support/timespec-sub.c

   1 /* Subtract two struct timespec values.
   2    Copyright (C) 2011-2024 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 "timespec.h"
  25
  26 #include "intprops.h"
  27
  28 struct timespec
  29 timespec_sub (struct timespec a, struct timespec b)
  30 {
  31   time_t rs = a.tv_sec;
  32   time_t bs = b.tv_sec;
  33   int ns = a.tv_nsec - b.tv_nsec;
  34   int rns = ns;
  35
  36   if (ns < 0)
  37     {
  38       rns = ns + TIMESPEC_HZ;
  39       time_t bs1;
  40       if (!INT_ADD_WRAPV (bs, 1, &bs1))
  41         bs = bs1;
  42       else if (- TYPE_SIGNED (time_t) < rs)
  43         rs--;
  44       else
  45         goto low_overflow;
  46     }
  47
  48   if (INT_SUBTRACT_WRAPV (rs, bs, &rs))
  49     {
  50       if (0 < bs)
  51         {
  52         low_overflow:
  53           rs = TYPE_MINIMUM (time_t);
  54           rns = 0;
  55         }
  56       else
  57         {
  58           rs = TYPE_MAXIMUM (time_t);
  59           rns = TIMESPEC_HZ - 1;
  60         }
  61     }
  62
  63   return (struct timespec) { .tv_sec = rs, .tv_nsec = rns };
  64 }