Path: utzoo!attcan!uunet!husc6!mailrus!purdue!i.cc.purdue.edu!k.cc.purdue.edu!l.cc.purdue.edu!cik
From: cik@l.cc.purdue.edu (Herman Rubin)
Newsgroups: comp.arch
Subject: Re: RISC v. CISC --more misconceptions
Summary: Wrong question.  I am interested in a BIT stream.
Message-ID: <1012@l.cc.purdue.edu>
Date: 4 Nov 88 19:12:38 GMT
References: <156@gloom.UUCP> <18931@apple.Apple.COM> <40@sopwith.UUCP> <232@taux02.UUCP>
Organization: Purdue University Statistics Department
Lines: 26

In article <232@taux02.UUCP>, yuval@taux02.UUCP (Gideon Yuval) writes:
> 
> If you want to find the first (bottom) "1" bit in a machine word X, try:
> 
> table [  (X xor (X-1)) mod 37 ] 

The question I asked is the spacing between BITS in a BIT stream.  It is
possible that the best way on a particular machine is to use words, but 
not here.

What is wanted is to get the distance to the next bit in the stream on
demand (this can be vectorized) and then pass over to the next location
for the next step.  Once a particular bit in the stream is read, it cannot
be used for anything else.

A similar problem is a conditional transfer on the next bit.  The whole 
process is bit-oriented, and some extraordinary procedure must be used to
use larger units.

There is also the problem of the bit stream becoming empty and needing
refilling.  In some cases, this problem can be minimized, even to the 
point of some cases being able to ignore it.  But it cannot be eliminated.
-- 
Herman Rubin, Dept. of Statistics, Purdue Univ., West Lafayette IN47907
Phone: (317)494-6054
hrubin@l.cc.purdue.edu (Internet, bitnet, UUCP)