Porter Stemmer

// https://svn.apache.org/repos/asf/lucene/lucene.net/tags/Lucene.Net_2_9_1/src/Lucene.Net/Analysis/PorterStemmer.cs
public class PorterStemmer
{
    private char[] b;
    private int i, j, k, k0;
    private bool dirty = false;
    private const int INC = 50; /* unit of size whereby b is increased */
    private const int EXTRA = 1;

    public PorterStemmer()
    {
        b = new char[INC];
        i = 0;
    }

    /// <summary> reset() resets the stemmer so it can stem another word.  If you invoke
    /// the stemmer by calling add(char) and then stem(), you must call reset()
    /// before starting another word.
    /// </summary>
    public virtual void Reset()
    {
        i = 0; dirty = false;
    }

    /// <summary> Add a character to the word being stemmed.  When you are finished
    /// adding characters, you can call stem(void) to process the word.
    /// </summary>
    public virtual void Add(char ch)
    {
        if (b.Length <= i + EXTRA)
        {
            char[] new_b = new char[b.Length + INC];
            Array.Copy(b, 0, new_b, 0, b.Length);
            b = new_b;
        }
        b[i++] = ch;
    }

    /// <summary> After a word has been stemmed, it can be retrieved by toString(),
    /// or a reference to the internal buffer can be retrieved by getResultBuffer
    /// and getResultLength (which is generally more efficient.)
    /// </summary>
    public override System.String ToString()
    {
        return new System.String(b, 0, i);
    }

    /// <summary> Returns the length of the word resulting from the stemming process.</summary>
    public virtual int GetResultLength()
    {
        return i;
    }

    /// <summary> Returns a reference to a character buffer containing the results of
    /// the stemming process.  You also need to consult getResultLength()
    /// to determine the length of the result.
    /// </summary>
    public virtual char[] GetResultBuffer()
    {
        return b;
    }

    private bool Cons(int i)
    {
        switch (b[i])
        {

            case 'a':
            case 'e':
            case 'i':
            case 'o':
            case 'u':
                return false;

            case 'y':
                return (i == k0) ? true : !Cons(i - 1);

            default:
                return true;

        }
    }

    /* m() measures the number of consonant sequences between k0 and j. if c is
    a consonant sequence and v a vowel sequence, and <..> indicates arbitrary
    presence,

    <c><v>       gives 0
    <c>vc<v>     gives 1
    <c>vcvc<v>   gives 2
    <c>vcvcvc<v> gives 3
    ....
    */

    private int M()
    {
        int n = 0;
        int i = k0;
        while (true)
        {
            if (i > j)
                return n;
            if (!Cons(i))
                break;
            i++;
        }
        i++;
        while (true)
        {
            while (true)
            {
                if (i > j)
                    return n;
                if (Cons(i))
                    break;
                i++;
            }
            i++;
            n++;
            while (true)
            {
                if (i > j)
                    return n;
                if (!Cons(i))
                    break;
                i++;
            }
            i++;
        }
    }

    /* vowelinstem() is true <=> k0,...j contains a vowel */

    private bool Vowelinstem()
    {
        int i;
        for (i = k0; i <= j; i++)
            if (!Cons(i))
                return true;
        return false;
    }

    /* doublec(j) is true <=> j,(j-1) contain a double consonant. */

    private bool Doublec(int j)
    {
        if (j < k0 + 1)
            return false;
        if (b[j] != b[j - 1])
            return false;
        return Cons(j);
    }

    /* cvc(i) is true <=> i-2,i-1,i has the form consonant - vowel - consonant
    and also if the second c is not w,x or y. this is used when trying to
    restore an e at the end of a short word. e.g.

    cav(e), lov(e), hop(e), crim(e), but
    snow, box, tray.

    */

    private bool Cvc(int i)
    {
        if (i < k0 + 2 || !Cons(i) || Cons(i - 1) || !Cons(i - 2))
            return false;
        else
        {
            int ch = b[i];
            if (ch == 'w' || ch == 'x' || ch == 'y')
                return false;
        }
        return true;
    }

    private bool Ends(System.String s)
    {
        int l = s.Length;
        int o = k - l + 1;
        if (o < k0)
            return false;
        for (int i = 0; i < l; i++)
            if (b[o + i] != s[i])
                return false;
        j = k - l;
        return true;
    }

    /* setto(s) sets (j+1),...k to the characters in the string s, readjusting
    k. */

    internal virtual void Setto(System.String s)
    {
        int l = s.Length;
        int o = j + 1;
        for (int i = 0; i < l; i++)
            b[o + i] = s[i];
        k = j + l;
        dirty = true;
    }

    /* r(s) is used further down. */

    internal virtual void R(System.String s)
    {
        if (M() > 0)
            Setto(s);
    }

    /* step1() gets rid of plurals and -ed or -ing. e.g.

