
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  This  software  consists  of  voluntary  contributions  made  by  many
  individuals  on  behalf  of  the  Egothor  Project  and was originally
  created by Leo Galambos (Leo.G@seznam.cz).
*/
package org.egothor.stemmer;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Iterator;
import java.util.List;

/**
 * The Lift class is a data structure that is a variation of a Patricia trie.
 *
 * <p>Lift's <i>raison d'etre</i> is to implement reduction of the trie via the Lift-Up method.,
 * which makes the data structure less liable to overstemming.
 */
public class Lift extends Reduce {
  boolean changeSkip;

  /**
   * Constructor for the Lift object.
   *
   * @param changeSkip when set to <code>true</code>, comparison of two Cells takes a skip command
   *     into account
   */
  public Lift(boolean changeSkip) {
    this.changeSkip = changeSkip;
  }

  /**
   * Optimize (eliminate rows with no content) the given Trie and return the reduced Trie.
   *
   * @param orig the Trie to optimized
   * @return the reduced Trie
   */
  @Override
  public Trie optimize(Trie orig) {
    List<CharSequence> cmds = orig.cmds;
    List<Row> rows = new ArrayList<>();
    List<Row> orows = orig.rows;
    int remap[] = new int[orows.size()];

    for (int j = orows.size() - 1; j >= 0; j--) {
      liftUp(orows.get(j), orows);
    }

    Arrays.fill(remap, -1);
    rows = removeGaps(orig.root, orows, new ArrayList<Row>(), remap);

    return new Trie(orig.forward, remap[orig.root], cmds, rows);
  }

  /**
   * Reduce the trie using Lift-Up reduction.
   *
   * <p>The Lift-Up reduction propagates all leaf-values (patch commands), where possible, to higher
   * levels which are closer to the root of the trie.
   *
   * @param in the Row to consider when optimizing
   * @param nodes contains the patch commands
   */
  public void liftUp(Row in, List<Row> nodes) {
    Iterator<Cell> i = in.cells.values().iterator();
    for (; i.hasNext(); ) {
      Cell c = i.next();
      if (c.ref >= 0) {
        Row to = nodes.get(c.ref);
        int sum = to.uniformCmd(changeSkip);
        if (sum >= 0) {
          if (sum == c.cmd) {
            if (changeSkip) {
              if (c.skip != to.uniformSkip + 1) {
                continue;
              }
              c.skip = to.uniformSkip + 1;
            } else {
              c.skip = 0;
            }
            c.cnt += to.uniformCnt;
            c.ref = -1;
          } else if (c.cmd < 0) {
            c.cnt = to.uniformCnt;
            c.cmd = sum;
            c.ref = -1;
            if (changeSkip) {
              c.skip = to.uniformSkip + 1;
            } else {
              c.skip = 0;
            }
          }
        }
      }
    }
  }
}