Re: Counting bits by formula?

Jens.Toerring_at_physik.fu-berlin.de
Date: 09/29/04 

Date: 29 Sep 2004 18:39:16 GMT

Thomas G. Marshall <tgm2tothe10thpower@replacetextwithnumber.hotmail.com> wrote:

> I've often wondered is there a way of counting the 1 bits in an integer of
> whatever bit-width by formula, that is, /not/ by looping and testing? And
> /without/ an exhaustive boolean expression testing each value (or bit)
> individually.

> Using arithmetic, bitwise, even boolean operators is ok, just so long as it
> isn't doing the "obvious" test of every bit individually.

> I'm /not/ looking for something bitwise exhaustive of this form (in any
> language that would support it):

> !!(num & 128) + !!(num & 64) + ...etc.

> Any ideas?

Would look-up tables do after splitting the integer into chunks
fitting the size of the table?
                                   Regards, Jens 

-- 
  \   Jens Thoms Toerring  ___  Jens.Toerring@physik.fu-berlin.de
   \__________________________  http://www.toerring.de

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