    caresses  ->  caress
    ponies    ->  poni
    ties      ->  ti
    caress    ->  caress
    cats      ->  cat

    feed      ->  feed
    agreed    ->  agree
    disabled  ->  disable

    matting   ->  mat
    mating    ->  mate
    meeting   ->  meet
    milling   ->  mill
    messing   ->  mess

    meetings  ->  meet

    */

    private void Step1()
    {
        if (b[k] == 's')
        {
            if (Ends("sses"))
                k -= 2;
            else if (Ends("ies"))
                Setto("i");
            else if (b[k - 1] != 's')
                k--;
        }
        if (Ends("eed"))
        {
            if (M() > 0)
                k--;
        }
        else if ((Ends("ed") || Ends("ing")) && Vowelinstem())
        {
            k = j;
            if (Ends("at"))
                Setto("ate");
            else if (Ends("bl"))
                Setto("ble");
            else if (Ends("iz"))
                Setto("ize");
            else if (Doublec(k))
            {
                int ch = b[k--];
                if (ch == 'l' || ch == 's' || ch == 'z')
                    k++;
            }
            else if (M() == 1 && Cvc(k))
                Setto("e");
        }
    }

    /* step2() turns terminal y to i when there is another vowel in the stem. */

    private void Step2()
    {
        if (Ends("y") && Vowelinstem())
        {
            b[k] = 'i';
            dirty = true;
        }
    }

    /* step3() maps double suffices to single ones. so -ization ( = -ize plus
    -ation) maps to -ize etc. note that the string before the suffix must give
    m() > 0. */

    private void Step3()
    {
        if (k == k0)
            return; /* For Bug 1 */
        switch (b[k - 1])
        {

            case 'a':
                if (Ends("ational"))
                {
                    R("ate"); break;
                }
                if (Ends("tional"))
                {
                    R("tion"); break;
                }
                break;

            case 'c':
                if (Ends("enci"))
                {
                    R("ence"); break;
                }
                if (Ends("anci"))
                {
                    R("ance"); break;
                }
                break;

            case 'e':
                if (Ends("izer"))
                {
                    R("ize"); break;
                }
                break;

            case 'l':
                if (Ends("bli"))
                {
                    R("ble"); break;
                }
                if (Ends("alli"))
                {
                    R("al"); break;
                }
                if (Ends("entli"))
                {
                    R("ent"); break;
                }
                if (Ends("eli"))
                {
                    R("e"); break;
                }
                if (Ends("ousli"))
                {
                    R("ous"); break;
                }
                break;

            case 'o':
                if (Ends("ization"))
                {
                    R("ize"); break;
                }
                if (Ends("ation"))
                {
                    R("ate"); break;
                }
                if (Ends("ator"))
                {
                    R("ate"); break;
                }
                break;

            case 's':
                if (Ends("alism"))
                {
                    R("al"); break;
                }
                if (Ends("iveness"))
                {
                    R("ive"); break;
                }
                if (Ends("fulness"))
                {
                    R("ful"); break;
                }
                if (Ends("ousness"))
                {
                    R("ous"); break;
                }
                break;

            case 't':
                if (Ends("aliti"))
                {
                    R("al"); break;
                }
                if (Ends("iviti"))
                {
                    R("ive"); break;
                }
                if (Ends("biliti"))
                {
                    R("ble"); break;
                }
                break;

            case 'g':
                if (Ends("logi"))
                {
                    R("log"); break;
                }
                break;
        }
    }

    /* step4() deals with -ic-, -full, -ness etc. similar strategy to step3. */

    private void Step4()
    {
        switch (b[k])
        {

            case 'e':
                if (Ends("icate"))
                {
                    R("ic"); break;
                }
                if (Ends("ative"))
                {
                    R(""); break;
                }
                if (Ends("alize"))
                {
                    R("al"); break;
                }
                break;

            case 'i':
                if (Ends("iciti"))
                {
                    R("ic"); break;
                }
                break;

            case 'l':
                if (Ends("ical"))
                {
                    R("ic"); break;
                }
                if (Ends("ful"))
                {
                    R(""); break;
                }
                break;

            case 's':
                if (Ends("ness"))
                {
                    R(""); break;
                }
                break;
        }
    }

    /* step5() takes off -ant, -ence etc., in context <c>vcvc<v>. */

    private void Step5()
    {
        if (k == k0)
            return; /* for Bug 1 */
        switch (b[k - 1])
        {

            case 'a':
                if (Ends("al"))
                    break;
                return;

            case 'c':
                if (Ends("ance"))
                    break;
                if (Ends("ence"))
                    break;
                return;

            case 'e':
                if (Ends("er"))
                    break; return;

            case 'i':
                if (Ends("ic"))
                    break; return;

            case 'l':
                if (Ends("able"))
                    break;
                if (Ends("ible"))
                    break; return;

            case 'n':
                if (Ends("ant"))
                    break;
                if (Ends("ement"))
                    break;
                if (Ends("ment"))
                    break;
                /* element etc. not stripped before the m */
                if (Ends("ent"))
                    break;
                return;

            case 'o':
                if (Ends("ion") && j >= 0 && (b[j] == 's' || b[j] == 't'))
                    break;
                /* j >= 0 fixes Bug 2 */
                if (Ends("ou"))
                    break;
                return;
            /* takes care of -ous */

            case 's':
                if (Ends("ism"))
                    break;
                return;

            case 't':
                if (Ends("ate"))
                    break;
                if (Ends("iti"))
                    break;
                return;

            case 'u':
                if (Ends("ous"))
                    break;
                return;

            case 'v':
                if (Ends("ive"))
                    break;
                return;

            case 'z':
                if (Ends("ize"))
                    break;
                return;

            default:
                return;

