text: /**
   * \addtogroup stimer
   * @{
   */
  
  /**
   * \file
   * Timer of seconds library implementation.
   * \author
   * Adam Dunkels <adam@sics.se>, Nicolas Tsiftes <nvt@sics.se>
   */
  
  /*
   * Copyright (c) 2004, 2008, Swedish Institute of Computer Science.
   * 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.
   *
   * Author: Adam Dunkels <adam@sics.se>, Nicolas Tsiftes <nvt@sics.se>
   *
   */
  
  #include "time.h"
  #include "uIP/sys/stimer.h"
  
  #define SCLOCK_GEQ(a, b)	((time_t)((a) - (b)) < \
  				((time_t)(~((time_t)0)) >> 1))
  
  /*---------------------------------------------------------------------------*/
  /**
   * Set a timer.
   *
   * This function is used to set a timer for a time sometime in the
   * future. The function stimer_expired() will evaluate to true after
   * the timer has expired.
   *
   * \param t A pointer to the timer
   * \param interval The interval before the timer expires.
   *
   */
  void
  stimer_set( seconds_timer_ptr t, const time_t interval )
  {
    t->interval = interval;
    t->start = time(NULL);
  }
  /*---------------------------------------------------------------------------*/
  /**
   * Reset the timer with the same interval.
   *
   * This function resets the timer with the same interval that was
   * given to the stimer_set() function. The start point of the interval
   * is the exact time that the timer last expired. Therefore, this
   * function will cause the timer to be stable over time, unlike the
   * stimer_restart() function.
   *
   * \param t A pointer to the timer.
   *
   * \sa stimer_restart()
   */
  void
  stimer_reset( seconds_timer_ptr t )
  {
    t->start += t->interval;
  }
  /*---------------------------------------------------------------------------*/
  /**
   * Restart the timer from the current point in time
   *
   * This function restarts a timer with the same interval that was
   * given to the stimer_set() function. The timer will start at the
   * current time.
   *
   * \note A periodic timer will drift if this function is used to reset
   * it. For periodic timers, use the stimer_reset() function instead.
   *
   * \param t A pointer to the timer.
   *
   * \sa stimer_reset()
   */
  void
  stimer_restart( seconds_timer_ptr t )
  {
    t->start = time(NULL);
  }
  /*---------------------------------------------------------------------------*/
  /**
   * Check if a timer has expired.
   *
   * This function tests if a timer has expired and returns true or
   * false depending on its status.
   *
   * \param t A pointer to the timer
   *
   * \return Non-zero if the timer has expired, zero otherwise.
   *
   */
  int16_t
  stimer_expired( seconds_timer_ptr t )
  {
    return SCLOCK_GEQ(time(NULL), t->start + t->interval);
  }
  /*---------------------------------------------------------------------------*/
  /**
   * The time until the timer expires
   *
   * This function returns the time until the timer expires.
   *
   * \param t A pointer to the timer
   *
   * \return The time until the timer expires
   *
   */
  time_t
  stimer_remaining( seconds_timer_ptr t )
  {
    return t->start + t->interval - time(NULL);
  }
  /*---------------------------------------------------------------------------*/
  /**
   * The time elapsed since the timer started
   *
   * This function returns the time elapsed.
   *
   * \param t A pointer to the timer
   *
   * \return The time elapsed since the last start of the timer
   *
   */
  time_t
  stimer_elapsed( seconds_timer_ptr t )
  {
    return time(NULL) - t->start;
  }
  
  /*---------------------------------------------------------------------------*/
  
  /** @} */
  