/* Subtract two struct timespec values.

   Copyright (C) 2011-2017 Free Software Foundation, Inc.

   This program is free software: you can redistribute it and/or modify

   it under the terms of the GNU General Public License as published by

   the Free Software Foundation; either version 3 of the License, or

   (at your option) any later version.

   This program is distributed in the hope that it will be useful,

   but WITHOUT ANY WARRANTY; without even the implied warranty of

   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License

   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */

/* Written by Paul Eggert.  */

/* Return the difference between two timespec values A and B.  On

   overflow, return an extremal value.  This assumes 0 <= tv_nsec <

   TIMESPEC_RESOLUTION.  */

#include <config.h>

#include "timespec.h"

#include "intprops.h"

struct timespec

timespec_sub (struct timespec a, struct timespec b)

{

  time_t rs = a.tv_sec;

  time_t bs = b.tv_sec;

  int ns = a.tv_nsec - b.tv_nsec;

  int rns = ns;

  time_t tmin = TYPE_MINIMUM (time_t);

  time_t tmax = TYPE_MAXIMUM (time_t);

  if (ns < 0)

    {

      rns = ns + TIMESPEC_RESOLUTION;

      if (bs < tmax)

        bs++;

      else if (- TYPE_SIGNED (time_t) < rs)

        rs--;

      else

        goto low_overflow;

    }

  /* INT_SUBTRACT_WRAPV is not appropriate since time_t might be unsigned.

     In theory time_t might be narrower than int, so plain

     INT_SUBTRACT_OVERFLOW does not suffice.  */

  if (! INT_SUBTRACT_OVERFLOW (rs, bs) && tmin <= rs - bs && rs - bs <= tmax)

    rs -= bs;

  else

    {

      if (rs < 0)

        {

        low_overflow:

          rs = tmin;

          rns = 0;

        }

      else

        {

          rs = tmax;

          rns = TIMESPEC_RESOLUTION - 1;

        }

    }

  return make_timespec (rs, rns);

}