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

   1 /* Get frequency of the system processor.  IA-64/Linux version.
   2    Copyright (C) 2001-2014 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, see
  17    <http://www.gnu.org/licenses/>.  */
  18
  19 #include <ctype.h>
  20 #include <fcntl.h>
  21 #include <string.h>
  22 #include <unistd.h>
  23 #include <libc-internal.h>
  24
  25
  26 hp_timing_t
  27 __get_clockfreq (void)
  28 {
  29   /* We read the information from the /proc filesystem.  It contains at
  30      least one line like
  31         itc MHz    : 733.390988
  32      We search for this line and convert the number in an integer.  */
  33   static hp_timing_t result;
  34   int fd;
  35
  36   /* If this function was called before, we know the result.  */
  37   if (result != 0)
  38     return result;
  39
  40   fd = __open ("/proc/cpuinfo", O_RDONLY);
  41   if (__builtin_expect (fd != -1, 1))
  42     {
  43       /* XXX AFAIK the /proc filesystem can generate "files" only up
  44          to a size of 4096 bytes.  */
  45       char buf[4096];
  46       ssize_t n;
  47
  48       n = __read (fd, buf, sizeof buf);
  49       if (__builtin_expect (n, 1) > 0)
  50         {
  51           char *mhz = memmem (buf, n, "itc MHz", 7);
  52
  53           if (__builtin_expect (mhz != NULL, 1))
  54             {
  55               char *endp = buf + n;
  56               int seen_decpoint = 0;
  57               int ndigits = 0;
  58
  59               /* Search for the beginning of the string.  */
  60               while (mhz < endp && (*mhz < '0' || *mhz > '9') && *mhz != '\n')
  61                 ++mhz;
  62
  63               while (mhz < endp && *mhz != '\n')
  64                 {
  65                   if (*mhz >= '0' && *mhz <= '9')
  66                     {
  67                       result *= 10;
  68                       result += *mhz - '0';
  69                       if (seen_decpoint)
  70                         ++ndigits;
  71                     }
  72                   else if (*mhz == '.')
  73                     seen_decpoint = 1;
  74
  75                   ++mhz;
  76                 }
  77
  78               /* Compensate for missing digits at the end.  */
  79               while (ndigits++ < 6)
  80                 result *= 10;
  81             }
  82         }
  83
  84       __close (fd);
  85     }
  86
  87   return result;
  88 }