Fifo.h

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// -*- lsst-c++ -*-

/* 
 * LSST Data Management System
 * Copyright 2008, 2009, 2010 LSST Corporation.
 * 
 * This product includes software developed by the
 * LSST Project (http://www.lsst.org/).
 *
 * 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 3 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 LSST License Statement and 
 * the GNU General Public License along with this program.  If not, 
 * see <http://www.lsstcorp.org/LegalNotices/>.
 */
 

#ifndef LSST_AP_FIFO_H
#define LSST_AP_FIFO_H

#include "boost/noncopyable.hpp"
#include "boost/static_assert.hpp"

#include "lsst/pex/exceptions.h"

#include "Common.h"


namespace lsst { namespace ap {

template <int NumEntries>
class Fifo : private boost::noncopyable {

    // NumEntries must be a positive power of 2
    BOOST_STATIC_ASSERT(NumEntries > 0 && (NumEntries & (NumEntries - 1)) == 0);

public :

    Fifo() { clear(); }

    void clear() {
        _size  = 0;
        _back  = 0;
        _front = 0;
    }

    bool empty() const {
        return _size == 0;
    }

    bool full() const {
        return _size == NumEntries;
    }

    void enqueue(boost::int64_t const elt) {
        int sz = _size;
        if (sz == NumEntries) {
            throw LSST_EXCEPT(lsst::pex::exceptions::LengthError,
                              "unable to insert element into full FIFO");
        }
        int i = _back;
        _buffer[i] = elt;
        _back = (i + 1) & (NumEntries - 1);
        _size = sz + 1;
    }

    boost::int64_t dequeue() {
        int sz = _size;
        if (sz == 0) {
            throw LSST_EXCEPT(lsst::pex::exceptions::LengthError,
                              "unable to remove element from empty FIFO");
        }
        int i = _front;
        boost::int64_t elt = _buffer[i];
        _front = (i + 1) & (NumEntries - 1);
        _size = sz - 1;
        return elt;
    }

private :

    boost::int64_t _buffer[NumEntries];
    int _size;
    int _back;
    int _front;
};


}} // end of namespace lsst::ap

#endif // LSST_AP_FIFO_H