sysdeps/unix/sysv/linux/ia64/get_clockfreq.c

   1 /* Get frequency of the system processor.  IA-64/Linux version.
   2    Copyright (C) 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         itc MHz    : 733.390988
  33      We search for this line and convert the number in an integer.  */
  34   static hp_timing_t result;
  35   int fd;
  36
  37   /* If this function was called before, we know the result.  */
  38   if (result != 0)
  39     return result;
  40
  41   fd = open ("/proc/cpuinfo", O_RDONLY);
  42   if (__builtin_expect (fd != -1, 1))
  43     {
  44       /* XXX AFAIK the /proc filesystem can generate "files" only up
  45          to a size of 4096 bytes.  */
  46       char buf[4096];
  47       ssize_t n;
  48
  49       n = read (fd, buf, sizeof buf);
  50       if (__builtin_expect (n, 1) > 0)
  51         {
  52           char *mhz = memmem (buf, n, "itc MHz", 7);
  53
  54           if (__builtin_expect (mhz != NULL, 1))
  55             {
  56               char *endp = buf + n;
  57               int seen_decpoint = 0;
  58               int ndigits = 0;
  59
  60               /* Search for the beginning of the string.  */
  61               while (mhz < endp && (*mhz < '0' || *mhz > '9') && *mhz != '\n')
  62                 ++mhz;
  63
  64               while (mhz < endp && *mhz != '\n')
  65                 {
  66                   if (*mhz >= '0' && *mhz <= '9')
  67                     {
  68                       result *= 10;
  69                       result += *mhz - '0';
  70                       if (seen_decpoint)
  71                         ++ndigits;
  72                     }
  73                   else if (*mhz == '.')
  74                     seen_decpoint = 1;
  75
  76                   ++mhz;
  77                 }
  78
  79               /* Compensate for missing digits at the end.  */
  80               while (ndigits++ < 6)
  81                 result *= 10;
  82             }
  83         }
  84
  85       close (fd);
  86     }
  87
  88   return result;
  89 }