Path: utzoo!dciem!nrcaer!sce!greg
From: greg@sce.carleton.ca (Greg Franks)
Newsgroups: comp.arch
Subject: Re: RISC v. CISC --more misconceptions
Message-ID: <499@sce.carleton.ca>
Date: 4 Nov 88 16:14:38 GMT
Article-I.D.: sce.499
References: <156@gloom.UUCP> <18931@apple.Apple.COM> <40@sopwith.UUCP> <19762@apple.Apple.COM> <1002@l.cc.purdue.edu> <19811@apple.Apple.COM4 Nov 88 16:14:38 GMT
Reply-To: greg@sce.UUCP (Greg Franks)
Organization: Systems Eng., Carleton Univ., Ottawa, Canada
Lines: 34

In article <19811@apple.Apple.COM> baum@apple.UUCP (Allen Baum) writes:
#>In article <1002@l.cc.purdue.edu> cik@l.cc.purdue.edu (Herman Rubin) writes:
#(in response to me about integer multiplies)
#>They are rare because a good programmer knows that they are slow and
#>difficult to program.  If an operation takes 10 lines of code, each of
#>which is expanded into one or more hardware instructions, why use it
#>unless you cannot find a way around it?  The way around it may be clumsy,
#>but it is very likely to beat the unavailable operation.
#
#I'm going further than that. I'm saying they are rare because the are
#unnecessary. They are rare because in the USUAL case they can be strength
#reduced to additions by an optimizing compiler. This is faster than using
#the obvious multiply instruction.
#
#Integer numeric intensive applications are relatively RARE. You
#(Herman Rubin personally) may do them all the time, in which case you
#don't think they are rare, but as a precentage of programs run by all
#computers, they are.
#

Integer multiplies are VERY POPULAR, if you look in the right place.
TI (TMS320) and Motorola (The NeXT machine) and many others are making
lots of money selling digital signal processing chips.  These chips
perform FFT's and all sorts of other operations which perform multiple
MULTIPLY and ADD very quickly.

However, many chip makers are now going to floating point in their
DSP's, so the lowly integer multiply may once again become somewhat
useless. 
-- 
Greg Franks                  Systems and Computer Engineering, 
utzoo!dciem!nrcaer!sce!greg  Carleton University, Ottawa, Ontario, Canada.
greg@sce.carleton.ca
   ACME Electric: When you can't find your shorts, call us!