circularqueue.h

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/**
 * Marlin 3D Printer Firmware
 * Copyright (c) 2019 MarlinFirmware [https://github.com/MarlinFirmware/Marlin]
 *
 * Based on Sprinter and grbl.
 * Copyright (c) 2011 Camiel Gubbels / Erik van der Zalm
 *
 * 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 GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 *
 */
#pragma once
 
#include <stdint.h>
 
/**
 * @brief   Circular Queue class
 * @details Implementation of the classic ring buffer data structure
 */
template<typename T, uint8_t N>
class CircularQueue {
  private:
 
    /**
     * @brief   Buffer structure
     * @details This structure consolidates all the overhead required to handle
     *          a circular queue such as the pointers and the buffer vector.
     */
    struct buffer_t {
      uint8_t head;
      uint8_t tail;
      uint8_t count;
      uint8_t size;
      T queue[N];
    } buffer;
 
  public:
    /**
     * @brief   Class constructor
     * @details This class requires two template parameters, T defines the type
     *          of item this queue will handle and N defines the maximum number of
     *          items that can be stored on the queue.
     */
    CircularQueue<T, N>() {
      buffer.size = N;
      buffer.count = buffer.head = buffer.tail = 0;
    }
 
    /**
     * @brief   Removes and returns a item from the queue
     * @details Removes the oldest item on the queue, pointed to by the
     *          buffer_t head field. The item is returned to the caller.
     * @return  type T item
     */
    T dequeue() {
      if (isEmpty()) return T();
 
      uint8_t index = buffer.head;
 
      --buffer.count;
      if (++buffer.head == buffer.size)
        buffer.head = 0;
 
      return buffer.queue[index];
    }
 
    /**
     * @brief   Adds an item to the queue
     * @details Adds an item to the queue on the location pointed by the buffer_t
     *          tail variable. Returns false if no queue space is available.
     * @param   item Item to be added to the queue
     * @return  true if the operation was successful
     */
    bool enqueue(T const &item) {
      if (isFull()) return false;
 
      buffer.queue[buffer.tail] = item;
 
      ++buffer.count;
      if (++buffer.tail == buffer.size)
        buffer.tail = 0;
 
      return true;
    }
 
    /**
     * @brief   Checks if the queue has no items
     * @details Returns true if there are no items on the queue, false otherwise.
     * @return  true if queue is empty
     */
    bool isEmpty() { return buffer.count == 0; }
 
    /**
     * @brief   Checks if the queue is full
     * @details Returns true if the queue is full, false otherwise.
     * @return  true if queue is full
     */
    bool isFull() { return buffer.count == buffer.size; }
 
    /**
     * @brief   Gets the queue size
     * @details Returns the maximum number of items a queue can have.
     * @return  the queue size
     */
    uint8_t size() { return buffer.size; }
 
    /**
     * @brief   Gets the next item from the queue without removing it
     * @details Returns the next item in the queue without removing it
     *          or updating the pointers.
     * @return  first item in the queue
     */
    T peek() { return buffer.queue[buffer.head]; }
 
    /**
     * @brief Gets the number of items on the queue
     * @details Returns the current number of items stored on the queue.
     * @return number of items in the queue
     */
    uint8_t count() { return buffer.count; }
};