Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!ames!vsi1!wyse!mips!mash
From: mash@mips.COM (John Mashey)
Newsgroups: comp.arch
Subject: Re: RISC vs unaligned data
Message-ID: <16541@winchester.mips.COM>
Date: 4 Apr 89 04:09:30 GMT
References: <355@bnr-fos.UUCP> <13@microsoft.UUCP> <16058@cup.portal.com> <370@bnr-fos.UUCP> <11222@tekecs.GWD.TEK.COM> <16407@winchester.mips.COM> <9931@polyslo.CalPoly.EDU>
Reply-To: mash@mips.COM (John Mashey)
Organization: MIPS Computer Systems, Sunnyvale, CA
Lines: 22

In article <9931@polyslo.CalPoly.EDU> cquenel@polyslo.CalPoly.EDU (46 more school days) writes:
>In article <16407@winchester.mips.COM> mash@mips.COM (John Mashey) writes:
>>Of course, if N == 100 (if you were doing it with exceptions, perhaps),
>>you now get + 5-15, i.e., 6-16X slower, which is clearly ungood, and
>>only survivable for debugging.
>
>	Wait a sec, aren't you comparing the proverbial
>	mis-matched fruits here ?
....
>	Using exceptions to handle mis-aligned data isn't
>	quite as bad as your (admittedly back-of-the-envelope)
>	figure of 6-16X would suggest.

Good point!  It's certainly not as bad as that in practice.   I can't remember
how bad it really was in practice, except that we had a lot of pressure
to get the compiler support in, AFTER the handle-by-exception code was
already in use.
-- 
-john mashey	DISCLAIMER: <generic disclaimer, I speak for me only, etc>
UUCP: 	{ames,decwrl,prls,pyramid}!mips!mash  OR  mash@mips.com
DDD:  	408-991-0253 or 408-720-1700, x253
USPS: 	MIPS Computer Systems, 930 E. Arques, Sunnyvale, CA 94086