sysdeps/unix/sysv/linux/clock.c

   1 /* Copyright (C) 1991, 1992, 1996, 1999 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, see
  16    <http://www.gnu.org/licenses/>.  */
  17
  18 #include <sys/times.h>
  19 #include <time.h>
  20 #include <unistd.h>
  21
  22 /* Return the time used by the program so far (user time + system time).  */
  23 clock_t
  24 clock (void)
  25 {
  26   struct tms buf;
  27   long clk_tck = __sysconf (_SC_CLK_TCK);
  28
  29   /* We don't check for errors here.  The only error the kernel
  30      returns is EFAULT if the value cannot be written to the struct we
  31      pass a pointer to.  Otherwise the kernel returns an `unsigned
  32      long' value which is the number of jiffies since system start.
  33      But this number can be negative (when read as `long') when the
  34      system is up for some time.  Ignoring errors should therefore
  35      have no negative impacts but solve the problem.  */
  36   __times (&buf);
  37
  38   return
  39     (clk_tck <= CLOCKS_PER_SEC)
  40     ? ((unsigned long) buf.tms_utime + buf.tms_stime) * (CLOCKS_PER_SEC
  41                                                          / clk_tck)
  42     : ((unsigned long) buf.tms_utime + buf.tms_stime) / (clk_tck
  43                                                          / CLOCKS_PER_SEC);
  44 }