Re: multiplication by constant - quick comparison of algorithms

bgb@iexist.att.com (Brian G Beuning)
Sun, 25 Oct 1992 17:41:42 GMT

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Newsgroups: comp.compilers
From: bgb@iexist.att.com (Brian G Beuning)
Organization: AT&T
Date: Sun, 25 Oct 1992 17:41:42 GMT
References: 92-10-079
Keywords: arithmetic, optimize

wu@sequent.com (Youfeng Wu):
> For all numbers in [2, 10000], there is a total number of 64612 one's in
> their binary represenations, and the following compares the total number
> of add/sub/shift instructions used to perform all of the multiplications


Isn't it a little dangerous to use sub? Won't it overflow sometimes when
the multiply would not.


I thought I would mention that this topic is covered in Knuth Volume 2,
section 4.6.3. There he is talking about reducing multiplications in
exponentiation but the techniques should also apply to reducing additions
in multiplication.


Brian Beuning
--


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