bit count or bit set && Python3

[Chris Angelico]

On Fri, Oct 26, 2012 at 2:25 AM, Christian Heimes <christian at python.org> wrote:
> Simple, easy, faster than a Python loop but not very elegant:
>
>    bin(number).count("1")

Unlikely to be fast.

What you may want is some sort of hybrid loop/lookup approach. Do you
know what your highest bit number is going to be? For instance, are
all your integers 32-bit? You could use something like this:

c = bitcount[n&255] + bitcount[n>>8&255] + bitcount[n>>16&255] + bitcount[n>>24]

where bitcount is a list of 256 values, giving the counts for each
value from 0 to 255.

Profile and test. :)

ChrisA