support/timespec-add.c

   1 /* Add two struct timespec values.
   2    Copyright (C) 2011-2019 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 sum of two timespec values A and B.  On overflow, return
  21    an extremal value.  This assumes 0 <= tv_nsec < TIMESPEC_HZ.  */
  22
  23 #include <config.h>
  24 #include "timespec.h"
  25
  26 #include "intprops.h"
  27
  28 struct timespec
  29 timespec_add (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 nsd = ns - TIMESPEC_HZ;
  35   int rns = ns;
  36   time_t tmin = TYPE_MINIMUM (time_t);
  37   time_t tmax = TYPE_MAXIMUM (time_t);
  38
  39   if (0 <= nsd)
  40     {
  41       rns = nsd;
  42       if (bs < tmax)
  43         bs++;
  44       else if (rs < 0)
  45         rs++;
  46       else
  47         goto high_overflow;
  48     }
  49
  50   /* INT_ADD_WRAPV is not appropriate since time_t might be unsigned.
  51      In theory time_t might be narrower than int, so plain
  52      INT_ADD_OVERFLOW does not suffice.  */
  53   if (! INT_ADD_OVERFLOW (rs, bs) && tmin <= rs + bs && rs + bs <= tmax)
  54     rs += bs;
  55   else
  56     {
  57       if (rs < 0)
  58         {
  59           rs = tmin;
  60           rns = 0;
  61         }
  62       else
  63         {
  64         high_overflow:
  65           rs = tmax;
  66           rns = TIMESPEC_HZ - 1;
  67         }
  68     }
  69
  70   return make_timespec (rs, rns);
  71 }