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From: boogaard@ruunsa.fys.ruu.nl (Martin vdBoogaard)
Newsgroups: comp.lang.c
Subject: Induction variable type / vc on Convex
Keywords: unsigned int, int, convex, vc, vectorizing compiler
Message-ID: <1946@ruunsa.fys.ruu.nl>
Date: 21 Feb 91 23:46:39 GMT
Organization: University of Utrecht, Dept. of Physics
Lines: 24

I use the Convex vectorizing C compiler vc (version 3.0) with -O2
optimization to compile a piece of C code featuring some simple array
manipulations. The array indices are non-negative, so I use an unsigned
int as an array index. To my surprise this inhibits vectorization of
even the simplest array operation. Using int instead of unsigned int
solves the problem.

Is there an optimization expert who can brief me on why unsigned int
indices are a problem to the Convex code optimizer? More in general,
am I wrong in using unsigned int instead of int in the first place?

I've found that some people reading this group get irritated by
OS-specific questions. I'm sorry, I haven't yet found newsgroups
comp.unix.convex or comp.lang.c.vector.


Martin J. van den Boogaard         | Dept. of Atomic & Interface Physics
                                   | Debye Institute--Utrecht University
boogaard@fys.ruu.nl                | P.O. Box 80.000, NL-3508 TA Utrecht
boogaard@hutruu51.bitnet           | the Netherlands, +31 30 532904
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