1 /* clock_getres -- Get the resolution of a POSIX clockid_t.
2 Copyright (C) 1999-2021 Free Software Foundation, Inc.
3 This file is part of the GNU C Library.
4
5 The GNU C Library is free software; you can redistribute it and/or
6 modify it under the terms of the GNU Lesser General Public
7 License as published by the Free Software Foundation; either
8 version 2.1 of the License, or (at your option) any later version.
9
10 The GNU C Library is distributed in the hope that it will be useful,
11 but WITHOUT ANY WARRANTY; without even the implied warranty of
12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
13 Lesser General Public License for more details.
14
15 You should have received a copy of the GNU Lesser General Public
16 License along with the GNU C Library; if not, see
17 <https://www.gnu.org/licenses/>. */
18
19 #include <errno.h>
20 #include <stdint.h>
21 #include <time.h>
22 #include <unistd.h>
23 #include <sys/param.h>
24 #include <libc-internal.h>
25 #include <shlib-compat.h>
26
27 static inline int
realtime_getres(struct timespec * res)28 realtime_getres (struct timespec *res)
29 {
30 long int clk_tck = __sysconf (_SC_CLK_TCK);
31
32 if (__glibc_likely (clk_tck != -1))
33 {
34 /* This implementation assumes that the realtime clock has a
35 resolution higher than 1 second. This is the case for any
36 reasonable implementation. */
37 res->tv_sec = 0;
38 res->tv_nsec = 1000000000 / clk_tck;
39 return 0;
40 }
41
42 return -1;
43 }
44
45
46 /* Get resolution of clock. */
47 int
__clock_getres(clockid_t clock_id,struct timespec * res)48 __clock_getres (clockid_t clock_id, struct timespec *res)
49 {
50 int retval = -1;
51
52 switch (clock_id)
53 {
54 case CLOCK_REALTIME:
55 retval = realtime_getres (res);
56 break;
57
58 default:
59 __set_errno (EINVAL);
60 break;
61 }
62
63 return retval;
64 }
65 libc_hidden_def (__clock_getres)
66
67 versioned_symbol (libc, __clock_getres, clock_getres, GLIBC_2_17);
68 /* clock_getres moved to libc in version 2.17;
69 old binaries may expect the symbol version it had in librt. */
70 #if SHLIB_COMPAT (libc, GLIBC_2_2, GLIBC_2_17)
71 strong_alias (__clock_getres, __clock_getres_2);
72 compat_symbol (libc, __clock_getres_2, clock_getres, GLIBC_2_2);
73 #endif
74