Date: Tue, 15 Jul 1997 23:02:39 -0400 (EDT)
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To: eyal DOT ben-david AT aks DOT com, djgpp AT delorie DOT com
From: Chirayu Krishnappa <chirayu AT radiolink DOT net>
Subject: Re: odd or even # of 1's (was: no subject)
Precedence: bulk


>Here are some functions to calculate the number of bits of an integer
>value.
>
>Method  1
>~~~~~~
>Twice faster than shift method (on avg) since the number of
>loops == the number of bits.  (from Ratko Tomic)
>
>int  bit_count_1 (long x)
>{
>     int n = 0;
>/*
>**  The loop will execute once for each bit of x set, this is in average
>**  twice as fast as the shift/test method.
>*/
>     if (x)
>          do
>          {
>                         n++;
>                    x &= (x-1);
>          } while (x);
>
>     return n;
>}
>

How can that be? Are'nt compares much slower than shifts. (The if(x) line).
How does it work?

>Method  2
>~~~~~~
>This Method is even faster than method 1.
>(Magic algorithm also by  Ratko Tomic)


Thanks a lot. I'll check them out and get back to u.

>For more information about it look at  SNIPPETS home page. This
>is a huge collection of useful C code fragments, functions and programs.
>
>http://www.brokersys.com/snippets/
>
Will check it out. Thanks again. Wonder why a search engine never turns up
with such sites!

Bye,

Chirayu Krishnappa:
------------------
e-mail: chirayu AT poboxes DOT com
Phone:  91 080 3332616.
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