Calculating Elapsed Time

[Grant Edwards]

On 2005-12-07, Grant Edwards <grante at visi.com> wrote:

>>>> for f in range(10): 
> ...  print t()-t()
> ... 
> -4.05311584473e-06
> -1.90734863281e-06
> -1.90734863281e-06
> -2.14576721191e-06
> -2.86102294922e-06
> -1.90734863281e-06
> -2.14576721191e-06
> -2.14576721191e-06
> -9.53674316406e-07
> -1.90734863281e-06
>
> The min delta seen is 0.95us.  I'm guessing thats
> function/system call overhead and not timer resolution.

After looking at the implimentation of time.time under Linux,
it should have _exactly_ 1us resolution.  I suspect that on a
Linux platform the resolution of time.time() is being limited
by IEEE double representation.

Yup:

>>> print len("%0.0f" % (time.time()*1e6,))
16

1us resolution for the time.time() value requires 16
significant digits.  That's more than IEEE 64bit floating point
can represent accurately, and why the apparent resolution of
time.time() under Linux is only approximately 1us.

-- 
Grant Edwards                   grante             Yow!  Should I do my BOBBIE
                                  at               VINTON medley?
                               visi.com