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/** @file
* @brief Metadata for a term in a document
*/
/* 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>
/// Metadata for a term in a document
class TermInfo {
Xapian::termcount wdf;
/** Split point in the position range.
*
* To allow more efficient insertion of positions, we support the
* positions being split into two sorted ranges, and if this is the
* case, split will be > 0 and there will be two sorted ranges [0, split)
* and [split, positions.size()).
*
* If split is 0, then [0, positions.size()) form a single sorted range.
*
* If positions.empty(), then split > 0 indicates that the term has been
* deleted (this allows us to delete terms without invalidating existing
* TermIterator objects).
*
* Use type unsigned here to avoid bloating this structure. More than
* 4 billion positions in one document is not sensible (and not possible
* unless termpos is configured to be 64 bit).
*/
mutable unsigned split = 0;
/** Positions at which the term occurs.
*
* The entries are sorted in strictly increasing order (so duplicate
* entries are not allowed).
*/
mutable Xapian::VecCOW<Xapian::termpos> positions;
/** Merge sorted ranges before and after @a split. */
void merge() const;
public:
/** Constructor.
*
* @param wdf_ Within-document frequency
*/
explicit TermInfo(Xapian::termcount wdf_) : wdf(wdf_) {}
/** Constructor which also adds an initial position.
*
* @param wdf_ Within-document frequency
* @param termpos Position to add
*/
TermInfo(Xapian::termcount wdf_, Xapian::termpos termpos) : wdf(wdf_) {
positions.push_back(termpos);
}
/// Get a pointer to the positions.
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(); }
/// Get the within-document frequency.
Xapian::termcount get_wdf() const { return wdf; }
/** Increase within-document frequency.
*
* @return true if the term was flagged as deleted before the operation.
*/
bool increase_wdf(Xapian::termcount delta) {
if (rare(is_deleted())) {
split = 0;
wdf = delta;
return true;
}
wdf += delta;
return false;
}
/** Decrease within-document frequency.
*
* @return true If the adjusted wdf is zero and there are no positions.
*/
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;
}
/** Add a position.
*
* If @a termpos is already present, this is a no-op.
*
* @param wdf_inc wdf increment
* @param termpos Position to add
*
* @return true if the term was flagged as deleted before the operation.
*/
bool add_position(Xapian::termcount wdf_inc, Xapian::termpos termpos);
/** Append a position.
*
* The position must be >= the largest currently in the list.
*/
void append_position(Xapian::termpos termpos) {
positions.push_back(termpos);
}
/** Remove a position.
*
* @param termpos Position to remove
*
* @return If @a termpos wasn't present, returns false.
*/
bool remove_position(Xapian::termpos termpos);
/** Remove a range of positions.
*
* @param termpos_first First position to remove
* @param termpos_last Last position to remove
*
* It's OK if there are no positions in the specified range.
*
* @return the number of positions removed.
*/
Xapian::termpos remove_positions(Xapian::termpos termpos_first,
Xapian::termpos termpos_last);
/** Has this term been deleted from this document?
*
* We flag entries as deleted instead of actually deleting them to avoid
* invalidating existing TermIterator objects.
*/
bool is_deleted() const { return positions.empty() && split > 0; }
};
#endif // XAPIAN_INCLUDED_TERMINFO_H
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