src/Lucene.Net.Analysis.Common/Analysis/En/EnglishMinimalStemmer.cs

namespace Lucene.Net.Analysis.En
{
    /*
     * 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.
     */

    /// <summary>
    /// Minimal plural stemmer for English.
    /// <para>
    /// This stemmer implements the "S-Stemmer" from
    /// <c>How Effective Is Suffixing?</c>
    /// Donna Harman.
    /// </para>
    /// </summary>
    public class EnglishMinimalStemmer
    {
        public virtual int Stem(char[] s, int len)
        {
            if (len < 3 || s[len - 1] != 's')
            {
                return len;
            }

            switch (s[len - 2])
            {
                case 'u':
                case 's':
                    return len;
                case 'e':
                    if (len > 3 && s[len - 3] == 'i' && s[len - 4] != 'a' && s[len - 4] != 'e')
                    {
                        s[len - 3] = 'y';
                        return len - 2;
                    }
                    if (s[len - 3] == 'i' || s[len - 3] == 'a' || s[len - 3] == 'o' || s[len - 3] == 'e')
                    {
                        return len; // intentional fallthrough
                    }
                    break;
            }
            return len - 1;
        }
    }
}