sysdeps/posix/clock_getres.c

   1 /* Copyright (C) 1999, 2000 Free Software Foundation, Inc.
   2    This file is part of the GNU C Library.
   3
   4    The GNU C Library is free software; you can redistribute it and/or
   5    modify it under the terms of the GNU Library General Public License as
   6    published by the Free Software Foundation; either version 2 of the
   7    License, or (at your option) any later version.
   8
   9    The GNU C Library is distributed in the hope that it will be useful,
  10    but WITHOUT ANY WARRANTY; without even the implied warranty of
  11    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  12    Library General Public License for more details.
  13
  14    You should have received a copy of the GNU Library General Public
  15    License along with the GNU C Library; see the file COPYING.LIB.  If not,
  16    write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
  17    Boston, MA 02111-1307, USA.  */
  18
  19 #include <errno.h>
  20 #include <unistd.h>
  21 #include <sys/time.h>
  22
  23
  24 #ifndef EXTRA_CLOCK_CASES
  25 # define EXTRA_CLOCK_CASES
  26 #endif
  27
  28 /* Get resolution of clock.  */
  29 int
  30 clock_getres (clockid_t clock_id, struct timespec *res)
  31 {
  32   int retval = -1;
  33
  34   switch (clock_id)
  35     {
  36     case CLOCK_REALTIME:
  37       {
  38         long int clk_tck = sysconf (_SC_CLK_TCK);
  39
  40         if (__builtin_expect (clk_tck != -1, 1))
  41           {
  42             /* This implementation assumes that the realtime clock has a
  43                resolution higher than 1 second.  This is the case for any
  44                reasonable implementation.  */
  45             res->tv_sec = 0;
  46             res->tv_nsec = 1000000000 / clk_tck;
  47
  48             retval = 0;
  49           }
  50       }
  51       break;
  52
  53       EXTRA_CLOCK_CASES
  54
  55     default:
  56       __set_errno (EINVAL);
  57       break;
  58     }
  59
  60   return retval;
  61 }