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Date: Fri, 26 Oct 2012 02:31:53 +1100
Subject: Re: bit count or bit set && Python3
From: Chris Angelico <rosuav@gmail.com>
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Xref: csiph.com comp.lang.python:32135

On Fri, Oct 26, 2012 at 2:25 AM, Christian Heimes <christian@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