Newsgroups: comp.arch
Path: utzoo!utgpu!news-server.csri.toronto.edu!torsqnt!hybrid!scifi!bywater!uunet!kithrup!sef
From: sef@kithrup.COM (Sean Eric Fagan)
Subject: Re: new instructions
Organization: Kithrup Enterprises, Ltd.
Date: Thu, 23 May 1991 08:42:58 GMT
Message-ID: <1991May23.084258.5062@kithrup.COM>
References: <1991May22.001620.751@craycos.com>

In article <1991May22.001620.751@craycos.com> rh@craycos.com (Robert Herndon) writes:
>but population count and leading zero count
>on a word value are quite useful, yet (though I'm not a compiler writer)
>I can't think of easy methods for a (non-vector) compiler to use these
>instructions often.

You can do pop count quite quickly with table lookup.  Yes, you have to
break it up, but, on a byte-addressable machine, it's not a major hassle.
You will need a 256-byte table, of course, but that, also, isn't a major
hassle.  CLZ I can also do somewhat quickly with table lookup on a
byte-addressable machine.

-- 
Sean Eric Fagan  | "I made the universe, but please don't blame me for it;
sef@kithrup.COM  |  I had a bellyache at the time."
-----------------+           -- The Turtle (Stephen King, _It_)
Any opinions expressed are my own, and generally unpopular with others.