text: /*
   * Copyright (c) 2017, George Oikonomou - http://www.spd.gr
   * Copyright (c) 2017, James Pope
   * 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 copyright holder 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 COPYRIGHT HOLDERS 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
   * COPYRIGHT HOLDER 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.
   */
  /*---------------------------------------------------------------------------*/
  /**
   * \addtogroup doubly-linked-circular-list
   * @{
   *
   * \file
   *   Implementation of circular, doubly-linked lists
   */
  /*---------------------------------------------------------------------------*/
  #include "contiki.h"
  #include "lib/dbl-circ-list.h"
  
  #include <stdint.h>
  #include <stdbool.h>
  #include <string.h>
  /*---------------------------------------------------------------------------*/
  struct dblcl {
    struct dblcl *next;
    struct dblcl *previous;
  };
  /*---------------------------------------------------------------------------*/
  void
  dbl_circ_list_init(dbl_circ_list_t dblcl)
  {
    *dblcl = NULL;
  }
  /*---------------------------------------------------------------------------*/
  void *
  dbl_circ_list_head(dbl_circ_list_t dblcl)
  {
    return *dblcl;
  }
  /*---------------------------------------------------------------------------*/
  void *
  dbl_circ_list_tail(dbl_circ_list_t dblcl)
  {
    struct dblcl *this;
  
    if(*dblcl == NULL) {
      return NULL;
    }
  
    for(this = *dblcl; this->next != *dblcl; this = this->next);
  
    return this;
  }
  /*---------------------------------------------------------------------------*/
  void
  dbl_circ_list_remove(dbl_circ_list_t dblcl, void *element)
  {
    struct dblcl *this;
  
    if(*dblcl == NULL || element == NULL) {
      return;
    }
  
    this = *dblcl;
  
    do {
      if(this == element) {
        this->previous->next = this->next;
        this->next->previous = this->previous;
  
        /* We need to update the head of the list if we removed the head */
        if(*dblcl == element) {
          *dblcl = this->next == this ? NULL : this->next;
        }
  
        this->next = NULL;
        this->previous = NULL;
  
        return;
      }
  
      this = this->next;
    } while(this != *dblcl);
  }
  /*---------------------------------------------------------------------------*/
  void
  dbl_circ_list_add_head(dbl_circ_list_t dblcl, void *element)
  {
    struct dblcl *head;
  
    if(element == NULL) {
      return;
    }
  
    /* Don't add twice */
    dbl_circ_list_remove(dblcl, element);
  
    head = dbl_circ_list_head(dblcl);
  
    if(head == NULL) {
      /* If the list was empty */
      ((struct dblcl *)element)->next = element;
      ((struct dblcl *)element)->previous = element;
    } else {
      /* If the list was not empty */
      ((struct dblcl *)element)->next = head;
      ((struct dblcl *)element)->previous = head->previous;
      head->previous->next = element;
      head->previous = element;
    }
  
    *dblcl = element;
  }
  /*---------------------------------------------------------------------------*/
  void
  dbl_circ_list_add_tail(dbl_circ_list_t dblcl, void *element)
  {
    struct dblcl *tail;
  
    if(element == NULL) {
      return;
    }
  
    /* Don't add twice */
    dbl_circ_list_remove(dblcl, element);
  
    tail = dbl_circ_list_tail(dblcl);
  
    if(tail == NULL) {
      /* If the list was empty */
      ((struct dblcl *)element)->next = element;
      ((struct dblcl *)element)->previous = element;
      *dblcl = element;
    } else {
      /* If the list was not empty */
      ((struct dblcl *)element)->next = *dblcl;
      ((struct dblcl *)element)->previous = tail;
      tail->next->previous = element;
      tail->next = element;
    }
  }
  /*---------------------------------------------------------------------------*/
  void
  dbl_circ_list_add_after(dbl_circ_list_t dblcl, void *existing, void *element)
  {
    if(element == NULL || existing == NULL) {
      return;
    }
  
    /* Don't add twice */
    dbl_circ_list_remove(dblcl, element);
  
    ((struct dblcl *)element)->next = ((struct dblcl *)existing)->next;
    ((struct dblcl *)element)->previous = existing;
    ((struct dblcl *)existing)->next->previous = element;
    ((struct dblcl *)existing)->next = element;
  }
  /*---------------------------------------------------------------------------*/
  void
  dbl_circ_list_add_before(dbl_circ_list_t dblcl, void *existing, void *element)
  {
    if(element == NULL || existing == NULL) {
      return;
    }
  
    /* Don't add twice */
    dbl_circ_list_remove(dblcl, element);
  
    ((struct dblcl *)element)->next = existing;
    ((struct dblcl *)element)->previous = ((struct dblcl *)existing)->previous;
    ((struct dblcl *)existing)->previous->next = element;
    ((struct dblcl *)existing)->previous = element;
  
    /* If we added before the list's head, we must update the head */
    if(*dblcl == existing) {
      *dblcl = element;
    }
  }
  /*---------------------------------------------------------------------------*/
  unsigned long
  dbl_circ_list_length(dbl_circ_list_t dblcl)
  {
    unsigned long len = 1;
    struct dblcl *this;
  
    if(*dblcl == NULL) {
      return 0;
    }
  
    for(this = *dblcl; this->next != *dblcl; this = this->next) {
      len++;
    }
  
    return len;
  }
  /*---------------------------------------------------------------------------*/
  bool
  dbl_circ_list_is_empty(dbl_circ_list_t dblcl)
  {
    return *dblcl == NULL ? true : false;
  }
  /*---------------------------------------------------------------------------*/
  /** @} */
  