text: /*
   * Copyright (c) 2015, SICS Swedish ICT.
   * All rights reserved.
   *
   * Redistribution and use in source and binary forms, with or without
   * modification, are permitted provided that the following conditions
   * are met:
   * 1. Redistributions of source code must retain the above copyright
   *    notice, this list of conditions and the following disclaimer.
   * 2. Redistributions in binary form must reproduce the above copyright
   *    notice, this list of conditions and the following disclaimer in the
   *    documentation and/or other materials provided with the distribution.
   * 3. Neither the name of the Institute nor the names of its contributors
   *    may be used to endorse or promote products derived from this software
   *    without specific prior written permission.
   *
   * THIS SOFTWARE IS PROVIDED BY THE INSTITUTE AND CONTRIBUTORS ``AS IS'' AND
   * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   * ARE DISCLAIMED.  IN NO EVENT SHALL THE INSTITUTE OR CONTRIBUTORS BE LIABLE
   * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   * SUCH DAMAGE.
   *
   * This file is part of the Contiki operating system.
   *
   */
  
  /**
   * \file
   *         ringbufindex library. Implements basic support for ring buffers
   *         of any type, as opposed to the os/lib/ringbuf module which
   *         is only for byte arrays. Simply returns index in the ringbuf
   *         rather than actual elements. The ringbuf size must be power of two.
   *         Like the original ringbuf, this module implements atomic put and get.
   * \author
   *         Simon Duquennoy <simonduq@sics.se>
   *         based on Contiki's os/lib/ringbuf library by Adam Dunkels
   */
  
  #include <string.h>
  #include "lib/ringbufindex.h"
  
  /* Initialize a ring buffer. The size must be a power of two */
  void
  ringbufindex_init(struct ringbufindex *r, uint8_t size)
  {
    r->mask = size - 1;
    r->put_ptr = 0;
    r->get_ptr = 0;
  }
  /* Put one element to the ring buffer */
  int
  ringbufindex_put(struct ringbufindex *r)
  {
    /* Check if buffer is full. If it is full, return 0 to indicate that
       the element was not inserted.
  
       XXX: there is a potential risk for a race condition here, because
       the ->get_ptr field may be written concurrently by the
       ringbufindex_get() function. To avoid this, access to ->get_ptr must
       be atomic. We use an uint8_t type, which makes access atomic on
       most platforms, but C does not guarantee this.
     */
    if(((r->put_ptr - r->get_ptr) & r->mask) == r->mask) {
      return 0;
    }
    r->put_ptr = (r->put_ptr + 1) & r->mask;
    return 1;
  }
  /* Check if there is space to put an element.
   * Return the index where the next element is to be added */
  int
  ringbufindex_peek_put(const struct ringbufindex *r)
  {
    /* Check if there are bytes in the buffer. If so, we return the
       first one. If there are no bytes left, we return -1.
     */
    if(((r->put_ptr - r->get_ptr) & r->mask) == r->mask) {
      return -1;
    }
    return r->put_ptr;
  }
  /* Remove the first element and return its index */
  int
  ringbufindex_get(struct ringbufindex *r)
  {
    int get_ptr;
  
    /* Check if there are bytes in the buffer. If so, we return the
       first one and increase the pointer. If there are no bytes left, we
       return -1.
  
       XXX: there is a potential risk for a race condition here, because
       the ->put_ptr field may be written concurrently by the
       ringbufindex_put() function. To avoid this, access to ->get_ptr must
       be atomic. We use an uint8_t type, which makes access atomic on
       most platforms, but C does not guarantee this.
     */
    if(((r->put_ptr - r->get_ptr) & r->mask) > 0) {
      get_ptr = r->get_ptr;
      r->get_ptr = (r->get_ptr + 1) & r->mask;
      return get_ptr;
    } else {
      return -1;
    }
  }
  /* Return the index of the first element
   * (which will be removed if calling ringbufindex_peek) */
  int
  ringbufindex_peek_get(const struct ringbufindex *r)
  {
    /* Check if there are bytes in the buffer. If so, we return the
       first one. If there are no bytes left, we return -1.
     */
    if(((r->put_ptr - r->get_ptr) & r->mask) > 0) {
      return r->get_ptr;
    } else {
      return -1;
    }
  }
  /* Return the ring buffer size */
  int
  ringbufindex_size(const struct ringbufindex *r)
  {
    return r->mask + 1;
  }
  /* Return the number of elements currently in the ring buffer */
  int
  ringbufindex_elements(const struct ringbufindex *r)
  {
    return (r->put_ptr - r->get_ptr) & r->mask;
  }
  /* Is the ring buffer full? */
  int
  ringbufindex_full(const struct ringbufindex *r)
  {
    return ((r->put_ptr - r->get_ptr) & r->mask) == r->mask;
  }
  /* Is the ring buffer empty? */
  int
  ringbufindex_empty(const struct ringbufindex *r)
  {
    return ringbufindex_elements(r) == 0;
  }
  