timespec-add.c 1.64 KB
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/* Add two struct timespec values.

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   Copyright (C) 2011-2020 Free Software Foundation, Inc.
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   This program is free software: you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; either version 3 of the License, or
   (at your option) any later version.

   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License
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   along with this program.  If not, see <https://www.gnu.org/licenses/>.  */
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/* Written by Paul Eggert.  */

/* Return the sum of two timespec values A and B.  On overflow, return
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   an extremal value.  This assumes 0 <= tv_nsec < TIMESPEC_HZ.  */
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#include <config.h>
#include "timespec.h"

#include "intprops.h"

struct timespec
timespec_add (struct timespec a, struct timespec b)
{
  time_t rs = a.tv_sec;
  time_t bs = b.tv_sec;
  int ns = a.tv_nsec + b.tv_nsec;
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  int nsd = ns - TIMESPEC_HZ;
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  int rns = ns;

  if (0 <= nsd)
    {
      rns = nsd;
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      time_t bs1;
      if (!INT_ADD_WRAPV (bs, 1, &bs1))
        bs = bs1;
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      else if (rs < 0)
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        rs++;
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      else
        goto high_overflow;
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    }

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  if (INT_ADD_WRAPV (rs, bs, &rs))
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    {
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      if (bs < 0)
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        {
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          rs = TYPE_MINIMUM (time_t);
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          rns = 0;
        }
      else
        {
        high_overflow:
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          rs = TYPE_MAXIMUM (time_t);
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          rns = TIMESPEC_HZ - 1;
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        }
    }

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  return make_timespec (rs, rns);
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}