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From: daveb@geac.UUCP (Brown)
Newsgroups: comp.arch
Subject: Re: What should be in hardware but isn't
Message-ID: <1472@geac.UUCP>
Date: Thu, 24-Sep-87 08:09:26 EDT
Article-I.D.: geac.1472
Posted: Thu Sep 24 08:09:26 1987
Date-Received: Sat, 26-Sep-87 09:39:37 EDT
References: <581@l.cc.purdue.edu> <8646@utzoo.UUCP>
Reply-To: daveb@geac.UUCP (Dave Collier-Brown)
Organization: The little blue rock next to that twinkly star.
Lines: 21

In article <8646@utzoo.UUCP> henry@utzoo.UUCP (Henry Spencer) writes:
|[discussion of operations in the MC 68881]
||  ... Another is to find the distance to the next
||  one in a bit stream, with an interrupt if the stream is emptied...
| 
| On most modern machines it should be possible to write a loop that will do
| this at very nearly full memory bandwidth, looking at a byte or a word at
| a time and using table lookup for the final bit-picking.  I am constantly
| amused by people who scream for bit-flipping instructions when doing it a
| byte or a word at a time, using table lookup for non-trivial functions, is
| still faster.  "Work smart, not hard".
| 

The distance-to-next bit instruction is, for operands of about 2-4
words in lenght, called "floating normalize".  A chess program
(Johnathon Schaefer's) I once worked on used this...
-- 
 David Collier-Brown.                 {mnetor|yetti|utgpu}!geac!daveb
 Geac Computers International Inc.,   |  Computer Science loses its
 350 Steelcase Road,Markham, Ontario, |  memory (if not its mind)
 CANADA, L3R 1B3 (416) 475-0525 x3279 |  every 6 months.