terminfo.h

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/* Copyright 2017,2018,2019 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, see
 * <https://www.gnu.org/licenses/>.
 */
 
#ifndef XAPIAN_INCLUDED_TERMINFO_H
#define XAPIAN_INCLUDED_TERMINFO_H
 
#include "api/smallvector.h"
#include <xapian/types.h>
 
class TermInfo {
    Xapian::termcount wdf;
 
    mutable unsigned split = 0;
 
    mutable Xapian::VecCOW<Xapian::termpos> positions;
 
    void merge() const;
 
  public:
    explicit TermInfo(Xapian::termcount wdf_) : wdf(wdf_) {}
 
    TermInfo(Xapian::termcount wdf_, Xapian::termpos termpos) : wdf(wdf_) {
        positions.push_back(termpos);
    }
 
    const Xapian::VecCOW<Xapian::termpos>* get_positions() const {
        if (split) merge();
        return &positions;
    }
 
    bool has_positions() const { return !positions.empty(); }
 
    size_t count_positions() const { return positions.size(); }
 
    Xapian::termcount get_wdf() const { return wdf; }
 
    bool increase_wdf(Xapian::termcount delta) {
        if (rare(is_deleted())) {
            split = 0;
            wdf = delta;
            return true;
        }
        wdf += delta;
        return false;
    }
 
    bool decrease_wdf(Xapian::termcount delta) {
        // Saturating arithmetic - don't let the wdf go below zero.
        if (wdf >= delta) {
            wdf -= delta;
        } else {
            wdf = 0;
        }
        if (wdf == 0 && positions.empty()) {
            // Flag term as deleted if no wdf or positions.
            split = 1;
            return true;
        }
        return false;
    }
 
    bool remove() {
        if (is_deleted())
            return false;
        positions.clear();
        split = 1;
        return true;
    }
 
    bool add_position(Xapian::termcount wdf_inc, Xapian::termpos termpos);
 
    void append_position(Xapian::termpos termpos) {
        positions.push_back(termpos);
    }
 
    bool remove_position(Xapian::termpos termpos);
 
    Xapian::termpos remove_positions(Xapian::termpos termpos_first,
                                     Xapian::termpos termpos_last);
 
    bool is_deleted() const { return positions.empty() && split > 0; }
};
 
#endif // XAPIAN_INCLUDED_TERMINFO_H