manual/examples/timeval_subtract.c

   1 /* struct timeval subtraction.
   2    Copyright (C) 1991-2017 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, if not, see <http://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 }