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/* Subtract two struct timespec values.
Copyright (C) 2011-2017 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 <https://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;
time_t tmin = TYPE_MINIMUM (time_t);
time_t tmax = TYPE_MAXIMUM (time_t);
if (ns < 0)
{
rns = ns + TIMESPEC_RESOLUTION;
if (bs < tmax)
bs++;
else if (- TYPE_SIGNED (time_t) < rs)
rs--;
else
goto low_overflow;
}
/* INT_SUBTRACT_WRAPV is not appropriate since time_t might be unsigned.
In theory time_t might be narrower than int, so plain
INT_SUBTRACT_OVERFLOW does not suffice. */
if (! INT_SUBTRACT_OVERFLOW (rs, bs) && tmin <= rs - bs && rs - bs <= tmax)
rs -= bs;
else
{
if (rs < 0)
{
low_overflow:
rs = tmin;
rns = 0;
}
else
{
rs = tmax;
rns = TIMESPEC_RESOLUTION - 1;
}
}
return make_timespec (rs, rns);
}
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