sysdeps/posix/clock_getres.c

   1 /* Copyright (C) 1999, 2000, 2001 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 Lesser General Public
   6    License as published by the Free Software Foundation; either
   7    version 2.1 of the 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    Lesser General Public License for more details.
  13
  14    You should have received a copy of the GNU Lesser General Public
  15    License along with the GNU C Library; if not, write to the Free
  16    Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
  17    02111-1307 USA.  */
  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
  26
  27 #if HP_TIMING_AVAIL
  28 /* Clock frequency of the processor.  */
  29 static long int nsec;
  30 #endif
  31
  32
  33 /* Get resolution of clock.  */
  34 int
  35 clock_getres (clockid_t clock_id, struct timespec *res)
  36 {
  37   int retval = -1;
  38
  39   switch (clock_id)
  40     {
  41     case CLOCK_REALTIME:
  42       {
  43         long int clk_tck = sysconf (_SC_CLK_TCK);
  44
  45         if (__builtin_expect (clk_tck != -1, 1))
  46           {
  47             /* This implementation assumes that the realtime clock has a
  48                resolution higher than 1 second.  This is the case for any
  49                reasonable implementation.  */
  50             res->tv_sec = 0;
  51             res->tv_nsec = 1000000000 / clk_tck;
  52
  53             retval = 0;
  54           }
  55       }
  56       break;
  57
  58 #if HP_TIMING_AVAIL
  59     case CLOCK_PROCESS_CPUTIME_ID:
  60     case CLOCK_THREAD_CPUTIME_ID:
  61       {
  62         if (__builtin_expect (nsec == 0, 0))
  63           {
  64             hp_timing_t freq;
  65
  66             /* This can only happen if we haven't initialized the `freq'
  67                variable yet.  Do this now. We don't have to protect this
  68                code against multiple execution since all of them should
  69                lead to the same result.  */
  70             freq = __get_clockfreq ();
  71             if (__builtin_expect (freq == 0, 0))
  72               /* Something went wrong.  */
  73               break;
  74
  75             nsec = MAX (UINT64_C (1000000000) / freq, 1);
  76           }
  77
  78         /* File in the values.  The seconds are always zero (unless we
  79            have a 1Hz machine).  */
  80         res->tv_sec = 0;
  81         res->tv_nsec = nsec;
  82
  83         retval = 0;
  84       }
  85       break;
  86 #endif
  87
  88     default:
  89       __set_errno (EINVAL);
  90       break;
  91     }
  92
  93   return retval;
  94 }