Path: utzoo!utgpu!water!watmath!clyde!ima!think!barmar
From: barmar@think.COM (Barry Margolin)
Newsgroups: comp.arch
Subject: Re: RISC is a nasty no-no!
Message-ID: <17415@think.UUCP>
Date: 3 Mar 88 02:26:27 GMT
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Reply-To: barmar@fafnir.think.com.UUCP (Barry Margolin)
Organization: Thinking Machines Corporation, Cambridge, MA
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In article <7514@boring.cwi.nl> dik@cwi.nl (Dik T. Winter) writes:
>In article <7482@apple.UUCP> baum@apple.UUCP (Allen Baum) writes:
> > (power of two array sizes are pretty common!),

For scientific programming (the major application of supercomputers),
is this really true?  What scientific applications naturally map onto
power-of-two arrays?  I suspect that making arrays a power of two in
size is a habit mostly of systems programmers, who know to make things
fit neatly into memory pages in order to reduce paging.

>I agree with most (CDC Cyber does not have a true integer multiply either).
>when you start programming on supers you will soon
>learn that power of two array sizes are the worse choice you can make.

Could you explain why this is so?  Maybe there are architectures where
it doesn't make a difference, but I can't imagine why power of two
would be WORSE than other sizes.

Barry Margolin
Thinking Machines Corp.

barmar@think.com
uunet!think!barmar