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/*************************************************************************
* Copyright (C) 2008 Tavian Barnes <tavianator@gmail.com> *
* *
* This file is part of The Sandglass Library. *
* *
* The Sandglass Library is free software; you can redistribute it *
* and/or modify it under the terms of the GNU Lesser General Public *
* License as published by the Free Software Foundation; either version *
* 3 of the License, or (at your option) any later version. *
* *
* The Sandglass Library 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 *
* Lesser General Public License for more details. *
* *
* You should have received a copy of the GNU Lesser General Public *
* License along with this program. If not, see *
* <http://www.gnu.org/licenses/>. *
*************************************************************************/
#include "sandglass_impl.h"
#include "sandglass.h"
#include <time.h>
#include <unistd.h>
/* Gets the number of clock ticks per second */
double
sandglass_tsc_resolution()
{
static long tsc = 0, grains1, grains2;
int monotonic;
struct timespec ts;
if (tsc == 0) {
monotonic = sysconf(_SC_MONOTONIC_CLOCK) > 0;
if (monotonic) {
if (clock_gettime(CLOCK_MONOTONIC, &ts) != 0)
return 0.0/0.0;
} else {
if (clock_gettime(CLOCK_REALTIME, &ts) != 0)
return 0.0/0.0;
}
tsc = sandglass_get_tsc();
grains1 = sandglass_timespec_grains(&ts);
grains2 = grains1;
while (((grains2 >= grains1) ? grains2 - grains1
: 2000000000L + (grains2 - grains1))
< 10000000L)
{
if (monotonic) {
if (clock_gettime(CLOCK_MONOTONIC, &ts) != 0)
return 0.0/0.0;
} else {
if (clock_gettime(CLOCK_REALTIME, &ts) != 0)
return 0.0/0.0;
}
grains2 = sandglass_timespec_grains(&ts);
}
tsc = sandglass_get_tsc() - tsc;
}
return tsc*1.0e9/(grains2 - grains1);
}
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