backends/brass/brass_alltermslist.cc

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/* brass_alltermslist.cc: A termlist containing all terms in a brass database.
 *
 * Copyright (C) 2005,2007,2008,2009,2010 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 "brass_alltermslist.h"
#include "brass_postlist.h"

#include "debuglog.h"
#include "pack.h"
#include "stringutils.h"

void
BrassAllTermsList::read_termfreq_and_collfreq() const
{
    LOGCALL_VOID(DB, "BrassAllTermsList::read_termfreq_and_collfreq", NO_ARGS);
    Assert(!current_term.empty());
    Assert(!at_end());

    // Unpack the termfreq and collfreq from the tag.  Only do this if
    // one or other is actually read.
    cursor->read_tag();
    const char *p = cursor->current_tag.data();
    const char *pend = p + cursor->current_tag.size();
    BrassPostList::read_number_of_entries(&p, pend, &termfreq, &collfreq);
}

BrassAllTermsList::~BrassAllTermsList()
{
    LOGCALL_DTOR(DB, "BrassAllTermsList");
    delete cursor;
}

string
BrassAllTermsList::get_termname() const
{
    LOGCALL(DB, string, "BrassAllTermsList::get_termname", NO_ARGS);
    Assert(!current_term.empty());
    Assert(!at_end());
    RETURN(current_term);
}

Xapian::doccount
BrassAllTermsList::get_termfreq() const
{
    LOGCALL(DB, Xapian::doccount, "BrassAllTermsList::get_termfreq", NO_ARGS);
    Assert(!current_term.empty());
    Assert(!at_end());
    if (termfreq == 0) read_termfreq_and_collfreq();
    RETURN(termfreq);
}

Xapian::termcount
BrassAllTermsList::get_collection_freq() const
{
    LOGCALL(DB, Xapian::termcount, "BrassAllTermsList::get_collection_freq", NO_ARGS);
    Assert(!current_term.empty());
    Assert(!at_end());
    if (termfreq == 0) read_termfreq_and_collfreq();
    RETURN(collfreq);
}

TermList *
BrassAllTermsList::next()
{
    LOGCALL(DB, TermList *, "BrassAllTermsList::next", NO_ARGS);
    Assert(!at_end());
    // Set termfreq to 0 to indicate no termfreq/collfreq have been read for
    // the current term.
    termfreq = 0;

    if (rare(!cursor)) {
        cursor = database->postlist_table.cursor_get();
        Assert(cursor); // The postlist table isn't optional.

        if (prefix.empty()) {
            (void)cursor->find_entry_ge(string("\x00\xff", 2));
        } else {
            const string & key = pack_brass_postlist_key(prefix);
            if (cursor->find_entry_ge(key)) {
                // The exact term we asked for is there, so just copy it rather
                // than wasting effort unpacking it from the key.
                current_term = prefix;
                RETURN(NULL);
            }
        }
        goto first_time;
    }

    while (true) {
        cursor->next();
first_time:
        if (cursor->after_end()) {
            current_term.resize(0);
            RETURN(NULL);
        }

        const char *p = cursor->current_key.data();
        const char *pend = p + cursor->current_key.size();
        if (!unpack_string_preserving_sort(&p, pend, current_term)) {
            throw Xapian::DatabaseCorruptError("PostList table key has unexpected format");
        }

        // If this key is for the first chunk of a postlist, we're done.
        // Otherwise we need to skip past continuation chunks until we find the
        // first chunk of the next postlist.
        if (p == pend) break;
    }

    if (!startswith(current_term, prefix)) {
        // We've reached the end of the prefixed terms.
        cursor->to_end();
        current_term.resize(0);
    }

    RETURN(NULL);
}

TermList *
BrassAllTermsList::skip_to(const string &term)
{
    LOGCALL(DB, TermList *, "BrassAllTermsList::skip_to", term);
    Assert(!at_end());
    // Set termfreq to 0 to indicate no termfreq/collfreq have been read for
    // the current term.
    termfreq = 0;

    if (rare(!cursor)) {
        cursor = database->postlist_table.cursor_get();
        Assert(cursor); // The postlist table isn't optional.
    }

    string key = pack_brass_postlist_key(term);
    if (cursor->find_entry_ge(key)) {
        // The exact term we asked for is there, so just copy it rather than
        // wasting effort unpacking it from the key.
        current_term = term;
    } else {
        if (cursor->after_end()) {
            current_term.resize(0);
            RETURN(NULL);
        }

        const char *p = cursor->current_key.data();
        const char *pend = p + cursor->current_key.size();
        if (!unpack_string_preserving_sort(&p, pend, current_term)) {
            throw Xapian::DatabaseCorruptError("PostList table key has unexpected format");
        }
    }

    if (!startswith(current_term, prefix)) {
        // We've reached the end of the prefixed terms.
        cursor->to_end();
        current_term.resize(0);
    }

    RETURN(NULL);
}

bool
BrassAllTermsList::at_end() const
{
    LOGCALL(DB, bool, "BrassAllTermsList::at_end", NO_ARGS);
    RETURN(cursor && cursor->after_end());
}

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