dblqueue.cpp

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/*----------------------------------------------------------------------------*/
/*                                                                            */
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/* Copyright (c) 2005-2014 Rexx Language Association. All rights reserved.    */
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/*----------------------------------------------------------------------------*/
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include "dblqueue.hpp"
#include "regexp.hpp"
 
// constructor: initialize the double queue
doubleQueue::doubleQueue(int n) : memory(NULL), size(n), head(n/2), tail((n/2)+1)
{
  memory = (int*) malloc(sizeof(int)*size);
  put(SCAN);  // insert delimiter
}
 
// destructor: free memory
doubleQueue::~doubleQueue()
{
  if (memory) free(memory);
}
 
/**************************************************/
/* doubleQueue::push                              */
/*                                                */
/* push an element at the beginning of the queue. */
/**************************************************/
void doubleQueue::push(int value)
{
  memory[head] = value;
  if (head == 0) enlarge();
  head--;
}
 
/*******************************************/
/* doubleQueue::put                        */
/*                                         */
/* put an element at the end of the queue. */
/*******************************************/
void doubleQueue::put(int value)
{
  memory[tail] = value;
  tail++;
  if (tail == size) enlarge();
}
 
/****************************************************/
/* doubleQueue::pop                                 */
/*                                                  */
/* get the first element of the queue and remove it */
/* from the queue.                                  */
/****************************************************/
int doubleQueue::pop()
{
  int value = 0;
 
  if (head < tail) {
    head++;
    value = memory[head];
  }
 
  return value;
}
 
/*******************************************************/
/* doubleQueue::enlarge                                */
/*                                                     */
/* the queue is an array holding the elements. if the  */
/* head or tail pointer pass the limits of the array,  */
/* it needs to be enlarged. reallocation is used here. */
/*******************************************************/
void doubleQueue::enlarge()
{
  int *newmemory = (int*) malloc(sizeof(int)*2*size);
  int *oldmemory = memory;
  int offset = size>>2;
 
  if (newmemory) {
//    memset(newmemory,0x00,sizeof(int)*2*size);
    memcpy(newmemory+offset,memory,size*sizeof(int));
    head+=offset;
    tail+=offset;
    size<<=1;
    memory = newmemory;
    free(oldmemory);
  }
}