Path: utzoo!utgpu!attcan!uunet!mcvax!dik
From: dik@cwi.nl (Dik T. Winter)
Newsgroups: comp.arch
Subject: Re: Leading zero and pop count
Message-ID: <7711@boring.cwi.nl>
Date: 10 Nov 88 21:51:52 GMT
References: <10882@hall.cray.com> <705@convex.UUCP>
Organization: CWI, Amsterdam
Lines: 14

In article <705@convex.UUCP> loeliger@convex.com (Jon Loeliger) writes:
 > Yep, they are used elsewhere.  Convex C1 and C2 both have trailing-zero-count
 > and population counts.  There is actually an esoteric reason to prefer a
 > leading zero count over a trailing count....

The best reason is of course that, given a popcount instruction, getting a
trailing zero count takes only four instructions(*).  Getting a leading
zero count takes a few more.

(*) POPCOUNT(AND(NOT(X),X-1))
-- 
dik t. winter, cwi, amsterdam, nederland
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