[Vala] Port of the Porter stemmer to Vala (more detailed description)

[Serge Hulne <serge hulne gmail com>]

A more detailed description:

http://tartarus.org/martin/PorterStemmer/

http://tartarus.org/martin/PorterStemmer/def.txt


Serge Hulne.


PS: The code as plain text:

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using GLib;
using Posix;


class Stemmer {
    private char[] b;
    private int i;                /* offset into b */
    private int    i_end;          /* offset to end of stemmed word */
    private int    j;
    private int k;
    private static int INC = 50;
    /* unit of size whereby b is increased */


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

    /**
     * Add a character to the word being stemmed.  When you are finished
     * adding characters, you can call stem(void) to stem the word.
     */

    public void add(char ch) {
        if (i == b.length) {
            char[] new_b = new char[i+INC];
            for (int c = 0; c < i; c++)
                new_b[c] = b[c];
            b = new_b;
        }
        b[i++] = ch;
    }


    /** Adds wLen characters to the word being stemmed contained in a
portion
     * of a char[] array. This is like repeated calls of add(char ch), but
     * faster.
     */

    public void add2(char[] w, int wLen) {
        if (i+wLen >= b.length) {
            char[] new_b = new char[i+wLen+INC];
            for (int c = 0; c < i; c++)
                new_b[c] = b[c];
            b = new_b;
        }
        for (int c = 0; c < wLen; c++)
            b[i++] = w[c];
    }

    /**
     * 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.)
     */
    public string ToString() {
        var s = (string) b;
        //return new string(b,0,i_end);
        return s.slice(0,i_end);
    }

    /**
     * Returns the length of the word resulting from the stemming process.
     */
    public int getResultLength() {
        return i_end;
    }

    /**
     * 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.
     */
    public char[] getResultBuffer() {
        return b;
    }

    /* cons(i) is true <=> b[i] is a consonant. */
    private bool cons(int i) {
        switch (b[i]) {
        case 'a':
        case 'e':
        case 'i':
        case 'o':
        case 'u':
            return false;
        case 'y':
            return (i==0) ? true : !cons(i-1);
        default:
            return true;
        }
    }

    /* m() measures the number of consonant sequences between 0 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 = 0;
        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 <=> 0,...j contains a vowel */
    private bool vowelinstem() {
        int i;
        for (i = 0; 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 < 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 < 2 || !cons(i) || cons(i-1) || !cons(i-2))
            return false;
        int ch = b[i];
        if (ch == 'w' || ch == 'x' || ch == 'y')
            return false;
        return true;
    }

    private bool ends(string s) {
        int l = s.length;
        int o = k-l+1;
        if (o < 0)
            return false;
        char[] sc = (char[]) s.data;
        for (int i = 0; i < l; i++)
            if (b[o+i] != sc[i])
                return false;
        j = k-l;
        return true;
    }

    /* setto(s) sets (j+1),...k to the characters in the string s,
readjusting
       k. */
    private void setto(string s) {
        int l = s.length;
        int o = j+1;
        char[] sc = (char[]) s.data;
        for (int i = 0; i < l; i++)
            b[o+i] = sc[i];
        k = j+l;
    }

    /* r(s) is used further down. */
    private void r(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() {
        //print("->step1()\n");
        if (b[k] == 's') {
            if (ends("sses"))
                k -= 2;
            else if (ends("ies"))
                //setto("");
                setto("");
            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)) {
                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() {
        //print("->step2()\n");
        if (ends("y") && vowelinstem())
            b[k] = 'i';
    }

    /* 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() {
        //print("->step3()\n");
        if (k == 0)
            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;
        default :
            break;
        }
    }

    /* step4() deals with -ic-, -full, -ness etc. similar strategy to
step3. */
    private void step4() {
        //print("->step4()\n");
        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() {
        //print("->step5()\n");
        if (k == 0)
            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() {
        //print("->step6()\n");
        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--;
    }

    /** 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().
     */
    public void stem() {
        k = i - 1;
        if (k > 1) {
            step1();
            step2();
            step3();
            step4();
            step5();
            step6();
        }
        i_end = k+1;
        i = 0;
    }
}


/** Test program for demonstrating the Stemmer.  It reads text from a
 * a list of files, stems each word, and writes the result to standard
 * output. Note that the word stemmed is expected to be in lower case:
 * forcing lower case must be done outside the Stemmer class.
 * Usage: Stemmer file-name file-name ...
 */


/*
int main(string[] args) {
    //print("Hello\n");
    var s = new Stemmer();



    if (args.length>1){
        var w = args[1];
        //print("w = %s\n", w);
        s.add2((char[])w.data, w.length);
        s.stem();
        //print("%s\n", s.ToString());
    }

    return 0;
}
*/
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