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From: parke@star.enet.dec.com (Bill Parke)
Newsgroups: comp.lang.c
Subject: Re: count of bits set in a long
Message-ID: <1990Sep25.163315@star.enet.dec.com>
Date: 25 Sep 90 20:35:06 GMT
References: <661@atcmpe.atcmp.nl> <37545@ut-emx.uucp>
Sender: newsdaemon@shlump.nac.dec.com
Reply-To: parke@star.enet.dec.com (Bill Parke)
Organization: Digital Equipment Corporation, Nashua NH
Lines: 53

In article <661@atcmpe.atcmp.nl>, jc@atcmp.nl (Jan Christiaan van Winkel)
writes:
|> From: jc@atcmp.nl (Jan Christiaan van Winkel)
|> Newsgroups: comp.lang.c
|> Subject: Re: count of bits set in a long
|> 
|> From article <37545@ut-emx.uucp>, by nwagner@ut-emx.uucp (Neal R. Wagner):
|> > 
|> >   I need a fast method to count the number of bits that are set in a
32-bit
|> > integer on a Sun 3/80 running 4.0.3 SunOS.  The brute-force method
follows.
|> 
|> How about:
|> 
|> int bit_count(i)
|> unsigned long i;
|> {
|> 	int k=0;
|> 	for (; i!=0; i>>=1) k += (i & 1);
|> 	return k;
|> }
|> -- 
|> ___  __ 
____________________________________________________________________
|>    |/  \   Jan Christiaan van Winkel      Tel: +31 80 566880  jc@atcmp.nl
|>    |       AT Computing   P.O. Box 1428   6501 BK Nijmegen    The
Netherlands
|> __/ \__/
____________________________________________________________________
|> 

Actually I like:

int bitcount(int i)
{
	register int c = 0 ;
	while(i) {
	    i &= (i-1) ;
	    c++ ;
	    }
	return c ;
}

Better.

--
Bill Parke 			parke%star.enet.dec@decwrl.dec.com
VMS Development			decwrl!star.enet.dec.com!parke
Digital Equipment Corp		parke@star.enet.dec.com
110 Spit Brook Road ZK01-1/F22, Nashua NH 03063

The views expressed are my own.