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[ping][PATCH v2][BZ #12515] Improve precision of clock function


Ping!

On Tue, May 21, 2013 at 09:44:41PM +0530, Siddhesh Poyarekar wrote:
> On Tue, May 21, 2013 at 09:00:09AM -0700, Paul Eggert wrote:
> > On 05/21/13 08:34, Siddhesh Poyarekar wrote:
> > 
> > > +    return (clock_t) ((ts.tv_nsec * CLOCKS_PER_SEC) / 1000000000
> > > +		      + ts.tv_sec * CLOCKS_PER_SEC);
> > 
> > First, there's no need to cast to clock_t, and in general it's better
> > to avoid casts if they're not needed.
> 
> OK, cast removed.
>  
> > Second, ts.tv_nsec * CLOCKS_PER_SEC might overflow on a machine
> > with 32-bit 'long', and afterwards the resulting division by 1000000000
> > won't wrap around to the "correct" value.
> > 
> > How about this instead?
> > 
> > 	return (ts.tv_sec * CLOCKS_PER_SEC
> > 		+ ts.tv_nsec / (1000000000 / CLOCKS_PER_SEC));
> 
> Thanks, patch updated and tested.  OK to go in with this change?
> After the PLT fix is reviewed of course.
> 
> Siddhesh
> 
> 2013-05-21  Siddhesh Poyarekar  <siddhesh@redhat.com>
> 	    Paul Eggert  <eggert@cs.ucla.edu>
> 
> 	[BZ #12515]
> 	* sysdeps/unix/sysv/linux/clock.c (clock): Use result from
> 	CLOCK_PROCESS_CPUTIME_ID clock if available.
> 
> 
> diff --git a/sysdeps/unix/sysv/linux/clock.c b/sysdeps/unix/sysv/linux/clock.c
> index 5268d33..e4e2065 100644
> --- a/sysdeps/unix/sysv/linux/clock.c
> +++ b/sysdeps/unix/sysv/linux/clock.c
> @@ -23,6 +23,14 @@
>  clock_t
>  clock (void)
>  {
> +  struct timespec ts;
> +
> +  if (__clock_gettime (CLOCK_PROCESS_CPUTIME_ID, &ts) == 0)
> +    return (ts.tv_sec * CLOCKS_PER_SEC
> +	    + ts.tv_nsec / (1000000000 / CLOCKS_PER_SEC));
> +
> +  /* clock_gettime failed.  This will only occur if CLOCK_PROCESS_CPUTIME_ID is
> +     not supported by the kernel.  Fall back to __times.  */
>    struct tms buf;
>    long clk_tck = __sysconf (_SC_CLK_TCK);
>  


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