lucene/analysis/common/src/java/org/apache/lucene/analysis/ru/RussianLightStemmer.java

/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.lucene.analysis.ru;

/*
 * This algorithm is updated based on code located at:
 * http://members.unine.ch/jacques.savoy/clef/
 *
 * Full copyright for that code follows:
 */

/*
 * Copyright (c) 2005, Jacques Savoy
 * 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 author 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 HOLDER 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.
 */

import static org.apache.lucene.analysis.util.StemmerUtil.*;

/**
 * Light Stemmer for Russian.
 *
 * <p>This stemmer implements the following algorithm: <i>Indexing and Searching Strategies for the
 * Russian Language.</i> Ljiljana Dolamic and Jacques Savoy.
 */
public class RussianLightStemmer {

  public int stem(char s[], int len) {
    len = removeCase(s, len);
    return normalize(s, len);
  }

  private int normalize(char s[], int len) {
    if (len > 3)
      switch (s[len - 1]) {
        case 'ь':
        case 'и':
          return len - 1;
        case 'н':
          if (s[len - 2] == 'н') return len - 1;
      }
    return len;
  }

  private int removeCase(char s[], int len) {
    if (len > 6 && (endsWith(s, len, "иями") || endsWith(s, len, "оями"))) return len - 4;

    if (len > 5
        && (endsWith(s, len, "иям")
            || endsWith(s, len, "иях")
            || endsWith(s, len, "оях")
            || endsWith(s, len, "ями")
            || endsWith(s, len, "оям")
            || endsWith(s, len, "оьв")
            || endsWith(s, len, "ами")
            || endsWith(s, len, "его")
            || endsWith(s, len, "ему")
            || endsWith(s, len, "ери")
            || endsWith(s, len, "ими")
            || endsWith(s, len, "ого")
            || endsWith(s, len, "ому")
            || endsWith(s, len, "ыми")
            || endsWith(s, len, "оев"))) return len - 3;

    if (len > 4
        && (endsWith(s, len, "ая")
            || endsWith(s, len, "яя")
            || endsWith(s, len, "ях")
            || endsWith(s, len, "юю")
            || endsWith(s, len, "ах")
            || endsWith(s, len, "ею")
            || endsWith(s, len, "их")
            || endsWith(s, len, "ия")
            || endsWith(s, len, "ию")
            || endsWith(s, len, "ьв")
            || endsWith(s, len, "ою")
            || endsWith(s, len, "ую")
            || endsWith(s, len, "ям")
            || endsWith(s, len, "ых")
            || endsWith(s, len, "ея")
            || endsWith(s, len, "ам")
            || endsWith(s, len, "ем")
            || endsWith(s, len, "ей")
            || endsWith(s, len, "ём")
            || endsWith(s, len, "ев")
            || endsWith(s, len, "ий")
            || endsWith(s, len, "им")
            || endsWith(s, len, "ое")
            || endsWith(s, len, "ой")
            || endsWith(s, len, "ом")
            || endsWith(s, len, "ов")
            || endsWith(s, len, "ые")
            || endsWith(s, len, "ый")
            || endsWith(s, len, "ым")
            || endsWith(s, len, "ми"))) return len - 2;

    if (len > 3)
      switch (s[len - 1]) {
        case 'а':
        case 'е':
        case 'и':
        case 'о':
        case 'у':
        case 'й':
        case 'ы':
        case 'я':
        case 'ь':
          return len - 1;
      }

    return len;
  }
}