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, write to the Free
  16    Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
  17    02111-1307 USA.  */
  18
  19 #include <sys/times.h>
  20 #include <time.h>
  21 #include <unistd.h>
  22
  23 /* Return the time used by the program so far (user time + system time).  */
  24 clock_t
  25 clock (void)
  26 {
  27   struct tms buf;
  28   long clk_tck = __sysconf (_SC_CLK_TCK);
  29
  30   /* We don't check for errors here.  The only error the kernel
  31      returns is EFAULT if the value cannot be written to the struct we
  32      pass a pointer to.  Otherwise the kernel returns an `unsigned
  33      long' value which is the number of jiffies since system start.
  34      But this number can be negative (when read as `long') when the
  35      system is up for some time.  Ignoring errors should therefore
  36      have no negative impacts but solve the problem.  */
  37   __times (&buf);
  38
  39   return
  40     (clk_tck <= CLOCKS_PER_SEC)
  41     ? ((unsigned long) buf.tms_utime + buf.tms_stime) * (CLOCKS_PER_SEC
  42                                                          / clk_tck)
  43     : ((unsigned long) buf.tms_utime + buf.tms_stime) / (clk_tck
  44                                                          / CLOCKS_PER_SEC);
  45 }