From: bs@gauss.mitre.org (Robert D. Silverman)
Newsgroups: comp.arch,comp.lang.misc
Subject: Re: Hardware Support for Numeric Algorithms
Date: 12 Nov 92 13:18:56 GMT
Organization: Research Computer Facility, MITRE Corporation, Bedford, MA

In article <1992Nov10.153705.27804@yrloc.ipsa.reuter.COM> rbe@yrloc.ipsa.reuter.COM (Robert Bernecky) writes:
:In article <1992Nov5.202412.7266@linus.mitre.org> bs@gauss.mitre.org (Robert D. Silverman) writes:
:>In article <1992Oct29.153514.22927@yrloc.ipsa.reuter.COM> rbe@yrloc.ipsa.reuter.COM (Robert Bernecky) writes:
:>:
:>:I write programs for correctness and maintainability first, THEN worry
:>:about little details such as performance. If you create something that's
:> 
:>You've probably never done any large scale computing.
:>
:>I measure the run time of my algorithms in MIPS-YEARS.  A MIPS-YEAR
:>is a 1 MIPS machine running for 1 year, or approximately 3.1 x 10^13
:>instructions.  Jobs that take several hundred MIPS-YEARS are not uncommon.
:
:Bad guess, unless Crays, 3090s (Yes, I know they barely count) and
:a bit of CM-2 don't count.
 
Several hundred MIPS-YEARS is a Cray running for a whole year or two. What jobs
have you run on Cray-class computers that take a whole year? 

The COST of such a job is staggering.

And I run many such jobs.

:Perhaps your code REALLY is MIPS-years in complexity. OR, it could
:be that failure to design properly leads to that complexity, whereas
:careful thought could reduce it to months or less. Since I don't
 
I suggest you read some of my papers in Math. Comp. (and elsewhere). Then you 
can decide whether I know what I am doing.

:understand your problem, I can only speculate. However, I DO know

Methods for computing discrete logs in large finite fields; methods for
factoring large integers; other problems in computational number theory.
See my survey article in the August 1991 issue of Notices of the AMS.

:that algorithmic excellence is the way to get speed, NOT dinking
:around with what you perceive to be a bottleneck at the bit-diddling
:level. AFTER you have the algorithm right, THEN you start tweaking
 
And what makes you think that Herman (or I) does not have the right
algorithm? He knows far more about the mathematics of what he is doing than
you (or I).
 
It is assumed that the algorithm is right, in all of these discussions.

:bits. Optimization before design is usually a bad idea. 
 
Spouting aphorisms adds little to this discussion. Especially since you
are assuming facts not in evidence. (i.e. you are assuming that the
optimization came before the design).

:>Needless to say, there are people who have to worry about speed FIRST,
:>and that other considerations are (almost) irrelevent.
:
:Are you saying that speed is more important than correct answers? 
 
Now you are being a pedant. It is always assumed that one wants the right 
answer. Noone has ever suggested otherwise. It is assumed that the algorithm
has been designed and coded to work correctly. What we are discussing is
the notion that some people seem to have that "correct style" is more
important than speed.

--
Bob Silverman
These are my opinions and not MITRE's.
Mitre Corporation, Bedford, MA 01730
"You can lead a horse's ass to knowledge, but you can't make him think"
Newsgroups: comp.arch