queryparser/termgenerator_internal.cc

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/* Copyright (C) 2007 Olly Betts
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301 USA
 */

#include <config.h>

#include "termgenerator_internal.h"

#include <xapian/document.h>
#include <xapian/queryparser.h>
#include <xapian/unicode.h>

#include "stringutils.h"

#include <string>

using namespace std;

namespace Xapian {

// Put a limit on the size of terms to help prevent the index being bloated
// by useless junk terms.
static const unsigned int MAX_PROB_TERM_LENGTH = 64;
// FIXME: threshold is currently in bytes of UTF-8 representation, not unicode
// characters - what actually makes most sense here?

// FIXME: Add API to allow control of how stemming is used?

inline bool
U_isupper(unsigned ch) {
    return (ch < 128 && C_isupper((unsigned char)ch));
}

inline unsigned check_wordchar(unsigned ch) {
    if (Unicode::is_wordchar(ch)) return Unicode::tolower(ch);
    return 0;
}

inline bool
should_stem(const std::string & term)
{
    const unsigned int SHOULD_STEM_MASK =
        (1 << Unicode::LOWERCASE_LETTER) |
        (1 << Unicode::TITLECASE_LETTER) |
        (1 << Unicode::MODIFIER_LETTER) |
        (1 << Unicode::OTHER_LETTER);
    Utf8Iterator u(term);
    return ((SHOULD_STEM_MASK >> Unicode::get_category(*u)) & 1);
}

inline unsigned check_infix(unsigned ch) {
    if (ch == '\'' || ch == '&' || ch == 0xb7 || ch == 0x5f4 || ch == 0x2027) {
        // Unicode includes all these except '&' in it's word boundary rules,
        // as well as 0x2019 (which we handle below) and ':' (for Swedish
        // apparently, but we ignore this for now as it's problematic in
        // real world cases).
        return ch;
    }
    // 0x2019 is Unicode apostrophe and single closing quote.
    // 0x201b is Unicode single opening quote with the tail rising.
    if (ch == 0x2019 || ch == 0x201b) return '\'';
    return 0;
}

inline unsigned check_infix_digit(unsigned ch) {
    // This list of characters comes from Unicode's word identifying algorithm.
    switch (ch) {
        case ',':
        case '.':
        case ';':
        case 0x037e: // GREEK QUESTION MARK
        case 0x0589: // ARMENIAN FULL STOP
        case 0x060D: // ARABIC DATE SEPARATOR
        case 0x07F8: // NKO COMMA
        case 0x2044: // FRACTION SLASH
        case 0xFE10: // PRESENTATION FORM FOR VERTICAL COMMA
        case 0xFE13: // PRESENTATION FORM FOR VERTICAL COLON
        case 0xFE14: // PRESENTATION FORM FOR VERTICAL SEMICOLON
            return ch;
    }
    return 0;
}

inline bool
is_digit(unsigned ch) {
    return (Unicode::get_category(ch) == Unicode::DECIMAL_DIGIT_NUMBER);
}

inline unsigned check_suffix(unsigned ch) {
    if (ch == '+' || ch == '#') return ch;
    // FIXME: what about '-'?
    return 0;
}

// FIXME: add API for this:
#define STOPWORDS_NONE 0
#define STOPWORDS_IGNORE 1
#define STOPWORDS_INDEX_UNSTEMMED_ONLY 2

void
TermGenerator::Internal::index_text(Utf8Iterator itor, termcount weight,
                                    const string & prefix, bool with_positions)
{
    int stop_mode = STOPWORDS_INDEX_UNSTEMMED_ONLY;

    if (!stopper) stop_mode = STOPWORDS_NONE;

    while (true) {
        // Advance to the start of the next term.
        unsigned ch;
        while (true) {
            if (itor == Utf8Iterator()) return;
            ch = check_wordchar(*itor);
            if (ch) break;
            ++itor;
        }

        string term;
        // Look for initials separated by '.' (e.g. P.T.O., U.N.C.L.E).
        // Don't worry if there's a trailing '.' or not.
        if (U_isupper(*itor)) {
            const Utf8Iterator end;
            Utf8Iterator p = itor;
            do {
                Unicode::append_utf8(term, Unicode::tolower(*p++));
            } while (p != end && *p == '.' && ++p != end && U_isupper(*p));
            // One letter does not make an acronym!  If we handled a single
            // uppercase letter here, we wouldn't catch M&S below.
            if (term.size() > 1) {
                // Check there's not a (lower case) letter or digit
                // immediately after it.
                if (p == end || !Unicode::is_wordchar(*p)) {
                    itor = p;
                    goto endofterm;
                }
            }
            term.resize(0);
        }

        while (true) {
            unsigned prevch;
            do {
                Unicode::append_utf8(term, ch);
                prevch = ch;
                if (++itor == Utf8Iterator()) goto endofterm;
                ch = check_wordchar(*itor);
            } while (ch);

            Utf8Iterator next(itor);
            ++next;
            if (next == Utf8Iterator()) break;
            unsigned nextch = check_wordchar(*next);
            if (!nextch) break;
            unsigned infix_ch = *itor;
            if (is_digit(prevch) && is_digit(*next)) {
                infix_ch = check_infix_digit(infix_ch);
            } else {
                // Handle things like '&' in AT&T, apostrophes, etc.
                infix_ch = check_infix(infix_ch);
            }
            if (!infix_ch) break;
            Unicode::append_utf8(term, infix_ch);
            ch = nextch;
            itor = next;
        }

        {
            size_t len = term.size();
            unsigned count = 0;
            while ((ch = check_suffix(*itor))) {
                if (++count > 3) {
                    term.resize(len);
                    break;
                }
                Unicode::append_utf8(term, ch);
                if (++itor == Utf8Iterator()) goto endofterm;
            }
            // Don't index fish+chips as fish+ chips.
            if (Unicode::is_wordchar(*itor))
                term.resize(len);
        }

endofterm:
        if (term.size() > MAX_PROB_TERM_LENGTH) continue;

        if (stop_mode == STOPWORDS_IGNORE && (*stopper)(term)) continue;

        if (with_positions) {
            doc.add_posting(prefix + term, ++termpos, weight);
        } else {
            doc.add_term(prefix + term, weight);
        }
        if ((flags & FLAG_SPELLING) && prefix.empty()) db.add_spelling(term);

        if (!stemmer.internal.get()) continue;

        if (stop_mode == STOPWORDS_INDEX_UNSTEMMED_ONLY && (*stopper)(term))
            continue;

        // Note, this uses the lowercased term, but that's OK as we only
        // want to avoid stemming terms starting with a digit.
        if (!should_stem(term)) continue;

        // Add stemmed form without positional information.
        string stem("Z");
        stem += prefix;
        stem += stemmer(term);
        doc.add_term(stem, weight);
    }
}

}

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