79 lines
2.1 KiB
C
79 lines
2.1 KiB
C
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/* Get the system clock resolution.
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Copyright 2021-2022 Free Software Foundation, Inc.
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This file is free software: you can redistribute it and/or modify
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it under the terms of the GNU Lesser General Public License as
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published by the Free Software Foundation, either version 3 of the
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License, or (at your option) any later version.
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This file is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser 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. */
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#include <config.h>
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#include "timespec.h"
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static long int _GL_ATTRIBUTE_CONST
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gcd (long int a, long int b)
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{
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while (b != 0)
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{
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long int r = a % b;
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a = b;
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b = r;
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}
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return a;
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}
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/* Return the system time resolution in nanoseconds. */
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long int
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gettime_res (void)
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{
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struct timespec res;
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#if defined CLOCK_REALTIME && HAVE_CLOCK_GETRES
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clock_getres (CLOCK_REALTIME, &res);
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#elif defined HAVE_TIMESPEC_GETRES
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timespec_getres (&res, TIME_UTC);
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#else
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/* Guess high and let the later code deduce better. */
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res.tv_sec = 1;
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res.tv_nsec = 0;
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#endif
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/* On all Gnulib platforms the following calculations do not overflow. */
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long int hz = TIMESPEC_HZ;
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long int r = hz * res.tv_sec + res.tv_nsec;
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/* On some platforms, clock_getres (CLOCK_REALTIME, ...) yields a
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too-large resolution, under the mistaken theory that it should
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return the timer interval. For example, on AIX 7.2 POWER8
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clock_getres yields 10 ms even though clock_gettime yields 1 µs
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resolution. Work around the problem with high probability by
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trying clock_gettime several times and observing the resulting
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bounds on resolution. */
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for (int i = 0; 1 < r && i < 32; i++)
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{
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struct timespec now = current_timespec ();
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r = gcd (r, now.tv_nsec ? now.tv_nsec : hz);
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}
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return r;
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}
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/*
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* Hey Emacs!
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* Local Variables:
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* coding: utf-8
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* End:
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*/
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