glibc/sysdeps/unix/sysv/linux/clock.c

/* Copyright (C) 1991, 1992, 1996, 1999 Free Software Foundation, Inc.
   This file is part of the GNU C Library.

   The GNU C Library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Lesser General Public
   License as published by the Free Software Foundation; either
   version 2.1 of the License, or (at your option) any later version.

   The GNU C Library is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public
   License along with the GNU C Library; if not, see
   <http://www.gnu.org/licenses/>.  */

#include <sys/times.h>
#include <time.h>
#include <unistd.h>

/* Return the time used by the program so far (user time + system time).  */
clock_t
clock (void)
{
  struct tms buf;
  long clk_tck = __sysconf (_SC_CLK_TCK);

  /* We don't check for errors here.  The only error the kernel
     returns is EFAULT if the value cannot be written to the struct we
     pass a pointer to.  Otherwise the kernel returns an `unsigned
     long' value which is the number of jiffies since system start.
     But this number can be negative (when read as `long') when the
     system is up for some time.  Ignoring errors should therefore
     have no negative impacts but solve the problem.  */
  __times (&buf);

  return
    (clk_tck <= CLOCKS_PER_SEC)
    ? ((unsigned long) buf.tms_utime + buf.tms_stime) * (CLOCKS_PER_SEC
							 / clk_tck)
    : ((unsigned long) buf.tms_utime + buf.tms_stime) / (clk_tck
							 / CLOCKS_PER_SEC);
}