        }
        if (M() > 1)
            k = j;
    }

    /* step6() removes a final -e if m() > 1. */

    private void Step6()
    {
        j = k;
        if (b[k] == 'e')
        {
            int a = M();
            if (a > 1 || a == 1 && !Cvc(k - 1))
                k--;
        }
        if (b[k] == 'l' && Doublec(k) && M() > 1)
            k--;
    }


    /// <summary> Stem a word provided as a String.  Returns the result as a String.</summary>
    public virtual System.String Stem(System.String s)
    {
        if (Stem(s.ToCharArray(), s.Length))
        {
            return ToString();
        }
        else
            return s;
    }

    /// <summary>Stem a word contained in a char[].  Returns true if the stemming process
    /// resulted in a word different from the input.  You can retrieve the
    /// result with getResultLength()/getResultBuffer() or toString().
    /// </summary>
    public virtual bool Stem(char[] word)
    {
        return Stem(word, word.Length);
    }

    /// <summary>Stem a word contained in a portion of a char[] array.  Returns
    /// true if the stemming process resulted in a word different from
    /// the input.  You can retrieve the result with
    /// getResultLength()/getResultBuffer() or toString().
    /// </summary>
    public virtual bool Stem(char[] wordBuffer, int offset, int wordLen)
    {
        Reset();
        if (b.Length < wordLen)
        {
            char[] new_b = new char[wordLen + EXTRA];
            b = new_b;
        }
        Array.Copy(wordBuffer, offset, b, 0, wordLen);
        i = wordLen;
        return Stem(0);
    }

    /// <summary>Stem a word contained in a leading portion of a char[] array.
    /// Returns true if the stemming process resulted in a word different
    /// from the input.  You can retrieve the result with
    /// getResultLength()/getResultBuffer() or toString().
    /// </summary>
    public virtual bool Stem(char[] word, int wordLen)
    {
        return Stem(word, 0, wordLen);
    }

    /// <summary>Stem the word placed into the Stemmer buffer through calls to add().
    /// Returns true if the stemming process resulted in a word different
    /// from the input.  You can retrieve the result with
    /// getResultLength()/getResultBuffer() or toString().
    /// </summary>
    public virtual bool Stem()
    {
        return Stem(0);
    }

    public virtual bool Stem(int i0)
    {
        k = i - 1;
        k0 = i0;
        if (k > k0 + 1)
        {
            Step1(); Step2(); Step3(); Step4(); Step5(); Step6();
        }
        // Also, a word is considered dirty if we lopped off letters
        // Thanks to Ifigenia Vairelles for pointing this out.
        if (i != k + 1)
            dirty = true;
        i = k + 1;
        return dirty;
    }

    /// <summary>Test program for demonstrating the Stemmer.  It reads a file and
    /// stems each word, writing the result to standard out.
    /// Usage: Stemmer file-name
    /// </summary>
    [STAThread]
    public static void Main(System.String[] args)
    {
        PorterStemmer s = new PorterStemmer();

        for (int i = 0; i < args.Length; i++)
        {
            try
            {
                System.IO.Stream in_Renamed = new System.IO.FileStream(args[i], System.IO.FileMode.Open, System.IO.FileAccess.Read);
                byte[] buffer = new byte[1024];
                int bufferLen, offset, ch;

                bufferLen = in_Renamed.Read(buffer, 0, buffer.Length);
                offset = 0;
                s.Reset();

                while (true)
                {
                    if (offset < bufferLen)
                        ch = buffer[offset++];
                    else
                    {
                        bufferLen = in_Renamed.Read(buffer, 0, buffer.Length);
                        offset = 0;
                        if (bufferLen < 0)
                            ch = -1;
                        else
                            ch = buffer[offset++];
                    }

                    if (System.Char.IsLetter((char)ch))
                    {
                        s.Add(System.Char.ToLower((char)ch));
                    }
                    else
                    {
                        s.Stem();
                        System.Console.Out.Write(s.ToString());
                        s.Reset();
                        if (ch < 0)
                            break;
                        else
                        {
                            System.Console.Out.Write((char)ch);
                        }
                    }
                }

                in_Renamed.Close();
            }
            catch (System.IO.IOException e)
            {
                System.Console.Out.WriteLine("error reading " + args[i]);
            }
        }
    }
}