diff options
Diffstat (limited to 'sysdeps/unix/i386/i586/clock_gettime.c')
| -rw-r--r-- | sysdeps/unix/i386/i586/clock_gettime.c | 71 |
1 files changed, 71 insertions, 0 deletions
diff --git a/sysdeps/unix/i386/i586/clock_gettime.c b/sysdeps/unix/i386/i586/clock_gettime.c new file mode 100644 index 0000000000..f623cecd09 --- /dev/null +++ b/sysdeps/unix/i386/i586/clock_gettime.c @@ -0,0 +1,71 @@ +/* Copyright (C) 1999, 2000 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 Library General Public License as + published by the Free Software Foundation; either version 2 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 + Library General Public License for more details. + + You should have received a copy of the GNU Library General Public + License along with the GNU C Library; see the file COPYING.LIB. If not, + write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330, + Boston, MA 02111-1307, USA. */ + +#include <sys/time.h> + +/* This implementation uses the TSC register in modern (i586 and up) IA-32 + processors (most modern clones also provide it). Since we need the + resolution of the clock and since determining this is not cheap, we + cache the value. But this means that systems with processors running + at different speeds or process migration to machines with slower or + faster processors will not work without changes. */ + + +/* Function to determine processor frequency. */ +extern unsigned long long int __get_glockfreq (void); + +/* Clock frequency of the processor. We make it a 64-bit variable + because some jokers are already playing with processors with more + than 4GHz. */ +static unsigned long long int freq; + + +/* We add an limitation here: we assume that the machine is not up as + long as it takes to wrap-around the 64-bit timestamp counter. On a + 4GHz machine it would take 136 years of uptime to wrap around so + this "limitation" is not severe. */ +#define EXTRA_CLOCK_CASES \ + case __CLOCK_HIGHRES: \ + { \ + unsigned long long int tsc; \ + \ + if (__builtin_expect (freq != 0, 0)) \ + { \ + /* This can only happen if we haven't initialized the `freq' \ + variable yet. Do this now. We don't have to protect this \ + code against multiple execution since all of them should \ + lead to the same result. */ \ + freq = __get_clockfreq (); \ + if (__builtin_expect (freq == 0, 0)) \ + /* Something went wrong. */ \ + break; \ + } \ + \ + /* Get the current counter. */ \ + asm volatile ("rdtsc" : "=A" (tsc)); \ + \ + /* Compute the seconds. */ \ + tp->tv_sec = tsc / freq; \ + \ + /* And the nanoseconds. This computation should be stable until \ + we get machines with about 16GHz frequency. */ \ + tp->tv_nsec = ((tsc % freq) * 1000000000ULL) / freq; \ + } \ + break; + +#include <sysdeps/unix/clock_gettime.c> |