Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!watmath!clyde!caip!rutgers!husc6!seismo!ut-sally!nather
From: nather@ut-sally.UUCP (Ed Nather)
Newsgroups: net.arch
Subject: Re: really long integer arithmetic vs floating point
Message-ID: <6054@ut-sally.UUCP>
Date: Mon, 20-Oct-86 17:03:19 EDT
Article-I.D.: ut-sally.6054
Posted: Mon Oct 20 17:03:19 1986
Date-Received: Tue, 21-Oct-86 07:08:16 EDT
References: <340@euroies.UUCP> <1989@videovax.UUCP> <722@mips.UUCP> <753@polaris.UUCP>
Organization: U. Texas CS Dept., Austin, Texas
Lines: 21
Keywords: numerical analysis, loss of precision
Summary: but ... but ...

In article <753@polaris.UUCP>, josh@polaris.UUCP (Josh Knight) writes:
> Indeed, the proposal to use long integers is wasteful
> of the very resource that is usually in short supply in these calculations,
> namely memory (reference to all the "no virtual memory MY Cray!" verbage).
> When Ed stores the mass of a 10 solar mass star in his simulation of the
> evolution of an open cluster as a 512 bit integer, approximately 500 of
> the bits are wasted on meaningless precision.  

I guess I didn't really make myself clear in my original posting.  I
didn't mean to imply that ONLY 512 bit integers would be available, but
COULD be available, just as bytes and double-bytes are availble as
subsets of the 32-bit integers on a Vax (ooops -- sorry, Josh).
It would not be an unreasonable implementation to have registers of,
say, 128 bits, so "quad integers" of 512 bits would have to be
operated on in 4 pieces.  My point was to substitute integer operations
for floating ones and still retain workable precision.
-- 
Ed Nather
Astronomy Dept, U of Texas @ Austin
{allegra,ihnp4}!{noao,ut-sally}!utastro!nather
nather@astro.AS.UTEXAS.EDU