/****************************************************************************
 * sched/clock/clock_timespec_subtract.c
 *
 *   Copyright (C) 2015 Gregory Nutt. All rights reserved.
 *   Author: Gregory Nutt <gnutt@nuttx.org>
 *
 * 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 NuttX 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 OWNER 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.
 *
 ****************************************************************************/

/****************************************************************************
 * Included Files
 ****************************************************************************/

#include <nuttx/config.h>

#include <stdint.h>
#include <time.h>

#include "clock/clock.h"

/****************************************************************************
 * Public Functions
 ****************************************************************************/

/****************************************************************************
 * Name:  clock_timespec_subtract
 *
 * Description:
 *   Subtract timespec ts2 from to1 and return the result in ts3.
 *   Zero is returned if the time difference is negative.
 *
 * Input Parameters:
 *   ts1 and ts2: The two timespecs to be subtracted (ts1 - ts2)
 *   ts3: The location to return the result (may be ts1 or ts2)
 *
 * Returned Value:
 *   None
 *
 ****************************************************************************/

void clock_timespec_subtract(FAR const struct timespec *ts1,
                             FAR const struct timespec *ts2,
                             FAR struct timespec *ts3)
{
  time_t sec;
  long nsec;

  if (ts1->tv_sec < ts2->tv_sec)
    {
      sec  = 0;
      nsec = 0;
    }
  else if (ts1->tv_sec == ts2->tv_sec && ts1->tv_nsec <= ts2->tv_nsec)
    {
      sec  = 0;
      nsec = 0;
    }
  else
    {
      sec = ts1->tv_sec - ts2->tv_sec;
      if (ts1->tv_nsec < ts2->tv_nsec)
        {
          nsec = (ts1->tv_nsec + NSEC_PER_SEC) - ts2->tv_nsec;
          sec--;
        }
      else
        {
          nsec = ts1->tv_nsec - ts2->tv_nsec;
        }
    }

  ts3->tv_sec = sec;
  ts3->tv_nsec = nsec;
}