timespec-sub.c 1.67 KB
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/* Subtract 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 difference between two timespec values A and B.  On
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   overflow, return an extremal value.  This assumes 0 <= tv_nsec <
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   TIMESPEC_HZ.  */
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#include <config.h>
#include "timespec.h"

#include "intprops.h"

struct timespec
timespec_sub (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;
  int rns = ns;

  if (ns < 0)
    {
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      rns = ns + TIMESPEC_HZ;
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      time_t bs1;
      if (!INT_ADD_WRAPV (bs, 1, &bs1))
        bs = bs1;
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      else if (- TYPE_SIGNED (time_t) < rs)
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        rs--;
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      else
        goto low_overflow;
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    }

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  if (INT_SUBTRACT_WRAPV (rs, bs, &rs))
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    {
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      if (0 < bs)
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        {
        low_overflow:
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          rs = TYPE_MINIMUM (time_t);
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          rns = 0;
        }
      else
        {
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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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}