Path: utzoo!attcan!uunet!lll-winken!ncis!helios.ee.lbl.gov!pasteur!ucbvax!agate!bionet!csd4.milw.wisc.edu!mailrus!ncar!gatech!hubcap!landman
From: landman@Sun.COM (Howard A. Landman)
Newsgroups: comp.parallel
Subject: Re: Clever programming tricks wanted
Message-ID: <4150@hubcap.UUCP>
Date: 19 Jan 89 21:33:14 GMT
Sender: fpst@hubcap.UUCP
Lines: 17
Approved: parallel@hubcap.clemson.edu

In article <4131@hubcap.UUCP> dave@vax1.cc.uakron.edu (David Stoutamire) writes:
>I have invented a technique for counting one bits that I used
>in a bit representation of a board game to do lickety-split
>move generation.

This is essentially the same as the code I posted earlier.  I should point out,
however, that for EXTREMELY high performance applications it is much faster
to have lookup tables.  For 32-bit words this gets impractical, but it is
quite reasonable to break it into 16-bit halves, look up the two counts, and
sum them together.  This requires only 5 instructions (mask, lookup, shift,
lookup, add).  The counts can't get larger than 5 bits, so the table takes
no more than 64KB.

Your mileage may vary depending on cache size ...

	Howard A. Landman
	landman@hanami.sun.com