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Re: counting bits [message #34099 is a reply to message #34095]

Tue, 18 February 2003 08:10

eddie haskell
Messages: 29
Registered: September 1998

Junior Member

Craig Markwardt wrote:

> Okay, here's a problem I've always solved by the brute force method:
>
> * what is the lowest / highest bit position set in an integer?
>
> For example, a the lowest bit position in the binary number 11010100
> is 2 (bit positions are labeled starting with 0 of course). The brute
> force method involves testing each bit in succession using something
> like (VALUE AND 2L^I) for each I, until a set bit is found.

I have not done any checking to see if this is any faster than a brute force
method but you could use something like this to get the lowest and highest set
bits:

IDL> n = 212 ;11010100
IDL> nbits = 8
IDL> print,(indgen(nbits))[(where((n and 2l^lindgen(nbits)) ne 0))[[0,nbits]]]

2 7

An issue with this is that N=0 will return [0,0] (the same as N=1), but
checking for a N of zero can easily be done beforehand.

Cheers,
eddie

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[Message index]

		Re: counting bits By: Craig Markwardt on Wed, 19 February 2003 21:31
		Re: counting bits By: Dick Jackson on Wed, 19 February 2003 07:47
		Re: counting bits By: Craig Markwardt on Tue, 18 February 2003 15:10
		Re: counting bits By: JD Smith on Tue, 18 February 2003 14:58
		Re: counting bits By: David Fanning on Tue, 18 February 2003 13:55
		Re: counting bits By: Rick Towler on Tue, 18 February 2003 13:27
		Re: counting bits By: JD Smith on Tue, 18 February 2003 11:56
		Re: counting bits By: eddie haskell on Tue, 18 February 2003 08:10
		Re: counting bits By: David Fanning on Mon, 17 February 2003 21:09
		Re: counting bits By: Craig Markwardt on Mon, 17 February 2003 20:45
		Re: counting bits By: JD Smith on Mon, 17 February 2003 15:54
		Re: counting bits By: David Fanning on Mon, 17 February 2003 12:41
		Re: counting bits By: David Fanning on Mon, 17 February 2003 12:38
		Re: counting bits By: JD Smith on Thu, 20 February 2003 07:43
		Re: counting bits By: JD Smith on Thu, 20 February 2003 07:24

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