Odometer.h

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// -*- mode: c++; c-basic-offset:4 -*-

// This file is part of libdap, A C++ implementation of the OPeNDAP Data
// Access Protocol.

// Copyright (c) 2015 OPeNDAP, Inc.
// Author: James Gallagher <jgallagher@opendap.org>
//
// This library is free software; you can redistribute it and/or
// modify it under the terms of the GNU Lesser General Public
// License as published by the Free Software Foundation; either
// version 2.1 of the License, or (at your option) any later version.
//
// This library 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
// Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public
// License along with this library; if not, write to the Free Software
// Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
//
// You can contact OPeNDAP, Inc. at PO Box 112, Saunderstown, RI. 02874-0112.

#ifndef ODOMETER_H_
#define ODOMETER_H_

#include <vector>

namespace libdap {

class Odometer
{
public:
    typedef std::vector<unsigned int> shape;

private:
    // The state set by the ctor
    shape d_shape;
    unsigned int d_highest_offset;
    unsigned int d_rank;

    // The varying state of the Odometer
    shape d_indices;
    unsigned int d_offset;

public:
    Odometer(shape shape) :
            d_shape(shape), d_offset(0)
    {
        d_rank = d_shape.size();

        d_highest_offset = 1;
        for (unsigned int i = 0; i < d_rank; ++i) {
            d_highest_offset *= d_shape.at(i);
        }

        d_indices.resize(d_rank, 0);
    }

    /*
     *  reset(): zero internal state
     *  next(): move to the next element, incrementing the shape information and returning an offset into a linear vector for that element.
     *                  Calling next() when the object is at the last element should return one past the last element. calling next() after that should throw an exception.
     *  vector<int> indices(): for the given state of the odometer, return the indices that match the offset.
     *  offset(): return the offset
     *  end(): should return one past the last valid offset - the value returned by next() when it indicates all elements/indices have been visited.
     *
     */

    void reset()
    {
        for (unsigned int i = 0; i < d_rank; ++i)
            d_indices.at(i) = 0;
        d_offset = 0;
    }

    inline unsigned int next()
    {
        // if (d_offset == d_highest_offset) throw Error("Attempt to move beyond the end of an array in the indexing software.");

        // About 2.4 seconds for 10^9 elements
        shape::reverse_iterator si = d_shape.rbegin();
        for (shape::reverse_iterator i = d_indices.rbegin(), e = d_indices.rend(); i != e; ++i, ++si) {
            if (++(*i) == *si) {
                *i = 0;
            }
            else {
                break;
            }
        }

        return ++d_offset;
    }

    // This version throws Error if offset() == end()
    unsigned int next_safe();

    inline void indices(shape &indices)
    {
        indices = d_indices;
    }

    inline unsigned int offset()
    {
        return d_offset;
    }

    inline unsigned int end()
    {
        return d_highest_offset;
    }

};

}       // namespace libdap

#endif /* ODOMETER_H_ */