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/* Subtract two struct timespec values.
Copyright (C) 2011-2015 Free Software Foundation, Inc.
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
along with this program. If not, see <http://www.gnu.org/licenses/>. */
/* Written by Paul Eggert. */
/* Return the difference between two timespec values A and B. On
overflow, return an extremal value. This assumes 0 <= tv_nsec <
TIMESPEC_RESOLUTION. */
#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)
{
rns = ns + TIMESPEC_RESOLUTION;
if (rs == TYPE_MINIMUM (time_t))
{
if (bs <= 0)
goto low_overflow;
bs--;
}
else
rs--;
}
if (INT_SUBTRACT_OVERFLOW (rs, bs))
{
if (rs < 0)
{
low_overflow:
rs = TYPE_MINIMUM (time_t);
rns = 0;
}
else
{
rs = TYPE_MAXIMUM (time_t);
rns = TIMESPEC_RESOLUTION - 1;
}
}
else
rs -= bs;
return make_timespec (rs, rns);
}
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