Re: Multiply by a constant --> shift-and-adds algorithm?

n8tm@aol.com (N8TM)
11 Nov 1997 13:35:57 -0500

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From: n8tm@aol.com (N8TM)
Newsgroups: comp.compilers
Date: 11 Nov 1997 13:35:57 -0500
Organization: AOL http://www.aol.com
References: 97-11-051
Keywords: arithmetic, optimize

Don't most of the compilers attempt to minimize the use of additional
registers and additional analysis by just recording the steps which
would be taken in a software multiplication? We're only trying to
develop the short sequences which would be faster than the
multiplication instruction which most processors have nowadays. If I
want to generate more compact code, I'll compile for a PPC604 even
though I'm running on a 603, in which case gcc/g77 use shifts
sparingly. I haven't checked lately, but gcc used to perform strength
reduction more often when shift-add sequences were avoided.


Tim
--

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