1  /* struct timeval subtraction.
       2     Copyright (C) 1991-2023 Free Software Foundation, Inc.
       3  
       4     This program is free software; you can redistribute it and/or
       5     modify it under the terms of the GNU General Public License
       6     as published by the Free Software Foundation; either version 2
       7     of the License, or (at your option) any later version.
       8  
       9     This program is distributed in the hope that it will be useful,
      10     but WITHOUT ANY WARRANTY; without even the implied warranty of
      11     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
      12     GNU General Public License for more details.
      13  
      14     You should have received a copy of the GNU General Public License
      15     along with this program; if not, see <https://www.gnu.org/licenses/>.
      16  */
      17  
      18  /* Subtract the `struct timeval' values X and Y,
      19     storing the result in RESULT.
      20     Return 1 if the difference is negative, otherwise 0.  */
      21  
      22  int
      23  timeval_subtract (struct timeval *result, struct timeval *x, struct timeval *y)
      24  {
      25    /* Perform the carry for the later subtraction by updating @var{y}. */
      26    if (x->tv_usec < y->tv_usec) {
      27      int nsec = (y->tv_usec - x->tv_usec) / 1000000 + 1;
      28      y->tv_usec -= 1000000 * nsec;
      29      y->tv_sec += nsec;
      30    }
      31    if (x->tv_usec - y->tv_usec > 1000000) {
      32      int nsec = (x->tv_usec - y->tv_usec) / 1000000;
      33      y->tv_usec += 1000000 * nsec;
      34      y->tv_sec -= nsec;
      35    }
      36  
      37    /* Compute the time remaining to wait.
      38       @code{tv_usec} is certainly positive. */
      39    result->tv_sec = x->tv_sec - y->tv_sec;
      40    result->tv_usec = x->tv_usec - y->tv_usec;
      41  
      42    /* Return 1 if result is negative. */
      43    return x->tv_sec < y->tv_sec;
      44  }