1  /* Subtract two struct timespec values.
       2     Copyright (C) 2011-2023 Free Software Foundation, Inc.
       3     This file is part of the GNU C Library and is also part of gnulib.
       4     Patches to this file should be submitted to both projects.
       5  
       6     The GNU C Library is free software; you can redistribute it and/or
       7     modify it under the terms of the GNU Lesser General Public
       8     License as published by the Free Software Foundation; either
       9     version 2.1 of the License, or (at your option) any later version.
      10  
      11     The GNU C Library is distributed in the hope that it will be useful,
      12     but WITHOUT ANY WARRANTY; without even the implied warranty of
      13     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
      14     Lesser General Public License for more details.
      15  
      16     You should have received a copy of the GNU Lesser General Public
      17     License along with the GNU C Library; if not, see
      18     <https://www.gnu.org/licenses/>.  */
      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 "intprops.h"
      28  
      29  struct timespec
      30  timespec_sub (struct timespec a, struct timespec b)
      31  {
      32    time_t rs = a.tv_sec;
      33    time_t bs = b.tv_sec;
      34    int ns = a.tv_nsec - b.tv_nsec;
      35    int rns = ns;
      36  
      37    if (ns < 0)
      38      {
      39        rns = ns + TIMESPEC_HZ;
      40        time_t bs1;
      41        if (!INT_ADD_WRAPV (bs, 1, &bs1))
      42          bs = bs1;
      43        else if (- TYPE_SIGNED (time_t) < rs)
      44          rs--;
      45        else
      46          goto low_overflow;
      47      }
      48  
      49    if (INT_SUBTRACT_WRAPV (rs, bs, &rs))
      50      {
      51        if (0 < bs)
      52          {
      53          low_overflow:
      54            rs = TYPE_MINIMUM (time_t);
      55            rns = 0;
      56          }
      57        else
      58          {
      59            rs = TYPE_MAXIMUM (time_t);
      60            rns = TIMESPEC_HZ - 1;
      61          }
      62      }
      63  
      64    return (struct timespec) { .tv_sec = rs, .tv_nsec = rns };
      65  }