Path: utzoo!attcan!uunet!oddjob!uwvax!dogie!uwmcsd1!ig!agate!ucbvax!cogsci.berkeley.edu!jsilva
From: jsilva@cogsci.berkeley.edu (John Silva)
Newsgroups: comp.unix.xenix
Subject: Re: "sped up" compresses
Keywords: compress,286,speed,speedup,SLOWER!
Message-ID: <25269@ucbvax.BERKELEY.EDU>
Date: 28 Jul 88 02:21:20 GMT
References: <60@libove.UUCP>
Sender: usenet@ucbvax.BERKELEY.EDU
Reply-To: jsilva@cogsci.berkeley.edu (John Silva)
Distribution: comp
Organization: University of California, Berkeley
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libove@libove.UUCP writes:

>Well, I received two sets of speedup sources - one from ucbvax!cogsci!jsilva
>and a second from hutch@hubcap.clemson.edu (gatech!hubcap.clemson.edu!hutch)
>and I built compress with the two of these upgrades (one at a time, of
>course; the two speedups replace the same routine) and then I compressed
>a copy of /xenix and a 500K text file with each.
>
>Results:
>file		straight compress	+jsilva		+hutch
>
>/xenix		3.2s			4.8s		3.7s
>500K text	4.9s			5.0s		5.1s
>
>Now, I don't know if I did something funny, but I've been at this kind
>of stuff for a while, and I don't think I missed anything.
>
>So, has anyone else tried these "speed-ups" out yet? What results did
>you get? For me, obviously, I am staying with the distribution version!
>-- 
>-Jay Libove {pitt|bellcore}!darth!libove!libove *or* Jay.Libove@andrew.cmu.edu

I'm not sure what was going on, but it sounds to me like your compiler was
generating the proper instructions in the first place.  You wouldn't happen
to be running a 386 box, would you?  If so, that explains the slowdown.
(Doesn't help to replace a 32 bit shift instruction with a function call to
several 16 bit shifts...)

Your figures sound like the cpu time figures from csh's 'time' command.  In
my tests, the user time decreased, the cpu time increased, the actual elapsed
time decreased (this is where I drew the percentage speedup percentages from),
and cpu utilization increased.  Did you take your figures from the x.xs field
that 'time' returns?

BTW, I also recieved a copy of hutch's speedup code, and found that his code
was optimized much better than my code was.  He did miss one place where he
could remove one instruction, however. (I have since re-optimized my routines,
which are now nearly identical to hutch's routines...  So much for original
looking code.... :)

Both sets of routines seem to work fine, however, so I wouldn't be concerned
about which set to use.  Both definately speed compress up more than 25%
when used with a 286 compiler.

John P. Silva
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