Division and right shift in python

[Mark Tolonen]

"Cevahir Demirkiran" <cevomed at gmail.com> wrote in message 
news:3f74e020908251648k7b391a09g78b155507b2f23c4 at mail.gmail.com...
> Hi,
>
> I would like to do a floor division by a power of 2 in python to make it
> faster than / (modular division in 2.x).
> However, it is slower.
> What is the reason of that?
> I checked them via:
>
> def f2(x,n):
>    t1 = clock()
>    r = x/pow(2,n)
>    t2 = clock()
>    print (t2-t1)
>    print r
>    t2 = clock()
>    r = x>>n
>    t3 = clock()
>    print (t3-t2)
>    print r
>

It's not slower on my system, but note the inconsistent results also:

>>> f2(1024,5)
3.47396033483e-06
32
2.19077375482e-06
32
>>> f2(1024,5)
4.84135603429e-06
32
3.08499440393e-06
32
>>> f2(1024,5)
4.6782844052e-06
32
3.77604384028e-06
32

Time it with timeit...

C:\>python -m timeit -n 10000000 -s x=1024 "x>>5"
10000000 loops, best of 3: 0.113 usec per loop

C:\>python -m timeit -n 10000000 -s x=1024 "x/pow(2,5)"
10000000 loops, best of 3: 0.468 usec per loop

Right-shift is over 4x faster.

-Mark