Re: Constant divisions, remainders

kelsey@flora.ccs.northeastern.edu
Tue, 27 Oct 1992 21:55:30 GMT

          From comp.compilers
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Constant divisions, remainders rutt@paradise.mti.sgi.com (1992-10-20)
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Re: Constant divisions, remainders kelsey@flora.ccs.northeastern.edu (1992-10-27)
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Newsgroups: comp.compilers
From: kelsey@flora.ccs.northeastern.edu
Organization: Compilers Central
Date: Tue, 27 Oct 1992 21:55:30 GMT
References: 92-10-075
Keywords: arithmetic, comment

rutt@paradise.mti.sgi.com writes:
    I saw you post regarding constant multiplications on comp.compilers. I
    was curious as to whether you have any ideas about divisons and remainders
    by constants. ...


Just a reminder to all you compiler writers out there that in two's
complement


          X / 2**N == X >> N


is not always true if X < 0.
                                                                -Richard Kelsey
                                                                  kelsey@ccs.northeastern.edu
[Good point. In many cases the shift is still faster even with the extra
code to make negative answers round correctly. -John]
--

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