Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!usc!zaphod.mps.ohio-state.edu!rpi!leah!bingvaxu!vu0310
From: vu0310@bingvaxu.cc.binghamton.edu (R. Kym Horsell)
Newsgroups: comp.arch
Subject: Re: F.P. vs. arbitrary-precision
Message-ID: <3977@bingvaxu.cc.binghamton.edu>
Date: 10 Sep 90 20:47:50 GMT
References: <3755@osc.COM> <4513@taux01.nsc.com> <119244@linus.mitre.org> <6837.26e7ee92@vax1.tcd.ie> <119612@linus.mitre.org>
Reply-To: vu0310@bingvaxu.cc.binghamton.edu.cc.binghamton.edu (R. Kym Horsell)
Organization: SUNY Binghamton, NY
Lines: 37

In article <119612@linus.mitre.org> bs@faron.UUCP (Robert D. Silverman) writes:
\\\
>Everyone keeps quoting this '99% of the time' stuff to me. I should
>like to point out that there are applications for which having
>32 x 32 -- > 64   and 64 / 32 = 32 quotient & remainder  are absolutely
>essential. Basically, ANYTHING involving multiprecision arithmetic
^^^^^^^^^^^
>requires these. (on a 32 bit machine that is)
 ^^^^^^^^
\\\

Don't you mean `useful' of `efficient' here? 

The RISC folks probably have the right attitude here -- only that stuff
that happens a lot, or is _absolutely_, logically _required_ need be
implemented in h/w (either that, or can be `tacked on' to what you
were going to do anyway as make no matter to the cost)-- design
time means $$$$ after all, right?

int x int -> long isn't _required_ for MP calcs, it's just _convenient_.
For example, the `bc' U*X calculator uses bytes to store pairs
of decimal digits and then uses good old int x int -> int to perform
a paper-and-pencil multiply.

Another technique is using `carryless' modular arithmetic with
appropriate bases (e.g. 2^k+1).

So maybe some people burn a _lot_ of cycles doing this sort of
stuff (I do myself as it happens), do the economics of design time,
marketting & area indicate that h/w must support it? Maybe that 
Si could be better spent doing things that actually happen a _lot_?

-Kym Horsell

P.S. I'm still interested in how much of the Sun Sparc's `bc' is
	written in assembler; it's _awful_ fast. So far no
	takers to my original post...