sysdeps/unix/sysv/linux/i386/get_clockfreq.c

   1 /* Get frequency of the system processor.  i386/Linux version.
   2    Copyright (C) 2000, 2001 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4
   5    The GNU C Library is free software; you can redistribute it and/or
   6    modify it under the terms of the GNU Lesser General Public
   7    License as published by the Free Software Foundation; either
   8    version 2.1 of the License, or (at your option) any later version.
   9
  10    The GNU C Library is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13    Lesser General Public License for more details.
  14
  15    You should have received a copy of the GNU Lesser General Public
  16    License along with the GNU C Library; if not, write to the Free
  17    Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
  18    02111-1307 USA.  */
  19
  20 #include <ctype.h>
  21 #include <fcntl.h>
  22 #include <string.h>
  23 #include <unistd.h>
  24 #include <libc-internal.h>
  25
  26
  27 hp_timing_t
  28 __get_clockfreq (void)
  29 {
  30   /* We read the information from the /proc filesystem.  It contains at
  31      least one line like
  32         cpu MHz         : 497.840237
  33      or also
  34         cpu MHz         : 497.841
  35      We search for this line and convert the number in an integer.  */
  36   static hp_timing_t result;
  37   int fd;
  38
  39   /* If this function was called before, we know the result.  */
  40   if (result != 0)
  41     return result;
  42
  43   fd = open ("/proc/cpuinfo", O_RDONLY);
  44   if (__builtin_expect (fd != -1, 1))
  45     {
  46       /* XXX AFAIK the /proc filesystem can generate "files" only up
  47          to a size of 4096 bytes.  */
  48       char buf[4096];
  49       ssize_t n;
  50
  51       n = read (fd, buf, sizeof buf);
  52       if (__builtin_expect (n, 1) > 0)
  53         {
  54           char *mhz = memmem (buf, n, "cpu MHz", 7);
  55
  56           if (__builtin_expect (mhz != NULL, 1))
  57             {
  58               char *endp = buf + n;
  59               int seen_decpoint = 0;
  60               int ndigits = 0;
  61
  62               /* Search for the beginning of the string.  */
  63               while (mhz < endp && (*mhz < '0' || *mhz > '9') && *mhz != '\n')
  64                 ++mhz;
  65
  66               while (mhz < endp && *mhz != '\n')
  67                 {
  68                   if (*mhz >= '0' && *mhz <= '9')
  69                     {
  70                       result *= 10;
  71                       result += *mhz - '0';
  72                       if (seen_decpoint)
  73                         ++ndigits;
  74                     }
  75                   else if (*mhz == '.')
  76                     seen_decpoint = 1;
  77
  78                   ++mhz;
  79                 }
  80
  81               /* Compensate for missing digits at the end.  */
  82               while (ndigits++ < 6)
  83                 result *= 10;
  84             }
  85         }
  86
  87       close (fd);
  88     }
  89
  90   return result;
  91 }