gah@ugcs.caltech.edu (glen herrmannsfeldt)
20 Dec 2001 00:43:17 -0500

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32x32=64 gah@ugcs.caltech.edu (2001-12-20)
Re: 32x32=64 RLWatkins@CompuServe.Com (R. L. Watkins) (2001-12-22)
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From: gah@ugcs.caltech.edu (glen herrmannsfeldt)
Newsgroups: comp.compilers
Date: 20 Dec 2001 00:43:17 -0500
Organization: California Institute of Technology, Pasadena
Summary: 64 bit multiplication
Keywords: arithmetic, comment
Posted-Date: 20 Dec 2001 00:43:17 EST

There is a discussion in comp.arch that wandered from its initial
discussion about typesetting to C code.

The point was made that mutliplying two 32 bit numbers, with one or
both cast to a 64 bit type, could be done using a 32 x 32 multiply
with 64 bit product instruction that many machines have. (Using the
"as if" rule)

The question, then, is do any compilers perform this optimization?

-- glen
[They sure did it for 16x16 -> 32 -John]

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