queue.h

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/****************************************************************************
 *
 *  MODULE:     iostream
 *
 
 *  COPYRIGHT (C) 2007 Laura Toma
 *
 *
 
 *  Iostream is a library that implements streams, external memory
 *  sorting on streams, and an external memory priority queue on
 *  streams. These are the fundamental components used in external
 *  memory algorithms.
 
 * Credits: The library was developed by Laura Toma.  The kernel of
 * class STREAM is based on the similar class existent in the GPL TPIE
 * project developed at Duke University. The sorting and priority
 * queue have been developed by Laura Toma based on communications
 * with Rajiv Wickremesinghe. The library was developed as part of
 * porting Terraflow to GRASS in 2001.  PEARL upgrades in 2003 by
 * Rajiv Wickremesinghe as part of the Terracost project.
 
 *
 *  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.  *
 *  **************************************************************************/
 
#ifndef QUEUE_H
#define QUEUE_H
 
#include <assert.h>
#include <iostream>
 
template <class T>
class queue {
private:
    T *data;
    int size;
    int head; // first valid location (if data)
    int tail; // next free location
    int len;
    void grow();
 
public:
    queue(int size = 4096);
    ~queue();
    bool enqueue(T &);
    bool dequeue(T *);
    bool peek(int offset, T *);
    bool isEmpty() const { return len == 0; };
    // int length() const { return len; };
    unsigned int length() const { return (unsigned int)len; };
};
 
template <class T>
queue<T>::queue(int vsize) : size(vsize)
{
 
    if (size <= 0)
        size = 64; /* default */
 
    data = new T[size];
    head = 0;
    tail = 0;
    len = 0;
}
 
template <class T>
queue<T>::~queue()
{
    delete[] data;
}
 
template <class T>
bool queue<T>::enqueue(T &elt)
{
    if (len == size)
        grow();
    assert(len < size);
    data[tail] = elt;
    tail = (tail + 1) % size;
    len++;
    return true;
}
 
template <class T>
bool queue<T>::dequeue(T *elt)
{
    if (len > 0) {
        *elt = data[head];
        head = (head + 1) % size;
        len--;
        return true;
    }
    return false;
}
 
template <class T>
bool queue<T>::peek(int offset, T *elt)
{
    if (len > offset) {
        int pos = (head + offset) % size;
        *elt = data[pos];
        return true;
    }
    return false;
}
 
template <class T>
void queue<T>::grow()
{
    T *data2 = new T[size * 2];
    int k = head;
    for (int i = 0; i < len; i++) {
        data2[i] = data[k];
        k = (k + 1) % size;
    }
    head = 0;
    tail = len;
    delete[] data;
    data = data2;
    size *= 2;
}
 
#endif // QUEUE_H