File: index_segment.h

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/*
**      SWISH++
**      index_segment.h
**
**      Copyright (C) 1998  Paul J. Lucas
**
**      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., 675 Mass Ave, Cambridge, MA 02139, USA.
*/

#ifndef index_segment_H
#define index_segment_H

// standard
#include <cstddef>                              /* for ptrdiff_t */
#include <iterator>
#include <sys/types.h>                          /* for off_t */

// local
#include "mmap_file.h"

//*****************************************************************************
//
// SYNOPSIS
//
        class index_segment
//
// DESCRIPTION
//
//      An instance of this class is used to access either the word, stop-word,
//      file, or meta-name index portions of a generated index.
//
//      By implementing fully-blown random access iterators for it, the STL
//      algorithms work, in particular binary_search() and equal_range() that
//      are used to do look ups.
//
//*****************************************************************************
{
public:
    ////////// typedefs ///////////////////////////////////////////////////////

    typedef unsigned long size_type;
    typedef ptrdiff_t difference_type;

    typedef char const* value_type;
    typedef char const** const_pointer;
    typedef char const* const_reference;

    enum segment_id {
        isi_word        = 0,
        isi_stop_word   = 1,
        isi_dir         = 2,
        isi_file        = 3,
        isi_meta_name   = 4
    };

    ////////// constructors ///////////////////////////////////////////////////

    index_segment() { }
    index_segment( PJL::mmap_file const &file, segment_id id ) {
        set_index_file( file, id );
    }

    ////////// member functions ///////////////////////////////////////////////

    void        set_index_file( PJL::mmap_file const&, segment_id );
    size_type   size() const                    { return num_entries_; }

    const_reference operator[]( size_type i ) const {
        return begin_ + offset_[ i ];
    }

    ////////// iterators //////////////////////////////////////////////////////

    class const_iterator;
    friend class const_iterator;

    class const_iterator :
        public std::iterator< std::random_access_iterator_tag, value_type > {
    private:
        index_segment const *index_;
        size_type i_;
        const_iterator( index_segment const *index, size_type i ) :
            index_( index ), i_( i ) { }
        friend class index_segment;
    public:
        const_iterator() { }

        const_reference operator*() const { return (*index_)[ i_ ]; }

        const_iterator& operator++() {
            return ++i_, *this;
        }
        const_iterator& operator--() {
            return --i_, *this;
        }
        const_iterator operator++(int) {
            return const_iterator( index_, i_++ );
        }
        const_iterator operator--(int) {
            return const_iterator( index_, i_-- );
        }
        const_iterator& operator+=( int n ) {
            return i_ += n, *this;
        }
        const_iterator& operator-=( int n ) {
            return i_ -= n, *this;
        }

        friend bool
        operator==( const_iterator const &i, const_iterator const &j ) {
            return i.i_ == j.i_;
        }
        friend bool
        operator!=( const_iterator const &i, const_iterator const &j ) {
            return !( i == j );
        }

        friend const_iterator
        operator+( const_iterator const &i, int n ) {
            return const_iterator( i.index_, i.i_ + n );
        }
        friend const_iterator
        operator-( const_iterator const &i, int n ) {
            return const_iterator( i.index_, i.i_ - n );
        }

        friend difference_type
        operator-( const_iterator const &i, const_iterator const &j ) {
            return i.i_ - j.i_;
        }

        // default copy constructor is OK
        // default assignment operator is OK
    };

    const_iterator begin() const {
        return const_iterator( this, 0 );
    }
    const_iterator end() const {
        return const_iterator( this, num_entries_ );
    }
private:
    PJL::mmap_file::const_iterator  begin_;
    size_type                       num_entries_;
    off_t const                     *offset_;
};

#endif  /* index_segment_H */
/* vim:set et sw=4 ts=4: */