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Re: bit count or bit set && Python3

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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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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

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Re: bit count or bit set && Python3 Chris Angelico <rosuav@gmail.com> - 2012-10-26 02:31 +1100
  Re: bit count or bit set && Python3 Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-10-25 15:57 +0000
    Re: bit count or bit set && Python3 rusi <rustompmody@gmail.com> - 2012-10-25 09:17 -0700
      Re: bit count or bit set && Python3 Chris Angelico <rosuav@gmail.com> - 2012-10-26 03:29 +1100
        Re: bit count or bit set && Python3 rusi <rustompmody@gmail.com> - 2012-10-25 09:37 -0700
      Re: bit count or bit set && Python3 Mark Lawrence <breamoreboy@yahoo.co.uk> - 2012-10-25 17:44 +0100
      Re: bit count or bit set && Python3 Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-10-25 17:16 +0000
    Re: bit count or bit set && Python3 Serhiy Storchaka <storchaka@gmail.com> - 2012-10-25 22:07 +0300
    Re: bit count or bit set && Python3 Neil Cerutti <neilc@norwich.edu> - 2012-10-25 20:00 +0000
      Re: bit count or bit set && Python3 Neil Cerutti <neilc@norwich.edu> - 2012-10-25 20:04 +0000
      Re: bit count or bit set && Python3 Ian Kelly <ian.g.kelly@gmail.com> - 2012-10-25 14:20 -0600
        Re: bit count or bit set && Python3 Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-10-25 23:48 +0000
        Re: bit count or bit set && Python3 Neil Cerutti <neilc@norwich.edu> - 2012-10-26 12:56 +0000
    Re: bit count or bit set && Python3 Charles Hixson <charleshixsn@earthlink.net> - 2012-10-25 09:08 -0700
    Re: bit count or bit set && Python3 Mark Lawrence <breamoreboy@yahoo.co.uk> - 2012-10-25 22:51 +0100

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