From: vecna AT engin DOT umich DOT edu (Jimmy Wan)
Newsgroups: comp.os.msdos.djgpp
Subject: Re: Strength reducing? [was Re: DJGPP V2.01 loop unrolling bug]
Date: Mon, 28 Oct 96 05:14:44 GMT
Organization: University of Michigan
Lines: 21
Message-ID: <551fg8$mk4@lastactionhero.rs.itd.umich.edu>
References: <199610211814 DOT OAA10948 AT delorie DOT com> <54t1pb$77r AT news DOT service DOT uci DOT edu>
NNTP-Posting-Host: pm121-22.dialip.mich.net
To: djgpp AT delorie DOT com
DJ-Gateway: from newsgroup comp.os.msdos.djgpp

In article <54t1pb$77r AT news DOT service DOT uci DOT edu>,
   beppu AT rigel DOT oac DOT uci DOT edu (John Beppu) wrote:
>In article <199610211814 DOT OAA10948 AT delorie DOT com>,
>Troy D. Van Horn <trvanhor AT UCollege DOT edu> wrote:
>>Aren't loop unrolling and strenth reducing two different
>>optimizations?
>
>  What is __strength reduction__?  I've never heard of
>  this optimzation technique before.

Strength reduction is the use of simpler and less complex instructions
to do the same thing.  For example, instead of multiplying an integer
by 2, left shift it by 1.  Much much faster.  Personally, I explicitly
use the shifts in my code anyway.  BTW, anyone have a clock cycle
listing for 486's, P5's and P6's?  Or know where I can get one?  I have
one for the 8086 and the 80186 and those really aren't going to do me
any good...

Jimmy Wan               University of Michigan-Computer Engineering
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