1  /* clock_getres -- Get the resolution of a POSIX clockid_t.
       2     Copyright (C) 1999-2023 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
      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        if (res)
      38  	{
      39  	  res->tv_sec = 0;
      40  	  res->tv_nsec = 1000000000 / clk_tck;
      41  	}
      42        return 0;
      43      }
      44  
      45    return -1;
      46  }
      47  
      48  
      49  /* Get resolution of clock.  */
      50  int
      51  __clock_getres (clockid_t clock_id, struct timespec *res)
      52  {
      53    int retval = -1;
      54  
      55    switch (clock_id)
      56      {
      57      case CLOCK_REALTIME:
      58        retval = realtime_getres (res);
      59        break;
      60  
      61      default:
      62        __set_errno (EINVAL);
      63        break;
      64      }
      65  
      66    return retval;
      67  }
      68  libc_hidden_def (__clock_getres)
      69  
      70  versioned_symbol (libc, __clock_getres, clock_getres, GLIBC_2_17);
      71  /* clock_getres moved to libc in version 2.17;
      72     old binaries may expect the symbol version it had in librt.  */
      73  #if SHLIB_COMPAT (libc, GLIBC_2_2, GLIBC_2_17)
      74  strong_alias (__clock_getres, __clock_getres_2);
      75  compat_symbol (libc, __clock_getres_2, clock_getres, GLIBC_2_2);
      76  #endif