1  /* Subtract two struct timespec values.
       2  
       3     Copyright (C) 2011-2023 Free Software Foundation, Inc.
       4  
       5     This program is free software: you can redistribute it and/or modify
       6     it under the terms of the GNU General Public License as published by
       7     the Free Software Foundation, either version 3 of the License, or
       8     (at your option) any later version.
       9  
      10     This program is distributed in the hope that it will be useful,
      11     but WITHOUT ANY WARRANTY; without even the implied warranty of
      12     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
      13     GNU General Public License for more details.
      14  
      15     You should have received a copy of the GNU General Public License
      16     along with this program.  If not, see <https://www.gnu.org/licenses/>.  */
      17  
      18  /* Written by Paul Eggert.  */
      19  
      20  /* Return the difference between two timespec values A and B.  On
      21     overflow, return an extremal value.  This assumes 0 <= tv_nsec <
      22     TIMESPEC_HZ.  */
      23  
      24  #include <config.h>
      25  #include "timespec.h"
      26  
      27  #include <stdckdint.h>
      28  #include "intprops.h"
      29  
      30  struct timespec
      31  timespec_sub (struct timespec a, struct timespec b)
      32  {
      33    time_t rs = a.tv_sec;
      34    time_t bs = b.tv_sec;
      35    int ns = a.tv_nsec - b.tv_nsec;
      36    int rns = ns;
      37  
      38    if (ns < 0)
      39      {
      40        rns = ns + TIMESPEC_HZ;
      41        time_t bs1;
      42        if (!ckd_add (&bs1, bs, 1))
      43          bs = bs1;
      44        else if (- TYPE_SIGNED (time_t) < rs)
      45          rs--;
      46        else
      47          goto low_overflow;
      48      }
      49  
      50    if (ckd_sub (&rs, rs, bs))
      51      {
      52        if (0 < bs)
      53          {
      54          low_overflow:
      55            rs = TYPE_MINIMUM (time_t);
      56            rns = 0;
      57          }
      58        else
      59          {
      60            rs = TYPE_MAXIMUM (time_t);
      61            rns = TIMESPEC_HZ - 1;
      62          }
      63      }
      64  
      65    return make_timespec (rs, rns);
      66  }