nuttx/libc/time/lib_difftime.c

/****************************************************************************
 * libc/time/lib_difftime.c
 *
 *   Copyright (C) 2016-2017 Gregory Nutt. All rights reserved.
 *   Author: Sebastien Lorquet <sebastien@lorquet.fr>
 *
 * 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,
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 * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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 *
 ****************************************************************************/

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

#include <nuttx/config.h>
#include <nuttx/compiler.h>

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

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

/****************************************************************************
 * Name:  difftime
 *
 * Description:
 *   The difftime() function returns the number of seconds elapsed
 *   between time time1 and time time0, represented as a double or a float.
 *   Float is used if the platform does not support double. However, when
 *   using a float, some precision may be lost for big differences.
 *
 ****************************************************************************/

#ifdef CONFIG_HAVE_DOUBLE
double difftime(time_t time1, time_t time0)
{
  return (double)time1 - (double)time0;
}
#else
float difftime(time_t time1, time_t time0)
{
  if (time1 >= time2)
    {
      /* Result will be positive (even though bit 31 may be set on very large
       * differences!)
       */

      return (float)((uint32_t)(time1 - time0));
    }
  else
    {
      /* Result will be negative.  REVISIT: Am I missing any case where bit 31
       * might not be set?
       */

      return (float)((int32_t)(time1 - time0));
    }
}
#endif