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From: bmw@aesat.UUCP (Bruce Walker)
Newsgroups: net.math,net.arch
Subject: Re: Integer division
Message-ID: <557@aesat.UUCP>
Date: Tue, 11-Feb-86 15:13:41 EST
Article-I.D.: aesat.557
Posted: Tue Feb 11 15:13:41 1986
Date-Received: Tue, 11-Feb-86 15:19:02 EST
Organization: AES Data Inc., Mississauga Ont., Canada
Lines: 32

| Is there someone out there who *wants* a/b to round towards 0 (for reasons
| that say that is the desired result)?  I asked that before and have not seen
| any affirmatives.
| 
| ucbvax!brahms!weemba	Matthew P Wiener/UCB Math Dept/Berkeley CA 94720

Yes, *I* want a/b to round toward 0, and for a good (although selfish)
reason.  (I also want divide to produce *both* result *and* remainder
which answers a question posed by someone else on just that point.)

When I write the firmware for the disk controller boards I design, I
want that code to run as fast as possible (so do you, if your machine
uses my board!).  When a logical block address is handed to me, I do an
integer divide by the number of sectors per track which produces both a
quotient and remainder.  The quotient will represent the track I should
seek, and the remainder represents the sector I should read.  No extra
work is done, and all the micros I would normally use for this kind of
purpose do what I expect. 

The above algorithm is simplified of course, one would normally have to
consider bad-block management etc., but the principle remains intact.

So, if as a result of this discussion, every uP manufacturer ups and
"fixes" his microcode, don't come crying to me that all your disk reads
take 20 more microseconds than they used to.

Bruce Walker     {allegra,ihnp4,linus,decvax}!utzoo!aesat!bmw

"I'd feel a lot worse if I wasn't so heavily sedated." -- Spinal Tap